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File: gcc.info,  Node: Top,  Next: G++ and GCC,  Up: (DIR)

Introduction
************

This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs.  It corresponds
to the compilers (GCC) version 4.4.7.  The internals of the GNU
compilers, including how to port them to new targets and some
information about how to write front ends for new languages, are
documented in a separate manual.  *Note Introduction: (gccint)Top.

* Menu:

* G++ and GCC::     You can compile C or C++ programs.
* Standards::       Language standards supported by GCC.
* Invoking GCC::    Command options supported by `gcc'.
* C Implementation:: How GCC implements the ISO C specification.
* C Extensions::    GNU extensions to the C language family.
* C++ Extensions::  GNU extensions to the C++ language.
* Objective-C::     GNU Objective-C runtime features.
* Compatibility::   Binary Compatibility
* Gcov::            `gcov'---a test coverage program.
* Trouble::         If you have trouble using GCC.
* Bugs::            How, why and where to report bugs.
* Service::         How to find suppliers of support for GCC.
* Contributing::    How to contribute to testing and developing GCC.

* Funding::         How to help assure funding for free software.
* GNU Project::     The GNU Project and GNU/Linux.

* Copying::         GNU General Public License says
                    how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors::    People who have contributed to GCC.

* Option Index::    Index to command line options.
* Keyword Index::   Index of concepts and symbol names.

File: gcc.info,  Node: G++ and GCC,  Next: Standards,  Prev: Top,  Up: Top

1 Programming Languages Supported by GCC
****************************************

GCC stands for "GNU Compiler Collection".  GCC is an integrated
distribution of compilers for several major programming languages.
These languages currently include C, C++, Objective-C, Objective-C++,
Java, Fortran, and Ada.

 The abbreviation "GCC" has multiple meanings in common use.  The
current official meaning is "GNU Compiler Collection", which refers
generically to the complete suite of tools.  The name historically stood
for "GNU C Compiler", and this usage is still common when the emphasis
is on compiling C programs.  Finally, the name is also used when
speaking of the "language-independent" component of GCC: code shared
among the compilers for all supported languages.

 The language-independent component of GCC includes the majority of the
optimizers, as well as the "back ends" that generate machine code for
various processors.

 The part of a compiler that is specific to a particular language is
called the "front end".  In addition to the front ends that are
integrated components of GCC, there are several other front ends that
are maintained separately.  These support languages such as Pascal,
Mercury, and COBOL.  To use these, they must be built together with GCC
proper.

 Most of the compilers for languages other than C have their own names.
The C++ compiler is G++, the Ada compiler is GNAT, and so on.  When we
talk about compiling one of those languages, we might refer to that
compiler by its own name, or as GCC.  Either is correct.

 Historically, compilers for many languages, including C++ and Fortran,
have been implemented as "preprocessors" which emit another high level
language such as C.  None of the compilers included in GCC are
implemented this way; they all generate machine code directly.  This
sort of preprocessor should not be confused with the "C preprocessor",
which is an integral feature of the C, C++, Objective-C and
Objective-C++ languages.

File: gcc.info,  Node: Standards,  Next: Invoking GCC,  Prev: G++ and GCC,  Up: Top

2 Language Standards Supported by GCC
*************************************

For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.

2.1 C language
==============

GCC supports three versions of the C standard, although support for the
most recent version is not yet complete.

 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990.  This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990.  There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard.  This standard,
in both its forms, is commonly known as "C89", or occasionally as
"C90", from the dates of ratification.  The ANSI standard, but not the
ISO standard, also came with a Rationale document.  To select this
standard in GCC, use one of the options `-ansi', `-std=c89' or
`-std=iso9899:1990'; to obtain all the diagnostics required by the
standard, you should also specify `-pedantic' (or `-pedantic-errors' if
you want them to be errors rather than warnings).  *Note Options
Controlling C Dialect: C Dialect Options.

 Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996.  GCC does not support the
uncorrected version.

 An amendment to the 1990 standard was published in 1995.  This
amendment added digraphs and `__STDC_VERSION__' to the language, but
otherwise concerned the library.  This amendment is commonly known as
"AMD1"; the amended standard is sometimes known as "C94" or "C95".  To
select this standard in GCC, use the option `-std=iso9899:199409'
(with, as for other standard versions, `-pedantic' to receive all
required diagnostics).

 A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as "C99".  GCC has incomplete support
for this standard version; see
`http://gcc.gnu.org/gcc-4.4/c99status.html' for details.  To select this
standard, use `-std=c99' or `-std=iso9899:1999'.  (While in
development, drafts of this standard version were referred to as "C9X".)

 Errors in the 1999 ISO C standard were corrected in three Technical
Corrigenda published in 2001, 2004 and 2007.  GCC does not support the
uncorrected version.

 By default, GCC provides some extensions to the C language that on
rare occasions conflict with the C standard.  *Note Extensions to the C
Language Family: C Extensions.  Use of the `-std' options listed above
will disable these extensions where they conflict with the C standard
version selected.  You may also select an extended version of the C
language explicitly with `-std=gnu89' (for C89 with GNU extensions) or
`-std=gnu99' (for C99 with GNU extensions).  The default, if no C
language dialect options are given, is `-std=gnu89'; this will change to
`-std=gnu99' in some future release when the C99 support is complete.
Some features that are part of the C99 standard are accepted as
extensions in C89 mode.

 The ISO C standard defines (in clause 4) two classes of conforming
implementation.  A "conforming hosted implementation" supports the
whole standard including all the library facilities; a "conforming
freestanding implementation" is only required to provide certain
library facilities: those in `<float.h>', `<limits.h>', `<stdarg.h>',
and `<stddef.h>'; since AMD1, also those in `<iso646.h>'; and in C99,
also those in `<stdbool.h>' and `<stdint.h>'.  In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a
"freestanding environment", required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined, and a "hosted environment", which is not
required, in which all the library facilities are provided and startup
is through a function `int main (void)' or `int main (int, char *[])'.
An OS kernel would be a freestanding environment; a program using the
facilities of an operating system would normally be in a hosted
implementation.

 GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation.  By default, it will act as the compiler for a hosted
implementation, defining `__STDC_HOSTED__' as `1' and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard.  To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
`-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below.  To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.

 GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations; to use the facilities of a hosted
environment, you will need to find them elsewhere (for example, in the
GNU C library).  *Note Standard Libraries: Standard Libraries.

 Most of the compiler support routines used by GCC are present in
`libgcc', but there are a few exceptions.  GCC requires the
freestanding environment provide `memcpy', `memmove', `memset' and
`memcmp'.  Finally, if `__builtin_trap' is used, and the target does
not implement the `trap' pattern, then GCC will emit a call to `abort'.

 For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
`http://gcc.gnu.org/readings.html'

2.2 C++ language
================

GCC supports the ISO C++ standard (1998) and contains experimental
support for the upcoming ISO C++ standard (200x).

 The original ISO C++ standard was published as the ISO standard
(ISO/IEC 14882:1998) and amended by a Technical Corrigenda published in
2003 (ISO/IEC 14882:2003). These standards are referred to as C++98 and
C++03, respectively. GCC implements the majority of C++98 (`export' is
a notable exception) and most of the changes in C++03.  To select this
standard in GCC, use one of the options `-ansi' or `-std=c++98'; to
obtain all the diagnostics required by the standard, you should also
specify `-pedantic' (or `-pedantic-errors' if you want them to be
errors rather than warnings).

 The ISO C++ committee is working on a new ISO C++ standard, dubbed
C++0x, that is intended to be published by 2009. C++0x contains several
changes to the C++ language, some of which have been implemented in an
experimental C++0x mode in GCC. The C++0x mode in GCC tracks the draft
working paper for the C++0x standard; the latest working paper is
available on the ISO C++ committee's web site at
`http://www.open-std.org/jtc1/sc22/wg21/'. For information regarding
the C++0x features available in the experimental C++0x mode, see
`http://gcc.gnu.org/projects/cxx0x.html'. To select this standard in
GCC, use the option `-std=c++0x'; to obtain all the diagnostics
required by the standard, you should also specify `-pedantic' (or
`-pedantic-errors' if you want them to be errors rather than warnings).

 By default, GCC provides some extensions to the C++ language; *Note
Options Controlling C++ Dialect: C++ Dialect Options.  Use of the
`-std' option listed above will disable these extensions.  You may also
select an extended version of the C++ language explicitly with
`-std=gnu++98' (for C++98 with GNU extensions) or `-std=gnu++0x' (for
C++0x with GNU extensions).  The default, if no C++ language dialect
options are given, is `-std=gnu++98'.

2.3 Objective-C and Objective-C++ languages
===========================================

There is no formal written standard for Objective-C or Objective-C++.
The most authoritative manual is "Object-Oriented Programming and the
Objective-C Language", available at a number of web sites:

   *
     `http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/'
     is a recent (and periodically updated) version;

   * `http://www.toodarkpark.org/computers/objc/' is an older example;

   * `http://www.gnustep.org' and `http://gcc.gnu.org/readings.html'
     have additional useful information.

 *Note GNAT Reference Manual: (gnat_rm)Top, for information on standard
conformance and compatibility of the Ada compiler.

 *Note Standards: (gfortran)Standards, for details of standards
supported by GNU Fortran.

 *Note Compatibility with the Java Platform: (gcj)Compatibility, for
details of compatibility between `gcj' and the Java Platform.

File: gcc.info,  Node: Invoking GCC,  Next: C Implementation,  Prev: Standards,  Up: Top

3 GCC Command Options
*********************

When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking.  The "overall options" allow you to stop this
process at an intermediate stage.  For example, the `-c' option says
not to run the linker.  Then the output consists of object files output
by the assembler.

 Other options are passed on to one stage of processing.  Some options
control the preprocessor and others the compiler itself.  Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.

 Most of the command line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly.  If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.

 *Note Compiling C++ Programs: Invoking G++, for a summary of special
options for compiling C++ programs.

 The `gcc' program accepts options and file names as operands.  Many
options have multi-letter names; therefore multiple single-letter
options may _not_ be grouped: `-dv' is very different from `-d -v'.

 You can mix options and other arguments.  For the most part, the order
you use doesn't matter.  Order does matter when you use several options
of the same kind; for example, if you specify `-L' more than once, the
directories are searched in the order specified.  Also, the placement
of the `-l' option is significant.

 Many options have long names starting with `-f' or with `-W'--for
example, `-fmove-loop-invariants', `-Wformat' and so on.  Most of these
have both positive and negative forms; the negative form of `-ffoo'
would be `-fno-foo'.  This manual documents only one of these two
forms, whichever one is not the default.

 *Note Option Index::, for an index to GCC's options.

* Menu:

* Option Summary::      Brief list of all options, without explanations.
* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* Invoking G++::        Compiling C++ programs.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
                        and Objective-C++.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.
* Submodel Options::    Specifying minor hardware or convention variations,
                        such as 68010 vs 68020.
* Code Gen Options::    Specifying conventions for function calls, data layout
                        and register usage.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
* Running Protoize::    Automatically adding or removing function prototypes.

File: gcc.info,  Node: Option Summary,  Next: Overall Options,  Up: Invoking GCC

3.1 Option Summary
==================

Here is a summary of all the options, grouped by type.  Explanations are
in the following sections.

_Overall Options_
     *Note Options Controlling the Kind of Output: Overall Options.
          -c  -S  -E  -o FILE  -combine  -pipe  -pass-exit-codes
          -x LANGUAGE  -v  -###  --help[=CLASS[,...]]  --target-help
          --version -wrapper@FILE

_C Language Options_
     *Note Options Controlling C Dialect: C Dialect Options.
          -ansi  -std=STANDARD  -fgnu89-inline
          -aux-info FILENAME
          -fno-asm  -fno-builtin  -fno-builtin-FUNCTION
          -fhosted  -ffreestanding -fopenmp -fms-extensions
          -trigraphs  -no-integrated-cpp  -traditional  -traditional-cpp
          -fallow-single-precision  -fcond-mismatch -flax-vector-conversions
          -fsigned-bitfields  -fsigned-char
          -funsigned-bitfields  -funsigned-char

_C++ Language Options_
     *Note Options Controlling C++ Dialect: C++ Dialect Options.
          -fabi-version=N  -fno-access-control  -fcheck-new
          -fconserve-space  -ffriend-injection
          -fno-elide-constructors
          -fno-enforce-eh-specs
          -ffor-scope  -fno-for-scope  -fno-gnu-keywords
          -fno-implicit-templates
          -fno-implicit-inline-templates
          -fno-implement-inlines  -fms-extensions
          -fno-nonansi-builtins  -fno-operator-names
          -fno-optional-diags  -fpermissive
          -frepo  -fno-rtti  -fstats  -ftemplate-depth-N
          -fno-threadsafe-statics -fuse-cxa-atexit  -fno-weak  -nostdinc++
          -fno-default-inline  -fvisibility-inlines-hidden
          -fvisibility-ms-compat
          -Wabi  -Wctor-dtor-privacy
          -Wnon-virtual-dtor  -Wreorder
          -Weffc++  -Wstrict-null-sentinel
          -Wno-non-template-friend  -Wold-style-cast
          -Woverloaded-virtual  -Wno-pmf-conversions
          -Wsign-promo

_Objective-C and Objective-C++ Language Options_
     *Note Options Controlling Objective-C and Objective-C++ Dialects:
     Objective-C and Objective-C++ Dialect Options.
          -fconstant-string-class=CLASS-NAME
          -fgnu-runtime  -fnext-runtime
          -fno-nil-receivers
          -fobjc-call-cxx-cdtors
          -fobjc-direct-dispatch
          -fobjc-exceptions
          -fobjc-gc
          -freplace-objc-classes
          -fzero-link
          -gen-decls
          -Wassign-intercept
          -Wno-protocol  -Wselector
          -Wstrict-selector-match
          -Wundeclared-selector

_Language Independent Options_
     *Note Options to Control Diagnostic Messages Formatting: Language
     Independent Options.
          -fmessage-length=N
          -fdiagnostics-show-location=[once|every-line]
          -fdiagnostics-show-option

_Warning Options_
     *Note Options to Request or Suppress Warnings: Warning Options.
          -fsyntax-only  -pedantic  -pedantic-errors
          -w  -Wextra  -Wall  -Waddress  -Waggregate-return  -Warray-bounds
          -Wno-attributes -Wno-builtin-macro-redefined
          -Wc++-compat -Wc++0x-compat -Wcast-align  -Wcast-qual
          -Wchar-subscripts -Wclobbered  -Wcomment
          -Wconversion  -Wcoverage-mismatch  -Wno-deprecated
          -Wno-deprecated-declarations -Wdisabled-optimization
          -Wno-div-by-zero -Wempty-body  -Wenum-compare -Wno-endif-labels
          -Werror  -Werror=*
          -Wfatal-errors  -Wfloat-equal  -Wformat  -Wformat=2
          -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral
          -Wformat-security  -Wformat-y2k
          -Wframe-larger-than=LEN -Wignored-qualifiers
          -Wimplicit  -Wimplicit-function-declaration  -Wimplicit-int
          -Winit-self  -Winline
          -Wno-int-to-pointer-cast -Wno-invalid-offsetof
          -Winvalid-pch -Wlarger-than=LEN  -Wunsafe-loop-optimizations
          -Wlogical-op -Wlong-long
          -Wmain  -Wmissing-braces  -Wmissing-field-initializers
          -Wmissing-format-attribute  -Wmissing-include-dirs
          -Wmissing-noreturn  -Wno-mudflap
          -Wno-multichar  -Wnonnull  -Wno-overflow
          -Woverlength-strings  -Wpacked  -Wpacked-bitfield-compat  -Wpadded
          -Wparentheses  -Wpedantic-ms-format -Wno-pedantic-ms-format
          -Wpointer-arith  -Wno-pointer-to-int-cast
          -Wredundant-decls
          -Wreturn-type  -Wsequence-point  -Wshadow
          -Wsign-compare  -Wsign-conversion  -Wstack-protector
          -Wstrict-aliasing -Wstrict-aliasing=n
          -Wstrict-overflow -Wstrict-overflow=N
          -Wswitch  -Wswitch-default  -Wswitch-enum -Wsync-nand
          -Wsystem-headers  -Wtrigraphs  -Wtype-limits  -Wundef  -Wuninitialized
          -Wunknown-pragmas  -Wno-pragmas -Wunreachable-code
          -Wunused  -Wunused-function  -Wunused-label  -Wunused-parameter
          -Wunused-value  -Wunused-variable
          -Wunused-but-set-parameter -Wunused-but-set-variable -Wvariadic-macros -Wvla
          -Wvolatile-register-var  -Wwrite-strings

_C and Objective-C-only Warning Options_
          -Wbad-function-cast  -Wmissing-declarations
          -Wmissing-parameter-type  -Wmissing-prototypes  -Wnested-externs
          -Wold-style-declaration  -Wold-style-definition
          -Wstrict-prototypes  -Wtraditional  -Wtraditional-conversion
          -Wdeclaration-after-statement -Wpointer-sign

_Debugging Options_
     *Note Options for Debugging Your Program or GCC: Debugging Options.
          -dLETTERS  -dumpspecs  -dumpmachine  -dumpversion
          -fdbg-cnt-list -fdbg-cnt=COUNTER-VALUE-LIST
          -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links
          -fdump-translation-unit[-N]
          -fdump-class-hierarchy[-N]
          -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline
          -fdump-statistics
          -fdump-tree-all
          -fdump-tree-original[-N]
          -fdump-tree-optimized[-N]
          -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias
          -fdump-tree-ch
          -fdump-tree-ssa[-N] -fdump-tree-pre[-N]
          -fdump-tree-ccp[-N] -fdump-tree-dce[-N]
          -fdump-tree-gimple[-raw] -fdump-tree-mudflap[-N]
          -fdump-tree-dom[-N]
          -fdump-tree-dse[-N]
          -fdump-tree-phiopt[-N]
          -fdump-tree-forwprop[-N]
          -fdump-tree-copyrename[-N]
          -fdump-tree-nrv -fdump-tree-vect
          -fdump-tree-sink
          -fdump-tree-sra[-N]
          -fdump-tree-fre[-N]
          -fdump-tree-vrp[-N]
          -ftree-vectorizer-verbose=N
          -fdump-tree-storeccp[-N]
          -fdump-final-insns=FILE
          -fcompare-debug[=OPTS]  -fcompare-debug-second
          -feliminate-dwarf2-dups -feliminate-unused-debug-types
          -feliminate-unused-debug-symbols -femit-class-debug-always
          -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs
          -frandom-seed=STRING -fsched-verbose=N
          -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose
          -ftest-coverage  -ftime-report -fvar-tracking
          -fvar-tracking-assignments  -fvar-tracking-assignments-toggle
          -g  -gLEVEL  -gtoggle  -gcoff -gdwarf-VERSION
          -ggdb  -gstabs  -gstabs+  -gstrict-dwarf  -gno-strict-dwarf
          -gvms  -gxcoff  -gxcoff+
          -fno-merge-debug-strings -fno-dwarf2-cfi-asm
          -fdebug-prefix-map=OLD=NEW
          -femit-struct-debug-baseonly -femit-struct-debug-reduced
          -femit-struct-debug-detailed[=SPEC-LIST]
          -p  -pg  -print-file-name=LIBRARY  -print-libgcc-file-name
          -print-multi-directory  -print-multi-lib  -print-multi-os-directory
          -print-prog-name=PROGRAM  -print-search-dirs  -Q
          -print-sysroot -print-sysroot-headers-suffix
          -save-temps  -time[=FILE]

_Optimization Options_
     *Note Options that Control Optimization: Optimize Options.
          -falign-functions[=N] -falign-jumps[=N]
          -falign-labels[=N] -falign-loops[=N] -fassociative-math
          -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize
          -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves
          -fcheck-data-deps -fconserve-stack -fcprop-registers -fcrossjumping
          -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules -fcx-limited-range
          -fdata-sections -fdce -fdce
          -fdelayed-branch -fdelete-null-pointer-checks -fdse -fdse
          -fearly-inlining -fexpensive-optimizations -ffast-math
          -ffinite-math-only -ffloat-store -fforward-propagate
          -ffunction-sections -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm
          -fgcse-sm -fif-conversion -fif-conversion2 -findirect-inlining
          -finline-functions -finline-functions-called-once -finline-limit=N
          -finline-small-functions -fipa-cp -fipa-cp-clone -fipa-matrix-reorg -fipa-pta
          -fipa-pure-const -fipa-reference -fipa-struct-reorg
          -fipa-type-escape -fira-algorithm=ALGORITHM
          -fira-region=REGION -fira-coalesce -fno-ira-share-save-slots
          -fno-ira-share-spill-slots -fira-verbose=N
          -fivopts -fkeep-inline-functions -fkeep-static-consts
          -floop-block -floop-interchange -floop-strip-mine
          -fmerge-all-constants -fmerge-constants -fmodulo-sched
          -fmodulo-sched-allow-regmoves -fmove-loop-invariants -fmudflap
          -fmudflapir -fmudflapth -fno-branch-count-reg -fno-default-inline
          -fno-defer-pop -fno-function-cse -fno-guess-branch-probability
          -fno-inline -fno-math-errno -fno-peephole -fno-peephole2
          -fno-sched-interblock -fno-sched-spec -fno-signed-zeros
          -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss
          -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls
          -fpeel-loops -fpredictive-commoning -fprefetch-loop-arrays
          -fprofile-correction -fprofile-dir=PATH -fprofile-generate
          -fprofile-generate=PATH
          -fprofile-use -fprofile-use=PATH -fprofile-values
          -freciprocal-math -fregmove -frename-registers -freorder-blocks
          -freorder-blocks-and-partition -freorder-functions
          -frerun-cse-after-loop -freschedule-modulo-scheduled-loops
          -frounding-math -frtl-abstract-sequences -fsched2-use-superblocks
          -fsched2-use-traces -fsched-spec-load -fsched-spec-load-dangerous
          -fsched-stalled-insns-dep[=N] -fsched-stalled-insns[=N]
          -fschedule-insns -fschedule-insns2 -fsection-anchors -fsee
          -fselective-scheduling -fselective-scheduling2
          -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops
          -fsignaling-nans -fsingle-precision-constant -fsplit-ivs-in-unroller
          -fsplit-wide-types -fstack-protector -fstack-protector-all
          -fstrict-aliasing -fstrict-overflow -fthread-jumps -ftracer
          -ftree-builtin-call-dce -ftree-ccp -ftree-ch
          -ftree-coalesce-inline-vars -ftree-coalesce-vars
          -ftree-copy-prop -ftree-copyrename -ftree-dce
          -ftree-dominator-opts -ftree-dse -ftree-fre -ftree-loop-im
          -ftree-loop-distribution
          -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize
          -ftree-parallelize-loops=N -ftree-pre -ftree-reassoc
          -ftree-sink -ftree-sra -ftree-switch-conversion
          -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp
          -funit-at-a-time -funroll-all-loops -funroll-loops
          -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops
          -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb
          -fwhole-program
          --param NAME=VALUE
          -O  -O0  -O1  -O2  -O3  -Os

_Preprocessor Options_
     *Note Options Controlling the Preprocessor: Preprocessor Options.
          -AQUESTION=ANSWER
          -A-QUESTION[=ANSWER]
          -C  -dD  -dI  -dM  -dN
          -DMACRO[=DEFN]  -E  -H
          -idirafter DIR
          -include FILE  -imacros FILE
          -iprefix FILE  -iwithprefix DIR
          -iwithprefixbefore DIR  -isystem DIR
          -imultilib DIR -isysroot DIR
          -M  -MM  -MF  -MG  -MP  -MQ  -MT  -nostdinc
          -P  -fworking-directory  -remap
          -trigraphs  -undef  -UMACRO  -Wp,OPTION
          -Xpreprocessor OPTION

_Assembler Option_
     *Note Passing Options to the Assembler: Assembler Options.
          -Wa,OPTION  -Xassembler OPTION

_Linker Options_
     *Note Options for Linking: Link Options.
          OBJECT-FILE-NAME  -lLIBRARY
          -nostartfiles  -nodefaultlibs  -nostdlib -pie -rdynamic
          -s  -static  -static-libgcc  -shared  -shared-libgcc  -symbolic
          -T SCRIPT  -Wl,OPTION  -Xlinker OPTION
          -u SYMBOL

_Directory Options_
     *Note Options for Directory Search: Directory Options.
          -BPREFIX  -IDIR  -iquoteDIR  -LDIR
          -specs=FILE  -I- --sysroot=DIR

_Target Options_
     *Note Target Options::.
          -V VERSION  -b MACHINE

_Machine Dependent Options_
     *Note Hardware Models and Configurations: Submodel Options.

     _ARC Options_
          -EB  -EL
          -mmangle-cpu  -mcpu=CPU  -mtext=TEXT-SECTION
          -mdata=DATA-SECTION  -mrodata=READONLY-DATA-SECTION

     _ARM Options_
          -mapcs-frame  -mno-apcs-frame
          -mabi=NAME
          -mapcs-stack-check  -mno-apcs-stack-check
          -mapcs-float  -mno-apcs-float
          -mapcs-reentrant  -mno-apcs-reentrant
          -msched-prolog  -mno-sched-prolog
          -mlittle-endian  -mbig-endian  -mwords-little-endian
          -mfloat-abi=NAME  -msoft-float  -mhard-float  -mfpe
          -mthumb-interwork  -mno-thumb-interwork
          -mcpu=NAME  -march=NAME  -mfpu=NAME
          -mstructure-size-boundary=N
          -mabort-on-noreturn
          -mlong-calls  -mno-long-calls
          -msingle-pic-base  -mno-single-pic-base
          -mpic-register=REG
          -mnop-fun-dllimport
          -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns
          -mpoke-function-name
          -mthumb  -marm
          -mtpcs-frame  -mtpcs-leaf-frame
          -mcaller-super-interworking  -mcallee-super-interworking
          -mtp=NAME
          -mword-relocations
          -mfix-cortex-m3-ldrd

     _AVR Options_
          -mmcu=MCU  -msize  -mno-interrupts
          -mcall-prologues  -mno-tablejump  -mtiny-stack  -mint8

     _Blackfin Options_
          -mcpu=CPU[-SIREVISION]
          -msim -momit-leaf-frame-pointer  -mno-omit-leaf-frame-pointer
          -mspecld-anomaly  -mno-specld-anomaly  -mcsync-anomaly  -mno-csync-anomaly
          -mlow-64k -mno-low64k  -mstack-check-l1  -mid-shared-library
          -mno-id-shared-library  -mshared-library-id=N
          -mleaf-id-shared-library  -mno-leaf-id-shared-library
          -msep-data  -mno-sep-data  -mlong-calls  -mno-long-calls
          -mfast-fp -minline-plt -mmulticore  -mcorea  -mcoreb  -msdram
          -micplb

     _CRIS Options_
          -mcpu=CPU  -march=CPU  -mtune=CPU
          -mmax-stack-frame=N  -melinux-stacksize=N
          -metrax4  -metrax100  -mpdebug  -mcc-init  -mno-side-effects
          -mstack-align  -mdata-align  -mconst-align
          -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
          -melf  -maout  -melinux  -mlinux  -sim  -sim2
          -mmul-bug-workaround  -mno-mul-bug-workaround

     _CRX Options_
          -mmac -mpush-args

     _Darwin Options_
          -all_load  -allowable_client  -arch  -arch_errors_fatal
          -arch_only  -bind_at_load  -bundle  -bundle_loader
          -client_name  -compatibility_version  -current_version
          -dead_strip
          -dependency-file  -dylib_file  -dylinker_install_name
          -dynamic  -dynamiclib  -exported_symbols_list
          -filelist  -flat_namespace  -force_cpusubtype_ALL
          -force_flat_namespace  -headerpad_max_install_names
          -iframework
          -image_base  -init  -install_name  -keep_private_externs
          -multi_module  -multiply_defined  -multiply_defined_unused
          -noall_load   -no_dead_strip_inits_and_terms
          -nofixprebinding -nomultidefs  -noprebind  -noseglinkedit
          -pagezero_size  -prebind  -prebind_all_twolevel_modules
          -private_bundle  -read_only_relocs  -sectalign
          -sectobjectsymbols  -whyload  -seg1addr
          -sectcreate  -sectobjectsymbols  -sectorder
          -segaddr -segs_read_only_addr -segs_read_write_addr
          -seg_addr_table  -seg_addr_table_filename  -seglinkedit
          -segprot  -segs_read_only_addr  -segs_read_write_addr
          -single_module  -static  -sub_library  -sub_umbrella
          -twolevel_namespace  -umbrella  -undefined
          -unexported_symbols_list  -weak_reference_mismatches
          -whatsloaded -F -gused -gfull -mmacosx-version-min=VERSION
          -mkernel -mone-byte-bool

     _DEC Alpha Options_
          -mno-fp-regs  -msoft-float  -malpha-as  -mgas
          -mieee  -mieee-with-inexact  -mieee-conformant
          -mfp-trap-mode=MODE  -mfp-rounding-mode=MODE
          -mtrap-precision=MODE  -mbuild-constants
          -mcpu=CPU-TYPE  -mtune=CPU-TYPE
          -mbwx  -mmax  -mfix  -mcix
          -mfloat-vax  -mfloat-ieee
          -mexplicit-relocs  -msmall-data  -mlarge-data
          -msmall-text  -mlarge-text
          -mmemory-latency=TIME

     _DEC Alpha/VMS Options_
          -mvms-return-codes

     _FR30 Options_
          -msmall-model -mno-lsim

     _FRV Options_
          -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64
          -mhard-float  -msoft-float
          -malloc-cc  -mfixed-cc  -mdword  -mno-dword
          -mdouble  -mno-double
          -mmedia  -mno-media  -mmuladd  -mno-muladd
          -mfdpic  -minline-plt -mgprel-ro  -multilib-library-pic
          -mlinked-fp  -mlong-calls  -malign-labels
          -mlibrary-pic  -macc-4  -macc-8
          -mpack  -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
          -moptimize-membar -mno-optimize-membar
          -mscc  -mno-scc  -mcond-exec  -mno-cond-exec
          -mvliw-branch  -mno-vliw-branch
          -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
          -mno-nested-cond-exec  -mtomcat-stats
          -mTLS -mtls
          -mcpu=CPU

     _GNU/Linux Options_
          -muclibc

     _H8/300 Options_
          -mrelax  -mh  -ms  -mn  -mint32  -malign-300

     _HPPA Options_
          -march=ARCHITECTURE-TYPE
          -mbig-switch  -mdisable-fpregs  -mdisable-indexing
          -mfast-indirect-calls  -mgas  -mgnu-ld   -mhp-ld
          -mfixed-range=REGISTER-RANGE
          -mjump-in-delay -mlinker-opt -mlong-calls
          -mlong-load-store  -mno-big-switch  -mno-disable-fpregs
          -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
          -mno-jump-in-delay  -mno-long-load-store
          -mno-portable-runtime  -mno-soft-float
          -mno-space-regs  -msoft-float  -mpa-risc-1-0
          -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime
          -mschedule=CPU-TYPE  -mspace-regs  -msio  -mwsio
          -munix=UNIX-STD  -nolibdld  -static  -threads

     _i386 and x86-64 Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mfpmath=UNIT
          -masm=DIALECT  -mno-fancy-math-387
          -mno-fp-ret-in-387  -msoft-float
          -mno-wide-multiply  -mrtd  -malign-double
          -mpreferred-stack-boundary=NUM
          -mincoming-stack-boundary=NUM
          -mcld -mcx16 -msahf -mmovbe -mcrc32 -mrecip
          -mmmx  -msse  -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx
          -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfused-madd
          -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlwp
          -mthreads  -mno-align-stringops  -minline-all-stringops
          -minline-stringops-dynamically -mstringop-strategy=ALG
          -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
          -m96bit-long-double  -mregparm=NUM  -msseregparm
          -mveclibabi=TYPE -mpc32 -mpc64 -mpc80 -mstackrealign
          -momit-leaf-frame-pointer  -mno-red-zone -mno-tls-direct-seg-refs
          -mcmodel=CODE-MODEL
          -m32  -m64 -mlarge-data-threshold=NUM
          -msse2avx

     _i386 and x86-64 Windows Options_
          -mconsole -mcygwin -mno-cygwin -mdll
          -mnop-fun-dllimport -mthread -mwin32 -mwindows

     _IA-64 Options_
          -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld  -mno-pic
          -mvolatile-asm-stop  -mregister-names  -mno-sdata
          -mconstant-gp  -mauto-pic  -minline-float-divide-min-latency
          -minline-float-divide-max-throughput
          -minline-int-divide-min-latency
          -minline-int-divide-max-throughput
          -minline-sqrt-min-latency -minline-sqrt-max-throughput
          -mno-dwarf2-asm -mearly-stop-bits
          -mfixed-range=REGISTER-RANGE -mtls-size=TLS-SIZE
          -mtune=CPU-TYPE -mt -pthread -milp32 -mlp64
          -mno-sched-br-data-spec -msched-ar-data-spec -mno-sched-control-spec
          -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec
          -msched-ldc -mno-sched-control-ldc -mno-sched-spec-verbose
          -mno-sched-prefer-non-data-spec-insns
          -mno-sched-prefer-non-control-spec-insns
          -mno-sched-count-spec-in-critical-path

     _M32R/D Options_
          -m32r2 -m32rx -m32r
          -mdebug
          -malign-loops -mno-align-loops
          -missue-rate=NUMBER
          -mbranch-cost=NUMBER
          -mmodel=CODE-SIZE-MODEL-TYPE
          -msdata=SDATA-TYPE
          -mno-flush-func -mflush-func=NAME
          -mno-flush-trap -mflush-trap=NUMBER
          -G NUM

     _M32C Options_
          -mcpu=CPU -msim -memregs=NUMBER

     _M680x0 Options_
          -march=ARCH  -mcpu=CPU  -mtune=TUNE
          -m68000  -m68020  -m68020-40  -m68020-60  -m68030  -m68040
          -m68060  -mcpu32  -m5200  -m5206e  -m528x  -m5307  -m5407
          -mcfv4e  -mbitfield  -mno-bitfield  -mc68000  -mc68020
          -mnobitfield  -mrtd  -mno-rtd  -mdiv  -mno-div  -mshort
          -mno-short  -mhard-float  -m68881  -msoft-float  -mpcrel
          -malign-int  -mstrict-align  -msep-data  -mno-sep-data
          -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library
          -mxgot -mno-xgot

     _M68hc1x Options_
          -m6811  -m6812  -m68hc11  -m68hc12   -m68hcs12
          -mauto-incdec  -minmax  -mlong-calls  -mshort
          -msoft-reg-count=COUNT

     _MCore Options_
          -mhardlit  -mno-hardlit  -mdiv  -mno-div  -mrelax-immediates
          -mno-relax-immediates  -mwide-bitfields  -mno-wide-bitfields
          -m4byte-functions  -mno-4byte-functions  -mcallgraph-data
          -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes  -mno-lsim
          -mlittle-endian  -mbig-endian  -m210  -m340  -mstack-increment

     _MIPS Options_
          -EL  -EB  -march=ARCH  -mtune=ARCH
          -mips1  -mips2  -mips3  -mips4  -mips32  -mips32r2
          -mips64  -mips64r2
          -mips16  -mno-mips16  -mflip-mips16
          -minterlink-mips16  -mno-interlink-mips16
          -mabi=ABI  -mabicalls  -mno-abicalls
          -mshared  -mno-shared  -mplt  -mno-plt  -mxgot  -mno-xgot
          -mgp32  -mgp64  -mfp32  -mfp64  -mhard-float  -msoft-float
          -msingle-float  -mdouble-float  -mdsp  -mno-dsp  -mdspr2  -mno-dspr2
          -mfpu=FPU-TYPE
          -msmartmips  -mno-smartmips
          -mpaired-single  -mno-paired-single  -mdmx  -mno-mdmx
          -mips3d  -mno-mips3d  -mmt  -mno-mt  -mllsc  -mno-llsc
          -mlong64  -mlong32  -msym32  -mno-sym32
          -GNUM  -mlocal-sdata  -mno-local-sdata
          -mextern-sdata  -mno-extern-sdata  -mgpopt  -mno-gopt
          -membedded-data  -mno-embedded-data
          -muninit-const-in-rodata  -mno-uninit-const-in-rodata
          -mcode-readable=SETTING
          -msplit-addresses  -mno-split-addresses
          -mexplicit-relocs  -mno-explicit-relocs
          -mcheck-zero-division  -mno-check-zero-division
          -mdivide-traps  -mdivide-breaks
          -mmemcpy  -mno-memcpy  -mlong-calls  -mno-long-calls
          -mmad  -mno-mad  -mfused-madd  -mno-fused-madd  -nocpp
          -mfix-r4000  -mno-fix-r4000  -mfix-r4400  -mno-fix-r4400
          -mfix-r10000 -mno-fix-r10000  -mfix-vr4120  -mno-fix-vr4120
          -mfix-vr4130  -mno-fix-vr4130  -mfix-sb1  -mno-fix-sb1
          -mflush-func=FUNC  -mno-flush-func
          -mbranch-cost=NUM  -mbranch-likely  -mno-branch-likely
          -mfp-exceptions -mno-fp-exceptions
          -mvr4130-align -mno-vr4130-align

     _MMIX Options_
          -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon  -mabi=gnu
          -mabi=mmixware  -mzero-extend  -mknuthdiv  -mtoplevel-symbols
          -melf  -mbranch-predict  -mno-branch-predict  -mbase-addresses
          -mno-base-addresses  -msingle-exit  -mno-single-exit

     _MN10300 Options_
          -mmult-bug  -mno-mult-bug
          -mam33  -mno-am33
          -mam33-2  -mno-am33-2
          -mreturn-pointer-on-d0
          -mno-crt0  -mrelax

     _PDP-11 Options_
          -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10
          -mbcopy  -mbcopy-builtin  -mint32  -mno-int16
          -mint16  -mno-int32  -mfloat32  -mno-float64
          -mfloat64  -mno-float32  -mabshi  -mno-abshi
          -mbranch-expensive  -mbranch-cheap
          -msplit  -mno-split  -munix-asm  -mdec-asm

     _picoChip Options_
          -mae=AE_TYPE -mvliw-lookahead=N
          -msymbol-as-address -mno-inefficient-warnings

     _PowerPC Options_ See RS/6000 and PowerPC Options.

     _RS/6000 and PowerPC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -mpower  -mno-power  -mpower2  -mno-power2
          -mpowerpc  -mpowerpc64  -mno-powerpc
          -maltivec  -mno-altivec
          -mpowerpc-gpopt  -mno-powerpc-gpopt
          -mpowerpc-gfxopt  -mno-powerpc-gfxopt
          -mmfcrf  -mno-mfcrf  -mpopcntb  -mno-popcntb -mpopcntd -mno-popcntd
          -mfprnd  -mno-fprnd
          -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp
          -mnew-mnemonics  -mold-mnemonics
          -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc
          -m64  -m32  -mxl-compat  -mno-xl-compat  -mpe
          -malign-power  -malign-natural
          -msoft-float  -mhard-float  -mmultiple  -mno-multiple
          -msingle-float -mdouble-float -msimple-fpu
          -mstring  -mno-string  -mupdate  -mno-update
          -mavoid-indexed-addresses  -mno-avoid-indexed-addresses
          -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
          -mstrict-align  -mno-strict-align  -mrelocatable
          -mno-relocatable  -mrelocatable-lib  -mno-relocatable-lib
          -mtoc  -mno-toc  -mlittle  -mlittle-endian  -mbig  -mbig-endian
          -mdynamic-no-pic  -maltivec -mswdiv
          -mprioritize-restricted-insns=PRIORITY
          -msched-costly-dep=DEPENDENCE_TYPE
          -minsert-sched-nops=SCHEME
          -mcall-sysv  -mcall-netbsd
          -maix-struct-return  -msvr4-struct-return
          -mabi=ABI-TYPE -msecure-plt -mbss-plt
          -misel -mno-isel
          -misel=yes  -misel=no
          -mspe -mno-spe
          -mspe=yes  -mspe=no
          -mpaired
          -mgen-cell-microcode -mwarn-cell-microcode
          -mvrsave -mno-vrsave
          -mmulhw -mno-mulhw
          -mdlmzb -mno-dlmzb
          -mfloat-gprs=yes  -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double
          -mprototype  -mno-prototype
          -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
          -msdata=OPT  -mvxworks  -G NUM  -pthread

     _S/390 and zSeries Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mhard-float  -msoft-float  -mhard-dfp -mno-hard-dfp
          -mlong-double-64 -mlong-double-128
          -mbackchain  -mno-backchain -mpacked-stack  -mno-packed-stack
          -msmall-exec  -mno-small-exec  -mmvcle -mno-mvcle
          -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch
          -mtpf-trace -mno-tpf-trace  -mfused-madd  -mno-fused-madd
          -mwarn-framesize  -mwarn-dynamicstack  -mstack-size -mstack-guard
          -mhotpatch=HALFWORDS,HALFWORDS

     _Score Options_
          -meb -mel
          -mnhwloop
          -muls
          -mmac
          -mscore5 -mscore5u -mscore7 -mscore7d

     _SH Options_
          -m1  -m2  -m2e  -m3  -m3e
          -m4-nofpu  -m4-single-only  -m4-single  -m4
          -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al
          -m5-64media  -m5-64media-nofpu
          -m5-32media  -m5-32media-nofpu
          -m5-compact  -m5-compact-nofpu
          -mb  -ml  -mdalign  -mrelax
          -mbigtable  -mfmovd  -mhitachi -mrenesas -mno-renesas -mnomacsave
          -mieee  -mbitops  -misize  -minline-ic_invalidate -mpadstruct  -mspace
          -mprefergot  -musermode -multcost=NUMBER -mdiv=STRATEGY
          -mdivsi3_libfunc=NAME -mfixed-range=REGISTER-RANGE
          -madjust-unroll -mindexed-addressing -mgettrcost=NUMBER -mpt-fixed
          -minvalid-symbols

     _SPARC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -m32  -m64  -mapp-regs  -mno-app-regs
          -mfaster-structs  -mno-faster-structs
          -mfpu  -mno-fpu  -mhard-float  -msoft-float
          -mhard-quad-float  -msoft-quad-float
          -mimpure-text  -mno-impure-text  -mlittle-endian
          -mstack-bias  -mno-stack-bias
          -munaligned-doubles  -mno-unaligned-doubles
          -mv8plus  -mno-v8plus  -mvis  -mno-vis
          -threads -pthreads -pthread

     _SPU Options_
          -mwarn-reloc -merror-reloc
          -msafe-dma -munsafe-dma
          -mbranch-hints
          -msmall-mem -mlarge-mem -mstdmain
          -mfixed-range=REGISTER-RANGE

     _System V Options_
          -Qy  -Qn  -YP,PATHS  -Ym,DIR

     _V850 Options_
          -mlong-calls  -mno-long-calls  -mep  -mno-ep
          -mprolog-function  -mno-prolog-function  -mspace
          -mtda=N  -msda=N  -mzda=N
          -mapp-regs  -mno-app-regs
          -mdisable-callt  -mno-disable-callt
          -mv850e1
          -mv850e
          -mv850  -mbig-switch

     _VAX Options_
          -mg  -mgnu  -munix

     _VxWorks Options_
          -mrtp  -non-static  -Bstatic  -Bdynamic
          -Xbind-lazy  -Xbind-now

     _x86-64 Options_ See i386 and x86-64 Options.

     _Xstormy16 Options_
          -msim

     _Xtensa Options_
          -mconst16 -mno-const16
          -mfused-madd  -mno-fused-madd
          -mserialize-volatile  -mno-serialize-volatile
          -mtext-section-literals  -mno-text-section-literals
          -mtarget-align  -mno-target-align
          -mlongcalls  -mno-longcalls

     _zSeries Options_ See S/390 and zSeries Options.

_Code Generation Options_
     *Note Options for Code Generation Conventions: Code Gen Options.
          -fcall-saved-REG  -fcall-used-REG
          -ffixed-REG  -fexceptions
          -fnon-call-exceptions  -funwind-tables
          -fasynchronous-unwind-tables
          -finhibit-size-directive  -finstrument-functions
          -finstrument-functions-exclude-function-list=SYM,SYM,...
          -finstrument-functions-exclude-file-list=FILE,FILE,...
          -fno-common  -fno-ident
          -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
          -fno-jump-tables
          -frecord-gcc-switches
          -freg-struct-return  -fshort-enums
          -fshort-double  -fshort-wchar
          -fverbose-asm  -fpack-struct[=N]  -fstack-check
          -fstack-limit-register=REG  -fstack-limit-symbol=SYM
          -fno-stack-limit  -fargument-alias  -fargument-noalias
          -fargument-noalias-global  -fargument-noalias-anything
          -fleading-underscore  -ftls-model=MODEL
          -ftrapv  -fwrapv  -fbounds-check
          -fvisibility


* Menu:

* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C
                        and Objective-C++.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.

File: gcc.info,  Node: Overall Options,  Next: Invoking G++,  Prev: Option Summary,  Up: Invoking GCC

3.2 Options Controlling the Kind of Output
==========================================

Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order.  GCC is capable of
preprocessing and compiling several files either into several assembler
input files, or into one assembler input file; then each assembler
input file produces an object file, and linking combines all the object
files (those newly compiled, and those specified as input) into an
executable file.

 For any given input file, the file name suffix determines what kind of
compilation is done:

`FILE.c'
     C source code which must be preprocessed.

`FILE.i'
     C source code which should not be preprocessed.

`FILE.ii'
     C++ source code which should not be preprocessed.

`FILE.m'
     Objective-C source code.  Note that you must link with the
     `libobjc' library to make an Objective-C program work.

`FILE.mi'
     Objective-C source code which should not be preprocessed.

`FILE.mm'
`FILE.M'
     Objective-C++ source code.  Note that you must link with the
     `libobjc' library to make an Objective-C++ program work.  Note
     that `.M' refers to a literal capital M.

`FILE.mii'
     Objective-C++ source code which should not be preprocessed.

`FILE.h'
     C, C++, Objective-C or Objective-C++ header file to be turned into
     a precompiled header.

`FILE.cc'
`FILE.cp'
`FILE.cxx'
`FILE.cpp'
`FILE.CPP'
`FILE.c++'
`FILE.C'
     C++ source code which must be preprocessed.  Note that in `.cxx',
     the last two letters must both be literally `x'.  Likewise, `.C'
     refers to a literal capital C.

`FILE.mm'
`FILE.M'
     Objective-C++ source code which must be preprocessed.

`FILE.mii'
     Objective-C++ source code which should not be preprocessed.

`FILE.hh'
`FILE.H'
`FILE.hp'
`FILE.hxx'
`FILE.hpp'
`FILE.HPP'
`FILE.h++'
`FILE.tcc'
     C++ header file to be turned into a precompiled header.

`FILE.f'
`FILE.for'
`FILE.ftn'
     Fixed form Fortran source code which should not be preprocessed.

`FILE.F'
`FILE.FOR'
`FILE.fpp'
`FILE.FPP'
`FILE.FTN'
     Fixed form Fortran source code which must be preprocessed (with
     the traditional preprocessor).

`FILE.f90'
`FILE.f95'
`FILE.f03'
`FILE.f08'
     Free form Fortran source code which should not be preprocessed.

`FILE.F90'
`FILE.F95'
`FILE.F03'
`FILE.F08'
     Free form Fortran source code which must be preprocessed (with the
     traditional preprocessor).

`FILE.ads'
     Ada source code file which contains a library unit declaration (a
     declaration of a package, subprogram, or generic, or a generic
     instantiation), or a library unit renaming declaration (a package,
     generic, or subprogram renaming declaration).  Such files are also
     called "specs".

`FILE.adb'
     Ada source code file containing a library unit body (a subprogram
     or package body).  Such files are also called "bodies".

`FILE.s'
     Assembler code.

`FILE.S'
`FILE.sx'
     Assembler code which must be preprocessed.

`OTHER'
     An object file to be fed straight into linking.  Any file name
     with no recognized suffix is treated this way.

 You can specify the input language explicitly with the `-x' option:

`-x LANGUAGE'
     Specify explicitly the LANGUAGE for the following input files
     (rather than letting the compiler choose a default based on the
     file name suffix).  This option applies to all following input
     files until the next `-x' option.  Possible values for LANGUAGE
     are:
          c  c-header  c-cpp-output
          c++  c++-header  c++-cpp-output
          objective-c  objective-c-header  objective-c-cpp-output
          objective-c++ objective-c++-header objective-c++-cpp-output
          assembler  assembler-with-cpp
          ada
          f77  f77-cpp-input f95  f95-cpp-input
          java

`-x none'
     Turn off any specification of a language, so that subsequent files
     are handled according to their file name suffixes (as they are if
     `-x' has not been used at all).

`-pass-exit-codes'
     Normally the `gcc' program will exit with the code of 1 if any
     phase of the compiler returns a non-success return code.  If you
     specify `-pass-exit-codes', the `gcc' program will instead return
     with numerically highest error produced by any phase that returned
     an error indication.  The C, C++, and Fortran frontends return 4,
     if an internal compiler error is encountered.

 If you only want some of the stages of compilation, you can use `-x'
(or filename suffixes) to tell `gcc' where to start, and one of the
options `-c', `-S', or `-E' to say where `gcc' is to stop.  Note that
some combinations (for example, `-x cpp-output -E') instruct `gcc' to
do nothing at all.

`-c'
     Compile or assemble the source files, but do not link.  The linking
     stage simply is not done.  The ultimate output is in the form of an
     object file for each source file.

     By default, the object file name for a source file is made by
     replacing the suffix `.c', `.i', `.s', etc., with `.o'.

     Unrecognized input files, not requiring compilation or assembly,
     are ignored.

`-S'
     Stop after the stage of compilation proper; do not assemble.  The
     output is in the form of an assembler code file for each
     non-assembler input file specified.

     By default, the assembler file name for a source file is made by
     replacing the suffix `.c', `.i', etc., with `.s'.

     Input files that don't require compilation are ignored.

`-E'
     Stop after the preprocessing stage; do not run the compiler
     proper.  The output is in the form of preprocessed source code,
     which is sent to the standard output.

     Input files which don't require preprocessing are ignored.

`-o FILE'
     Place output in file FILE.  This applies regardless to whatever
     sort of output is being produced, whether it be an executable file,
     an object file, an assembler file or preprocessed C code.

     If `-o' is not specified, the default is to put an executable file
     in `a.out', the object file for `SOURCE.SUFFIX' in `SOURCE.o', its
     assembler file in `SOURCE.s', a precompiled header file in
     `SOURCE.SUFFIX.gch', and all preprocessed C source on standard
     output.

`-v'
     Print (on standard error output) the commands executed to run the
     stages of compilation.  Also print the version number of the
     compiler driver program and of the preprocessor and the compiler
     proper.

`-###'
     Like `-v' except the commands are not executed and all command
     arguments are quoted.  This is useful for shell scripts to capture
     the driver-generated command lines.

`-pipe'
     Use pipes rather than temporary files for communication between the
     various stages of compilation.  This fails to work on some systems
     where the assembler is unable to read from a pipe; but the GNU
     assembler has no trouble.

`-combine'
     If you are compiling multiple source files, this option tells the
     driver to pass all the source files to the compiler at once (for
     those languages for which the compiler can handle this).  This
     will allow intermodule analysis (IMA) to be performed by the
     compiler.  Currently the only language for which this is supported
     is C.  If you pass source files for multiple languages to the
     driver, using this option, the driver will invoke the compiler(s)
     that support IMA once each, passing each compiler all the source
     files appropriate for it.  For those languages that do not support
     IMA this option will be ignored, and the compiler will be invoked
     once for each source file in that language.  If you use this
     option in conjunction with `-save-temps', the compiler will
     generate multiple pre-processed files (one for each source file),
     but only one (combined) `.o' or `.s' file.

`--help'
     Print (on the standard output) a description of the command line
     options understood by `gcc'.  If the `-v' option is also specified
     then `--help' will also be passed on to the various processes
     invoked by `gcc', so that they can display the command line options
     they accept.  If the `-Wextra' option has also been specified
     (prior to the `--help' option), then command line options which
     have no documentation associated with them will also be displayed.

`--target-help'
     Print (on the standard output) a description of target-specific
     command line options for each tool.  For some targets extra
     target-specific information may also be printed.

`--help={CLASS|[^]QUALIFIER}[,...]'
     Print (on the standard output) a description of the command line
     options understood by the compiler that fit into all specified
     classes and qualifiers.  These are the supported classes:

    `optimizers'
          This will display all of the optimization options supported
          by the compiler.

    `warnings'
          This will display all of the options controlling warning
          messages produced by the compiler.

    `target'
          This will display target-specific options.  Unlike the
          `--target-help' option however, target-specific options of the
          linker and assembler will not be displayed.  This is because
          those tools do not currently support the extended `--help='
          syntax.

    `params'
          This will display the values recognized by the `--param'
          option.

    LANGUAGE
          This will display the options supported for LANGUAGE, where
          LANGUAGE is the name of one of the languages supported in this
          version of GCC.

    `common'
          This will display the options that are common to all
          languages.

     These are the supported qualifiers:

    `undocumented'
          Display only those options which are undocumented.

    `joined'
          Display options which take an argument that appears after an
          equal sign in the same continuous piece of text, such as:
          `--help=target'.

    `separate'
          Display options which take an argument that appears as a
          separate word following the original option, such as: `-o
          output-file'.

     Thus for example to display all the undocumented target-specific
     switches supported by the compiler the following can be used:

          --help=target,undocumented

     The sense of a qualifier can be inverted by prefixing it with the
     `^' character, so for example to display all binary warning
     options (i.e., ones that are either on or off and that do not take
     an argument), which have a description the following can be used:

          --help=warnings,^joined,^undocumented

     The argument to `--help=' should not consist solely of inverted
     qualifiers.

     Combining several classes is possible, although this usually
     restricts the output by so much that there is nothing to display.
     One case where it does work however is when one of the classes is
     TARGET.  So for example to display all the target-specific
     optimization options the following can be used:

          --help=target,optimizers

     The `--help=' option can be repeated on the command line.  Each
     successive use will display its requested class of options,
     skipping those that have already been displayed.

     If the `-Q' option appears on the command line before the
     `--help=' option, then the descriptive text displayed by `--help='
     is changed.  Instead of describing the displayed options, an
     indication is given as to whether the option is enabled, disabled
     or set to a specific value (assuming that the compiler knows this
     at the point where the `--help=' option is used).

     Here is a truncated example from the ARM port of `gcc':

            % gcc -Q -mabi=2 --help=target -c
            The following options are target specific:
            -mabi=                                2
            -mabort-on-noreturn                   [disabled]
            -mapcs                                [disabled]

     The output is sensitive to the effects of previous command line
     options, so for example it is possible to find out which
     optimizations are enabled at `-O2' by using:

          -Q -O2 --help=optimizers

     Alternatively you can discover which binary optimizations are
     enabled by `-O3' by using:

          gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
          gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
          diff /tmp/O2-opts /tmp/O3-opts | grep enabled

`--version'
     Display the version number and copyrights of the invoked GCC.

`-wrapper'
     Invoke all subcommands under a wrapper program. It takes a single
     comma separated list as an argument, which will be used to invoke
     the wrapper:

          gcc -c t.c -wrapper gdb,--args

     This will invoke all subprograms of gcc under "gdb -args", thus
     cc1 invocation will be "gdb -args cc1 ...".

`@FILE'
     Read command-line options from FILE.  The options read are
     inserted in place of the original @FILE option.  If FILE does not
     exist, or cannot be read, then the option will be treated
     literally, and not removed.

     Options in FILE are separated by whitespace.  A whitespace
     character may be included in an option by surrounding the entire
     option in either single or double quotes.  Any character
     (including a backslash) may be included by prefixing the character
     to be included with a backslash.  The FILE may itself contain
     additional @FILE options; any such options will be processed
     recursively.

File: gcc.info,  Node: C Dialect Options,  Next: C++ Dialect Options,  Prev: Invoking G++,  Up: Invoking GCC

3.4 Options Controlling C Dialect
=================================

The following options control the dialect of C (or languages derived
from C, such as C++, Objective-C and Objective-C++) that the compiler
accepts:

`-ansi'
     In C mode, this is equivalent to `-std=c89'. In C++ mode, it is
     equivalent to `-std=c++98'.

     This turns off certain features of GCC that are incompatible with
     ISO C90 (when compiling C code), or of standard C++ (when
     compiling C++ code), such as the `asm' and `typeof' keywords, and
     predefined macros such as `unix' and `vax' that identify the type
     of system you are using.  It also enables the undesirable and
     rarely used ISO trigraph feature.  For the C compiler, it disables
     recognition of C++ style `//' comments as well as the `inline'
     keyword.

     The alternate keywords `__asm__', `__extension__', `__inline__'
     and `__typeof__' continue to work despite `-ansi'.  You would not
     want to use them in an ISO C program, of course, but it is useful
     to put them in header files that might be included in compilations
     done with `-ansi'.  Alternate predefined macros such as `__unix__'
     and `__vax__' are also available, with or without `-ansi'.

     The `-ansi' option does not cause non-ISO programs to be rejected
     gratuitously.  For that, `-pedantic' is required in addition to
     `-ansi'.  *Note Warning Options::.

     The macro `__STRICT_ANSI__' is predefined when the `-ansi' option
     is used.  Some header files may notice this macro and refrain from
     declaring certain functions or defining certain macros that the
     ISO standard doesn't call for; this is to avoid interfering with
     any programs that might use these names for other things.

     Functions that would normally be built in but do not have semantics
     defined by ISO C (such as `alloca' and `ffs') are not built-in
     functions when `-ansi' is used.  *Note Other built-in functions
     provided by GCC: Other Builtins, for details of the functions
     affected.

`-std='
     Determine the language standard. *Note Language Standards
     Supported by GCC: Standards, for details of these standard
     versions.  This option is currently only supported when compiling
     C or C++.

     The compiler can accept several base standards, such as `c89' or
     `c++98', and GNU dialects of those standards, such as `gnu89' or
     `gnu++98'.  By specifying a base standard, the compiler will
     accept all programs following that standard and those using GNU
     extensions that do not contradict it.  For example, `-std=c89'
     turns off certain features of GCC that are incompatible with ISO
     C90, such as the `asm' and `typeof' keywords, but not other GNU
     extensions that do not have a meaning in ISO C90, such as omitting
     the middle term of a `?:' expression. On the other hand, by
     specifying a GNU dialect of a standard, all features the compiler
     support are enabled, even when those features change the meaning
     of the base standard and some strict-conforming programs may be
     rejected.  The particular standard is used by `-pedantic' to
     identify which features are GNU extensions given that version of
     the standard. For example `-std=gnu89 -pedantic' would warn about
     C++ style `//' comments, while `-std=gnu99 -pedantic' would not.

     A value for this option must be provided; possible values are

    `c89'
    `iso9899:1990'
          Support all ISO C90 programs (certain GNU extensions that
          conflict with ISO C90 are disabled). Same as `-ansi' for C
          code.

    `iso9899:199409'
          ISO C90 as modified in amendment 1.

    `c99'
    `c9x'
    `iso9899:1999'
    `iso9899:199x'
          ISO C99.  Note that this standard is not yet fully supported;
          see `http://gcc.gnu.org/gcc-4.4/c99status.html' for more
          information.  The names `c9x' and `iso9899:199x' are
          deprecated.

    `gnu89'
          GNU dialect of ISO C90 (including some C99 features). This is
          the default for C code.

    `gnu99'
    `gnu9x'
          GNU dialect of ISO C99.  When ISO C99 is fully implemented in
          GCC, this will become the default.  The name `gnu9x' is
          deprecated.

    `c++98'
          The 1998 ISO C++ standard plus amendments. Same as `-ansi' for
          C++ code.

    `gnu++98'
          GNU dialect of `-std=c++98'.  This is the default for C++
          code.

    `c++0x'
          The working draft of the upcoming ISO C++0x standard. This
          option enables experimental features that are likely to be
          included in C++0x. The working draft is constantly changing,
          and any feature that is enabled by this flag may be removed
          from future versions of GCC if it is not part of the C++0x
          standard.

    `gnu++0x'
          GNU dialect of `-std=c++0x'. This option enables experimental
          features that may be removed in future versions of GCC.

`-fgnu89-inline'
     The option `-fgnu89-inline' tells GCC to use the traditional GNU
     semantics for `inline' functions when in C99 mode.  *Note An
     Inline Function is As Fast As a Macro: Inline.  This option is
     accepted and ignored by GCC versions 4.1.3 up to but not including
     4.3.  In GCC versions 4.3 and later it changes the behavior of GCC
     in C99 mode.  Using this option is roughly equivalent to adding the
     `gnu_inline' function attribute to all inline functions (*note
     Function Attributes::).

     The option `-fno-gnu89-inline' explicitly tells GCC to use the C99
     semantics for `inline' when in C99 or gnu99 mode (i.e., it
     specifies the default behavior).  This option was first supported
     in GCC 4.3.  This option is not supported in C89 or gnu89 mode.

     The preprocessor macros `__GNUC_GNU_INLINE__' and
     `__GNUC_STDC_INLINE__' may be used to check which semantics are in
     effect for `inline' functions.  *Note Common Predefined Macros:
     (cpp)Common Predefined Macros.

`-aux-info FILENAME'
     Output to the given filename prototyped declarations for all
     functions declared and/or defined in a translation unit, including
     those in header files.  This option is silently ignored in any
     language other than C.

     Besides declarations, the file indicates, in comments, the origin
     of each declaration (source file and line), whether the
     declaration was implicit, prototyped or unprototyped (`I', `N' for
     new or `O' for old, respectively, in the first character after the
     line number and the colon), and whether it came from a declaration
     or a definition (`C' or `F', respectively, in the following
     character).  In the case of function definitions, a K&R-style list
     of arguments followed by their declarations is also provided,
     inside comments, after the declaration.

`-fno-asm'
     Do not recognize `asm', `inline' or `typeof' as a keyword, so that
     code can use these words as identifiers.  You can use the keywords
     `__asm__', `__inline__' and `__typeof__' instead.  `-ansi' implies
     `-fno-asm'.

     In C++, this switch only affects the `typeof' keyword, since `asm'
     and `inline' are standard keywords.  You may want to use the
     `-fno-gnu-keywords' flag instead, which has the same effect.  In
     C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects
     the `asm' and `typeof' keywords, since `inline' is a standard
     keyword in ISO C99.

`-fno-builtin'
`-fno-builtin-FUNCTION'
     Don't recognize built-in functions that do not begin with
     `__builtin_' as prefix.  *Note Other built-in functions provided
     by GCC: Other Builtins, for details of the functions affected,
     including those which are not built-in functions when `-ansi' or
     `-std' options for strict ISO C conformance are used because they
     do not have an ISO standard meaning.

     GCC normally generates special code to handle certain built-in
     functions more efficiently; for instance, calls to `alloca' may
     become single instructions that adjust the stack directly, and
     calls to `memcpy' may become inline copy loops.  The resulting
     code is often both smaller and faster, but since the function
     calls no longer appear as such, you cannot set a breakpoint on
     those calls, nor can you change the behavior of the functions by
     linking with a different library.  In addition, when a function is
     recognized as a built-in function, GCC may use information about
     that function to warn about problems with calls to that function,
     or to generate more efficient code, even if the resulting code
     still contains calls to that function.  For example, warnings are
     given with `-Wformat' for bad calls to `printf', when `printf' is
     built in, and `strlen' is known not to modify global memory.

     With the `-fno-builtin-FUNCTION' option only the built-in function
     FUNCTION is disabled.  FUNCTION must not begin with `__builtin_'.
     If a function is named that is not built-in in this version of
     GCC, this option is ignored.  There is no corresponding
     `-fbuiltin-FUNCTION' option; if you wish to enable built-in
     functions selectively when using `-fno-builtin' or
     `-ffreestanding', you may define macros such as:

          #define abs(n)          __builtin_abs ((n))
          #define strcpy(d, s)    __builtin_strcpy ((d), (s))

`-fhosted'
     Assert that compilation takes place in a hosted environment.  This
     implies `-fbuiltin'.  A hosted environment is one in which the
     entire standard library is available, and in which `main' has a
     return type of `int'.  Examples are nearly everything except a
     kernel.  This is equivalent to `-fno-freestanding'.

`-ffreestanding'
     Assert that compilation takes place in a freestanding environment.
     This implies `-fno-builtin'.  A freestanding environment is one in
     which the standard library may not exist, and program startup may
     not necessarily be at `main'.  The most obvious example is an OS
     kernel.  This is equivalent to `-fno-hosted'.

     *Note Language Standards Supported by GCC: Standards, for details
     of freestanding and hosted environments.

`-fopenmp'
     Enable handling of OpenMP directives `#pragma omp' in C/C++ and
     `!$omp' in Fortran.  When `-fopenmp' is specified, the compiler
     generates parallel code according to the OpenMP Application
     Program Interface v2.5 `http://www.openmp.org/'.  This option
     implies `-pthread', and thus is only supported on targets that
     have support for `-pthread'.

`-fms-extensions'
     Accept some non-standard constructs used in Microsoft header files.

     Some cases of unnamed fields in structures and unions are only
     accepted with this option.  *Note Unnamed struct/union fields
     within structs/unions: Unnamed Fields, for details.

`-trigraphs'
     Support ISO C trigraphs.  The `-ansi' option (and `-std' options
     for strict ISO C conformance) implies `-trigraphs'.

`-no-integrated-cpp'
     Performs a compilation in two passes: preprocessing and compiling.
     This option allows a user supplied "cc1", "cc1plus", or "cc1obj"
     via the `-B' option.  The user supplied compilation step can then
     add in an additional preprocessing step after normal preprocessing
     but before compiling.  The default is to use the integrated cpp
     (internal cpp)

     The semantics of this option will change if "cc1", "cc1plus", and
     "cc1obj" are merged.

`-traditional'
`-traditional-cpp'
     Formerly, these options caused GCC to attempt to emulate a
     pre-standard C compiler.  They are now only supported with the
     `-E' switch.  The preprocessor continues to support a pre-standard
     mode.  See the GNU CPP manual for details.

`-fcond-mismatch'
     Allow conditional expressions with mismatched types in the second
     and third arguments.  The value of such an expression is void.
     This option is not supported for C++.

`-flax-vector-conversions'
     Allow implicit conversions between vectors with differing numbers
     of elements and/or incompatible element types.  This option should
     not be used for new code.

`-funsigned-char'
     Let the type `char' be unsigned, like `unsigned char'.

     Each kind of machine has a default for what `char' should be.  It
     is either like `unsigned char' by default or like `signed char' by
     default.

     Ideally, a portable program should always use `signed char' or
     `unsigned char' when it depends on the signedness of an object.
     But many programs have been written to use plain `char' and expect
     it to be signed, or expect it to be unsigned, depending on the
     machines they were written for.  This option, and its inverse, let
     you make such a program work with the opposite default.

     The type `char' is always a distinct type from each of `signed
     char' or `unsigned char', even though its behavior is always just
     like one of those two.

`-fsigned-char'
     Let the type `char' be signed, like `signed char'.

     Note that this is equivalent to `-fno-unsigned-char', which is the
     negative form of `-funsigned-char'.  Likewise, the option
     `-fno-signed-char' is equivalent to `-funsigned-char'.

`-fsigned-bitfields'
`-funsigned-bitfields'
`-fno-signed-bitfields'
`-fno-unsigned-bitfields'
     These options control whether a bit-field is signed or unsigned,
     when the declaration does not use either `signed' or `unsigned'.
     By default, such a bit-field is signed, because this is
     consistent: the basic integer types such as `int' are signed types.

File: gcc.info,  Node: C++ Dialect Options,  Next: Objective-C and Objective-C++ Dialect Options,  Prev: C Dialect Options,  Up: Invoking GCC

3.5 Options Controlling C++ Dialect
===================================

This section describes the command-line options that are only meaningful
for C++ programs; but you can also use most of the GNU compiler options
regardless of what language your program is in.  For example, you might
compile a file `firstClass.C' like this:

     g++ -g -frepo -O -c firstClass.C

In this example, only `-frepo' is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.

 Here is a list of options that are _only_ for compiling C++ programs:

`-fabi-version=N'
     Use version N of the C++ ABI.  Version 2 is the version of the C++
     ABI that first appeared in G++ 3.4.  Version 1 is the version of
     the C++ ABI that first appeared in G++ 3.2.  Version 0 will always
     be the version that conforms most closely to the C++ ABI
     specification.  Therefore, the ABI obtained using version 0 will
     change as ABI bugs are fixed.

     The default is version 2.

`-fno-access-control'
     Turn off all access checking.  This switch is mainly useful for
     working around bugs in the access control code.

`-fcheck-new'
     Check that the pointer returned by `operator new' is non-null
     before attempting to modify the storage allocated.  This check is
     normally unnecessary because the C++ standard specifies that
     `operator new' will only return `0' if it is declared `throw()',
     in which case the compiler will always check the return value even
     without this option.  In all other cases, when `operator new' has
     a non-empty exception specification, memory exhaustion is
     signalled by throwing `std::bad_alloc'.  See also `new (nothrow)'.

`-fconserve-space'
     Put uninitialized or runtime-initialized global variables into the
     common segment, as C does.  This saves space in the executable at
     the cost of not diagnosing duplicate definitions.  If you compile
     with this flag and your program mysteriously crashes after
     `main()' has completed, you may have an object that is being
     destroyed twice because two definitions were merged.

     This option is no longer useful on most targets, now that support
     has been added for putting variables into BSS without making them
     common.

`-fno-deduce-init-list'
     Disable deduction of a template type parameter as
     std::initializer_list from a brace-enclosed initializer list, i.e.

          template <class T> auto forward(T t) -> decltype (realfn (t))
          {
            return realfn (t);
          }

          void f()
          {
            forward({1,2}); // call forward<std::initializer_list<int>>
          }

     This option is present because this deduction is an extension to
     the current specification in the C++0x working draft, and there was
     some concern about potential overload resolution problems.

`-ffriend-injection'
     Inject friend functions into the enclosing namespace, so that they
     are visible outside the scope of the class in which they are
     declared.  Friend functions were documented to work this way in
     the old Annotated C++ Reference Manual, and versions of G++ before
     4.1 always worked that way.  However, in ISO C++ a friend function
     which is not declared in an enclosing scope can only be found
     using argument dependent lookup.  This option causes friends to be
     injected as they were in earlier releases.

     This option is for compatibility, and may be removed in a future
     release of G++.

`-fno-elide-constructors'
     The C++ standard allows an implementation to omit creating a
     temporary which is only used to initialize another object of the
     same type.  Specifying this option disables that optimization, and
     forces G++ to call the copy constructor in all cases.

`-fno-enforce-eh-specs'
     Don't generate code to check for violation of exception
     specifications at runtime.  This option violates the C++ standard,
     but may be useful for reducing code size in production builds,
     much like defining `NDEBUG'.  This does not give user code
     permission to throw exceptions in violation of the exception
     specifications; the compiler will still optimize based on the
     specifications, so throwing an unexpected exception will result in
     undefined behavior.

`-ffor-scope'
`-fno-for-scope'
     If `-ffor-scope' is specified, the scope of variables declared in
     a for-init-statement is limited to the `for' loop itself, as
     specified by the C++ standard.  If `-fno-for-scope' is specified,
     the scope of variables declared in a for-init-statement extends to
     the end of the enclosing scope, as was the case in old versions of
     G++, and other (traditional) implementations of C++.

     The default if neither flag is given to follow the standard, but
     to allow and give a warning for old-style code that would
     otherwise be invalid, or have different behavior.

`-fno-gnu-keywords'
     Do not recognize `typeof' as a keyword, so that code can use this
     word as an identifier.  You can use the keyword `__typeof__'
     instead.  `-ansi' implies `-fno-gnu-keywords'.

`-fno-implicit-templates'
     Never emit code for non-inline templates which are instantiated
     implicitly (i.e. by use); only emit code for explicit
     instantiations.  *Note Template Instantiation::, for more
     information.

`-fno-implicit-inline-templates'
     Don't emit code for implicit instantiations of inline templates,
     either.  The default is to handle inlines differently so that
     compiles with and without optimization will need the same set of
     explicit instantiations.

`-fno-implement-inlines'
     To save space, do not emit out-of-line copies of inline functions
     controlled by `#pragma implementation'.  This will cause linker
     errors if these functions are not inlined everywhere they are
     called.

`-fms-extensions'
     Disable pedantic warnings about constructs used in MFC, such as
     implicit int and getting a pointer to member function via
     non-standard syntax.

`-fno-nonansi-builtins'
     Disable built-in declarations of functions that are not mandated by
     ANSI/ISO C.  These include `ffs', `alloca', `_exit', `index',
     `bzero', `conjf', and other related functions.

`-fno-operator-names'
     Do not treat the operator name keywords `and', `bitand', `bitor',
     `compl', `not', `or' and `xor' as synonyms as keywords.

`-fno-optional-diags'
     Disable diagnostics that the standard says a compiler does not
     need to issue.  Currently, the only such diagnostic issued by G++
     is the one for a name having multiple meanings within a class.

`-fpermissive'
     Downgrade some diagnostics about nonconformant code from errors to
     warnings.  Thus, using `-fpermissive' will allow some
     nonconforming code to compile.

`-frepo'
     Enable automatic template instantiation at link time.  This option
     also implies `-fno-implicit-templates'.  *Note Template
     Instantiation::, for more information.

`-fno-rtti'
     Disable generation of information about every class with virtual
     functions for use by the C++ runtime type identification features
     (`dynamic_cast' and `typeid').  If you don't use those parts of
     the language, you can save some space by using this flag.  Note
     that exception handling uses the same information, but it will
     generate it as needed. The `dynamic_cast' operator can still be
     used for casts that do not require runtime type information, i.e.
     casts to `void *' or to unambiguous base classes.

`-fstats'
     Emit statistics about front-end processing at the end of the
     compilation.  This information is generally only useful to the G++
     development team.

`-fstrict-enums'
     Allow the compiler to optimize using the assumption that a value of
     enumeration type can only be one of the values of the enumeration
     (as defined in the C++ standard; basically, a value which can be
     represented in the minimum number of bits needed to represent all
     the enumerators).  This assumption may not be valid if the program
     uses a cast to convert an arbitrary integer value to the
     enumeration type.

`-ftemplate-depth-N'
     Set the maximum instantiation depth for template classes to N.  A
     limit on the template instantiation depth is needed to detect
     endless recursions during template class instantiation.  ANSI/ISO
     C++ conforming programs must not rely on a maximum depth greater
     than 17.

`-fno-threadsafe-statics'
     Do not emit the extra code to use the routines specified in the C++
     ABI for thread-safe initialization of local statics.  You can use
     this option to reduce code size slightly in code that doesn't need
     to be thread-safe.

`-fuse-cxa-atexit'
     Register destructors for objects with static storage duration with
     the `__cxa_atexit' function rather than the `atexit' function.
     This option is required for fully standards-compliant handling of
     static destructors, but will only work if your C library supports
     `__cxa_atexit'.

`-fno-use-cxa-get-exception-ptr'
     Don't use the `__cxa_get_exception_ptr' runtime routine.  This
     will cause `std::uncaught_exception' to be incorrect, but is
     necessary if the runtime routine is not available.

`-fvisibility-inlines-hidden'
     This switch declares that the user does not attempt to compare
     pointers to inline methods where the addresses of the two functions
     were taken in different shared objects.

     The effect of this is that GCC may, effectively, mark inline
     methods with `__attribute__ ((visibility ("hidden")))' so that
     they do not appear in the export table of a DSO and do not require
     a PLT indirection when used within the DSO.  Enabling this option
     can have a dramatic effect on load and link times of a DSO as it
     massively reduces the size of the dynamic export table when the
     library makes heavy use of templates.

     The behavior of this switch is not quite the same as marking the
     methods as hidden directly, because it does not affect static
     variables local to the function or cause the compiler to deduce
     that the function is defined in only one shared object.

     You may mark a method as having a visibility explicitly to negate
     the effect of the switch for that method.  For example, if you do
     want to compare pointers to a particular inline method, you might
     mark it as having default visibility.  Marking the enclosing class
     with explicit visibility will have no effect.

     Explicitly instantiated inline methods are unaffected by this
     option as their linkage might otherwise cross a shared library
     boundary.  *Note Template Instantiation::.

`-fvisibility-ms-compat'
     This flag attempts to use visibility settings to make GCC's C++
     linkage model compatible with that of Microsoft Visual Studio.

     The flag makes these changes to GCC's linkage model:

       1. It sets the default visibility to `hidden', like
          `-fvisibility=hidden'.

       2. Types, but not their members, are not hidden by default.

       3. The One Definition Rule is relaxed for types without explicit
          visibility specifications which are defined in more than one
          different shared object: those declarations are permitted if
          they would have been permitted when this option was not used.

     In new code it is better to use `-fvisibility=hidden' and export
     those classes which are intended to be externally visible.
     Unfortunately it is possible for code to rely, perhaps
     accidentally, on the Visual Studio behavior.

     Among the consequences of these changes are that static data
     members of the same type with the same name but defined in
     different shared objects will be different, so changing one will
     not change the other; and that pointers to function members
     defined in different shared objects may not compare equal.  When
     this flag is given, it is a violation of the ODR to define types
     with the same name differently.

`-fno-weak'
     Do not use weak symbol support, even if it is provided by the
     linker.  By default, G++ will use weak symbols if they are
     available.  This option exists only for testing, and should not be
     used by end-users; it will result in inferior code and has no
     benefits.  This option may be removed in a future release of G++.

`-nostdinc++'
     Do not search for header files in the standard directories
     specific to C++, but do still search the other standard
     directories.  (This option is used when building the C++ library.)

 In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:

`-fno-default-inline'
     Do not assume `inline' for functions defined inside a class scope.
     *Note Options That Control Optimization: Optimize Options.  Note
     that these functions will have linkage like inline functions; they
     just won't be inlined by default.

`-Wabi (C, Objective-C, C++ and Objective-C++ only)'
     Warn when G++ generates code that is probably not compatible with
     the vendor-neutral C++ ABI.  Although an effort has been made to
     warn about all such cases, there are probably some cases that are
     not warned about, even though G++ is generating incompatible code.
     There may also be cases where warnings are emitted even though the
     code that is generated will be compatible.

     You should rewrite your code to avoid these warnings if you are
     concerned about the fact that code generated by G++ may not be
     binary compatible with code generated by other compilers.

     The known incompatibilities at this point include:

        * Incorrect handling of tail-padding for bit-fields.  G++ may
          attempt to pack data into the same byte as a base class.  For
          example:

               struct A { virtual void f(); int f1 : 1; };
               struct B : public A { int f2 : 1; };

          In this case, G++ will place `B::f2' into the same byte
          as`A::f1'; other compilers will not.  You can avoid this
          problem by explicitly padding `A' so that its size is a
          multiple of the byte size on your platform; that will cause
          G++ and other compilers to layout `B' identically.

        * Incorrect handling of tail-padding for virtual bases.  G++
          does not use tail padding when laying out virtual bases.  For
          example:

               struct A { virtual void f(); char c1; };
               struct B { B(); char c2; };
               struct C : public A, public virtual B {};

          In this case, G++ will not place `B' into the tail-padding for
          `A'; other compilers will.  You can avoid this problem by
          explicitly padding `A' so that its size is a multiple of its
          alignment (ignoring virtual base classes); that will cause
          G++ and other compilers to layout `C' identically.

        * Incorrect handling of bit-fields with declared widths greater
          than that of their underlying types, when the bit-fields
          appear in a union.  For example:

               union U { int i : 4096; };

          Assuming that an `int' does not have 4096 bits, G++ will make
          the union too small by the number of bits in an `int'.

        * Empty classes can be placed at incorrect offsets.  For
          example:

               struct A {};

               struct B {
                 A a;
                 virtual void f ();
               };

               struct C : public B, public A {};

          G++ will place the `A' base class of `C' at a nonzero offset;
          it should be placed at offset zero.  G++ mistakenly believes
          that the `A' data member of `B' is already at offset zero.

        * Names of template functions whose types involve `typename' or
          template template parameters can be mangled incorrectly.

               template <typename Q>
               void f(typename Q::X) {}

               template <template <typename> class Q>
               void f(typename Q<int>::X) {}

          Instantiations of these templates may be mangled incorrectly.


     It also warns psABI related changes.  The known psABI changes at
     this point include:

        * For SYSV/x86-64, when passing union with long double, it is
          changed to pass in memory as specified in psABI.  For example:

               union U {
                 long double ld;
                 int i;
               };

          `union U' will always be passed in memory.


`-Wctor-dtor-privacy (C++ and Objective-C++ only)'
     Warn when a class seems unusable because all the constructors or
     destructors in that class are private, and it has neither friends
     nor public static member functions.

`-Wnon-virtual-dtor (C++ and Objective-C++ only)'
     Warn when a class has virtual functions and accessible non-virtual
     destructor, in which case it would be possible but unsafe to delete
     an instance of a derived class through a pointer to the base class.
     This warning is also enabled if -Weffc++ is specified.

`-Wreorder (C++ and Objective-C++ only)'
     Warn when the order of member initializers given in the code does
     not match the order in which they must be executed.  For instance:

          struct A {
            int i;
            int j;
            A(): j (0), i (1) { }
          };

     The compiler will rearrange the member initializers for `i' and
     `j' to match the declaration order of the members, emitting a
     warning to that effect.  This warning is enabled by `-Wall'.

 The following `-W...' options are not affected by `-Wall'.

`-Weffc++ (C++ and Objective-C++ only)'
     Warn about violations of the following style guidelines from Scott
     Meyers' `Effective C++' book:

        * Item 11:  Define a copy constructor and an assignment
          operator for classes with dynamically allocated memory.

        * Item 12:  Prefer initialization to assignment in constructors.

        * Item 14:  Make destructors virtual in base classes.

        * Item 15:  Have `operator=' return a reference to `*this'.

        * Item 23:  Don't try to return a reference when you must
          return an object.


     Also warn about violations of the following style guidelines from
     Scott Meyers' `More Effective C++' book:

        * Item 6:  Distinguish between prefix and postfix forms of
          increment and decrement operators.

        * Item 7:  Never overload `&&', `||', or `,'.


     When selecting this option, be aware that the standard library
     headers do not obey all of these guidelines; use `grep -v' to
     filter out those warnings.

`-Wstrict-null-sentinel (C++ and Objective-C++ only)'
     Warn also about the use of an uncasted `NULL' as sentinel.  When
     compiling only with GCC this is a valid sentinel, as `NULL' is
     defined to `__null'.  Although it is a null pointer constant not a
     null pointer, it is guaranteed to be of the same size as a
     pointer.  But this use is not portable across different compilers.

`-Wno-non-template-friend (C++ and Objective-C++ only)'
     Disable warnings when non-templatized friend functions are declared
     within a template.  Since the advent of explicit template
     specification support in G++, if the name of the friend is an
     unqualified-id (i.e., `friend foo(int)'), the C++ language
     specification demands that the friend declare or define an
     ordinary, nontemplate function.  (Section 14.5.3).  Before G++
     implemented explicit specification, unqualified-ids could be
     interpreted as a particular specialization of a templatized
     function.  Because this non-conforming behavior is no longer the
     default behavior for G++, `-Wnon-template-friend' allows the
     compiler to check existing code for potential trouble spots and is
     on by default.  This new compiler behavior can be turned off with
     `-Wno-non-template-friend' which keeps the conformant compiler code
     but disables the helpful warning.

`-Wold-style-cast (C++ and Objective-C++ only)'
     Warn if an old-style (C-style) cast to a non-void type is used
     within a C++ program.  The new-style casts (`dynamic_cast',
     `static_cast', `reinterpret_cast', and `const_cast') are less
     vulnerable to unintended effects and much easier to search for.

`-Woverloaded-virtual (C++ and Objective-C++ only)'
     Warn when a function declaration hides virtual functions from a
     base class.  For example, in:

          struct A {
            virtual void f();
          };

          struct B: public A {
            void f(int);
          };

     the `A' class version of `f' is hidden in `B', and code like:

          B* b;
          b->f();

     will fail to compile.

`-Wno-pmf-conversions (C++ and Objective-C++ only)'
     Disable the diagnostic for converting a bound pointer to member
     function to a plain pointer.

`-Wsign-promo (C++ and Objective-C++ only)'
     Warn when overload resolution chooses a promotion from unsigned or
     enumerated type to a signed type, over a conversion to an unsigned
     type of the same size.  Previous versions of G++ would try to
     preserve unsignedness, but the standard mandates the current
     behavior.

          struct A {
            operator int ();
            A& operator = (int);
          };

          main ()
          {
            A a,b;
            a = b;
          }

     In this example, G++ will synthesize a default `A& operator =
     (const A&);', while cfront will use the user-defined `operator ='.

File: gcc.info,  Node: Objective-C and Objective-C++ Dialect Options,  Next: Language Independent Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

3.6 Options Controlling Objective-C and Objective-C++ Dialects
==============================================================

(NOTE: This manual does not describe the Objective-C and Objective-C++
languages themselves.  See *Note Language Standards Supported by GCC:
Standards, for references.)

 This section describes the command-line options that are only
meaningful for Objective-C and Objective-C++ programs, but you can also
use most of the language-independent GNU compiler options.  For
example, you might compile a file `some_class.m' like this:

     gcc -g -fgnu-runtime -O -c some_class.m

In this example, `-fgnu-runtime' is an option meant only for
Objective-C and Objective-C++ programs; you can use the other options
with any language supported by GCC.

 Note that since Objective-C is an extension of the C language,
Objective-C compilations may also use options specific to the C
front-end (e.g., `-Wtraditional').  Similarly, Objective-C++
compilations may use C++-specific options (e.g., `-Wabi').

 Here is a list of options that are _only_ for compiling Objective-C
and Objective-C++ programs:

`-fconstant-string-class=CLASS-NAME'
     Use CLASS-NAME as the name of the class to instantiate for each
     literal string specified with the syntax `@"..."'.  The default
     class name is `NXConstantString' if the GNU runtime is being used,
     and `NSConstantString' if the NeXT runtime is being used (see
     below).  The `-fconstant-cfstrings' option, if also present, will
     override the `-fconstant-string-class' setting and cause `@"..."'
     literals to be laid out as constant CoreFoundation strings.

`-fgnu-runtime'
     Generate object code compatible with the standard GNU Objective-C
     runtime.  This is the default for most types of systems.

`-fnext-runtime'
     Generate output compatible with the NeXT runtime.  This is the
     default for NeXT-based systems, including Darwin and Mac OS X.
     The macro `__NEXT_RUNTIME__' is predefined if (and only if) this
     option is used.

`-fno-nil-receivers'
     Assume that all Objective-C message dispatches (e.g., `[receiver
     message:arg]') in this translation unit ensure that the receiver
     is not `nil'.  This allows for more efficient entry points in the
     runtime to be used.  Currently, this option is only available in
     conjunction with the NeXT runtime on Mac OS X 10.3 and later.

`-fobjc-call-cxx-cdtors'
     For each Objective-C class, check if any of its instance variables
     is a C++ object with a non-trivial default constructor.  If so,
     synthesize a special `- (id) .cxx_construct' instance method that
     will run non-trivial default constructors on any such instance
     variables, in order, and then return `self'.  Similarly, check if
     any instance variable is a C++ object with a non-trivial
     destructor, and if so, synthesize a special `- (void)
     .cxx_destruct' method that will run all such default destructors,
     in reverse order.

     The `- (id) .cxx_construct' and/or `- (void) .cxx_destruct' methods
     thusly generated will only operate on instance variables declared
     in the current Objective-C class, and not those inherited from
     superclasses.  It is the responsibility of the Objective-C runtime
     to invoke all such methods in an object's inheritance hierarchy.
     The `- (id) .cxx_construct' methods will be invoked by the runtime
     immediately after a new object instance is allocated; the `-
     (void) .cxx_destruct' methods will be invoked immediately before
     the runtime deallocates an object instance.

     As of this writing, only the NeXT runtime on Mac OS X 10.4 and
     later has support for invoking the `- (id) .cxx_construct' and `-
     (void) .cxx_destruct' methods.

`-fobjc-direct-dispatch'
     Allow fast jumps to the message dispatcher.  On Darwin this is
     accomplished via the comm page.

`-fobjc-exceptions'
     Enable syntactic support for structured exception handling in
     Objective-C, similar to what is offered by C++ and Java.  This
     option is unavailable in conjunction with the NeXT runtime on Mac
     OS X 10.2 and earlier.

            @try {
              ...
                 @throw expr;
              ...
            }
            @catch (AnObjCClass *exc) {
              ...
                @throw expr;
              ...
                @throw;
              ...
            }
            @catch (AnotherClass *exc) {
              ...
            }
            @catch (id allOthers) {
              ...
            }
            @finally {
              ...
                @throw expr;
              ...
            }

     The `@throw' statement may appear anywhere in an Objective-C or
     Objective-C++ program; when used inside of a `@catch' block, the
     `@throw' may appear without an argument (as shown above), in which
     case the object caught by the `@catch' will be rethrown.

     Note that only (pointers to) Objective-C objects may be thrown and
     caught using this scheme.  When an object is thrown, it will be
     caught by the nearest `@catch' clause capable of handling objects
     of that type, analogously to how `catch' blocks work in C++ and
     Java.  A `@catch(id ...)' clause (as shown above) may also be
     provided to catch any and all Objective-C exceptions not caught by
     previous `@catch' clauses (if any).

     The `@finally' clause, if present, will be executed upon exit from
     the immediately preceding `@try ... @catch' section.  This will
     happen regardless of whether any exceptions are thrown, caught or
     rethrown inside the `@try ... @catch' section, analogously to the
     behavior of the `finally' clause in Java.

     There are several caveats to using the new exception mechanism:

        * Although currently designed to be binary compatible with
          `NS_HANDLER'-style idioms provided by the `NSException'
          class, the new exceptions can only be used on Mac OS X 10.3
          (Panther) and later systems, due to additional functionality
          needed in the (NeXT) Objective-C runtime.

        * As mentioned above, the new exceptions do not support handling
          types other than Objective-C objects.   Furthermore, when
          used from Objective-C++, the Objective-C exception model does
          not interoperate with C++ exceptions at this time.  This
          means you cannot `@throw' an exception from Objective-C and
          `catch' it in C++, or vice versa (i.e., `throw ... @catch').

     The `-fobjc-exceptions' switch also enables the use of
     synchronization blocks for thread-safe execution:

            @synchronized (ObjCClass *guard) {
              ...
            }

     Upon entering the `@synchronized' block, a thread of execution
     shall first check whether a lock has been placed on the
     corresponding `guard' object by another thread.  If it has, the
     current thread shall wait until the other thread relinquishes its
     lock.  Once `guard' becomes available, the current thread will
     place its own lock on it, execute the code contained in the
     `@synchronized' block, and finally relinquish the lock (thereby
     making `guard' available to other threads).

     Unlike Java, Objective-C does not allow for entire methods to be
     marked `@synchronized'.  Note that throwing exceptions out of
     `@synchronized' blocks is allowed, and will cause the guarding
     object to be unlocked properly.

`-fobjc-gc'
     Enable garbage collection (GC) in Objective-C and Objective-C++
     programs.

`-freplace-objc-classes'
     Emit a special marker instructing `ld(1)' not to statically link in
     the resulting object file, and allow `dyld(1)' to load it in at
     run time instead.  This is used in conjunction with the
     Fix-and-Continue debugging mode, where the object file in question
     may be recompiled and dynamically reloaded in the course of
     program execution, without the need to restart the program itself.
     Currently, Fix-and-Continue functionality is only available in
     conjunction with the NeXT runtime on Mac OS X 10.3 and later.

`-fzero-link'
     When compiling for the NeXT runtime, the compiler ordinarily
     replaces calls to `objc_getClass("...")' (when the name of the
     class is known at compile time) with static class references that
     get initialized at load time, which improves run-time performance.
     Specifying the `-fzero-link' flag suppresses this behavior and
     causes calls to `objc_getClass("...")' to be retained.  This is
     useful in Zero-Link debugging mode, since it allows for individual
     class implementations to be modified during program execution.

`-gen-decls'
     Dump interface declarations for all classes seen in the source
     file to a file named `SOURCENAME.decl'.

`-Wassign-intercept (Objective-C and Objective-C++ only)'
     Warn whenever an Objective-C assignment is being intercepted by the
     garbage collector.

`-Wno-protocol (Objective-C and Objective-C++ only)'
     If a class is declared to implement a protocol, a warning is
     issued for every method in the protocol that is not implemented by
     the class.  The default behavior is to issue a warning for every
     method not explicitly implemented in the class, even if a method
     implementation is inherited from the superclass.  If you use the
     `-Wno-protocol' option, then methods inherited from the superclass
     are considered to be implemented, and no warning is issued for
     them.

`-Wselector (Objective-C and Objective-C++ only)'
     Warn if multiple methods of different types for the same selector
     are found during compilation.  The check is performed on the list
     of methods in the final stage of compilation.  Additionally, a
     check is performed for each selector appearing in a
     `@selector(...)'  expression, and a corresponding method for that
     selector has been found during compilation.  Because these checks
     scan the method table only at the end of compilation, these
     warnings are not produced if the final stage of compilation is not
     reached, for example because an error is found during compilation,
     or because the `-fsyntax-only' option is being used.

`-Wstrict-selector-match (Objective-C and Objective-C++ only)'
     Warn if multiple methods with differing argument and/or return
     types are found for a given selector when attempting to send a
     message using this selector to a receiver of type `id' or `Class'.
     When this flag is off (which is the default behavior), the
     compiler will omit such warnings if any differences found are
     confined to types which share the same size and alignment.

`-Wundeclared-selector (Objective-C and Objective-C++ only)'
     Warn if a `@selector(...)' expression referring to an undeclared
     selector is found.  A selector is considered undeclared if no
     method with that name has been declared before the
     `@selector(...)' expression, either explicitly in an `@interface'
     or `@protocol' declaration, or implicitly in an `@implementation'
     section.  This option always performs its checks as soon as a
     `@selector(...)' expression is found, while `-Wselector' only
     performs its checks in the final stage of compilation.  This also
     enforces the coding style convention that methods and selectors
     must be declared before being used.

`-print-objc-runtime-info'
     Generate C header describing the largest structure that is passed
     by value, if any.


File: gcc.info,  Node: Language Independent Options,  Next: Warning Options,  Prev: Objective-C and Objective-C++ Dialect Options,  Up: Invoking GCC

3.7 Options to Control Diagnostic Messages Formatting
=====================================================

Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...).  The options described
below can be used to control the diagnostic messages formatting
algorithm, e.g. how many characters per line, how often source location
information should be reported.  Right now, only the C++ front end can
honor these options.  However it is expected, in the near future, that
the remaining front ends would be able to digest them correctly.

`-fmessage-length=N'
     Try to format error messages so that they fit on lines of about N
     characters.  The default is 72 characters for `g++' and 0 for the
     rest of the front ends supported by GCC.  If N is zero, then no
     line-wrapping will be done; each error message will appear on a
     single line.

`-fdiagnostics-show-location=once'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit _once_ source location information; that
     is, in case the message is too long to fit on a single physical
     line and has to be wrapped, the source location won't be emitted
     (as prefix) again, over and over, in subsequent continuation
     lines.  This is the default behavior.

`-fdiagnostics-show-location=every-line'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit the same source location information (as
     prefix) for physical lines that result from the process of breaking
     a message which is too long to fit on a single line.

`-fdiagnostics-show-option'
     This option instructs the diagnostic machinery to add text to each
     diagnostic emitted, which indicates which command line option
     directly controls that diagnostic, when such an option is known to
     the diagnostic machinery.

`-Wcoverage-mismatch'
     Warn if feedback profiles do not match when using the
     `-fprofile-use' option.  If a source file was changed between
     `-fprofile-gen' and `-fprofile-use', the files with the profile
     feedback can fail to match the source file and GCC can not use the
     profile feedback information.  By default, GCC emits an error
     message in this case.  The option `-Wcoverage-mismatch' emits a
     warning instead of an error.  GCC does not use appropriate
     feedback profiles, so using this option can result in poorly
     optimized code.  This option is useful only in the case of very
     minor changes such as bug fixes to an existing code-base.


File: gcc.info,  Node: Warning Options,  Next: Debugging Options,  Prev: Language Independent Options,  Up: Invoking GCC

3.8 Options to Request or Suppress Warnings
===========================================

Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.

 The following language-independent options do not enable specific
warnings but control the kinds of diagnostics produced by GCC.

`-fsyntax-only'
     Check the code for syntax errors, but don't do anything beyond
     that.

`-w'
     Inhibit all warning messages.

`-Werror'
     Make all warnings into errors.

`-Werror='
     Make the specified warning into an error.  The specifier for a
     warning is appended, for example `-Werror=switch' turns the
     warnings controlled by `-Wswitch' into errors.  This switch takes a
     negative form, to be used to negate `-Werror' for specific
     warnings, for example `-Wno-error=switch' makes `-Wswitch'
     warnings not be errors, even when `-Werror' is in effect.  You can
     use the `-fdiagnostics-show-option' option to have each
     controllable warning amended with the option which controls it, to
     determine what to use with this option.

     Note that specifying `-Werror='FOO automatically implies `-W'FOO.
     However, `-Wno-error='FOO does not imply anything.

`-Wfatal-errors'
     This option causes the compiler to abort compilation on the first
     error occurred rather than trying to keep going and printing
     further error messages.


 You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.  For further, language-specific options also refer to *note
C++ Dialect Options:: and *note Objective-C and Objective-C++ Dialect
Options::.

`-pedantic'
     Issue all the warnings demanded by strict ISO C and ISO C++;
     reject all programs that use forbidden extensions, and some other
     programs that do not follow ISO C and ISO C++.  For ISO C, follows
     the version of the ISO C standard specified by any `-std' option
     used.

     Valid ISO C and ISO C++ programs should compile properly with or
     without this option (though a rare few will require `-ansi' or a
     `-std' option specifying the required version of ISO C).  However,
     without this option, certain GNU extensions and traditional C and
     C++ features are supported as well.  With this option, they are
     rejected.

     `-pedantic' does not cause warning messages for use of the
     alternate keywords whose names begin and end with `__'.  Pedantic
     warnings are also disabled in the expression that follows
     `__extension__'.  However, only system header files should use
     these escape routes; application programs should avoid them.
     *Note Alternate Keywords::.

     Some users try to use `-pedantic' to check programs for strict ISO
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ISO practices, but not all--only those for
     which ISO C _requires_ a diagnostic, and some others for which
     diagnostics have been added.

     A feature to report any failure to conform to ISO C might be
     useful in some instances, but would require considerable
     additional work and would be quite different from `-pedantic'.  We
     don't have plans to support such a feature in the near future.

     Where the standard specified with `-std' represents a GNU extended
     dialect of C, such as `gnu89' or `gnu99', there is a corresponding
     "base standard", the version of ISO C on which the GNU extended
     dialect is based.  Warnings from `-pedantic' are given where they
     are required by the base standard.  (It would not make sense for
     such warnings to be given only for features not in the specified
     GNU C dialect, since by definition the GNU dialects of C include
     all features the compiler supports with the given option, and
     there would be nothing to warn about.)

`-pedantic-errors'
     Like `-pedantic', except that errors are produced rather than
     warnings.

`-Wall'
     This enables all the warnings about constructions that some users
     consider questionable, and that are easy to avoid (or modify to
     prevent the warning), even in conjunction with macros.  This also
     enables some language-specific warnings described in *note C++
     Dialect Options:: and *note Objective-C and Objective-C++ Dialect
     Options::.

     `-Wall' turns on the following warning flags:

          -Waddress
          -Warray-bounds (only with `-O2')
          -Wc++0x-compat
          -Wchar-subscripts
          -Wimplicit-int
          -Wimplicit-function-declaration
          -Wcomment
          -Wformat
          -Wmain (only for C/ObjC and unless `-ffreestanding')
          -Wmissing-braces
          -Wnonnull
          -Wparentheses
          -Wpointer-sign
          -Wreorder
          -Wreturn-type
          -Wsequence-point
          -Wsign-compare (only in C++)
          -Wstrict-aliasing
          -Wstrict-overflow=1
          -Wswitch
          -Wtrigraphs
          -Wuninitialized
          -Wunknown-pragmas
          -Wunused-function
          -Wunused-label
          -Wunused-value
          -Wunused-variable
          -Wvolatile-register-var

     Note that some warning flags are not implied by `-Wall'.  Some of
     them warn about constructions that users generally do not consider
     questionable, but which occasionally you might wish to check for;
     others warn about constructions that are necessary or hard to
     avoid in some cases, and there is no simple way to modify the code
     to suppress the warning. Some of them are enabled by `-Wextra' but
     many of them must be enabled individually.

`-Wextra'
     This enables some extra warning flags that are not enabled by
     `-Wall'. (This option used to be called `-W'.  The older name is
     still supported, but the newer name is more descriptive.)

          -Wclobbered
          -Wempty-body
          -Wignored-qualifiers
          -Wmissing-field-initializers
          -Wmissing-parameter-type (C only)
          -Wold-style-declaration (C only)
          -Woverride-init
          -Wsign-compare
          -Wtype-limits
          -Wuninitialized
          -Wunused-parameter (only with `-Wunused' or `-Wall')

     The option `-Wextra' also prints warning messages for the
     following cases:

        * A pointer is compared against integer zero with `<', `<=',
          `>', or `>='.

        * (C++ only) An enumerator and a non-enumerator both appear in a
          conditional expression.

        * (C++ only) Ambiguous virtual bases.

        * (C++ only) Subscripting an array which has been declared
          `register'.

        * (C++ only) Taking the address of a variable which has been
          declared `register'.

        * (C++ only) A base class is not initialized in a derived
          class' copy constructor.


`-Wchar-subscripts'
     Warn if an array subscript has type `char'.  This is a common cause
     of error, as programmers often forget that this type is signed on
     some machines.  This warning is enabled by `-Wall'.

`-Wcomment'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a Backslash-Newline appears in a `//' comment.
     This warning is enabled by `-Wall'.

`-Wformat'
     Check calls to `printf' and `scanf', etc., to make sure that the
     arguments supplied have types appropriate to the format string
     specified, and that the conversions specified in the format string
     make sense.  This includes standard functions, and others
     specified by format attributes (*note Function Attributes::), in
     the `printf', `scanf', `strftime' and `strfmon' (an X/Open
     extension, not in the C standard) families (or other
     target-specific families).  Which functions are checked without
     format attributes having been specified depends on the standard
     version selected, and such checks of functions without the
     attribute specified are disabled by `-ffreestanding' or
     `-fno-builtin'.

     The formats are checked against the format features supported by
     GNU libc version 2.2.  These include all ISO C90 and C99 features,
     as well as features from the Single Unix Specification and some
     BSD and GNU extensions.  Other library implementations may not
     support all these features; GCC does not support warning about
     features that go beyond a particular library's limitations.
     However, if `-pedantic' is used with `-Wformat', warnings will be
     given about format features not in the selected standard version
     (but not for `strfmon' formats, since those are not in any version
     of the C standard).  *Note Options Controlling C Dialect: C
     Dialect Options.

     Since `-Wformat' also checks for null format arguments for several
     functions, `-Wformat' also implies `-Wnonnull'.

     `-Wformat' is included in `-Wall'.  For more control over some
     aspects of format checking, the options `-Wformat-y2k',
     `-Wno-format-extra-args', `-Wno-format-zero-length',
     `-Wformat-nonliteral', `-Wformat-security', and `-Wformat=2' are
     available, but are not included in `-Wall'.

`-Wformat-y2k'
     If `-Wformat' is specified, also warn about `strftime' formats
     which may yield only a two-digit year.

`-Wno-format-contains-nul'
     If `-Wformat' is specified, do not warn about format strings that
     contain NUL bytes.

`-Wno-format-extra-args'
     If `-Wformat' is specified, do not warn about excess arguments to a
     `printf' or `scanf' format function.  The C standard specifies
     that such arguments are ignored.

     Where the unused arguments lie between used arguments that are
     specified with `$' operand number specifications, normally
     warnings are still given, since the implementation could not know
     what type to pass to `va_arg' to skip the unused arguments.
     However, in the case of `scanf' formats, this option will suppress
     the warning if the unused arguments are all pointers, since the
     Single Unix Specification says that such unused arguments are
     allowed.

`-Wno-format-zero-length (C and Objective-C only)'
     If `-Wformat' is specified, do not warn about zero-length formats.
     The C standard specifies that zero-length formats are allowed.

`-Wformat-nonliteral'
     If `-Wformat' is specified, also warn if the format string is not a
     string literal and so cannot be checked, unless the format function
     takes its format arguments as a `va_list'.

`-Wformat-security'
     If `-Wformat' is specified, also warn about uses of format
     functions that represent possible security problems.  At present,
     this warns about calls to `printf' and `scanf' functions where the
     format string is not a string literal and there are no format
     arguments, as in `printf (foo);'.  This may be a security hole if
     the format string came from untrusted input and contains `%n'.
     (This is currently a subset of what `-Wformat-nonliteral' warns
     about, but in future warnings may be added to `-Wformat-security'
     that are not included in `-Wformat-nonliteral'.)

`-Wformat=2'
     Enable `-Wformat' plus format checks not included in `-Wformat'.
     Currently equivalent to `-Wformat -Wformat-nonliteral
     -Wformat-security -Wformat-y2k'.

`-Wnonnull (C and Objective-C only)'
     Warn about passing a null pointer for arguments marked as
     requiring a non-null value by the `nonnull' function attribute.

     `-Wnonnull' is included in `-Wall' and `-Wformat'.  It can be
     disabled with the `-Wno-nonnull' option.

`-Winit-self (C, C++, Objective-C and Objective-C++ only)'
     Warn about uninitialized variables which are initialized with
     themselves.  Note this option can only be used with the
     `-Wuninitialized' option.

     For example, GCC will warn about `i' being uninitialized in the
     following snippet only when `-Winit-self' has been specified:
          int f()
          {
            int i = i;
            return i;
          }

`-Wimplicit-int (C and Objective-C only)'
     Warn when a declaration does not specify a type.  This warning is
     enabled by `-Wall'.

`-Wimplicit-function-declaration (C and Objective-C only)'
     Give a warning whenever a function is used before being declared.
     In C99 mode (`-std=c99' or `-std=gnu99'), this warning is enabled
     by default and it is made into an error by `-pedantic-errors'.
     This warning is also enabled by `-Wall'.

`-Wimplicit'
     Same as `-Wimplicit-int' and `-Wimplicit-function-declaration'.
     This warning is enabled by `-Wall'.

`-Wignored-qualifiers (C and C++ only)'
     Warn if the return type of a function has a type qualifier such as
     `const'.  For ISO C such a type qualifier has no effect, since the
     value returned by a function is not an lvalue.  For C++, the
     warning is only emitted for scalar types or `void'.  ISO C
     prohibits qualified `void' return types on function definitions,
     so such return types always receive a warning even without this
     option.

     This warning is also enabled by `-Wextra'.

`-Wmain'
     Warn if the type of `main' is suspicious.  `main' should be a
     function with external linkage, returning int, taking either zero
     arguments, two, or three arguments of appropriate types.  This
     warning is enabled by default in C++ and is enabled by either
     `-Wall' or `-pedantic'.

`-Wmissing-braces'
     Warn if an aggregate or union initializer is not fully bracketed.
     In the following example, the initializer for `a' is not fully
     bracketed, but that for `b' is fully bracketed.

          int a[2][2] = { 0, 1, 2, 3 };
          int b[2][2] = { { 0, 1 }, { 2, 3 } };

     This warning is enabled by `-Wall'.

`-Wmissing-include-dirs (C, C++, Objective-C and Objective-C++ only)'
     Warn if a user-supplied include directory does not exist.

`-Wparentheses'
     Warn if parentheses are omitted in certain contexts, such as when
     there is an assignment in a context where a truth value is
     expected, or when operators are nested whose precedence people
     often get confused about.

     Also warn if a comparison like `x<=y<=z' appears; this is
     equivalent to `(x<=y ? 1 : 0) <= z', which is a different
     interpretation from that of ordinary mathematical notation.

     Also warn about constructions where there may be confusion to which
     `if' statement an `else' branch belongs.  Here is an example of
     such a case:

          {
            if (a)
              if (b)
                foo ();
            else
              bar ();
          }

     In C/C++, every `else' branch belongs to the innermost possible
     `if' statement, which in this example is `if (b)'.  This is often
     not what the programmer expected, as illustrated in the above
     example by indentation the programmer chose.  When there is the
     potential for this confusion, GCC will issue a warning when this
     flag is specified.  To eliminate the warning, add explicit braces
     around the innermost `if' statement so there is no way the `else'
     could belong to the enclosing `if'.  The resulting code would look
     like this:

          {
            if (a)
              {
                if (b)
                  foo ();
                else
                  bar ();
              }
          }

     This warning is enabled by `-Wall'.

`-Wsequence-point'
     Warn about code that may have undefined semantics because of
     violations of sequence point rules in the C and C++ standards.

     The C and C++ standards defines the order in which expressions in
     a C/C++ program are evaluated in terms of "sequence points", which
     represent a partial ordering between the execution of parts of the
     program: those executed before the sequence point, and those
     executed after it.  These occur after the evaluation of a full
     expression (one which is not part of a larger expression), after
     the evaluation of the first operand of a `&&', `||', `? :' or `,'
     (comma) operator, before a function is called (but after the
     evaluation of its arguments and the expression denoting the called
     function), and in certain other places.  Other than as expressed
     by the sequence point rules, the order of evaluation of
     subexpressions of an expression is not specified.  All these rules
     describe only a partial order rather than a total order, since,
     for example, if two functions are called within one expression
     with no sequence point between them, the order in which the
     functions are called is not specified.  However, the standards
     committee have ruled that function calls do not overlap.

     It is not specified when between sequence points modifications to
     the values of objects take effect.  Programs whose behavior
     depends on this have undefined behavior; the C and C++ standards
     specify that "Between the previous and next sequence point an
     object shall have its stored value modified at most once by the
     evaluation of an expression.  Furthermore, the prior value shall
     be read only to determine the value to be stored.".  If a program
     breaks these rules, the results on any particular implementation
     are entirely unpredictable.

     Examples of code with undefined behavior are `a = a++;', `a[n] =
     b[n++]' and `a[i++] = i;'.  Some more complicated cases are not
     diagnosed by this option, and it may give an occasional false
     positive result, but in general it has been found fairly effective
     at detecting this sort of problem in programs.

     The standard is worded confusingly, therefore there is some debate
     over the precise meaning of the sequence point rules in subtle
     cases.  Links to discussions of the problem, including proposed
     formal definitions, may be found on the GCC readings page, at
     `http://gcc.gnu.org/readings.html'.

     This warning is enabled by `-Wall' for C and C++.

`-Wreturn-type'
     Warn whenever a function is defined with a return-type that
     defaults to `int'.  Also warn about any `return' statement with no
     return-value in a function whose return-type is not `void'
     (falling off the end of the function body is considered returning
     without a value), and about a `return' statement with a expression
     in a function whose return-type is `void'.

     For C++, a function without return type always produces a
     diagnostic message, even when `-Wno-return-type' is specified.
     The only exceptions are `main' and functions defined in system
     headers.

     This warning is enabled by `-Wall'.

`-Wswitch'
     Warn whenever a `switch' statement has an index of enumerated type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  (The presence of a `default' label prevents this
     warning.)  `case' labels outside the enumeration range also
     provoke warnings when this option is used.  This warning is
     enabled by `-Wall'.

`-Wswitch-default'
     Warn whenever a `switch' statement does not have a `default' case.

`-Wswitch-enum'
     Warn whenever a `switch' statement has an index of enumerated type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  `case' labels outside the enumeration range also
     provoke warnings when this option is used.

`-Wsync-nand (C and C++ only)'
     Warn when `__sync_fetch_and_nand' and `__sync_nand_and_fetch'
     built-in functions are used.  These functions changed semantics in
     GCC 4.4.

`-Wtrigraphs'
     Warn if any trigraphs are encountered that might change the
     meaning of the program (trigraphs within comments are not warned
     about).  This warning is enabled by `-Wall'.

`-Wunused-but-set-parameter'
     Warn whenever a function parameter is assigned to, but otherwise
     unused (aside from its declaration).

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-but-set-variable'
     Warn whenever a local variable is assigned to, but otherwise unused
     (aside from its declaration).

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-function'
     Warn whenever a static function is declared but not defined or a
     non-inline static function is unused.  This warning is enabled by
     `-Wall'.

`-Wunused-label'
     Warn whenever a label is declared but not used.  This warning is
     enabled by `-Wall'.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-parameter'
     Warn whenever a function parameter is unused aside from its
     declaration.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-variable'
     Warn whenever a local variable or non-constant static variable is
     unused aside from its declaration.  This warning is enabled by
     `-Wall'.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-value'
     Warn whenever a statement computes a result that is explicitly not
     used. To suppress this warning cast the unused expression to
     `void'. This includes an expression-statement or the left-hand
     side of a comma expression that contains no side effects. For
     example, an expression such as `x[i,j]' will cause a warning, while
     `x[(void)i,j]' will not.

     This warning is enabled by `-Wall'.

`-Wunused'
     All the above `-Wunused' options combined.

     In order to get a warning about an unused function parameter, you
     must either specify `-Wextra -Wunused' (note that `-Wall' implies
     `-Wunused'), or separately specify `-Wunused-parameter'.

`-Wuninitialized'
     Warn if an automatic variable is used without first being
     initialized or if a variable may be clobbered by a `setjmp' call.
     In C++, warn if a non-static reference or non-static `const' member
     appears in a class without constructors.

     If you want to warn about code which uses the uninitialized value
     of the variable in its own initializer, use the `-Winit-self'
     option.

     These warnings occur for individual uninitialized or clobbered
     elements of structure, union or array variables as well as for
     variables which are uninitialized or clobbered as a whole.  They do
     not occur for variables or elements declared `volatile'.  Because
     these warnings depend on optimization, the exact variables or
     elements for which there are warnings will depend on the precise
     optimization options and version of GCC used.

     Note that there may be no warning about a variable that is used
     only to compute a value that itself is never used, because such
     computations may be deleted by data flow analysis before the
     warnings are printed.

     These warnings are made optional because GCC is not smart enough
     to see all the reasons why the code might be correct despite
     appearing to have an error.  Here is one example of how this can
     happen:

          {
            int x;
            switch (y)
              {
              case 1: x = 1;
                break;
              case 2: x = 4;
                break;
              case 3: x = 5;
              }
            foo (x);
          }

     If the value of `y' is always 1, 2 or 3, then `x' is always
     initialized, but GCC doesn't know this.  Here is another common
     case:

          {
            int save_y;
            if (change_y) save_y = y, y = new_y;
            ...
            if (change_y) y = save_y;
          }

     This has no bug because `save_y' is used only if it is set.

     This option also warns when a non-volatile automatic variable
     might be changed by a call to `longjmp'.  These warnings as well
     are possible only in optimizing compilation.

     The compiler sees only the calls to `setjmp'.  It cannot know
     where `longjmp' will be called; in fact, a signal handler could
     call it at any point in the code.  As a result, you may get a
     warning even when there is in fact no problem because `longjmp'
     cannot in fact be called at the place which would cause a problem.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as `noreturn'.  *Note Function
     Attributes::.

     This warning is enabled by `-Wall' or `-Wextra'.

`-Wunknown-pragmas'
     Warn when a #pragma directive is encountered which is not
     understood by GCC.  If this command line option is used, warnings
     will even be issued for unknown pragmas in system header files.
     This is not the case if the warnings were only enabled by the
     `-Wall' command line option.

`-Wno-pragmas'
     Do not warn about misuses of pragmas, such as incorrect parameters,
     invalid syntax, or conflicts between pragmas.  See also
     `-Wunknown-pragmas'.

`-Wstrict-aliasing'
     This option is only active when `-fstrict-aliasing' is active.  It
     warns about code which might break the strict aliasing rules that
     the compiler is using for optimization.  The warning does not
     catch all cases, but does attempt to catch the more common
     pitfalls.  It is included in `-Wall'.  It is equivalent to
     `-Wstrict-aliasing=3'

`-Wstrict-aliasing=n'
     This option is only active when `-fstrict-aliasing' is active.  It
     warns about code which might break the strict aliasing rules that
     the compiler is using for optimization.  Higher levels correspond
     to higher accuracy (fewer false positives).  Higher levels also
     correspond to more effort, similar to the way -O works.
     `-Wstrict-aliasing' is equivalent to `-Wstrict-aliasing=n', with
     n=3.

     Level 1: Most aggressive, quick, least accurate.  Possibly useful
     when higher levels do not warn but -fstrict-aliasing still breaks
     the code, as it has very few false negatives.  However, it has
     many false positives.  Warns for all pointer conversions between
     possibly incompatible types, even if never dereferenced.  Runs in
     the frontend only.

     Level 2: Aggressive, quick, not too precise.  May still have many
     false positives (not as many as level 1 though), and few false
     negatives (but possibly more than level 1).  Unlike level 1, it
     only warns when an address is taken.  Warns about incomplete
     types.  Runs in the frontend only.

     Level 3 (default for `-Wstrict-aliasing'): Should have very few
     false positives and few false negatives.  Slightly slower than
     levels 1 or 2 when optimization is enabled.  Takes care of the
     common punn+dereference pattern in the frontend:
     `*(int*)&some_float'.  If optimization is enabled, it also runs in
     the backend, where it deals with multiple statement cases using
     flow-sensitive points-to information.  Only warns when the
     converted pointer is dereferenced.  Does not warn about incomplete
     types.

`-Wstrict-overflow'
`-Wstrict-overflow=N'
     This option is only active when `-fstrict-overflow' is active.  It
     warns about cases where the compiler optimizes based on the
     assumption that signed overflow does not occur.  Note that it does
     not warn about all cases where the code might overflow: it only
     warns about cases where the compiler implements some optimization.
     Thus this warning depends on the optimization level.

     An optimization which assumes that signed overflow does not occur
     is perfectly safe if the values of the variables involved are such
     that overflow never does, in fact, occur.  Therefore this warning
     can easily give a false positive: a warning about code which is not
     actually a problem.  To help focus on important issues, several
     warning levels are defined.  No warnings are issued for the use of
     undefined signed overflow when estimating how many iterations a
     loop will require, in particular when determining whether a loop
     will be executed at all.

    `-Wstrict-overflow=1'
          Warn about cases which are both questionable and easy to
          avoid.  For example: `x + 1 > x'; with `-fstrict-overflow',
          the compiler will simplify this to `1'.  This level of
          `-Wstrict-overflow' is enabled by `-Wall'; higher levels are
          not, and must be explicitly requested.

    `-Wstrict-overflow=2'
          Also warn about other cases where a comparison is simplified
          to a constant.  For example: `abs (x) >= 0'.  This can only be
          simplified when `-fstrict-overflow' is in effect, because
          `abs (INT_MIN)' overflows to `INT_MIN', which is less than
          zero.  `-Wstrict-overflow' (with no level) is the same as
          `-Wstrict-overflow=2'.

    `-Wstrict-overflow=3'
          Also warn about other cases where a comparison is simplified.
          For example: `x + 1 > 1' will be simplified to `x > 0'.

    `-Wstrict-overflow=4'
          Also warn about other simplifications not covered by the
          above cases.  For example: `(x * 10) / 5' will be simplified
          to `x * 2'.

    `-Wstrict-overflow=5'
          Also warn about cases where the compiler reduces the
          magnitude of a constant involved in a comparison.  For
          example: `x + 2 > y' will be simplified to `x + 1 >= y'.
          This is reported only at the highest warning level because
          this simplification applies to many comparisons, so this
          warning level will give a very large number of false
          positives.

`-Warray-bounds'
     This option is only active when `-ftree-vrp' is active (default
     for -O2 and above). It warns about subscripts to arrays that are
     always out of bounds. This warning is enabled by `-Wall'.

`-Wno-div-by-zero'
     Do not warn about compile-time integer division by zero.  Floating
     point division by zero is not warned about, as it can be a
     legitimate way of obtaining infinities and NaNs.

`-Wsystem-headers'
     Print warning messages for constructs found in system header files.
     Warnings from system headers are normally suppressed, on the
     assumption that they usually do not indicate real problems and
     would only make the compiler output harder to read.  Using this
     command line option tells GCC to emit warnings from system headers
     as if they occurred in user code.  However, note that using
     `-Wall' in conjunction with this option will _not_ warn about
     unknown pragmas in system headers--for that, `-Wunknown-pragmas'
     must also be used.

`-Wfloat-equal'
     Warn if floating point values are used in equality comparisons.

     The idea behind this is that sometimes it is convenient (for the
     programmer) to consider floating-point values as approximations to
     infinitely precise real numbers.  If you are doing this, then you
     need to compute (by analyzing the code, or in some other way) the
     maximum or likely maximum error that the computation introduces,
     and allow for it when performing comparisons (and when producing
     output, but that's a different problem).  In particular, instead
     of testing for equality, you would check to see whether the two
     values have ranges that overlap; and this is done with the
     relational operators, so equality comparisons are probably
     mistaken.

`-Wtraditional (C and Objective-C only)'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and/or problematic constructs which
     should be avoided.

        * Macro parameters that appear within string literals in the
          macro body.  In traditional C macro replacement takes place
          within string literals, but does not in ISO C.

        * In traditional C, some preprocessor directives did not exist.
          Traditional preprocessors would only consider a line to be a
          directive if the `#' appeared in column 1 on the line.
          Therefore `-Wtraditional' warns about directives that
          traditional C understands but would ignore because the `#'
          does not appear as the first character on the line.  It also
          suggests you hide directives like `#pragma' not understood by
          traditional C by indenting them.  Some traditional
          implementations would not recognize `#elif', so it suggests
          avoiding it altogether.

        * A function-like macro that appears without arguments.

        * The unary plus operator.

        * The `U' integer constant suffix, or the `F' or `L' floating
          point constant suffixes.  (Traditional C does support the `L'
          suffix on integer constants.)  Note, these suffixes appear in
          macros defined in the system headers of most modern systems,
          e.g. the `_MIN'/`_MAX' macros in `<limits.h>'.  Use of these
          macros in user code might normally lead to spurious warnings,
          however GCC's integrated preprocessor has enough context to
          avoid warning in these cases.

        * A function declared external in one block and then used after
          the end of the block.

        * A `switch' statement has an operand of type `long'.

        * A non-`static' function declaration follows a `static' one.
          This construct is not accepted by some traditional C
          compilers.

        * The ISO type of an integer constant has a different width or
          signedness from its traditional type.  This warning is only
          issued if the base of the constant is ten.  I.e. hexadecimal
          or octal values, which typically represent bit patterns, are
          not warned about.

        * Usage of ISO string concatenation is detected.

        * Initialization of automatic aggregates.

        * Identifier conflicts with labels.  Traditional C lacks a
          separate namespace for labels.

        * Initialization of unions.  If the initializer is zero, the
          warning is omitted.  This is done under the assumption that
          the zero initializer in user code appears conditioned on e.g.
          `__STDC__' to avoid missing initializer warnings and relies
          on default initialization to zero in the traditional C case.

        * Conversions by prototypes between fixed/floating point values
          and vice versa.  The absence of these prototypes when
          compiling with traditional C would cause serious problems.
          This is a subset of the possible conversion warnings, for the
          full set use `-Wtraditional-conversion'.

        * Use of ISO C style function definitions.  This warning
          intentionally is _not_ issued for prototype declarations or
          variadic functions because these ISO C features will appear
          in your code when using libiberty's traditional C
          compatibility macros, `PARAMS' and `VPARAMS'.  This warning
          is also bypassed for nested functions because that feature is
          already a GCC extension and thus not relevant to traditional
          C compatibility.

`-Wtraditional-conversion (C and Objective-C only)'
     Warn if a prototype causes a type conversion that is different
     from what would happen to the same argument in the absence of a
     prototype.  This includes conversions of fixed point to floating
     and vice versa, and conversions changing the width or signedness
     of a fixed point argument except when the same as the default
     promotion.

`-Wdeclaration-after-statement (C and Objective-C only)'
     Warn when a declaration is found after a statement in a block.
     This construct, known from C++, was introduced with ISO C99 and is
     by default allowed in GCC.  It is not supported by ISO C90 and was
     not supported by GCC versions before GCC 3.0.  *Note Mixed
     Declarations::.

`-Wundef'
     Warn if an undefined identifier is evaluated in an `#if' directive.

`-Wno-endif-labels'
     Do not warn whenever an `#else' or an `#endif' are followed by
     text.

`-Wshadow'
     Warn whenever a local variable shadows another local variable,
     parameter or global variable or whenever a built-in function is
     shadowed.

`-Wlarger-than=LEN'
     Warn whenever an object of larger than LEN bytes is defined.

`-Wframe-larger-than=LEN'
     Warn if the size of a function frame is larger than LEN bytes.
     The computation done to determine the stack frame size is
     approximate and not conservative.  The actual requirements may be
     somewhat greater than LEN even if you do not get a warning.  In
     addition, any space allocated via `alloca', variable-length
     arrays, or related constructs is not included by the compiler when
     determining whether or not to issue a warning.

`-Wunsafe-loop-optimizations'
     Warn if the loop cannot be optimized because the compiler could not
     assume anything on the bounds of the loop indices.  With
     `-funsafe-loop-optimizations' warn if the compiler made such
     assumptions.

`-Wno-pedantic-ms-format (MinGW targets only)'
     Disables the warnings about non-ISO `printf' / `scanf' format
     width specifiers `I32', `I64', and `I' used on Windows targets
     depending on the MS runtime, when you are using the options
     `-Wformat' and `-pedantic' without gnu-extensions.

`-Wpointer-arith'
     Warn about anything that depends on the "size of" a function type
     or of `void'.  GNU C assigns these types a size of 1, for
     convenience in calculations with `void *' pointers and pointers to
     functions.  In C++, warn also when an arithmetic operation involves
     `NULL'.  This warning is also enabled by `-pedantic'.

`-Wtype-limits'
     Warn if a comparison is always true or always false due to the
     limited range of the data type, but do not warn for constant
     expressions.  For example, warn if an unsigned variable is
     compared against zero with `<' or `>='.  This warning is also
     enabled by `-Wextra'.

`-Wbad-function-cast (C and Objective-C only)'
     Warn whenever a function call is cast to a non-matching type.  For
     example, warn if `int malloc()' is cast to `anything *'.

`-Wc++-compat (C and Objective-C only)'
     Warn about ISO C constructs that are outside of the common subset
     of ISO C and ISO C++, e.g. request for implicit conversion from
     `void *' to a pointer to non-`void' type.

`-Wc++0x-compat (C++ and Objective-C++ only)'
     Warn about C++ constructs whose meaning differs between ISO C++
     1998 and ISO C++ 200x, e.g., identifiers in ISO C++ 1998 that will
     become keywords in ISO C++ 200x.  This warning is enabled by
     `-Wall'.

`-Wcast-qual'
     Warn whenever a pointer is cast so as to remove a type qualifier
     from the target type.  For example, warn if a `const char *' is
     cast to an ordinary `char *'.

`-Wcast-align'
     Warn whenever a pointer is cast such that the required alignment
     of the target is increased.  For example, warn if a `char *' is
     cast to an `int *' on machines where integers can only be accessed
     at two- or four-byte boundaries.

`-Wwrite-strings'
     When compiling C, give string constants the type `const
     char[LENGTH]' so that copying the address of one into a
     non-`const' `char *' pointer will get a warning.  These warnings
     will help you find at compile time code that can try to write into
     a string constant, but only if you have been very careful about
     using `const' in declarations and prototypes.  Otherwise, it will
     just be a nuisance. This is why we did not make `-Wall' request
     these warnings.

     When compiling C++, warn about the deprecated conversion from
     string literals to `char *'.  This warning is enabled by default
     for C++ programs.

`-Wclobbered'
     Warn for variables that might be changed by `longjmp' or `vfork'.
     This warning is also enabled by `-Wextra'.

`-Wconversion'
     Warn for implicit conversions that may alter a value. This includes
     conversions between real and integer, like `abs (x)' when `x' is
     `double'; conversions between signed and unsigned, like `unsigned
     ui = -1'; and conversions to smaller types, like `sqrtf (M_PI)'.
     Do not warn for explicit casts like `abs ((int) x)' and `ui =
     (unsigned) -1', or if the value is not changed by the conversion
     like in `abs (2.0)'.  Warnings about conversions between signed
     and unsigned integers can be disabled by using
     `-Wno-sign-conversion'.

     For C++, also warn for conversions between `NULL' and non-pointer
     types; confusing overload resolution for user-defined conversions;
     and conversions that will never use a type conversion operator:
     conversions to `void', the same type, a base class or a reference
     to them. Warnings about conversions between signed and unsigned
     integers are disabled by default in C++ unless `-Wsign-conversion'
     is explicitly enabled.

`-Wempty-body'
     Warn if an empty body occurs in an `if', `else' or `do while'
     statement.  This warning is also enabled by `-Wextra'.

`-Wenum-compare (C++ and Objective-C++ only)'
     Warn about a comparison between values of different enum types.
     This warning is enabled by default.

`-Wsign-compare'
     Warn when a comparison between signed and unsigned values could
     produce an incorrect result when the signed value is converted to
     unsigned.  This warning is also enabled by `-Wextra'; to get the
     other warnings of `-Wextra' without this warning, use `-Wextra
     -Wno-sign-compare'.

`-Wsign-conversion'
     Warn for implicit conversions that may change the sign of an
     integer value, like assigning a signed integer expression to an
     unsigned integer variable. An explicit cast silences the warning.
     In C, this option is enabled also by `-Wconversion'.

`-Waddress'
     Warn about suspicious uses of memory addresses. These include using
     the address of a function in a conditional expression, such as
     `void func(void); if (func)', and comparisons against the memory
     address of a string literal, such as `if (x == "abc")'.  Such uses
     typically indicate a programmer error: the address of a function
     always evaluates to true, so their use in a conditional usually
     indicate that the programmer forgot the parentheses in a function
     call; and comparisons against string literals result in unspecified
     behavior and are not portable in C, so they usually indicate that
     the programmer intended to use `strcmp'.  This warning is enabled
     by `-Wall'.

`-Wlogical-op'
     Warn about suspicious uses of logical operators in expressions.
     This includes using logical operators in contexts where a bit-wise
     operator is likely to be expected.

`-Waggregate-return'
     Warn if any functions that return structures or unions are defined
     or called.  (In languages where you can return an array, this also
     elicits a warning.)

`-Wno-attributes'
     Do not warn if an unexpected `__attribute__' is used, such as
     unrecognized attributes, function attributes applied to variables,
     etc.  This will not stop errors for incorrect use of supported
     attributes.

`-Wno-builtin-macro-redefined'
     Do not warn if certain built-in macros are redefined.  This
     suppresses warnings for redefinition of `__TIMESTAMP__',
     `__TIME__', `__DATE__', `__FILE__', and `__BASE_FILE__'.

`-Wstrict-prototypes (C and Objective-C only)'
     Warn if a function is declared or defined without specifying the
     argument types.  (An old-style function definition is permitted
     without a warning if preceded by a declaration which specifies the
     argument types.)

`-Wold-style-declaration (C and Objective-C only)'
     Warn for obsolescent usages, according to the C Standard, in a
     declaration. For example, warn if storage-class specifiers like
     `static' are not the first things in a declaration.  This warning
     is also enabled by `-Wextra'.

`-Wold-style-definition (C and Objective-C only)'
     Warn if an old-style function definition is used.  A warning is
     given even if there is a previous prototype.

`-Wmissing-parameter-type (C and Objective-C only)'
     A function parameter is declared without a type specifier in
     K&R-style functions:

          void foo(bar) { }

     This warning is also enabled by `-Wextra'.

`-Wmissing-prototypes (C and Objective-C only)'
     Warn if a global function is defined without a previous prototype
     declaration.  This warning is issued even if the definition itself
     provides a prototype.  The aim is to detect global functions that
     fail to be declared in header files.

`-Wmissing-declarations'
     Warn if a global function is defined without a previous
     declaration.  Do so even if the definition itself provides a
     prototype.  Use this option to detect global functions that are
     not declared in header files.  In C++, no warnings are issued for
     function templates, or for inline functions, or for functions in
     anonymous namespaces.

`-Wmissing-field-initializers'
     Warn if a structure's initializer has some fields missing.  For
     example, the following code would cause such a warning, because
     `x.h' is implicitly zero:

          struct s { int f, g, h; };
          struct s x = { 3, 4 };

     This option does not warn about designated initializers, so the
     following modification would not trigger a warning:

          struct s { int f, g, h; };
          struct s x = { .f = 3, .g = 4 };

     This warning is included in `-Wextra'.  To get other `-Wextra'
     warnings without this one, use `-Wextra
     -Wno-missing-field-initializers'.

`-Wmissing-noreturn'
     Warn about functions which might be candidates for attribute
     `noreturn'.  Note these are only possible candidates, not absolute
     ones.  Care should be taken to manually verify functions actually
     do not ever return before adding the `noreturn' attribute,
     otherwise subtle code generation bugs could be introduced.  You
     will not get a warning for `main' in hosted C environments.

`-Wmissing-format-attribute'
     Warn about function pointers which might be candidates for `format'
     attributes.  Note these are only possible candidates, not absolute
     ones.  GCC will guess that function pointers with `format'
     attributes that are used in assignment, initialization, parameter
     passing or return statements should have a corresponding `format'
     attribute in the resulting type.  I.e. the left-hand side of the
     assignment or initialization, the type of the parameter variable,
     or the return type of the containing function respectively should
     also have a `format' attribute to avoid the warning.

     GCC will also warn about function definitions which might be
     candidates for `format' attributes.  Again, these are only
     possible candidates.  GCC will guess that `format' attributes
     might be appropriate for any function that calls a function like
     `vprintf' or `vscanf', but this might not always be the case, and
     some functions for which `format' attributes are appropriate may
     not be detected.

`-Wno-multichar'
     Do not warn if a multicharacter constant (`'FOOF'') is used.
     Usually they indicate a typo in the user's code, as they have
     implementation-defined values, and should not be used in portable
     code.

`-Wnormalized=<none|id|nfc|nfkc>'
     In ISO C and ISO C++, two identifiers are different if they are
     different sequences of characters.  However, sometimes when
     characters outside the basic ASCII character set are used, you can
     have two different character sequences that look the same.  To
     avoid confusion, the ISO 10646 standard sets out some
     "normalization rules" which when applied ensure that two sequences
     that look the same are turned into the same sequence.  GCC can
     warn you if you are using identifiers which have not been
     normalized; this option controls that warning.

     There are four levels of warning that GCC supports.  The default is
     `-Wnormalized=nfc', which warns about any identifier which is not
     in the ISO 10646 "C" normalized form, "NFC".  NFC is the
     recommended form for most uses.

     Unfortunately, there are some characters which ISO C and ISO C++
     allow in identifiers that when turned into NFC aren't allowable as
     identifiers.  That is, there's no way to use these symbols in
     portable ISO C or C++ and have all your identifiers in NFC.
     `-Wnormalized=id' suppresses the warning for these characters.  It
     is hoped that future versions of the standards involved will
     correct this, which is why this option is not the default.

     You can switch the warning off for all characters by writing
     `-Wnormalized=none'.  You would only want to do this if you were
     using some other normalization scheme (like "D"), because
     otherwise you can easily create bugs that are literally impossible
     to see.

     Some characters in ISO 10646 have distinct meanings but look
     identical in some fonts or display methodologies, especially once
     formatting has been applied.  For instance `\u207F', "SUPERSCRIPT
     LATIN SMALL LETTER N", will display just like a regular `n' which
     has been placed in a superscript.  ISO 10646 defines the "NFKC"
     normalization scheme to convert all these into a standard form as
     well, and GCC will warn if your code is not in NFKC if you use
     `-Wnormalized=nfkc'.  This warning is comparable to warning about
     every identifier that contains the letter O because it might be
     confused with the digit 0, and so is not the default, but may be
     useful as a local coding convention if the programming environment
     is unable to be fixed to display these characters distinctly.

`-Wno-deprecated'
     Do not warn about usage of deprecated features.  *Note Deprecated
     Features::.

`-Wno-deprecated-declarations'
     Do not warn about uses of functions (*note Function Attributes::),
     variables (*note Variable Attributes::), and types (*note Type
     Attributes::) marked as deprecated by using the `deprecated'
     attribute.

`-Wno-overflow'
     Do not warn about compile-time overflow in constant expressions.

`-Woverride-init (C and Objective-C only)'
     Warn if an initialized field without side effects is overridden
     when using designated initializers (*note Designated Initializers:
     Designated Inits.).

     This warning is included in `-Wextra'.  To get other `-Wextra'
     warnings without this one, use `-Wextra -Wno-override-init'.

`-Wpacked'
     Warn if a structure is given the packed attribute, but the packed
     attribute has no effect on the layout or size of the structure.
     Such structures may be mis-aligned for little benefit.  For
     instance, in this code, the variable `f.x' in `struct bar' will be
     misaligned even though `struct bar' does not itself have the
     packed attribute:

          struct foo {
            int x;
            char a, b, c, d;
          } __attribute__((packed));
          struct bar {
            char z;
            struct foo f;
          };

`-Wpacked-bitfield-compat'
     The 4.1, 4.2 and 4.3 series of GCC ignore the `packed' attribute
     on bit-fields of type `char'.  This has been fixed in GCC 4.4 but
     the change can lead to differences in the structure layout.  GCC
     informs you when the offset of such a field has changed in GCC 4.4.
     For example there is no longer a 4-bit padding between field `a'
     and `b' in this structure:

          struct foo
          {
            char a:4;
            char b:8;
          } __attribute__ ((packed));

     This warning is enabled by default.  Use
     `-Wno-packed-bitfield-compat' to disable this warning.

`-Wpadded'
     Warn if padding is included in a structure, either to align an
     element of the structure or to align the whole structure.
     Sometimes when this happens it is possible to rearrange the fields
     of the structure to reduce the padding and so make the structure
     smaller.

`-Wredundant-decls'
     Warn if anything is declared more than once in the same scope,
     even in cases where multiple declaration is valid and changes
     nothing.

`-Wnested-externs (C and Objective-C only)'
     Warn if an `extern' declaration is encountered within a function.

`-Wunreachable-code'
     Warn if the compiler detects that code will never be executed.

     This option is intended to warn when the compiler detects that at
     least a whole line of source code will never be executed, because
     some condition is never satisfied or because it is after a
     procedure that never returns.

     It is possible for this option to produce a warning even though
     there are circumstances under which part of the affected line can
     be executed, so care should be taken when removing
     apparently-unreachable code.

     For instance, when a function is inlined, a warning may mean that
     the line is unreachable in only one inlined copy of the function.

     This option is not made part of `-Wall' because in a debugging
     version of a program there is often substantial code which checks
     correct functioning of the program and is, hopefully, unreachable
     because the program does work.  Another common use of unreachable
     code is to provide behavior which is selectable at compile-time.

`-Winline'
     Warn if a function can not be inlined and it was declared as
     inline.  Even with this option, the compiler will not warn about
     failures to inline functions declared in system headers.

     The compiler uses a variety of heuristics to determine whether or
     not to inline a function.  For example, the compiler takes into
     account the size of the function being inlined and the amount of
     inlining that has already been done in the current function.
     Therefore, seemingly insignificant changes in the source program
     can cause the warnings produced by `-Winline' to appear or
     disappear.

`-Wno-invalid-offsetof (C++ and Objective-C++ only)'
     Suppress warnings from applying the `offsetof' macro to a non-POD
     type.  According to the 1998 ISO C++ standard, applying `offsetof'
     to a non-POD type is undefined.  In existing C++ implementations,
     however, `offsetof' typically gives meaningful results even when
     applied to certain kinds of non-POD types. (Such as a simple
     `struct' that fails to be a POD type only by virtue of having a
     constructor.)  This flag is for users who are aware that they are
     writing nonportable code and who have deliberately chosen to
     ignore the warning about it.

     The restrictions on `offsetof' may be relaxed in a future version
     of the C++ standard.

`-Wno-int-to-pointer-cast (C and Objective-C only)'
     Suppress warnings from casts to pointer type of an integer of a
     different size.

`-Wno-pointer-to-int-cast (C and Objective-C only)'
     Suppress warnings from casts from a pointer to an integer type of a
     different size.

`-Winvalid-pch'
     Warn if a precompiled header (*note Precompiled Headers::) is
     found in the search path but can't be used.

`-Wlong-long'
     Warn if `long long' type is used.  This is default.  To inhibit
     the warning messages, use `-Wno-long-long'.  Flags `-Wlong-long'
     and `-Wno-long-long' are taken into account only when `-pedantic'
     flag is used.

`-Wvariadic-macros'
     Warn if variadic macros are used in pedantic ISO C90 mode, or the
     GNU alternate syntax when in pedantic ISO C99 mode.  This is
     default.  To inhibit the warning messages, use
     `-Wno-variadic-macros'.

`-Wvla'
     Warn if variable length array is used in the code.  `-Wno-vla'
     will prevent the `-pedantic' warning of the variable length array.

`-Wvolatile-register-var'
     Warn if a register variable is declared volatile.  The volatile
     modifier does not inhibit all optimizations that may eliminate
     reads and/or writes to register variables.  This warning is
     enabled by `-Wall'.

`-Wdisabled-optimization'
     Warn if a requested optimization pass is disabled.  This warning
     does not generally indicate that there is anything wrong with your
     code; it merely indicates that GCC's optimizers were unable to
     handle the code effectively.  Often, the problem is that your code
     is too big or too complex; GCC will refuse to optimize programs
     when the optimization itself is likely to take inordinate amounts
     of time.

`-Wpointer-sign (C and Objective-C only)'
     Warn for pointer argument passing or assignment with different
     signedness.  This option is only supported for C and Objective-C.
     It is implied by `-Wall' and by `-pedantic', which can be disabled
     with `-Wno-pointer-sign'.

`-Wstack-protector'
     This option is only active when `-fstack-protector' is active.  It
     warns about functions that will not be protected against stack
     smashing.

`-Wno-mudflap'
     Suppress warnings about constructs that cannot be instrumented by
     `-fmudflap'.

`-Woverlength-strings'
     Warn about string constants which are longer than the "minimum
     maximum" length specified in the C standard.  Modern compilers
     generally allow string constants which are much longer than the
     standard's minimum limit, but very portable programs should avoid
     using longer strings.

     The limit applies _after_ string constant concatenation, and does
     not count the trailing NUL.  In C89, the limit was 509 characters;
     in C99, it was raised to 4095.  C++98 does not specify a normative
     minimum maximum, so we do not diagnose overlength strings in C++.

     This option is implied by `-pedantic', and can be disabled with
     `-Wno-overlength-strings'.

File: gcc.info,  Node: Debugging Options,  Next: Optimize Options,  Prev: Warning Options,  Up: Invoking GCC

3.9 Options for Debugging Your Program or GCC
=============================================

GCC has various special options that are used for debugging either your
program or GCC:

`-g'
     Produce debugging information in the operating system's native
     format (stabs, COFF, XCOFF, or DWARF 2).  GDB can work with this
     debugging information.

     On most systems that use stabs format, `-g' enables use of extra
     debugging information that only GDB can use; this extra information
     makes debugging work better in GDB but will probably make other
     debuggers crash or refuse to read the program.  If you want to
     control for certain whether to generate the extra information, use
     `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', or `-gvms' (see
     below).

     GCC allows you to use `-g' with `-O'.  The shortcuts taken by
     optimized code may occasionally produce surprising results: some
     variables you declared may not exist at all; flow of control may
     briefly move where you did not expect it; some statements may not
     be executed because they compute constant results or their values
     were already at hand; some statements may execute in different
     places because they were moved out of loops.

     Nevertheless it proves possible to debug optimized output.  This
     makes it reasonable to use the optimizer for programs that might
     have bugs.

     The following options are useful when GCC is generated with the
     capability for more than one debugging format.

`-ggdb'
     Produce debugging information for use by GDB.  This means to use
     the most expressive format available (DWARF 2, stabs, or the
     native format if neither of those are supported), including GDB
     extensions if at all possible.

`-gstabs'
     Produce debugging information in stabs format (if that is
     supported), without GDB extensions.  This is the format used by
     DBX on most BSD systems.  On MIPS, Alpha and System V Release 4
     systems this option produces stabs debugging output which is not
     understood by DBX or SDB.  On System V Release 4 systems this
     option requires the GNU assembler.

`-feliminate-unused-debug-symbols'
     Produce debugging information in stabs format (if that is
     supported), for only symbols that are actually used.

`-femit-class-debug-always'
     Instead of emitting debugging information for a C++ class in only
     one object file, emit it in all object files using the class.
     This option should be used only with debuggers that are unable to
     handle the way GCC normally emits debugging information for
     classes because using this option will increase the size of
     debugging information by as much as a factor of two.

`-gstabs+'
     Produce debugging information in stabs format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gcoff'
     Produce debugging information in COFF format (if that is
     supported).  This is the format used by SDB on most System V
     systems prior to System V Release 4.

`-gxcoff'
     Produce debugging information in XCOFF format (if that is
     supported).  This is the format used by the DBX debugger on IBM
     RS/6000 systems.

`-gxcoff+'
     Produce debugging information in XCOFF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program, and may cause
     assemblers other than the GNU assembler (GAS) to fail with an
     error.

`-gdwarf-VERSION'
     Produce debugging information in DWARF format (if that is
     supported).  This is the format used by DBX on IRIX 6.  The value
     of VERSION may be either 2 or 3; the default version is 3.

     Note that with DWARF version 2 some ports require, and will always
     use, some non-conflicting DWARF 3 extensions in the unwind tables.

`-gstrict-dwarf'
     Disallow using extensions of later DWARF standard version than
     selected with `-gdwarf-VERSION'.  On most targets using
     non-conflicting DWARF extensions from later standard versions is
     allowed.

`-gno-strict-dwarf'
     Allow using extensions of later DWARF standard version than
     selected with `-gdwarf-VERSION'.

`-gvms'
     Produce debugging information in VMS debug format (if that is
     supported).  This is the format used by DEBUG on VMS systems.

`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gvmsLEVEL'
     Request debugging information and also use LEVEL to specify how
     much information.  The default level is 2.

     Level 0 produces no debug information at all.  Thus, `-g0' negates
     `-g'.

     Level 1 produces minimal information, enough for making backtraces
     in parts of the program that you don't plan to debug.  This
     includes descriptions of functions and external variables, but no
     information about local variables and no line numbers.

     Level 3 includes extra information, such as all the macro
     definitions present in the program.  Some debuggers support macro
     expansion when you use `-g3'.

     `-gdwarf-2' does not accept a concatenated debug level, because
     GCC used to support an option `-gdwarf' that meant to generate
     debug information in version 1 of the DWARF format (which is very
     different from version 2), and it would have been too confusing.
     That debug format is long obsolete, but the option cannot be
     changed now.  Instead use an additional `-gLEVEL' option to change
     the debug level for DWARF.

`-gtoggle'
     Turn off generation of debug info, if leaving out this option
     would have generated it, or turn it on at level 2 otherwise.  The
     position of this argument in the command line does not matter, it
     takes effect after all other options are processed, and it does so
     only once, no matter how many times it is given.  This is mainly
     intended to be used with `-fcompare-debug'.

`-fdump-final-insns[=FILE]'
     Dump the final internal representation (RTL) to FILE.  If the
     optional argument is omitted (or if FILE is `.'), the name of the
     dump file will be determined by appending `.gkd' to the
     compilation output file name.

`-fcompare-debug[=OPTS]'
     If no error occurs during compilation, run the compiler a second
     time, adding OPTS and `-fcompare-debug-second' to the arguments
     passed to the second compilation.  Dump the final internal
     representation in both compilations, and print an error if they
     differ.

     If the equal sign is omitted, the default `-gtoggle' is used.

     The environment variable `GCC_COMPARE_DEBUG', if defined, non-empty
     and nonzero, implicitly enables `-fcompare-debug'.  If
     `GCC_COMPARE_DEBUG' is defined to a string starting with a dash,
     then it is used for OPTS, otherwise the default `-gtoggle' is used.

     `-fcompare-debug=', with the equal sign but without OPTS, is
     equivalent to `-fno-compare-debug', which disables the dumping of
     the final representation and the second compilation, preventing
     even `GCC_COMPARE_DEBUG' from taking effect.

     To verify full coverage during `-fcompare-debug' testing, set
     `GCC_COMPARE_DEBUG' to say `-fcompare-debug-not-overridden', which
     GCC will reject as an invalid option in any actual compilation
     (rather than preprocessing, assembly or linking).  To get just a
     warning, setting `GCC_COMPARE_DEBUG' to `-w%n-fcompare-debug not
     overridden' will do.

`-fcompare-debug-second'
     This option is implicitly passed to the compiler for the second
     compilation requested by `-fcompare-debug', along with options to
     silence warnings, and omitting other options that would cause
     side-effect compiler outputs to files or to the standard output.
     Dump files and preserved temporary files are renamed so as to
     contain the `.gk' additional extension during the second
     compilation, to avoid overwriting those generated by the first.

     When this option is passed to the compiler driver, it causes the
     _first_ compilation to be skipped, which makes it useful for little
     other than debugging the compiler proper.

`-feliminate-dwarf2-dups'
     Compress DWARF2 debugging information by eliminating duplicated
     information about each symbol.  This option only makes sense when
     generating DWARF2 debugging information with `-gdwarf-2'.

`-femit-struct-debug-baseonly'
     Emit debug information for struct-like types only when the base
     name of the compilation source file matches the base name of file
     in which the struct was defined.

     This option substantially reduces the size of debugging
     information, but at significant potential loss in type information
     to the debugger.  See `-femit-struct-debug-reduced' for a less
     aggressive option.  See `-femit-struct-debug-detailed' for more
     detailed control.

     This option works only with DWARF 2.

`-femit-struct-debug-reduced'
     Emit debug information for struct-like types only when the base
     name of the compilation source file matches the base name of file
     in which the type was defined, unless the struct is a template or
     defined in a system header.

     This option significantly reduces the size of debugging
     information, with some potential loss in type information to the
     debugger.  See `-femit-struct-debug-baseonly' for a more
     aggressive option.  See `-femit-struct-debug-detailed' for more
     detailed control.

     This option works only with DWARF 2.

`-femit-struct-debug-detailed[=SPEC-LIST]'
     Specify the struct-like types for which the compiler will generate
     debug information.  The intent is to reduce duplicate struct debug
     information between different object files within the same program.

     This option is a detailed version of `-femit-struct-debug-reduced'
     and `-femit-struct-debug-baseonly', which will serve for most
     needs.

     A specification has the syntax
     [`dir:'|`ind:'][`ord:'|`gen:'](`any'|`sys'|`base'|`none')

     The optional first word limits the specification to structs that
     are used directly (`dir:') or used indirectly (`ind:').  A struct
     type is used directly when it is the type of a variable, member.
     Indirect uses arise through pointers to structs.  That is, when
     use of an incomplete struct would be legal, the use is indirect.
     An example is `struct one direct; struct two * indirect;'.

     The optional second word limits the specification to ordinary
     structs (`ord:') or generic structs (`gen:').  Generic structs are
     a bit complicated to explain.  For C++, these are non-explicit
     specializations of template classes, or non-template classes
     within the above.  Other programming languages have generics, but
     `-femit-struct-debug-detailed' does not yet implement them.

     The third word specifies the source files for those structs for
     which the compiler will emit debug information.  The values `none'
     and `any' have the normal meaning.  The value `base' means that
     the base of name of the file in which the type declaration appears
     must match the base of the name of the main compilation file.  In
     practice, this means that types declared in `foo.c' and `foo.h'
     will have debug information, but types declared in other header
     will not.  The value `sys' means those types satisfying `base' or
     declared in system or compiler headers.

     You may need to experiment to determine the best settings for your
     application.

     The default is `-femit-struct-debug-detailed=all'.

     This option works only with DWARF 2.

`-fno-merge-debug-strings'
     Direct the linker to not merge together strings in the debugging
     information which are identical in different object files.
     Merging is not supported by all assemblers or linkers.  Merging
     decreases the size of the debug information in the output file at
     the cost of increasing link processing time.  Merging is enabled
     by default.

`-fdebug-prefix-map=OLD=NEW'
     When compiling files in directory `OLD', record debugging
     information describing them as in `NEW' instead.

`-fno-dwarf2-cfi-asm'
     Emit DWARF 2 unwind info as compiler generated `.eh_frame' section
     instead of using GAS `.cfi_*' directives.

`-p'
     Generate extra code to write profile information suitable for the
     analysis program `prof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-pg'
     Generate extra code to write profile information suitable for the
     analysis program `gprof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-Q'
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

`-ftime-report'
     Makes the compiler print some statistics about the time consumed
     by each pass when it finishes.

`-fmem-report'
     Makes the compiler print some statistics about permanent memory
     allocation when it finishes.

`-fpre-ipa-mem-report'

`-fpost-ipa-mem-report'
     Makes the compiler print some statistics about permanent memory
     allocation before or after interprocedural optimization.

`-fprofile-arcs'
     Add code so that program flow "arcs" are instrumented.  During
     execution the program records how many times each branch and call
     is executed and how many times it is taken or returns.  When the
     compiled program exits it saves this data to a file called
     `AUXNAME.gcda' for each source file.  The data may be used for
     profile-directed optimizations (`-fbranch-probabilities'), or for
     test coverage analysis (`-ftest-coverage').  Each object file's
     AUXNAME is generated from the name of the output file, if
     explicitly specified and it is not the final executable, otherwise
     it is the basename of the source file.  In both cases any suffix
     is removed (e.g. `foo.gcda' for input file `dir/foo.c', or
     `dir/foo.gcda' for output file specified as `-o dir/foo.o').
     *Note Cross-profiling::.

`--coverage'
     This option is used to compile and link code instrumented for
     coverage analysis.  The option is a synonym for `-fprofile-arcs'
     `-ftest-coverage' (when compiling) and `-lgcov' (when linking).
     See the documentation for those options for more details.

        * Compile the source files with `-fprofile-arcs' plus
          optimization and code generation options.  For test coverage
          analysis, use the additional `-ftest-coverage' option.  You
          do not need to profile every source file in a program.

        * Link your object files with `-lgcov' or `-fprofile-arcs' (the
          latter implies the former).

        * Run the program on a representative workload to generate the
          arc profile information.  This may be repeated any number of
          times.  You can run concurrent instances of your program, and
          provided that the file system supports locking, the data
          files will be correctly updated.  Also `fork' calls are
          detected and correctly handled (double counting will not
          happen).

        * For profile-directed optimizations, compile the source files
          again with the same optimization and code generation options
          plus `-fbranch-probabilities' (*note Options that Control
          Optimization: Optimize Options.).

        * For test coverage analysis, use `gcov' to produce human
          readable information from the `.gcno' and `.gcda' files.
          Refer to the `gcov' documentation for further information.


     With `-fprofile-arcs', for each function of your program GCC
     creates a program flow graph, then finds a spanning tree for the
     graph.  Only arcs that are not on the spanning tree have to be
     instrumented: the compiler adds code to count the number of times
     that these arcs are executed.  When an arc is the only exit or
     only entrance to a block, the instrumentation code can be added to
     the block; otherwise, a new basic block must be created to hold
     the instrumentation code.

`-ftest-coverage'
     Produce a notes file that the `gcov' code-coverage utility (*note
     `gcov'--a Test Coverage Program: Gcov.) can use to show program
     coverage.  Each source file's note file is called `AUXNAME.gcno'.
     Refer to the `-fprofile-arcs' option above for a description of
     AUXNAME and instructions on how to generate test coverage data.
     Coverage data will match the source files more closely, if you do
     not optimize.

`-fdbg-cnt-list'
     Print the name and the counter upperbound for all debug counters.

`-fdbg-cnt=COUNTER-VALUE-LIST'
     Set the internal debug counter upperbound. COUNTER-VALUE-LIST is a
     comma-separated list of NAME:VALUE pairs which sets the upperbound
     of each debug counter NAME to VALUE.  All debug counters have the
     initial upperbound of UINT_MAX, thus dbg_cnt() returns true always
     unless the upperbound is set by this option.  e.g. With
     -fdbg-cnt=dce:10,tail_call:0 dbg_cnt(dce) will return true only
     for first 10 invocations and dbg_cnt(tail_call) will return false
     always.

`-dLETTERS'
`-fdump-rtl-PASS'
     Says to make debugging dumps during compilation at times specified
     by LETTERS.    This is used for debugging the RTL-based passes of
     the compiler.  The file names for most of the dumps are made by
     appending a pass number and a word to the DUMPNAME.  DUMPNAME is
     generated from the name of the output file, if explicitly
     specified and it is not an executable, otherwise it is the
     basename of the source file. These switches may have different
     effects when `-E' is used for preprocessing.

     Debug dumps can be enabled with a `-fdump-rtl' switch or some `-d'
     option LETTERS.  Here are the possible letters for use in PASS and
     LETTERS, and their meanings:

    `-fdump-rtl-alignments'
          Dump after branch alignments have been computed.

    `-fdump-rtl-asmcons'
          Dump after fixing rtl statements that have unsatisfied in/out
          constraints.

    `-fdump-rtl-auto_inc_dec'
          Dump after auto-inc-dec discovery.  This pass is only run on
          architectures that have auto inc or auto dec instructions.

    `-fdump-rtl-barriers'
          Dump after cleaning up the barrier instructions.

    `-fdump-rtl-bbpart'
          Dump after partitioning hot and cold basic blocks.

    `-fdump-rtl-bbro'
          Dump after block reordering.

    `-fdump-rtl-btl1'
    `-fdump-rtl-btl2'
          `-fdump-rtl-btl1' and `-fdump-rtl-btl2' enable dumping after
          the two branch target load optimization passes.

    `-fdump-rtl-bypass'
          Dump after jump bypassing and control flow optimizations.

    `-fdump-rtl-combine'
          Dump after the RTL instruction combination pass.

    `-fdump-rtl-compgotos'
          Dump after duplicating the computed gotos.

    `-fdump-rtl-ce1'
    `-fdump-rtl-ce2'
    `-fdump-rtl-ce3'
          `-fdump-rtl-ce1', `-fdump-rtl-ce2', and `-fdump-rtl-ce3'
          enable dumping after the three if conversion passes.

    `-fdump-rtl-cprop_hardreg'
          Dump after hard register copy propagation.

    `-fdump-rtl-csa'
          Dump after combining stack adjustments.

    `-fdump-rtl-cse1'
    `-fdump-rtl-cse2'
          `-fdump-rtl-cse1' and `-fdump-rtl-cse2' enable dumping after
          the two common sub-expression elimination passes.

    `-fdump-rtl-dce'
          Dump after the standalone dead code elimination passes.

    `-fdump-rtl-dbr'
          Dump after delayed branch scheduling.

    `-fdump-rtl-dce1'
    `-fdump-rtl-dce2'
          `-fdump-rtl-dce1' and `-fdump-rtl-dce2' enable dumping after
          the two dead store elimination passes.

    `-fdump-rtl-eh'
          Dump after finalization of EH handling code.

    `-fdump-rtl-eh_ranges'
          Dump after conversion of EH handling range regions.

    `-fdump-rtl-expand'
          Dump after RTL generation.

    `-fdump-rtl-fwprop1'
    `-fdump-rtl-fwprop2'
          `-fdump-rtl-fwprop1' and `-fdump-rtl-fwprop2' enable dumping
          after the two forward propagation passes.

    `-fdump-rtl-gcse1'
    `-fdump-rtl-gcse2'
          `-fdump-rtl-gcse1' and `-fdump-rtl-gcse2' enable dumping
          after global common subexpression elimination.

    `-fdump-rtl-init-regs'
          Dump after the initialization of the registers.

    `-fdump-rtl-initvals'
          Dump after the computation of the initial value sets.

    `-fdump-rtl-into_cfglayout'
          Dump after converting to cfglayout mode.

    `-fdump-rtl-ira'
          Dump after iterated register allocation.

    `-fdump-rtl-jump'
          Dump after the second jump optimization.

    `-fdump-rtl-loop2'
          `-fdump-rtl-loop2' enables dumping after the rtl loop
          optimization passes.

    `-fdump-rtl-mach'
          Dump after performing the machine dependent reorganization
          pass, if that pass exists.

    `-fdump-rtl-mode_sw'
          Dump after removing redundant mode switches.

    `-fdump-rtl-rnreg'
          Dump after register renumbering.

    `-fdump-rtl-outof_cfglayout'
          Dump after converting from cfglayout mode.

    `-fdump-rtl-peephole2'
          Dump after the peephole pass.

    `-fdump-rtl-postreload'
          Dump after post-reload optimizations.

    `-fdump-rtl-pro_and_epilogue'
          Dump after generating the function pro and epilogues.

    `-fdump-rtl-regmove'
          Dump after the register move pass.

    `-fdump-rtl-sched1'
    `-fdump-rtl-sched2'
          `-fdump-rtl-sched1' and `-fdump-rtl-sched2' enable dumping
          after the basic block scheduling passes.

    `-fdump-rtl-see'
          Dump after sign extension elimination.

    `-fdump-rtl-seqabstr'
          Dump after common sequence discovery.

    `-fdump-rtl-shorten'
          Dump after shortening branches.

    `-fdump-rtl-sibling'
          Dump after sibling call optimizations.

    `-fdump-rtl-split1'
    `-fdump-rtl-split2'
    `-fdump-rtl-split3'
    `-fdump-rtl-split4'
    `-fdump-rtl-split5'
          `-fdump-rtl-split1', `-fdump-rtl-split2',
          `-fdump-rtl-split3', `-fdump-rtl-split4' and
          `-fdump-rtl-split5' enable dumping after five rounds of
          instruction splitting.

    `-fdump-rtl-sms'
          Dump after modulo scheduling.  This pass is only run on some
          architectures.

    `-fdump-rtl-stack'
          Dump after conversion from GCC's "flat register file"
          registers to the x87's stack-like registers.  This pass is
          only run on x86 variants.

    `-fdump-rtl-subreg1'
    `-fdump-rtl-subreg2'
          `-fdump-rtl-subreg1' and `-fdump-rtl-subreg2' enable dumping
          after the two subreg expansion passes.

    `-fdump-rtl-unshare'
          Dump after all rtl has been unshared.

    `-fdump-rtl-vartrack'
          Dump after variable tracking.

    `-fdump-rtl-vregs'
          Dump after converting virtual registers to hard registers.

    `-fdump-rtl-web'
          Dump after live range splitting.

    `-fdump-rtl-regclass'
    `-fdump-rtl-subregs_of_mode_init'
    `-fdump-rtl-subregs_of_mode_finish'
    `-fdump-rtl-dfinit'
    `-fdump-rtl-dfinish'
          These dumps are defined but always produce empty files.

    `-fdump-rtl-all'
          Produce all the dumps listed above.

    `-dA'
          Annotate the assembler output with miscellaneous debugging
          information.

    `-dD'
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

    `-dH'
          Produce a core dump whenever an error occurs.

    `-dm'
          Print statistics on memory usage, at the end of the run, to
          standard error.

    `-dp'
          Annotate the assembler output with a comment indicating which
          pattern and alternative was used.  The length of each
          instruction is also printed.

    `-dP'
          Dump the RTL in the assembler output as a comment before each
          instruction.  Also turns on `-dp' annotation.

    `-dv'
          For each of the other indicated dump files
          (`-fdump-rtl-PASS'), dump a representation of the control
          flow graph suitable for viewing with VCG to `FILE.PASS.vcg'.

    `-dx'
          Just generate RTL for a function instead of compiling it.
          Usually used with `-fdump-rtl-expand'.

    `-dy'
          Dump debugging information during parsing, to standard error.

`-fdump-noaddr'
     When doing debugging dumps, suppress address output.  This makes
     it more feasible to use diff on debugging dumps for compiler
     invocations with different compiler binaries and/or different text
     / bss / data / heap / stack / dso start locations.

`-fdump-unnumbered'
     When doing debugging dumps, suppress instruction numbers and
     address output.  This makes it more feasible to use diff on
     debugging dumps for compiler invocations with different options,
     in particular with and without `-g'.

`-fdump-unnumbered-links'
     When doing debugging dumps (see `-d' option above), suppress
     instruction numbers for the links to the previous and next
     instructions in a sequence.

`-fdump-translation-unit (C++ only)'
`-fdump-translation-unit-OPTIONS (C++ only)'
     Dump a representation of the tree structure for the entire
     translation unit to a file.  The file name is made by appending
     `.tu' to the source file name.  If the `-OPTIONS' form is used,
     OPTIONS controls the details of the dump as described for the
     `-fdump-tree' options.

`-fdump-class-hierarchy (C++ only)'
`-fdump-class-hierarchy-OPTIONS (C++ only)'
     Dump a representation of each class's hierarchy and virtual
     function table layout to a file.  The file name is made by
     appending `.class' to the source file name.  If the `-OPTIONS'
     form is used, OPTIONS controls the details of the dump as
     described for the `-fdump-tree' options.

`-fdump-ipa-SWITCH'
     Control the dumping at various stages of inter-procedural analysis
     language tree to a file.  The file name is generated by appending
     a switch specific suffix to the source file name.  The following
     dumps are possible:

    `all'
          Enables all inter-procedural analysis dumps.

    `cgraph'
          Dumps information about call-graph optimization, unused
          function removal, and inlining decisions.

    `inline'
          Dump after function inlining.


`-fdump-statistics-OPTION'
     Enable and control dumping of pass statistics in a separate file.
     The file name is generated by appending a suffix ending in
     `.statistics' to the source file name.  If the `-OPTION' form is
     used, `-stats' will cause counters to be summed over the whole
     compilation unit while `-details' will dump every event as the
     passes generate them.  The default with no option is to sum
     counters for each function compiled.

`-fdump-tree-SWITCH'
`-fdump-tree-SWITCH-OPTIONS'
     Control the dumping at various stages of processing the
     intermediate language tree to a file.  The file name is generated
     by appending a switch specific suffix to the source file name.  If
     the `-OPTIONS' form is used, OPTIONS is a list of `-' separated
     options that control the details of the dump.  Not all options are
     applicable to all dumps, those which are not meaningful will be
     ignored.  The following options are available

    `address'
          Print the address of each node.  Usually this is not
          meaningful as it changes according to the environment and
          source file.  Its primary use is for tying up a dump file
          with a debug environment.

    `slim'
          Inhibit dumping of members of a scope or body of a function
          merely because that scope has been reached.  Only dump such
          items when they are directly reachable by some other path.
          When dumping pretty-printed trees, this option inhibits
          dumping the bodies of control structures.

    `raw'
          Print a raw representation of the tree.  By default, trees are
          pretty-printed into a C-like representation.

    `details'
          Enable more detailed dumps (not honored by every dump option).

    `stats'
          Enable dumping various statistics about the pass (not honored
          by every dump option).

    `blocks'
          Enable showing basic block boundaries (disabled in raw dumps).

    `vops'
          Enable showing virtual operands for every statement.

    `lineno'
          Enable showing line numbers for statements.

    `uid'
          Enable showing the unique ID (`DECL_UID') for each variable.

    `verbose'
          Enable showing the tree dump for each statement.

    `all'
          Turn on all options, except `raw', `slim', `verbose' and
          `lineno'.

     The following tree dumps are possible:
    `original'
          Dump before any tree based optimization, to `FILE.original'.

    `optimized'
          Dump after all tree based optimization, to `FILE.optimized'.

    `gimple'
          Dump each function before and after the gimplification pass
          to a file.  The file name is made by appending `.gimple' to
          the source file name.

    `cfg'
          Dump the control flow graph of each function to a file.  The
          file name is made by appending `.cfg' to the source file name.

    `vcg'
          Dump the control flow graph of each function to a file in VCG
          format.  The file name is made by appending `.vcg' to the
          source file name.  Note that if the file contains more than
          one function, the generated file cannot be used directly by
          VCG.  You will need to cut and paste each function's graph
          into its own separate file first.

    `ch'
          Dump each function after copying loop headers.  The file name
          is made by appending `.ch' to the source file name.

    `ssa'
          Dump SSA related information to a file.  The file name is
          made by appending `.ssa' to the source file name.

    `alias'
          Dump aliasing information for each function.  The file name
          is made by appending `.alias' to the source file name.

    `ccp'
          Dump each function after CCP.  The file name is made by
          appending `.ccp' to the source file name.

    `storeccp'
          Dump each function after STORE-CCP.  The file name is made by
          appending `.storeccp' to the source file name.

    `pre'
          Dump trees after partial redundancy elimination.  The file
          name is made by appending `.pre' to the source file name.

    `fre'
          Dump trees after full redundancy elimination.  The file name
          is made by appending `.fre' to the source file name.

    `copyprop'
          Dump trees after copy propagation.  The file name is made by
          appending `.copyprop' to the source file name.

    `store_copyprop'
          Dump trees after store copy-propagation.  The file name is
          made by appending `.store_copyprop' to the source file name.

    `dce'
          Dump each function after dead code elimination.  The file
          name is made by appending `.dce' to the source file name.

    `mudflap'
          Dump each function after adding mudflap instrumentation.  The
          file name is made by appending `.mudflap' to the source file
          name.

    `sra'
          Dump each function after performing scalar replacement of
          aggregates.  The file name is made by appending `.sra' to the
          source file name.

    `sink'
          Dump each function after performing code sinking.  The file
          name is made by appending `.sink' to the source file name.

    `dom'
          Dump each function after applying dominator tree
          optimizations.  The file name is made by appending `.dom' to
          the source file name.

    `dse'
          Dump each function after applying dead store elimination.
          The file name is made by appending `.dse' to the source file
          name.

    `phiopt'
          Dump each function after optimizing PHI nodes into
          straightline code.  The file name is made by appending
          `.phiopt' to the source file name.

    `forwprop'
          Dump each function after forward propagating single use
          variables.  The file name is made by appending `.forwprop' to
          the source file name.

    `copyrename'
          Dump each function after applying the copy rename
          optimization.  The file name is made by appending
          `.copyrename' to the source file name.

    `nrv'
          Dump each function after applying the named return value
          optimization on generic trees.  The file name is made by
          appending `.nrv' to the source file name.

    `vect'
          Dump each function after applying vectorization of loops.
          The file name is made by appending `.vect' to the source file
          name.

    `vrp'
          Dump each function after Value Range Propagation (VRP).  The
          file name is made by appending `.vrp' to the source file name.

    `all'
          Enable all the available tree dumps with the flags provided
          in this option.

`-ftree-vectorizer-verbose=N'
     This option controls the amount of debugging output the vectorizer
     prints.  This information is written to standard error, unless
     `-fdump-tree-all' or `-fdump-tree-vect' is specified, in which
     case it is output to the usual dump listing file, `.vect'.  For
     N=0 no diagnostic information is reported.  If N=1 the vectorizer
     reports each loop that got vectorized, and the total number of
     loops that got vectorized.  If N=2 the vectorizer also reports
     non-vectorized loops that passed the first analysis phase
     (vect_analyze_loop_form) - i.e. countable, inner-most, single-bb,
     single-entry/exit loops.  This is the same verbosity level that
     `-fdump-tree-vect-stats' uses.  Higher verbosity levels mean
     either more information dumped for each reported loop, or same
     amount of information reported for more loops: If N=3, alignment
     related information is added to the reports.  If N=4,
     data-references related information (e.g. memory dependences,
     memory access-patterns) is added to the reports.  If N=5, the
     vectorizer reports also non-vectorized inner-most loops that did
     not pass the first analysis phase (i.e., may not be countable, or
     may have complicated control-flow).  If N=6, the vectorizer
     reports also non-vectorized nested loops.  For N=7, all the
     information the vectorizer generates during its analysis and
     transformation is reported.  This is the same verbosity level that
     `-fdump-tree-vect-details' uses.

`-frandom-seed=STRING'
     This option provides a seed that GCC uses when it would otherwise
     use random numbers.  It is used to generate certain symbol names
     that have to be different in every compiled file.  It is also used
     to place unique stamps in coverage data files and the object files
     that produce them.  You can use the `-frandom-seed' option to
     produce reproducibly identical object files.

     The STRING should be different for every file you compile.

`-fsched-verbose=N'
     On targets that use instruction scheduling, this option controls
     the amount of debugging output the scheduler prints.  This
     information is written to standard error, unless
     `-fdump-rtl-sched1' or `-fdump-rtl-sched2' is specified, in which
     case it is output to the usual dump listing file, `.sched' or
     `.sched2' respectively.  However for N greater than nine, the
     output is always printed to standard error.

     For N greater than zero, `-fsched-verbose' outputs the same
     information as `-fdump-rtl-sched1' and `-fdump-rtl-sched2'.  For N
     greater than one, it also output basic block probabilities,
     detailed ready list information and unit/insn info.  For N greater
     than two, it includes RTL at abort point, control-flow and regions
     info.  And for N over four, `-fsched-verbose' also includes
     dependence info.

`-save-temps'
     Store the usual "temporary" intermediate files permanently; place
     them in the current directory and name them based on the source
     file.  Thus, compiling `foo.c' with `-c -save-temps' would produce
     files `foo.i' and `foo.s', as well as `foo.o'.  This creates a
     preprocessed `foo.i' output file even though the compiler now
     normally uses an integrated preprocessor.

     When used in combination with the `-x' command line option,
     `-save-temps' is sensible enough to avoid over writing an input
     source file with the same extension as an intermediate file.  The
     corresponding intermediate file may be obtained by renaming the
     source file before using `-save-temps'.

`-time[=FILE]'
     Report the CPU time taken by each subprocess in the compilation
     sequence.  For C source files, this is the compiler proper and
     assembler (plus the linker if linking is done).

     Without the specification of an output file, the output looks like
     this:

          # cc1 0.12 0.01
          # as 0.00 0.01

     The first number on each line is the "user time", that is time
     spent executing the program itself.  The second number is "system
     time", time spent executing operating system routines on behalf of
     the program.  Both numbers are in seconds.

     With the specification of an output file, the output is appended
     to the named file, and it looks like this:

          0.12 0.01 cc1 OPTIONS
          0.00 0.01 as OPTIONS

     The "user time" and the "system time" are moved before the program
     name, and the options passed to the program are displayed, so that
     one can later tell what file was being compiled, and with which
     options.

`-fvar-tracking'
     Run variable tracking pass.  It computes where variables are
     stored at each position in code.  Better debugging information is
     then generated (if the debugging information format supports this
     information).

     It is enabled by default when compiling with optimization (`-Os',
     `-O', `-O2', ...), debugging information (`-g') and the debug info
     format supports it.

`-fvar-tracking-assignments'
     Annotate assignments to user variables early in the compilation and
     attempt to carry the annotations over throughout the compilation
     all the way to the end, in an attempt to improve debug information
     while optimizing.

     It can be enabled even if var-tracking is disabled, in which case
     annotations will be created and maintained, but discarded at the
     end.

`-fvar-tracking-assignments-toggle'
     Toggle `-fvar-tracking-assignments', in the same way that
     `-gtoggle' toggles `-g'.

`-print-file-name=LIBRARY'
     Print the full absolute name of the library file LIBRARY that
     would be used when linking--and don't do anything else.  With this
     option, GCC does not compile or link anything; it just prints the
     file name.

`-print-multi-directory'
     Print the directory name corresponding to the multilib selected by
     any other switches present in the command line.  This directory is
     supposed to exist in `GCC_EXEC_PREFIX'.

`-print-multi-lib'
     Print the mapping from multilib directory names to compiler
     switches that enable them.  The directory name is separated from
     the switches by `;', and each switch starts with an `@' instead of
     the `-', without spaces between multiple switches.  This is
     supposed to ease shell-processing.

`-print-multi-os-directory'
     Print the path to OS libraries for the selected multilib, relative
     to some `lib' subdirectory.  If OS libraries are present in the
     `lib' subdirectory and no multilibs are used, this is usually just
     `.', if OS libraries are present in `libSUFFIX' sibling
     directories this prints e.g. `../lib64', `../lib' or `../lib32',
     or if OS libraries are present in `lib/SUBDIR' subdirectories it
     prints e.g. `amd64', `sparcv9' or `ev6'.

`-print-prog-name=PROGRAM'
     Like `-print-file-name', but searches for a program such as `cpp'.

`-print-libgcc-file-name'
     Same as `-print-file-name=libgcc.a'.

     This is useful when you use `-nostdlib' or `-nodefaultlibs' but
     you do want to link with `libgcc.a'.  You can do

          gcc -nostdlib FILES... `gcc -print-libgcc-file-name`

`-print-search-dirs'
     Print the name of the configured installation directory and a list
     of program and library directories `gcc' will search--and don't do
     anything else.

     This is useful when `gcc' prints the error message `installation
     problem, cannot exec cpp0: No such file or directory'.  To resolve
     this you either need to put `cpp0' and the other compiler
     components where `gcc' expects to find them, or you can set the
     environment variable `GCC_EXEC_PREFIX' to the directory where you
     installed them.  Don't forget the trailing `/'.  *Note Environment
     Variables::.

`-print-sysroot'
     Print the target sysroot directory that will be used during
     compilation.  This is the target sysroot specified either at
     configure time or using the `--sysroot' option, possibly with an
     extra suffix that depends on compilation options.  If no target
     sysroot is specified, the option prints nothing.

`-print-sysroot-headers-suffix'
     Print the suffix added to the target sysroot when searching for
     headers, or give an error if the compiler is not configured with
     such a suffix--and don't do anything else.

`-dumpmachine'
     Print the compiler's target machine (for example,
     `i686-pc-linux-gnu')--and don't do anything else.

`-dumpversion'
     Print the compiler version (for example, `3.0')--and don't do
     anything else.

`-dumpspecs'
     Print the compiler's built-in specs--and don't do anything else.
     (This is used when GCC itself is being built.)  *Note Spec Files::.

`-feliminate-unused-debug-types'
     Normally, when producing DWARF2 output, GCC will emit debugging
     information for all types declared in a compilation unit,
     regardless of whether or not they are actually used in that
     compilation unit.  Sometimes this is useful, such as if, in the
     debugger, you want to cast a value to a type that is not actually
     used in your program (but is declared).  More often, however, this
     results in a significant amount of wasted space.  With this
     option, GCC will avoid producing debug symbol output for types
     that are nowhere used in the source file being compiled.

File: gcc.info,  Node: Optimize Options,  Next: Preprocessor Options,  Prev: Debugging Options,  Up: Invoking GCC

3.10 Options That Control Optimization
======================================

These options control various sorts of optimizations.

 Without any optimization option, the compiler's goal is to reduce the
cost of compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.

 Turning on optimization flags makes the compiler attempt to improve
the performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.

 The compiler performs optimization based on the knowledge it has of the
program.  Compiling multiple files at once to a single output file mode
allows the compiler to use information gained from all of the files
when compiling each of them.

 Not all optimizations are controlled directly by a flag.  Only
optimizations that have a flag are listed.

`-O'
`-O1'
     Optimize.  Optimizing compilation takes somewhat more time, and a
     lot more memory for a large function.

     With `-O', the compiler tries to reduce code size and execution
     time, without performing any optimizations that take a great deal
     of compilation time.

     `-O' turns on the following optimization flags:
          -fauto-inc-dec
          -fcprop-registers
          -fdce
          -fdefer-pop
          -fdelayed-branch
          -fdse
          -fguess-branch-probability
          -fif-conversion2
          -fif-conversion
          -finline-small-functions
          -fipa-pure-const
          -fipa-reference
          -fmerge-constants
          -fsplit-wide-types
          -ftree-builtin-call-dce
          -ftree-ccp
          -ftree-ch
          -ftree-copyrename
          -ftree-dce
          -ftree-dominator-opts
          -ftree-dse
          -ftree-fre
          -ftree-sra
          -ftree-ter
          -funit-at-a-time

     `-O' also turns on `-fomit-frame-pointer' on machines where doing
     so does not interfere with debugging.

`-O2'
     Optimize even more.  GCC performs nearly all supported
     optimizations that do not involve a space-speed tradeoff.  As
     compared to `-O', this option increases both compilation time and
     the performance of the generated code.

     `-O2' turns on all optimization flags specified by `-O'.  It also
     turns on the following optimization flags:
          -fthread-jumps
          -falign-functions  -falign-jumps
          -falign-loops  -falign-labels
          -fcaller-saves
          -fcrossjumping
          -fcse-follow-jumps  -fcse-skip-blocks
          -fdelete-null-pointer-checks
          -fexpensive-optimizations
          -fgcse  -fgcse-lm
          -findirect-inlining
          -foptimize-sibling-calls
          -fpeephole2
          -fregmove
          -freorder-blocks  -freorder-functions
          -frerun-cse-after-loop
          -fsched-interblock  -fsched-spec
          -fschedule-insns  -fschedule-insns2
          -fstrict-aliasing -fstrict-overflow
          -ftree-switch-conversion
          -ftree-pre
          -ftree-vrp

     Please note the warning under `-fgcse' about invoking `-O2' on
     programs that use computed gotos.

`-O3'
     Optimize yet more.  `-O3' turns on all optimizations specified by
     `-O2' and also turns on the `-finline-functions',
     `-funswitch-loops', `-fpredictive-commoning',
     `-fgcse-after-reload', `-ftree-vectorize' and `-fipa-cp-clone'
     options.

`-O0'
     Reduce compilation time and make debugging produce the expected
     results.  This is the default.

`-Os'
     Optimize for size.  `-Os' enables all `-O2' optimizations that do
     not typically increase code size.  It also performs further
     optimizations designed to reduce code size.

     `-Os' disables the following optimization flags:
          -falign-functions  -falign-jumps  -falign-loops
          -falign-labels  -freorder-blocks  -freorder-blocks-and-partition
          -fprefetch-loop-arrays  -ftree-vect-loop-version

     If you use multiple `-O' options, with or without level numbers,
     the last such option is the one that is effective.

 Options of the form `-fFLAG' specify machine-independent flags.  Most
flags have both positive and negative forms; the negative form of
`-ffoo' would be `-fno-foo'.  In the table below, only one of the forms
is listed--the one you typically will use.  You can figure out the
other form by either removing `no-' or adding it.

 The following options control specific optimizations.  They are either
activated by `-O' options or are related to ones that are.  You can use
the following flags in the rare cases when "fine-tuning" of
optimizations to be performed is desired.

`-fno-default-inline'
     Do not make member functions inline by default merely because they
     are defined inside the class scope (C++ only).  Otherwise, when
     you specify `-O', member functions defined inside class scope are
     compiled inline by default; i.e., you don't need to add `inline'
     in front of the member function name.

`-fno-defer-pop'
     Always pop the arguments to each function call as soon as that
     function returns.  For machines which must pop arguments after a
     function call, the compiler normally lets arguments accumulate on
     the stack for several function calls and pops them all at once.

     Disabled at levels `-O', `-O2', `-O3', `-Os'.

`-fforward-propagate'
     Perform a forward propagation pass on RTL.  The pass tries to
     combine two instructions and checks if the result can be
     simplified.  If loop unrolling is active, two passes are performed
     and the second is scheduled after loop unrolling.

     This option is enabled by default at optimization levels `-O2',
     `-O3', `-Os'.

`-fomit-frame-pointer'
     Don't keep the frame pointer in a register for functions that
     don't need one.  This avoids the instructions to save, set up and
     restore frame pointers; it also makes an extra register available
     in many functions.  *It also makes debugging impossible on some
     machines.*

     On some machines, such as the VAX, this flag has no effect, because
     the standard calling sequence automatically handles the frame
     pointer and nothing is saved by pretending it doesn't exist.  The
     machine-description macro `FRAME_POINTER_REQUIRED' controls
     whether a target machine supports this flag.  *Note Register
     Usage: (gccint)Registers.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-foptimize-sibling-calls'
     Optimize sibling and tail recursive calls.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fno-inline'
     Don't pay attention to the `inline' keyword.  Normally this option
     is used to keep the compiler from expanding any functions inline.
     Note that if you are not optimizing, no functions can be expanded
     inline.

`-finline-small-functions'
     Integrate functions into their callers when their body is smaller
     than expected function call code (so overall size of program gets
     smaller).  The compiler heuristically decides which functions are
     simple enough to be worth integrating in this way.

     Enabled at level `-O2'.

`-findirect-inlining'
     Inline also indirect calls that are discovered to be known at
     compile time thanks to previous inlining.  This option has any
     effect only when inlining itself is turned on by the
     `-finline-functions' or `-finline-small-functions' options.

     Enabled at level `-O2'.

`-finline-functions'
     Integrate all simple functions into their callers.  The compiler
     heuristically decides which functions are simple enough to be worth
     integrating in this way.

     If all calls to a given function are integrated, and the function
     is declared `static', then the function is normally not output as
     assembler code in its own right.

     Enabled at level `-O3'.

`-finline-functions-called-once'
     Consider all `static' functions called once for inlining into their
     caller even if they are not marked `inline'.  If a call to a given
     function is integrated, then the function is not output as
     assembler code in its own right.

     Enabled at levels `-O1', `-O2', `-O3' and `-Os'.

`-fearly-inlining'
     Inline functions marked by `always_inline' and functions whose
     body seems smaller than the function call overhead early before
     doing `-fprofile-generate' instrumentation and real inlining pass.
     Doing so makes profiling significantly cheaper and usually
     inlining faster on programs having large chains of nested wrapper
     functions.

     Enabled by default.

`-finline-limit=N'
     By default, GCC limits the size of functions that can be inlined.
     This flag allows coarse control of this limit.  N is the size of
     functions that can be inlined in number of pseudo instructions.

     Inlining is actually controlled by a number of parameters, which
     may be specified individually by using `--param NAME=VALUE'.  The
     `-finline-limit=N' option sets some of these parameters as follows:

    `max-inline-insns-single'
          is set to N/2.

    `max-inline-insns-auto'
          is set to N/2.

     See below for a documentation of the individual parameters
     controlling inlining and for the defaults of these parameters.

     _Note:_ there may be no value to `-finline-limit' that results in
     default behavior.

     _Note:_ pseudo instruction represents, in this particular context,
     an abstract measurement of function's size.  In no way does it
     represent a count of assembly instructions and as such its exact
     meaning might change from one release to an another.

`-fkeep-inline-functions'
     In C, emit `static' functions that are declared `inline' into the
     object file, even if the function has been inlined into all of its
     callers.  This switch does not affect functions using the `extern
     inline' extension in GNU C89.  In C++, emit any and all inline
     functions into the object file.

`-fkeep-static-consts'
     Emit variables declared `static const' when optimization isn't
     turned on, even if the variables aren't referenced.

     GCC enables this option by default.  If you want to force the
     compiler to check if the variable was referenced, regardless of
     whether or not optimization is turned on, use the
     `-fno-keep-static-consts' option.

`-fmerge-constants'
     Attempt to merge identical constants (string constants and
     floating point constants) across compilation units.

     This option is the default for optimized compilation if the
     assembler and linker support it.  Use `-fno-merge-constants' to
     inhibit this behavior.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fmerge-all-constants'
     Attempt to merge identical constants and identical variables.

     This option implies `-fmerge-constants'.  In addition to
     `-fmerge-constants' this considers e.g. even constant initialized
     arrays or initialized constant variables with integral or floating
     point types.  Languages like C or C++ require each variable,
     including multiple instances of the same variable in recursive
     calls, to have distinct locations, so using this option will
     result in non-conforming behavior.

`-fmodulo-sched'
     Perform swing modulo scheduling immediately before the first
     scheduling pass.  This pass looks at innermost loops and reorders
     their instructions by overlapping different iterations.

`-fmodulo-sched-allow-regmoves'
     Perform more aggressive SMS based modulo scheduling with register
     moves allowed.  By setting this flag certain anti-dependences
     edges will be deleted which will trigger the generation of
     reg-moves based on the life-range analysis.  This option is
     effective only with `-fmodulo-sched' enabled.

`-fno-branch-count-reg'
     Do not use "decrement and branch" instructions on a count register,
     but instead generate a sequence of instructions that decrement a
     register, compare it against zero, then branch based upon the
     result.  This option is only meaningful on architectures that
     support such instructions, which include x86, PowerPC, IA-64 and
     S/390.

     The default is `-fbranch-count-reg'.

`-fno-function-cse'
     Do not put function addresses in registers; make each instruction
     that calls a constant function contain the function's address
     explicitly.

     This option results in less efficient code, but some strange hacks
     that alter the assembler output may be confused by the
     optimizations performed when this option is not used.

     The default is `-ffunction-cse'

`-fno-zero-initialized-in-bss'
     If the target supports a BSS section, GCC by default puts
     variables that are initialized to zero into BSS.  This can save
     space in the resulting code.

     This option turns off this behavior because some programs
     explicitly rely on variables going to the data section.  E.g., so
     that the resulting executable can find the beginning of that
     section and/or make assumptions based on that.

     The default is `-fzero-initialized-in-bss'.

`-fmudflap -fmudflapth -fmudflapir'
     For front-ends that support it (C and C++), instrument all risky
     pointer/array dereferencing operations, some standard library
     string/heap functions, and some other associated constructs with
     range/validity tests.  Modules so instrumented should be immune to
     buffer overflows, invalid heap use, and some other classes of C/C++
     programming errors.  The instrumentation relies on a separate
     runtime library (`libmudflap'), which will be linked into a
     program if `-fmudflap' is given at link time.  Run-time behavior
     of the instrumented program is controlled by the `MUDFLAP_OPTIONS'
     environment variable.  See `env MUDFLAP_OPTIONS=-help a.out' for
     its options.

     Use `-fmudflapth' instead of `-fmudflap' to compile and to link if
     your program is multi-threaded.  Use `-fmudflapir', in addition to
     `-fmudflap' or `-fmudflapth', if instrumentation should ignore
     pointer reads.  This produces less instrumentation (and therefore
     faster execution) and still provides some protection against
     outright memory corrupting writes, but allows erroneously read
     data to propagate within a program.

`-fthread-jumps'
     Perform optimizations where we check to see if a jump branches to a
     location where another comparison subsumed by the first is found.
     If so, the first branch is redirected to either the destination of
     the second branch or a point immediately following it, depending
     on whether the condition is known to be true or false.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fsplit-wide-types'
     When using a type that occupies multiple registers, such as `long
     long' on a 32-bit system, split the registers apart and allocate
     them independently.  This normally generates better code for those
     types, but may make debugging more difficult.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fcse-follow-jumps'
     In common subexpression elimination (CSE), scan through jump
     instructions when the target of the jump is not reached by any
     other path.  For example, when CSE encounters an `if' statement
     with an `else' clause, CSE will follow the jump when the condition
     tested is false.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fcse-skip-blocks'
     This is similar to `-fcse-follow-jumps', but causes CSE to follow
     jumps which conditionally skip over blocks.  When CSE encounters a
     simple `if' statement with no else clause, `-fcse-skip-blocks'
     causes CSE to follow the jump around the body of the `if'.

     Enabled at levels `-O2', `-O3', `-Os'.

`-frerun-cse-after-loop'
     Re-run common subexpression elimination after loop optimizations
     has been performed.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fgcse'
     Perform a global common subexpression elimination pass.  This pass
     also performs global constant and copy propagation.

     _Note:_ When compiling a program using computed gotos, a GCC
     extension, you may get better runtime performance if you disable
     the global common subexpression elimination pass by adding
     `-fno-gcse' to the command line.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fgcse-lm'
     When `-fgcse-lm' is enabled, global common subexpression
     elimination will attempt to move loads which are only killed by
     stores into themselves.  This allows a loop containing a
     load/store sequence to be changed to a load outside the loop, and
     a copy/store within the loop.

     Enabled by default when gcse is enabled.

`-fgcse-sm'
     When `-fgcse-sm' is enabled, a store motion pass is run after
     global common subexpression elimination.  This pass will attempt
     to move stores out of loops.  When used in conjunction with
     `-fgcse-lm', loops containing a load/store sequence can be changed
     to a load before the loop and a store after the loop.

     Not enabled at any optimization level.

`-fgcse-las'
     When `-fgcse-las' is enabled, the global common subexpression
     elimination pass eliminates redundant loads that come after stores
     to the same memory location (both partial and full redundancies).

     Not enabled at any optimization level.

`-fgcse-after-reload'
     When `-fgcse-after-reload' is enabled, a redundant load elimination
     pass is performed after reload.  The purpose of this pass is to
     cleanup redundant spilling.

`-funsafe-loop-optimizations'
     If given, the loop optimizer will assume that loop indices do not
     overflow, and that the loops with nontrivial exit condition are not
     infinite.  This enables a wider range of loop optimizations even if
     the loop optimizer itself cannot prove that these assumptions are
     valid.  Using `-Wunsafe-loop-optimizations', the compiler will
     warn you if it finds this kind of loop.

`-fcrossjumping'
     Perform cross-jumping transformation.  This transformation unifies
     equivalent code and save code size.  The resulting code may or may
     not perform better than without cross-jumping.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fauto-inc-dec'
     Combine increments or decrements of addresses with memory accesses.
     This pass is always skipped on architectures that do not have
     instructions to support this.  Enabled by default at `-O' and
     higher on architectures that support this.

`-fdce'
     Perform dead code elimination (DCE) on RTL.  Enabled by default at
     `-O' and higher.

`-fdse'
     Perform dead store elimination (DSE) on RTL.  Enabled by default
     at `-O' and higher.

`-fif-conversion'
     Attempt to transform conditional jumps into branch-less
     equivalents.  This include use of conditional moves, min, max, set
     flags and abs instructions, and some tricks doable by standard
     arithmetics.  The use of conditional execution on chips where it
     is available is controlled by `if-conversion2'.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fif-conversion2'
     Use conditional execution (where available) to transform
     conditional jumps into branch-less equivalents.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fdelete-null-pointer-checks'
     Use global dataflow analysis to identify and eliminate useless
     checks for null pointers.  The compiler assumes that dereferencing
     a null pointer would have halted the program.  If a pointer is
     checked after it has already been dereferenced, it cannot be null.

     In some environments, this assumption is not true, and programs can
     safely dereference null pointers.  Use
     `-fno-delete-null-pointer-checks' to disable this optimization for
     programs which depend on that behavior.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fexpensive-optimizations'
     Perform a number of minor optimizations that are relatively
     expensive.

     Enabled at levels `-O2', `-O3', `-Os'.

`-foptimize-register-move'
`-fregmove'
     Attempt to reassign register numbers in move instructions and as
     operands of other simple instructions in order to maximize the
     amount of register tying.  This is especially helpful on machines
     with two-operand instructions.

     Note `-fregmove' and `-foptimize-register-move' are the same
     optimization.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fira-algorithm=ALGORITHM'
     Use specified coloring algorithm for the integrated register
     allocator.  The ALGORITHM argument should be `priority' or `CB'.
     The first algorithm specifies Chow's priority coloring, the second
     one specifies Chaitin-Briggs coloring.  The second algorithm can
     be unimplemented for some architectures.  If it is implemented, it
     is the default because Chaitin-Briggs coloring as a rule generates
     a better code.

`-fira-region=REGION'
     Use specified regions for the integrated register allocator.  The
     REGION argument should be one of `all', `mixed', or `one'.  The
     first value means using all loops as register allocation regions,
     the second value which is the default means using all loops except
     for loops with small register pressure as the regions, and third
     one means using all function as a single region.  The first value
     can give best result for machines with small size and irregular
     register set, the third one results in faster and generates decent
     code and the smallest size code, and the default value usually
     give the best results in most cases and for most architectures.

`-fira-coalesce'
     Do optimistic register coalescing.  This option might be
     profitable for architectures with big regular register files.

`-fno-ira-share-save-slots'
     Switch off sharing stack slots used for saving call used hard
     registers living through a call.  Each hard register will get a
     separate stack slot and as a result function stack frame will be
     bigger.

`-fno-ira-share-spill-slots'
     Switch off sharing stack slots allocated for pseudo-registers.
     Each pseudo-register which did not get a hard register will get a
     separate stack slot and as a result function stack frame will be
     bigger.

`-fira-verbose=N'
     Set up how verbose dump file for the integrated register allocator
     will be.  Default value is 5.  If the value is greater or equal to
     10, the dump file will be stderr as if the value were N minus 10.

`-fdelayed-branch'
     If supported for the target machine, attempt to reorder
     instructions to exploit instruction slots available after delayed
     branch instructions.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fschedule-insns'
     If supported for the target machine, attempt to reorder
     instructions to eliminate execution stalls due to required data
     being unavailable.  This helps machines that have slow floating
     point or memory load instructions by allowing other instructions
     to be issued until the result of the load or floating point
     instruction is required.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fschedule-insns2'
     Similar to `-fschedule-insns', but requests an additional pass of
     instruction scheduling after register allocation has been done.
     This is especially useful on machines with a relatively small
     number of registers and where memory load instructions take more
     than one cycle.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fno-sched-interblock'
     Don't schedule instructions across basic blocks.  This is normally
     enabled by default when scheduling before register allocation, i.e.
     with `-fschedule-insns' or at `-O2' or higher.

`-fno-sched-spec'
     Don't allow speculative motion of non-load instructions.  This is
     normally enabled by default when scheduling before register
     allocation, i.e.  with `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load'
     Allow speculative motion of some load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load-dangerous'
     Allow speculative motion of more load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-fsched-stalled-insns'
`-fsched-stalled-insns=N'
     Define how many insns (if any) can be moved prematurely from the
     queue of stalled insns into the ready list, during the second
     scheduling pass.  `-fno-sched-stalled-insns' means that no insns
     will be moved prematurely, `-fsched-stalled-insns=0' means there
     is no limit on how many queued insns can be moved prematurely.
     `-fsched-stalled-insns' without a value is equivalent to
     `-fsched-stalled-insns=1'.

`-fsched-stalled-insns-dep'
`-fsched-stalled-insns-dep=N'
     Define how many insn groups (cycles) will be examined for a
     dependency on a stalled insn that is candidate for premature
     removal from the queue of stalled insns.  This has an effect only
     during the second scheduling pass, and only if
     `-fsched-stalled-insns' is used.  `-fno-sched-stalled-insns-dep'
     is equivalent to `-fsched-stalled-insns-dep=0'.
     `-fsched-stalled-insns-dep' without a value is equivalent to
     `-fsched-stalled-insns-dep=1'.

`-fsched2-use-superblocks'
     When scheduling after register allocation, do use superblock
     scheduling algorithm.  Superblock scheduling allows motion across
     basic block boundaries resulting on faster schedules.  This option
     is experimental, as not all machine descriptions used by GCC model
     the CPU closely enough to avoid unreliable results from the
     algorithm.

     This only makes sense when scheduling after register allocation,
     i.e. with `-fschedule-insns2' or at `-O2' or higher.

`-fsched2-use-traces'
     Use `-fsched2-use-superblocks' algorithm when scheduling after
     register allocation and additionally perform code duplication in
     order to increase the size of superblocks using tracer pass.  See
     `-ftracer' for details on trace formation.

     This mode should produce faster but significantly longer programs.
     Also without `-fbranch-probabilities' the traces constructed may
     not match the reality and hurt the performance.  This only makes
     sense when scheduling after register allocation, i.e. with
     `-fschedule-insns2' or at `-O2' or higher.

`-fsee'
     Eliminate redundant sign extension instructions and move the
     non-redundant ones to optimal placement using lazy code motion
     (LCM).

`-freschedule-modulo-scheduled-loops'
     The modulo scheduling comes before the traditional scheduling, if
     a loop was modulo scheduled we may want to prevent the later
     scheduling passes from changing its schedule, we use this option
     to control that.

`-fselective-scheduling'
     Schedule instructions using selective scheduling algorithm.
     Selective scheduling runs instead of the first scheduler pass.

`-fselective-scheduling2'
     Schedule instructions using selective scheduling algorithm.
     Selective scheduling runs instead of the second scheduler pass.

`-fsel-sched-pipelining'
     Enable software pipelining of innermost loops during selective
     scheduling.  This option has no effect until one of
     `-fselective-scheduling' or `-fselective-scheduling2' is turned on.

`-fsel-sched-pipelining-outer-loops'
     When pipelining loops during selective scheduling, also pipeline
     outer loops.  This option has no effect until
     `-fsel-sched-pipelining' is turned on.

`-fcaller-saves'
     Enable values to be allocated in registers that will be clobbered
     by function calls, by emitting extra instructions to save and
     restore the registers around such calls.  Such allocation is done
     only when it seems to result in better code than would otherwise
     be produced.

     This option is always enabled by default on certain machines,
     usually those which have no call-preserved registers to use
     instead.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fconserve-stack'
     Attempt to minimize stack usage.  The compiler will attempt to use
     less stack space, even if that makes the program slower.  This
     option implies setting the `large-stack-frame' parameter to 100
     and the `large-stack-frame-growth' parameter to 400.

`-ftree-reassoc'
     Perform reassociation on trees.  This flag is enabled by default
     at `-O' and higher.

`-ftree-pre'
     Perform partial redundancy elimination (PRE) on trees.  This flag
     is enabled by default at `-O2' and `-O3'.

`-ftree-fre'
     Perform full redundancy elimination (FRE) on trees.  The difference
     between FRE and PRE is that FRE only considers expressions that
     are computed on all paths leading to the redundant computation.
     This analysis is faster than PRE, though it exposes fewer
     redundancies.  This flag is enabled by default at `-O' and higher.

`-ftree-copy-prop'
     Perform copy propagation on trees.  This pass eliminates
     unnecessary copy operations.  This flag is enabled by default at
     `-O' and higher.

`-fipa-pure-const'
     Discover which functions are pure or constant.  Enabled by default
     at `-O' and higher.

`-fipa-reference'
     Discover which static variables do not escape cannot escape the
     compilation unit.  Enabled by default at `-O' and higher.

`-fipa-struct-reorg'
     Perform structure reorganization optimization, that change C-like
     structures layout in order to better utilize spatial locality.
     This transformation is effective for programs containing arrays of
     structures.  Available in two compilation modes: profile-based
     (enabled with `-fprofile-generate') or static (which uses built-in
     heuristics).  Require `-fipa-type-escape' to provide the safety of
     this transformation.  It works only in whole program mode, so it
     requires `-fwhole-program' and `-combine' to be enabled.
     Structures considered `cold' by this transformation are not
     affected (see `--param struct-reorg-cold-struct-ratio=VALUE').

     With this flag, the program debug info reflects a new structure
     layout.

`-fipa-pta'
     Perform interprocedural pointer analysis.  This option is
     experimental and does not affect generated code.

`-fipa-cp'
     Perform interprocedural constant propagation.  This optimization
     analyzes the program to determine when values passed to functions
     are constants and then optimizes accordingly.  This optimization
     can substantially increase performance if the application has
     constants passed to functions.  This flag is enabled by default at
     `-O2', `-Os' and `-O3'.

`-fipa-cp-clone'
     Perform function cloning to make interprocedural constant
     propagation stronger.  When enabled, interprocedural constant
     propagation will perform function cloning when externally visible
     function can be called with constant arguments.  Because this
     optimization can create multiple copies of functions, it may
     significantly increase code size (see `--param
     ipcp-unit-growth=VALUE').  This flag is enabled by default at
     `-O3'.

`-fipa-matrix-reorg'
     Perform matrix flattening and transposing.  Matrix flattening
     tries to replace a m-dimensional matrix with its equivalent
     n-dimensional matrix, where n < m.  This reduces the level of
     indirection needed for accessing the elements of the matrix. The
     second optimization is matrix transposing that attempts to change
     the order of the matrix's dimensions in order to improve cache
     locality.  Both optimizations need the `-fwhole-program' flag.
     Transposing is enabled only if profiling information is available.

`-ftree-sink'
     Perform forward store motion  on trees.  This flag is enabled by
     default at `-O' and higher.

`-ftree-ccp'
     Perform sparse conditional constant propagation (CCP) on trees.
     This pass only operates on local scalar variables and is enabled
     by default at `-O' and higher.

`-ftree-switch-conversion'
     Perform conversion of simple initializations in a switch to
     initializations from a scalar array.  This flag is enabled by
     default at `-O2' and higher.

`-ftree-dce'
     Perform dead code elimination (DCE) on trees.  This flag is
     enabled by default at `-O' and higher.

`-ftree-builtin-call-dce'
     Perform conditional dead code elimination (DCE) for calls to
     builtin functions that may set `errno' but are otherwise
     side-effect free.  This flag is enabled by default at `-O2' and
     higher if `-Os' is not also specified.

`-ftree-dominator-opts'
     Perform a variety of simple scalar cleanups (constant/copy
     propagation, redundancy elimination, range propagation and
     expression simplification) based on a dominator tree traversal.
     This also performs jump threading (to reduce jumps to jumps). This
     flag is enabled by default at `-O' and higher.

`-ftree-dse'
     Perform dead store elimination (DSE) on trees.  A dead store is a
     store into a memory location which will later be overwritten by
     another store without any intervening loads.  In this case the
     earlier store can be deleted.  This flag is enabled by default at
     `-O' and higher.

`-ftree-ch'
     Perform loop header copying on trees.  This is beneficial since it
     increases effectiveness of code motion optimizations.  It also
     saves one jump.  This flag is enabled by default at `-O' and
     higher.  It is not enabled for `-Os', since it usually increases
     code size.

`-ftree-loop-optimize'
     Perform loop optimizations on trees.  This flag is enabled by
     default at `-O' and higher.

`-ftree-loop-linear'
     Perform linear loop transformations on tree.  This flag can
     improve cache performance and allow further loop optimizations to
     take place.

`-floop-interchange'
     Perform loop interchange transformations on loops.  Interchanging
     two nested loops switches the inner and outer loops.  For example,
     given a loop like:
          DO J = 1, M
            DO I = 1, N
              A(J, I) = A(J, I) * C
            ENDDO
          ENDDO
     loop interchange will transform the loop as if the user had
     written:
          DO I = 1, N
            DO J = 1, M
              A(J, I) = A(J, I) * C
            ENDDO
          ENDDO
     which can be beneficial when `N' is larger than the caches,
     because in Fortran, the elements of an array are stored in memory
     contiguously by column, and the original loop iterates over rows,
     potentially creating at each access a cache miss.  This
     optimization applies to all the languages supported by GCC and is
     not limited to Fortran.  To use this code transformation, GCC has
     to be configured with `--with-ppl' and `--with-cloog' to enable the
     Graphite loop transformation infrastructure.

`-floop-strip-mine'
     Perform loop strip mining transformations on loops.  Strip mining
     splits a loop into two nested loops.  The outer loop has strides
     equal to the strip size and the inner loop has strides of the
     original loop within a strip.  For example, given a loop like:
          DO I = 1, N
            A(I) = A(I) + C
          ENDDO
     loop strip mining will transform the loop as if the user had
     written:
          DO II = 1, N, 4
            DO I = II, min (II + 3, N)
              A(I) = A(I) + C
            ENDDO
          ENDDO
     This optimization applies to all the languages supported by GCC
     and is not limited to Fortran.  To use this code transformation,
     GCC has to be configured with `--with-ppl' and `--with-cloog' to
     enable the Graphite loop transformation infrastructure.

`-floop-block'
     Perform loop blocking transformations on loops.  Blocking strip
     mines each loop in the loop nest such that the memory accesses of
     the element loops fit inside caches.  For example, given a loop
     like:
          DO I = 1, N
            DO J = 1, M
              A(J, I) = B(I) + C(J)
            ENDDO
          ENDDO
     loop blocking will transform the loop as if the user had written:
          DO II = 1, N, 64
            DO JJ = 1, M, 64
              DO I = II, min (II + 63, N)
                DO J = JJ, min (JJ + 63, M)
                  A(J, I) = B(I) + C(J)
                ENDDO
              ENDDO
            ENDDO
          ENDDO
     which can be beneficial when `M' is larger than the caches,
     because the innermost loop will iterate over a smaller amount of
     data that can be kept in the caches.  This optimization applies to
     all the languages supported by GCC and is not limited to Fortran.
     To use this code transformation, GCC has to be configured with
     `--with-ppl' and `--with-cloog' to enable the Graphite loop
     transformation infrastructure.

`-fcheck-data-deps'
     Compare the results of several data dependence analyzers.  This
     option is used for debugging the data dependence analyzers.

`-ftree-loop-distribution'
     Perform loop distribution.  This flag can improve cache
     performance on big loop bodies and allow further loop
     optimizations, like parallelization or vectorization, to take
     place.  For example, the loop
          DO I = 1, N
            A(I) = B(I) + C
            D(I) = E(I) * F
          ENDDO
     is transformed to
          DO I = 1, N
             A(I) = B(I) + C
          ENDDO
          DO I = 1, N
             D(I) = E(I) * F
          ENDDO

`-ftree-loop-im'
     Perform loop invariant motion on trees.  This pass moves only
     invariants that would be hard to handle at RTL level (function
     calls, operations that expand to nontrivial sequences of insns).
     With `-funswitch-loops' it also moves operands of conditions that
     are invariant out of the loop, so that we can use just trivial
     invariantness analysis in loop unswitching.  The pass also includes
     store motion.

`-ftree-loop-ivcanon'
     Create a canonical counter for number of iterations in the loop
     for that determining number of iterations requires complicated
     analysis.  Later optimizations then may determine the number
     easily.  Useful especially in connection with unrolling.

`-fivopts'
     Perform induction variable optimizations (strength reduction,
     induction variable merging and induction variable elimination) on
     trees.

`-ftree-parallelize-loops=n'
     Parallelize loops, i.e., split their iteration space to run in n
     threads.  This is only possible for loops whose iterations are
     independent and can be arbitrarily reordered.  The optimization is
     only profitable on multiprocessor machines, for loops that are
     CPU-intensive, rather than constrained e.g. by memory bandwidth.
     This option implies `-pthread', and thus is only supported on
     targets that have support for `-pthread'.

`-ftree-sra'
     Perform scalar replacement of aggregates.  This pass replaces
     structure references with scalars to prevent committing structures
     to memory too early.  This flag is enabled by default at `-O' and
     higher.

`-ftree-copyrename'
     Perform copy renaming on trees.  This pass attempts to rename
     compiler temporaries to other variables at copy locations, usually
     resulting in variable names which more closely resemble the
     original variables.  This flag is enabled by default at `-O' and
     higher.

`-ftree-coalesce-inlined-vars'
     Permit the copyrename pass to subject inlined variables to
     coalescing into other variables.  This may harm debug information
     of such inlined variables, but it will keep variables of the main
     function apart from each other, such that they are more likely to
     contain the expected values in a debugging session.

`-ftree-coalesce-vars'
     Permit the copyrename pass to subject all variables to SSA
     coalescing.  This may severely limit the ability to debug an
     optimized program compiled without `-fvar-tracking-assignments'.
     In the negated form, this flag prevents SSA coalescing of user
     variables, including inlined ones.

`-ftree-ter'
     Perform temporary expression replacement during the SSA->normal
     phase.  Single use/single def temporaries are replaced at their
     use location with their defining expression.  This results in
     non-GIMPLE code, but gives the expanders much more complex trees
     to work on resulting in better RTL generation.  This is enabled by
     default at `-O' and higher.

`-ftree-vectorize'
     Perform loop vectorization on trees. This flag is enabled by
     default at `-O3'.

`-ftree-vect-loop-version'
     Perform loop versioning when doing loop vectorization on trees.
     When a loop appears to be vectorizable except that data alignment
     or data dependence cannot be determined at compile time then
     vectorized and non-vectorized versions of the loop are generated
     along with runtime checks for alignment or dependence to control
     which version is executed.  This option is enabled by default
     except at level `-Os' where it is disabled.

`-fvect-cost-model'
     Enable cost model for vectorization.

`-ftree-vrp'
     Perform Value Range Propagation on trees.  This is similar to the
     constant propagation pass, but instead of values, ranges of values
     are propagated.  This allows the optimizers to remove unnecessary
     range checks like array bound checks and null pointer checks.
     This is enabled by default at `-O2' and higher.  Null pointer check
     elimination is only done if `-fdelete-null-pointer-checks' is
     enabled.

`-ftracer'
     Perform tail duplication to enlarge superblock size.  This
     transformation simplifies the control flow of the function
     allowing other optimizations to do better job.

`-funroll-loops'
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop.  `-funroll-loops' implies
     `-frerun-cse-after-loop'.  This option makes code larger, and may
     or may not make it run faster.

`-funroll-all-loops'
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered.  This usually makes programs run more
     slowly.  `-funroll-all-loops' implies the same options as
     `-funroll-loops',

`-fsplit-ivs-in-unroller'
     Enables expressing of values of induction variables in later
     iterations of the unrolled loop using the value in the first
     iteration.  This breaks long dependency chains, thus improving
     efficiency of the scheduling passes.

     Combination of `-fweb' and CSE is often sufficient to obtain the
     same effect.  However in cases the loop body is more complicated
     than a single basic block, this is not reliable.  It also does not
     work at all on some of the architectures due to restrictions in
     the CSE pass.

     This optimization is enabled by default.

`-fvariable-expansion-in-unroller'
     With this option, the compiler will create multiple copies of some
     local variables when unrolling a loop which can result in superior
     code.

`-fpredictive-commoning'
     Perform predictive commoning optimization, i.e., reusing
     computations (especially memory loads and stores) performed in
     previous iterations of loops.

     This option is enabled at level `-O3'.

`-fprefetch-loop-arrays'
     If supported by the target machine, generate instructions to
     prefetch memory to improve the performance of loops that access
     large arrays.

     This option may generate better or worse code; results are highly
     dependent on the structure of loops within the source code.

     Disabled at level `-Os'.

`-fno-peephole'
`-fno-peephole2'
     Disable any machine-specific peephole optimizations.  The
     difference between `-fno-peephole' and `-fno-peephole2' is in how
     they are implemented in the compiler; some targets use one, some
     use the other, a few use both.

     `-fpeephole' is enabled by default.  `-fpeephole2' enabled at
     levels `-O2', `-O3', `-Os'.

`-fno-guess-branch-probability'
     Do not guess branch probabilities using heuristics.

     GCC will use heuristics to guess branch probabilities if they are
     not provided by profiling feedback (`-fprofile-arcs').  These
     heuristics are based on the control flow graph.  If some branch
     probabilities are specified by `__builtin_expect', then the
     heuristics will be used to guess branch probabilities for the rest
     of the control flow graph, taking the `__builtin_expect' info into
     account.  The interactions between the heuristics and
     `__builtin_expect' can be complex, and in some cases, it may be
     useful to disable the heuristics so that the effects of
     `__builtin_expect' are easier to understand.

     The default is `-fguess-branch-probability' at levels `-O', `-O2',
     `-O3', `-Os'.

`-freorder-blocks'
     Reorder basic blocks in the compiled function in order to reduce
     number of taken branches and improve code locality.

     Enabled at levels `-O2', `-O3'.

`-freorder-blocks-and-partition'
     In addition to reordering basic blocks in the compiled function,
     in order to reduce number of taken branches, partitions hot and
     cold basic blocks into separate sections of the assembly and .o
     files, to improve paging and cache locality performance.

     This optimization is automatically turned off in the presence of
     exception handling, for linkonce sections, for functions with a
     user-defined section attribute and on any architecture that does
     not support named sections.

`-freorder-functions'
     Reorder functions in the object file in order to improve code
     locality.  This is implemented by using special subsections
     `.text.hot' for most frequently executed functions and
     `.text.unlikely' for unlikely executed functions.  Reordering is
     done by the linker so object file format must support named
     sections and linker must place them in a reasonable way.

     Also profile feedback must be available in to make this option
     effective.  See `-fprofile-arcs' for details.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fstrict-aliasing'
     Allow the compiler to assume the strictest aliasing rules
     applicable to the language being compiled.  For C (and C++), this
     activates optimizations based on the type of expressions.  In
     particular, an object of one type is assumed never to reside at
     the same address as an object of a different type, unless the
     types are almost the same.  For example, an `unsigned int' can
     alias an `int', but not a `void*' or a `double'.  A character type
     may alias any other type.

     Pay special attention to code like this:
          union a_union {
            int i;
            double d;
          };

          int f() {
            union a_union t;
            t.d = 3.0;
            return t.i;
          }
     The practice of reading from a different union member than the one
     most recently written to (called "type-punning") is common.  Even
     with `-fstrict-aliasing', type-punning is allowed, provided the
     memory is accessed through the union type.  So, the code above
     will work as expected.  *Note Structures unions enumerations and
     bit-fields implementation::.  However, this code might not:
          int f() {
            union a_union t;
            int* ip;
            t.d = 3.0;
            ip = &t.i;
            return *ip;
          }

     Similarly, access by taking the address, casting the resulting
     pointer and dereferencing the result has undefined behavior, even
     if the cast uses a union type, e.g.:
          int f() {
            double d = 3.0;
            return ((union a_union *) &d)->i;
          }

     The `-fstrict-aliasing' option is enabled at levels `-O2', `-O3',
     `-Os'.

`-fstrict-overflow'
     Allow the compiler to assume strict signed overflow rules,
     depending on the language being compiled.  For C (and C++) this
     means that overflow when doing arithmetic with signed numbers is
     undefined, which means that the compiler may assume that it will
     not happen.  This permits various optimizations.  For example, the
     compiler will assume that an expression like `i + 10 > i' will
     always be true for signed `i'.  This assumption is only valid if
     signed overflow is undefined, as the expression is false if `i +
     10' overflows when using twos complement arithmetic.  When this
     option is in effect any attempt to determine whether an operation
     on signed numbers will overflow must be written carefully to not
     actually involve overflow.

     This option also allows the compiler to assume strict pointer
     semantics: given a pointer to an object, if adding an offset to
     that pointer does not produce a pointer to the same object, the
     addition is undefined.  This permits the compiler to conclude that
     `p + u > p' is always true for a pointer `p' and unsigned integer
     `u'.  This assumption is only valid because pointer wraparound is
     undefined, as the expression is false if `p + u' overflows using
     twos complement arithmetic.

     See also the `-fwrapv' option.  Using `-fwrapv' means that integer
     signed overflow is fully defined: it wraps.  When `-fwrapv' is
     used, there is no difference between `-fstrict-overflow' and
     `-fno-strict-overflow' for integers.  With `-fwrapv' certain types
     of overflow are permitted.  For example, if the compiler gets an
     overflow when doing arithmetic on constants, the overflowed value
     can still be used with `-fwrapv', but not otherwise.

     The `-fstrict-overflow' option is enabled at levels `-O2', `-O3',
     `-Os'.

`-falign-functions'
`-falign-functions=N'
     Align the start of functions to the next power-of-two greater than
     N, skipping up to N bytes.  For instance, `-falign-functions=32'
     aligns functions to the next 32-byte boundary, but
     `-falign-functions=24' would align to the next 32-byte boundary
     only if this can be done by skipping 23 bytes or less.

     `-fno-align-functions' and `-falign-functions=1' are equivalent
     and mean that functions will not be aligned.

     Some assemblers only support this flag when N is a power of two;
     in that case, it is rounded up.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-falign-labels'
`-falign-labels=N'
     Align all branch targets to a power-of-two boundary, skipping up to
     N bytes like `-falign-functions'.  This option can easily make
     code slower, because it must insert dummy operations for when the
     branch target is reached in the usual flow of the code.

     `-fno-align-labels' and `-falign-labels=1' are equivalent and mean
     that labels will not be aligned.

     If `-falign-loops' or `-falign-jumps' are applicable and are
     greater than this value, then their values are used instead.

     If N is not specified or is zero, use a machine-dependent default
     which is very likely to be `1', meaning no alignment.

     Enabled at levels `-O2', `-O3'.

`-falign-loops'
`-falign-loops=N'
     Align loops to a power-of-two boundary, skipping up to N bytes
     like `-falign-functions'.  The hope is that the loop will be
     executed many times, which will make up for any execution of the
     dummy operations.

     `-fno-align-loops' and `-falign-loops=1' are equivalent and mean
     that loops will not be aligned.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-falign-jumps'
`-falign-jumps=N'
     Align branch targets to a power-of-two boundary, for branch targets
     where the targets can only be reached by jumping, skipping up to N
     bytes like `-falign-functions'.  In this case, no dummy operations
     need be executed.

     `-fno-align-jumps' and `-falign-jumps=1' are equivalent and mean
     that loops will not be aligned.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-funit-at-a-time'
     This option is left for compatibility reasons. `-funit-at-a-time'
     has no effect, while `-fno-unit-at-a-time' implies
     `-fno-toplevel-reorder' and `-fno-section-anchors'.

     Enabled by default.

`-fno-toplevel-reorder'
     Do not reorder top-level functions, variables, and `asm'
     statements.  Output them in the same order that they appear in the
     input file.  When this option is used, unreferenced static
     variables will not be removed.  This option is intended to support
     existing code which relies on a particular ordering.  For new
     code, it is better to use attributes.

     Enabled at level `-O0'.  When disabled explicitly, it also imply
     `-fno-section-anchors' that is otherwise enabled at `-O0' on some
     targets.

`-fweb'
     Constructs webs as commonly used for register allocation purposes
     and assign each web individual pseudo register.  This allows the
     register allocation pass to operate on pseudos directly, but also
     strengthens several other optimization passes, such as CSE, loop
     optimizer and trivial dead code remover.  It can, however, make
     debugging impossible, since variables will no longer stay in a
     "home register".

     Enabled by default with `-funroll-loops'.

`-fwhole-program'
     Assume that the current compilation unit represents whole program
     being compiled.  All public functions and variables with the
     exception of `main' and those merged by attribute
     `externally_visible' become static functions and in a affect gets
     more aggressively optimized by interprocedural optimizers.  While
     this option is equivalent to proper use of `static' keyword for
     programs consisting of single file, in combination with option
     `--combine' this flag can be used to compile most of smaller scale
     C programs since the functions and variables become local for the
     whole combined compilation unit, not for the single source file
     itself.

     This option is not supported for Fortran programs.

`-fcprop-registers'
     After register allocation and post-register allocation instruction
     splitting, we perform a copy-propagation pass to try to reduce
     scheduling dependencies and occasionally eliminate the copy.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fprofile-correction'
     Profiles collected using an instrumented binary for multi-threaded
     programs may be inconsistent due to missed counter updates. When
     this option is specified, GCC will use heuristics to correct or
     smooth out such inconsistencies. By default, GCC will emit an
     error message when an inconsistent profile is detected.

`-fprofile-dir=PATH'
     Set the directory to search the profile data files in to PATH.
     This option affects only the profile data generated by
     `-fprofile-generate', `-ftest-coverage', `-fprofile-arcs' and used
     by `-fprofile-use' and `-fbranch-probabilities' and its related
     options.  By default, GCC will use the current directory as PATH
     thus the profile data file will appear in the same directory as
     the object file.

`-fprofile-generate'
`-fprofile-generate=PATH'
     Enable options usually used for instrumenting application to
     produce profile useful for later recompilation with profile
     feedback based optimization.  You must use `-fprofile-generate'
     both when compiling and when linking your program.

     The following options are enabled: `-fprofile-arcs',
     `-fprofile-values', `-fvpt'.

     If PATH is specified, GCC will look at the PATH to find the
     profile feedback data files. See `-fprofile-dir'.

`-fprofile-use'
`-fprofile-use=PATH'
     Enable profile feedback directed optimizations, and optimizations
     generally profitable only with profile feedback available.

     The following options are enabled: `-fbranch-probabilities',
     `-fvpt', `-funroll-loops', `-fpeel-loops', `-ftracer'

     By default, GCC emits an error message if the feedback profiles do
     not match the source code.  This error can be turned into a
     warning by using `-Wcoverage-mismatch'.  Note this may result in
     poorly optimized code.

     If PATH is specified, GCC will look at the PATH to find the
     profile feedback data files. See `-fprofile-dir'.

 The following options control compiler behavior regarding floating
point arithmetic.  These options trade off between speed and
correctness.  All must be specifically enabled.

`-ffloat-store'
     Do not store floating point variables in registers, and inhibit
     other options that might change whether a floating point value is
     taken from a register or memory.

     This option prevents undesirable excess precision on machines such
     as the 68000 where the floating registers (of the 68881) keep more
     precision than a `double' is supposed to have.  Similarly for the
     x86 architecture.  For most programs, the excess precision does
     only good, but a few programs rely on the precise definition of
     IEEE floating point.  Use `-ffloat-store' for such programs, after
     modifying them to store all pertinent intermediate computations
     into variables.

`-ffast-math'
     Sets `-fno-math-errno', `-funsafe-math-optimizations',
     `-ffinite-math-only', `-fno-rounding-math', `-fno-signaling-nans'
     and `-fcx-limited-range'.

     This option causes the preprocessor macro `__FAST_MATH__' to be
     defined.

     This option is not turned on by any `-O' option since it can
     result in incorrect output for programs which depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions. It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.

`-fno-math-errno'
     Do not set ERRNO after calling math functions that are executed
     with a single instruction, e.g., sqrt.  A program that relies on
     IEEE exceptions for math error handling may want to use this flag
     for speed while maintaining IEEE arithmetic compatibility.

     This option is not turned on by any `-O' option since it can
     result in incorrect output for programs which depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions. It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.

     The default is `-fmath-errno'.

     On Darwin systems, the math library never sets `errno'.  There is
     therefore no reason for the compiler to consider the possibility
     that it might, and `-fno-math-errno' is the default.

`-funsafe-math-optimizations'
     Allow optimizations for floating-point arithmetic that (a) assume
     that arguments and results are valid and (b) may violate IEEE or
     ANSI standards.  When used at link-time, it may include libraries
     or startup files that change the default FPU control word or other
     similar optimizations.

     This option is not turned on by any `-O' option since it can
     result in incorrect output for programs which depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions. It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.  Enables
     `-fno-signed-zeros', `-fno-trapping-math', `-fassociative-math'
     and `-freciprocal-math'.

     The default is `-fno-unsafe-math-optimizations'.

`-fassociative-math'
     Allow re-association of operands in series of floating-point
     operations.  This violates the ISO C and C++ language standard by
     possibly changing computation result.  NOTE: re-ordering may
     change the sign of zero as well as ignore NaNs and inhibit or
     create underflow or overflow (and thus cannot be used on a code
     which relies on rounding behavior like `(x + 2**52) - 2**52)'.
     May also reorder floating-point comparisons and thus may not be
     used when ordered comparisons are required.  This option requires
     that both `-fno-signed-zeros' and `-fno-trapping-math' be in
     effect.  Moreover, it doesn't make much sense with
     `-frounding-math'.

     The default is `-fno-associative-math'.

`-freciprocal-math'
     Allow the reciprocal of a value to be used instead of dividing by
     the value if this enables optimizations.  For example `x / y' can
     be replaced with `x * (1/y)' which is useful if `(1/y)' is subject
     to common subexpression elimination.  Note that this loses
     precision and increases the number of flops operating on the value.

     The default is `-fno-reciprocal-math'.

`-ffinite-math-only'
     Allow optimizations for floating-point arithmetic that assume that
     arguments and results are not NaNs or +-Infs.

     This option is not turned on by any `-O' option since it can
     result in incorrect output for programs which depend on an exact
     implementation of IEEE or ISO rules/specifications for math
     functions. It may, however, yield faster code for programs that do
     not require the guarantees of these specifications.

     The default is `-fno-finite-math-only'.

`-fno-signed-zeros'
     Allow optimizations for floating point arithmetic that ignore the
     signedness of zero.  IEEE arithmetic specifies the behavior of
     distinct +0.0 and -0.0 values, which then prohibits simplification
     of expressions such as x+0.0 or 0.0*x (even with
     `-ffinite-math-only').  This option implies that the sign of a
     zero result isn't significant.

     The default is `-fsigned-zeros'.

`-fno-trapping-math'
     Compile code assuming that floating-point operations cannot
     generate user-visible traps.  These traps include division by
     zero, overflow, underflow, inexact result and invalid operation.
     This option requires that `-fno-signaling-nans' be in effect.
     Setting this option may allow faster code if one relies on
     "non-stop" IEEE arithmetic, for example.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

     The default is `-ftrapping-math'.

`-frounding-math'
     Disable transformations and optimizations that assume default
     floating point rounding behavior.  This is round-to-zero for all
     floating point to integer conversions, and round-to-nearest for
     all other arithmetic truncations.  This option should be specified
     for programs that change the FP rounding mode dynamically, or that
     may be executed with a non-default rounding mode.  This option
     disables constant folding of floating point expressions at
     compile-time (which may be affected by rounding mode) and
     arithmetic transformations that are unsafe in the presence of
     sign-dependent rounding modes.

     The default is `-fno-rounding-math'.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that are affected by rounding mode.
     Future versions of GCC may provide finer control of this setting
     using C99's `FENV_ACCESS' pragma.  This command line option will
     be used to specify the default state for `FENV_ACCESS'.

`-frtl-abstract-sequences'
     It is a size optimization method. This option is to find identical
     sequences of code, which can be turned into pseudo-procedures  and
     then  replace  all  occurrences with  calls to  the  newly created
     subroutine. It is kind of an opposite of `-finline-functions'.
     This optimization runs at RTL level.

`-fsignaling-nans'
     Compile code assuming that IEEE signaling NaNs may generate
     user-visible traps during floating-point operations.  Setting this
     option disables optimizations that may change the number of
     exceptions visible with signaling NaNs.  This option implies
     `-ftrapping-math'.

     This option causes the preprocessor macro `__SUPPORT_SNAN__' to be
     defined.

     The default is `-fno-signaling-nans'.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that affect signaling NaN behavior.

`-fsingle-precision-constant'
     Treat floating point constant as single precision constant instead
     of implicitly converting it to double precision constant.

`-fcx-limited-range'
     When enabled, this option states that a range reduction step is not
     needed when performing complex division.  Also, there is no
     checking whether the result of a complex multiplication or
     division is `NaN + I*NaN', with an attempt to rescue the situation
     in that case.  The default is `-fno-cx-limited-range', but is
     enabled by `-ffast-math'.

     This option controls the default setting of the ISO C99
     `CX_LIMITED_RANGE' pragma.  Nevertheless, the option applies to
     all languages.

`-fcx-fortran-rules'
     Complex multiplication and division follow Fortran rules.  Range
     reduction is done as part of complex division, but there is no
     checking whether the result of a complex multiplication or
     division is `NaN + I*NaN', with an attempt to rescue the situation
     in that case.

     The default is `-fno-cx-fortran-rules'.


 The following options control optimizations that may improve
performance, but are not enabled by any `-O' options.  This section
includes experimental options that may produce broken code.

`-fbranch-probabilities'
     After running a program compiled with `-fprofile-arcs' (*note
     Options for Debugging Your Program or `gcc': Debugging Options.),
     you can compile it a second time using `-fbranch-probabilities',
     to improve optimizations based on the number of times each branch
     was taken.  When the program compiled with `-fprofile-arcs' exits
     it saves arc execution counts to a file called `SOURCENAME.gcda'
     for each source file.  The information in this data file is very
     dependent on the structure of the generated code, so you must use
     the same source code and the same optimization options for both
     compilations.

     With `-fbranch-probabilities', GCC puts a `REG_BR_PROB' note on
     each `JUMP_INSN' and `CALL_INSN'.  These can be used to improve
     optimization.  Currently, they are only used in one place: in
     `reorg.c', instead of guessing which path a branch is mostly to
     take, the `REG_BR_PROB' values are used to exactly determine which
     path is taken more often.

`-fprofile-values'
     If combined with `-fprofile-arcs', it adds code so that some data
     about values of expressions in the program is gathered.

     With `-fbranch-probabilities', it reads back the data gathered
     from profiling values of expressions and adds `REG_VALUE_PROFILE'
     notes to instructions for their later usage in optimizations.

     Enabled with `-fprofile-generate' and `-fprofile-use'.

`-fvpt'
     If combined with `-fprofile-arcs', it instructs the compiler to add
     a code to gather information about values of expressions.

     With `-fbranch-probabilities', it reads back the data gathered and
     actually performs the optimizations based on them.  Currently the
     optimizations include specialization of division operation using
     the knowledge about the value of the denominator.

`-frename-registers'
     Attempt to avoid false dependencies in scheduled code by making use
     of registers left over after register allocation.  This
     optimization will most benefit processors with lots of registers.
     Depending on the debug information format adopted by the target,
     however, it can make debugging impossible, since variables will no
     longer stay in a "home register".

     Enabled by default with `-funroll-loops'.

`-ftracer'
     Perform tail duplication to enlarge superblock size.  This
     transformation simplifies the control flow of the function
     allowing other optimizations to do better job.

     Enabled with `-fprofile-use'.

`-funroll-loops'
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop.  `-funroll-loops' implies
     `-frerun-cse-after-loop', `-fweb' and `-frename-registers'.  It
     also turns on complete loop peeling (i.e. complete removal of
     loops with small constant number of iterations).  This option
     makes code larger, and may or may not make it run faster.

     Enabled with `-fprofile-use'.

`-funroll-all-loops'
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered.  This usually makes programs run more
     slowly.  `-funroll-all-loops' implies the same options as
     `-funroll-loops'.

`-fpeel-loops'
     Peels the loops for that there is enough information that they do
     not roll much (from profile feedback).  It also turns on complete
     loop peeling (i.e. complete removal of loops with small constant
     number of iterations).

     Enabled with `-fprofile-use'.

`-fmove-loop-invariants'
     Enables the loop invariant motion pass in the RTL loop optimizer.
     Enabled at level `-O1'

`-funswitch-loops'
     Move branches with loop invariant conditions out of the loop, with
     duplicates of the loop on both branches (modified according to
     result of the condition).

`-ffunction-sections'
`-fdata-sections'
     Place each function or data item into its own section in the output
     file if the target supports arbitrary sections.  The name of the
     function or the name of the data item determines the section's name
     in the output file.

     Use these options on systems where the linker can perform
     optimizations to improve locality of reference in the instruction
     space.  Most systems using the ELF object format and SPARC
     processors running Solaris 2 have linkers with such optimizations.
     AIX may have these optimizations in the future.

     Only use these options when there are significant benefits from
     doing so.  When you specify these options, the assembler and
     linker will create larger object and executable files and will
     also be slower.  You will not be able to use `gprof' on all
     systems if you specify this option and you may have problems with
     debugging if you specify both this option and `-g'.

`-fbranch-target-load-optimize'
     Perform branch target register load optimization before prologue /
     epilogue threading.  The use of target registers can typically be
     exposed only during reload, thus hoisting loads out of loops and
     doing inter-block scheduling needs a separate optimization pass.

`-fbranch-target-load-optimize2'
     Perform branch target register load optimization after prologue /
     epilogue threading.

`-fbtr-bb-exclusive'
     When performing branch target register load optimization, don't
     reuse branch target registers in within any basic block.

`-fstack-protector'
     Emit extra code to check for buffer overflows, such as stack
     smashing attacks.  This is done by adding a guard variable to
     functions with vulnerable objects.  This includes functions that
     call alloca, and functions with buffers larger than 8 bytes.  The
     guards are initialized when a function is entered and then checked
     when the function exits.  If a guard check fails, an error message
     is printed and the program exits.

`-fstack-protector-all'
     Like `-fstack-protector' except that all functions are protected.

`-fsection-anchors'
     Try to reduce the number of symbolic address calculations by using
     shared "anchor" symbols to address nearby objects.  This
     transformation can help to reduce the number of GOT entries and
     GOT accesses on some targets.

     For example, the implementation of the following function `foo':

          static int a, b, c;
          int foo (void) { return a + b + c; }

     would usually calculate the addresses of all three variables, but
     if you compile it with `-fsection-anchors', it will access the
     variables from a common anchor point instead.  The effect is
     similar to the following pseudocode (which isn't valid C):

          int foo (void)
          {
            register int *xr = &x;
            return xr[&a - &x] + xr[&b - &x] + xr[&c - &x];
          }

     Not all targets support this option.

`--param NAME=VALUE'
     In some places, GCC uses various constants to control the amount of
     optimization that is done.  For example, GCC will not inline
     functions that contain more that a certain number of instructions.
     You can control some of these constants on the command-line using
     the `--param' option.

     The names of specific parameters, and the meaning of the values,
     are tied to the internals of the compiler, and are subject to
     change without notice in future releases.

     In each case, the VALUE is an integer.  The allowable choices for
     NAME are given in the following table:

    `sra-max-structure-size'
          The maximum structure size, in bytes, at which the scalar
          replacement of aggregates (SRA) optimization will perform
          block copies.  The default value, 0, implies that GCC will
          select the most appropriate size itself.

    `sra-field-structure-ratio'
          The threshold ratio (as a percentage) between instantiated
          fields and the complete structure size.  We say that if the
          ratio of the number of bytes in instantiated fields to the
          number of bytes in the complete structure exceeds this
          parameter, then block copies are not used.  The default is 75.

    `struct-reorg-cold-struct-ratio'
          The threshold ratio (as a percentage) between a structure
          frequency and the frequency of the hottest structure in the
          program.  This parameter is used by struct-reorg optimization
          enabled by `-fipa-struct-reorg'.  We say that if the ratio of
          a structure frequency, calculated by profiling, to the
          hottest structure frequency in the program is less than this
          parameter, then structure reorganization is not applied to
          this structure.  The default is 10.

    `predictable-branch-cost-outcome'
          When branch is predicted to be taken with probability lower
          than this threshold (in percent), then it is considered well
          predictable. The default is 10.

    `max-crossjump-edges'
          The maximum number of incoming edges to consider for
          crossjumping.  The algorithm used by `-fcrossjumping' is
          O(N^2) in the number of edges incoming to each block.
          Increasing values mean more aggressive optimization, making
          the compile time increase with probably small improvement in
          executable size.

    `min-crossjump-insns'
          The minimum number of instructions which must be matched at
          the end of two blocks before crossjumping will be performed
          on them.  This value is ignored in the case where all
          instructions in the block being crossjumped from are matched.
          The default value is 5.

    `max-grow-copy-bb-insns'
          The maximum code size expansion factor when copying basic
          blocks instead of jumping.  The expansion is relative to a
          jump instruction.  The default value is 8.

    `max-goto-duplication-insns'
          The maximum number of instructions to duplicate to a block
          that jumps to a computed goto.  To avoid O(N^2) behavior in a
          number of passes, GCC factors computed gotos early in the
          compilation process, and unfactors them as late as possible.
          Only computed jumps at the end of a basic blocks with no more
          than max-goto-duplication-insns are unfactored.  The default
          value is 8.

    `max-delay-slot-insn-search'
          The maximum number of instructions to consider when looking
          for an instruction to fill a delay slot.  If more than this
          arbitrary number of instructions is searched, the time
          savings from filling the delay slot will be minimal so stop
          searching.  Increasing values mean more aggressive
          optimization, making the compile time increase with probably
          small improvement in executable run time.

    `max-delay-slot-live-search'
          When trying to fill delay slots, the maximum number of
          instructions to consider when searching for a block with
          valid live register information.  Increasing this arbitrarily
          chosen value means more aggressive optimization, increasing
          the compile time.  This parameter should be removed when the
          delay slot code is rewritten to maintain the control-flow
          graph.

    `max-gcse-memory'
          The approximate maximum amount of memory that will be
          allocated in order to perform the global common subexpression
          elimination optimization.  If more memory than specified is
          required, the optimization will not be done.

    `max-gcse-passes'
          The maximum number of passes of GCSE to run.  The default is
          1.

    `max-pending-list-length'
          The maximum number of pending dependencies scheduling will
          allow before flushing the current state and starting over.
          Large functions with few branches or calls can create
          excessively large lists which needlessly consume memory and
          resources.

    `max-inline-insns-single'
          Several parameters control the tree inliner used in gcc.
          This number sets the maximum number of instructions (counted
          in GCC's internal representation) in a single function that
          the tree inliner will consider for inlining.  This only
          affects functions declared inline and methods implemented in
          a class declaration (C++).  The default value is 450.

    `max-inline-insns-auto'
          When you use `-finline-functions' (included in `-O3'), a lot
          of functions that would otherwise not be considered for
          inlining by the compiler will be investigated.  To those
          functions, a different (more restrictive) limit compared to
          functions declared inline can be applied.  The default value
          is 90.

    `large-function-insns'
          The limit specifying really large functions.  For functions
          larger than this limit after inlining, inlining is
          constrained by `--param large-function-growth'.  This
          parameter is useful primarily to avoid extreme compilation
          time caused by non-linear algorithms used by the backend.
          The default value is 2700.

    `large-function-growth'
          Specifies maximal growth of large function caused by inlining
          in percents.  The default value is 100 which limits large
          function growth to 2.0 times the original size.

    `large-unit-insns'
          The limit specifying large translation unit.  Growth caused
          by inlining of units larger than this limit is limited by
          `--param inline-unit-growth'.  For small units this might be
          too tight (consider unit consisting of function A that is
          inline and B that just calls A three time.  If B is small
          relative to A, the growth of unit is 300\% and yet such
          inlining is very sane.  For very large units consisting of
          small inlineable functions however the overall unit growth
          limit is needed to avoid exponential explosion of code size.
          Thus for smaller units, the size is increased to `--param
          large-unit-insns' before applying `--param
          inline-unit-growth'.  The default is 10000

    `inline-unit-growth'
          Specifies maximal overall growth of the compilation unit
          caused by inlining.  The default value is 30 which limits
          unit growth to 1.3 times the original size.

    `ipcp-unit-growth'
          Specifies maximal overall growth of the compilation unit
          caused by interprocedural constant propagation.  The default
          value is 10 which limits unit growth to 1.1 times the
          original size.

    `large-stack-frame'
          The limit specifying large stack frames.  While inlining the
          algorithm is trying to not grow past this limit too much.
          Default value is 256 bytes.

    `large-stack-frame-growth'
          Specifies maximal growth of large stack frames caused by
          inlining in percents.  The default value is 1000 which limits
          large stack frame growth to 11 times the original size.

    `max-inline-insns-recursive'
    `max-inline-insns-recursive-auto'
          Specifies maximum number of instructions out-of-line copy of
          self recursive inline function can grow into by performing
          recursive inlining.

          For functions declared inline `--param
          max-inline-insns-recursive' is taken into account.  For
          function not declared inline, recursive inlining happens only
          when `-finline-functions' (included in `-O3') is enabled and
          `--param max-inline-insns-recursive-auto' is used.  The
          default value is 450.

    `max-inline-recursive-depth'
    `max-inline-recursive-depth-auto'
          Specifies maximum recursion depth used by the recursive
          inlining.

          For functions declared inline `--param
          max-inline-recursive-depth' is taken into account.  For
          function not declared inline, recursive inlining happens only
          when `-finline-functions' (included in `-O3') is enabled and
          `--param max-inline-recursive-depth-auto' is used.  The
          default value is 8.

    `min-inline-recursive-probability'
          Recursive inlining is profitable only for function having
          deep recursion in average and can hurt for function having
          little recursion depth by increasing the prologue size or
          complexity of function body to other optimizers.

          When profile feedback is available (see `-fprofile-generate')
          the actual recursion depth can be guessed from probability
          that function will recurse via given call expression.  This
          parameter limits inlining only to call expression whose
          probability exceeds given threshold (in percents).  The
          default value is 10.

    `inline-call-cost'
          Specify cost of call instruction relative to simple
          arithmetics operations (having cost of 1).  Increasing this
          cost disqualifies inlining of non-leaf functions and at the
          same time increases size of leaf function that is believed to
          reduce function size by being inlined.  In effect it
          increases amount of inlining for code having large
          abstraction penalty (many functions that just pass the
          arguments to other functions) and decrease inlining for code
          with low abstraction penalty.  The default value is 12.

    `min-vect-loop-bound'
          The minimum number of iterations under which a loop will not
          get vectorized when `-ftree-vectorize' is used.  The number
          of iterations after vectorization needs to be greater than
          the value specified by this option to allow vectorization.
          The default value is 0.

    `max-unrolled-insns'
          The maximum number of instructions that a loop should have if
          that loop is unrolled, and if the loop is unrolled, it
          determines how many times the loop code is unrolled.

    `max-average-unrolled-insns'
          The maximum number of instructions biased by probabilities of
          their execution that a loop should have if that loop is
          unrolled, and if the loop is unrolled, it determines how many
          times the loop code is unrolled.

    `max-unroll-times'
          The maximum number of unrollings of a single loop.

    `max-peeled-insns'
          The maximum number of instructions that a loop should have if
          that loop is peeled, and if the loop is peeled, it determines
          how many times the loop code is peeled.

    `max-peel-times'
          The maximum number of peelings of a single loop.

    `max-completely-peeled-insns'
          The maximum number of insns of a completely peeled loop.

    `max-completely-peel-times'
          The maximum number of iterations of a loop to be suitable for
          complete peeling.

    `max-completely-peel-loop-nest-depth'
          The maximum depth of a loop nest suitable for complete
          peeling.

    `max-unswitch-insns'
          The maximum number of insns of an unswitched loop.

    `max-unswitch-level'
          The maximum number of branches unswitched in a single loop.

    `lim-expensive'
          The minimum cost of an expensive expression in the loop
          invariant motion.

    `iv-consider-all-candidates-bound'
          Bound on number of candidates for induction variables below
          that all candidates are considered for each use in induction
          variable optimizations.  Only the most relevant candidates
          are considered if there are more candidates, to avoid
          quadratic time complexity.

    `iv-max-considered-uses'
          The induction variable optimizations give up on loops that
          contain more induction variable uses.

    `iv-always-prune-cand-set-bound'
          If number of candidates in the set is smaller than this value,
          we always try to remove unnecessary ivs from the set during
          its optimization when a new iv is added to the set.

    `scev-max-expr-size'
          Bound on size of expressions used in the scalar evolutions
          analyzer.  Large expressions slow the analyzer.

    `omega-max-vars'
          The maximum number of variables in an Omega constraint system.
          The default value is 128.

    `omega-max-geqs'
          The maximum number of inequalities in an Omega constraint
          system.  The default value is 256.

    `omega-max-eqs'
          The maximum number of equalities in an Omega constraint
          system.  The default value is 128.

    `omega-max-wild-cards'
          The maximum number of wildcard variables that the Omega
          solver will be able to insert.  The default value is 18.

    `omega-hash-table-size'
          The size of the hash table in the Omega solver.  The default
          value is 550.

    `omega-max-keys'
          The maximal number of keys used by the Omega solver.  The
          default value is 500.

    `omega-eliminate-redundant-constraints'
          When set to 1, use expensive methods to eliminate all
          redundant constraints.  The default value is 0.

    `vect-max-version-for-alignment-checks'
          The maximum number of runtime checks that can be performed
          when doing loop versioning for alignment in the vectorizer.
          See option ftree-vect-loop-version for more information.

    `vect-max-version-for-alias-checks'
          The maximum number of runtime checks that can be performed
          when doing loop versioning for alias in the vectorizer.  See
          option ftree-vect-loop-version for more information.

    `max-iterations-to-track'
          The maximum number of iterations of a loop the brute force
          algorithm for analysis of # of iterations of the loop tries
          to evaluate.

    `hot-bb-count-fraction'
          Select fraction of the maximal count of repetitions of basic
          block in program given basic block needs to have to be
          considered hot.

    `hot-bb-frequency-fraction'
          Select fraction of the maximal frequency of executions of
          basic block in function given basic block needs to have to be
          considered hot

    `max-predicted-iterations'
          The maximum number of loop iterations we predict statically.
          This is useful in cases where function contain single loop
          with known bound and other loop with unknown.  We predict the
          known number of iterations correctly, while the unknown
          number of iterations average to roughly 10.  This means that
          the loop without bounds would appear artificially cold
          relative to the other one.

    `align-threshold'
          Select fraction of the maximal frequency of executions of
          basic block in function given basic block will get aligned.

    `align-loop-iterations'
          A loop expected to iterate at lest the selected number of
          iterations will get aligned.

    `tracer-dynamic-coverage'
    `tracer-dynamic-coverage-feedback'
          This value is used to limit superblock formation once the
          given percentage of executed instructions is covered.  This
          limits unnecessary code size expansion.

          The `tracer-dynamic-coverage-feedback' is used only when
          profile feedback is available.  The real profiles (as opposed
          to statically estimated ones) are much less balanced allowing
          the threshold to be larger value.

    `tracer-max-code-growth'
          Stop tail duplication once code growth has reached given
          percentage.  This is rather hokey argument, as most of the
          duplicates will be eliminated later in cross jumping, so it
          may be set to much higher values than is the desired code
          growth.

    `tracer-min-branch-ratio'
          Stop reverse growth when the reverse probability of best edge
          is less than this threshold (in percent).

    `tracer-min-branch-ratio'
    `tracer-min-branch-ratio-feedback'
          Stop forward growth if the best edge do have probability
          lower than this threshold.

          Similarly to `tracer-dynamic-coverage' two values are
          present, one for compilation for profile feedback and one for
          compilation without.  The value for compilation with profile
          feedback needs to be more conservative (higher) in order to
          make tracer effective.

    `max-cse-path-length'
          Maximum number of basic blocks on path that cse considers.
          The default is 10.

    `max-cse-insns'
          The maximum instructions CSE process before flushing. The
          default is 1000.

    `max-aliased-vops'
          Maximum number of virtual operands per function allowed to
          represent aliases before triggering the alias partitioning
          heuristic.  Alias partitioning reduces compile times and
          memory consumption needed for aliasing at the expense of
          precision loss in alias information.  The default value for
          this parameter is 100 for -O1, 500 for -O2 and 1000 for -O3.

          Notice that if a function contains more memory statements
          than the value of this parameter, it is not really possible
          to achieve this reduction.  In this case, the compiler will
          use the number of memory statements as the value for
          `max-aliased-vops'.

    `avg-aliased-vops'
          Average number of virtual operands per statement allowed to
          represent aliases before triggering the alias partitioning
          heuristic.  This works in conjunction with
          `max-aliased-vops'.  If a function contains more than
          `max-aliased-vops' virtual operators, then memory symbols
          will be grouped into memory partitions until either the total
          number of virtual operators is below `max-aliased-vops' or
          the average number of virtual operators per memory statement
          is below `avg-aliased-vops'.  The default value for this
          parameter is 1 for -O1 and -O2, and 3 for -O3.

    `ggc-min-expand'
          GCC uses a garbage collector to manage its own memory
          allocation.  This parameter specifies the minimum percentage
          by which the garbage collector's heap should be allowed to
          expand between collections.  Tuning this may improve
          compilation speed; it has no effect on code generation.

          The default is 30% + 70% * (RAM/1GB) with an upper bound of
          100% when RAM >= 1GB.  If `getrlimit' is available, the
          notion of "RAM" is the smallest of actual RAM and
          `RLIMIT_DATA' or `RLIMIT_AS'.  If GCC is not able to
          calculate RAM on a particular platform, the lower bound of
          30% is used.  Setting this parameter and `ggc-min-heapsize'
          to zero causes a full collection to occur at every
          opportunity.  This is extremely slow, but can be useful for
          debugging.

    `ggc-min-heapsize'
          Minimum size of the garbage collector's heap before it begins
          bothering to collect garbage.  The first collection occurs
          after the heap expands by `ggc-min-expand'% beyond
          `ggc-min-heapsize'.  Again, tuning this may improve
          compilation speed, and has no effect on code generation.

          The default is the smaller of RAM/8, RLIMIT_RSS, or a limit
          which tries to ensure that RLIMIT_DATA or RLIMIT_AS are not
          exceeded, but with a lower bound of 4096 (four megabytes) and
          an upper bound of 131072 (128 megabytes).  If GCC is not able
          to calculate RAM on a particular platform, the lower bound is
          used.  Setting this parameter very large effectively disables
          garbage collection.  Setting this parameter and
          `ggc-min-expand' to zero causes a full collection to occur at
          every opportunity.

    `max-reload-search-insns'
          The maximum number of instruction reload should look backward
          for equivalent register.  Increasing values mean more
          aggressive optimization, making the compile time increase
          with probably slightly better performance.  The default value
          is 100.

    `max-cselib-memory-locations'
          The maximum number of memory locations cselib should take
          into account.  Increasing values mean more aggressive
          optimization, making the compile time increase with probably
          slightly better performance.  The default value is 500.

    `reorder-blocks-duplicate'
    `reorder-blocks-duplicate-feedback'
          Used by basic block reordering pass to decide whether to use
          unconditional branch or duplicate the code on its
          destination.  Code is duplicated when its estimated size is
          smaller than this value multiplied by the estimated size of
          unconditional jump in the hot spots of the program.

          The `reorder-block-duplicate-feedback' is used only when
          profile feedback is available and may be set to higher values
          than `reorder-block-duplicate' since information about the
          hot spots is more accurate.

    `max-sched-ready-insns'
          The maximum number of instructions ready to be issued the
          scheduler should consider at any given time during the first
          scheduling pass.  Increasing values mean more thorough
          searches, making the compilation time increase with probably
          little benefit.  The default value is 100.

    `max-sched-region-blocks'
          The maximum number of blocks in a region to be considered for
          interblock scheduling.  The default value is 10.

    `max-pipeline-region-blocks'
          The maximum number of blocks in a region to be considered for
          pipelining in the selective scheduler.  The default value is
          15.

    `max-sched-region-insns'
          The maximum number of insns in a region to be considered for
          interblock scheduling.  The default value is 100.

    `max-pipeline-region-insns'
          The maximum number of insns in a region to be considered for
          pipelining in the selective scheduler.  The default value is
          200.

    `min-spec-prob'
          The minimum probability (in percents) of reaching a source
          block for interblock speculative scheduling.  The default
          value is 40.

    `max-sched-extend-regions-iters'
          The maximum number of iterations through CFG to extend
          regions.  0 - disable region extension, N - do at most N
          iterations.  The default value is 0.

    `max-sched-insn-conflict-delay'
          The maximum conflict delay for an insn to be considered for
          speculative motion.  The default value is 3.

    `sched-spec-prob-cutoff'
          The minimal probability of speculation success (in percents),
          so that speculative insn will be scheduled.  The default
          value is 40.

    `sched-mem-true-dep-cost'
          Minimal distance (in CPU cycles) between store and load
          targeting same memory locations.  The default value is 1.

    `selsched-max-lookahead'
          The maximum size of the lookahead window of selective
          scheduling.  It is a depth of search for available
          instructions.  The default value is 50.

    `selsched-max-sched-times'
          The maximum number of times that an instruction will be
          scheduled during selective scheduling.  This is the limit on
          the number of iterations through which the instruction may be
          pipelined.  The default value is 2.

    `selsched-max-insns-to-rename'
          The maximum number of best instructions in the ready list
          that are considered for renaming in the selective scheduler.
          The default value is 2.

    `max-last-value-rtl'
          The maximum size measured as number of RTLs that can be
          recorded in an expression in combiner for a pseudo register
          as last known value of that register.  The default is 10000.

    `integer-share-limit'
          Small integer constants can use a shared data structure,
          reducing the compiler's memory usage and increasing its
          speed.  This sets the maximum value of a shared integer
          constant.  The default value is 256.

    `min-virtual-mappings'
          Specifies the minimum number of virtual mappings in the
          incremental SSA updater that should be registered to trigger
          the virtual mappings heuristic defined by
          virtual-mappings-ratio.  The default value is 100.

    `virtual-mappings-ratio'
          If the number of virtual mappings is virtual-mappings-ratio
          bigger than the number of virtual symbols to be updated, then
          the incremental SSA updater switches to a full update for
          those symbols.  The default ratio is 3.

    `ssp-buffer-size'
          The minimum size of buffers (i.e. arrays) that will receive
          stack smashing protection when `-fstack-protection' is used.

    `max-jump-thread-duplication-stmts'
          Maximum number of statements allowed in a block that needs to
          be duplicated when threading jumps.

    `max-fields-for-field-sensitive'
          Maximum number of fields in a structure we will treat in a
          field sensitive manner during pointer analysis.  The default
          is zero for -O0, and -O1 and 100 for -Os, -O2, and -O3.

    `prefetch-latency'
          Estimate on average number of instructions that are executed
          before prefetch finishes.  The distance we prefetch ahead is
          proportional to this constant.  Increasing this number may
          also lead to less streams being prefetched (see
          `simultaneous-prefetches').

    `simultaneous-prefetches'
          Maximum number of prefetches that can run at the same time.

    `l1-cache-line-size'
          The size of cache line in L1 cache, in bytes.

    `l1-cache-size'
          The size of L1 cache, in kilobytes.

    `l2-cache-size'
          The size of L2 cache, in kilobytes.

    `use-canonical-types'
          Whether the compiler should use the "canonical" type system.
          By default, this should always be 1, which uses a more
          efficient internal mechanism for comparing types in C++ and
          Objective-C++.  However, if bugs in the canonical type system
          are causing compilation failures, set this value to 0 to
          disable canonical types.

    `switch-conversion-max-branch-ratio'
          Switch initialization conversion will refuse to create arrays
          that are bigger than `switch-conversion-max-branch-ratio'
          times the number of branches in the switch.

    `max-partial-antic-length'
          Maximum length of the partial antic set computed during the
          tree partial redundancy elimination optimization
          (`-ftree-pre') when optimizing at `-O3' and above.  For some
          sorts of source code the enhanced partial redundancy
          elimination optimization can run away, consuming all of the
          memory available on the host machine.  This parameter sets a
          limit on the length of the sets that are computed, which
          prevents the runaway behavior.  Setting a value of 0 for this
          parameter will allow an unlimited set length.

    `sccvn-max-scc-size'
          Maximum size of a strongly connected component (SCC) during
          SCCVN processing.  If this limit is hit, SCCVN processing for
          the whole function will not be done and optimizations
          depending on it will be disabled.  The default maximum SCC
          size is 10000.

    `ira-max-loops-num'
          IRA uses a regional register allocation by default.  If a
          function contains loops more than number given by the
          parameter, only at most given number of the most frequently
          executed loops will form regions for the regional register
          allocation.  The default value of the parameter is 100.

    `ira-max-conflict-table-size'
          Although IRA uses a sophisticated algorithm of compression
          conflict table, the table can be still big for huge
          functions.  If the conflict table for a function could be
          more than size in MB given by the parameter, the conflict
          table is not built and faster, simpler, and lower quality
          register allocation algorithm will be used.  The algorithm do
          not use pseudo-register conflicts.  The default value of the
          parameter is 2000.

    `loop-invariant-max-bbs-in-loop'
          Loop invariant motion can be very expensive, both in compile
          time and in amount of needed compile time memory, with very
          large loops.  Loops with more basic blocks than this
          parameter won't have loop invariant motion optimization
          performed on them.  The default value of the parameter is
          1000 for -O1 and 10000 for -O2 and above.

    `max-vartrack-size'
          Sets a maximum number of hash table slots to use during
          variable tracking dataflow analysis of any function.  If this
          limit is exceeded with variable tracking at assignments
          enabled, analysis for that function is retried without it,
          after removing all debug insns from the function.  If the
          limit is exceeded even without debug insns, var tracking
          analysis is completely disabled for the function.  Setting
          the parameter to zero makes it unlimited.

    `min-nondebug-insn-uid'
          Use uids starting at this parameter for nondebug insns.  The
          range below the parameter is reserved exclusively for debug
          insns created by `-fvar-tracking-assignments', but debug
          insns may get (non-overlapping) uids above it if the reserved
          range is exhausted.


File: gcc.info,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

3.11 Options Controlling the Preprocessor
=========================================

These options control the C preprocessor, which is run on each C source
file before actual compilation.

 If you use the `-E' option, nothing is done except preprocessing.
Some of these options make sense only together with `-E' because they
cause the preprocessor output to be unsuitable for actual compilation.

`-Wp,OPTION'
     You can use `-Wp,OPTION' to bypass the compiler driver and pass
     OPTION directly through to the preprocessor.  If OPTION contains
     commas, it is split into multiple options at the commas.  However,
     many options are modified, translated or interpreted by the
     compiler driver before being passed to the preprocessor, and `-Wp'
     forcibly bypasses this phase.  The preprocessor's direct interface
     is undocumented and subject to change, so whenever possible you
     should avoid using `-Wp' and let the driver handle the options
     instead.

`-Xpreprocessor OPTION'
     Pass OPTION as an option to the preprocessor.  You can use this to
     supply system-specific preprocessor options which GCC does not
     know how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xpreprocessor' twice, once for the option and once for the
     argument.

`-D NAME'
     Predefine NAME as a macro, with definition `1'.

`-D NAME=DEFINITION'
     The contents of DEFINITION are tokenized and processed as if they
     appeared during translation phase three in a `#define' directive.
     In particular, the definition will be truncated by embedded
     newline characters.

     If you are invoking the preprocessor from a shell or shell-like
     program you may need to use the shell's quoting syntax to protect
     characters such as spaces that have a meaning in the shell syntax.

     If you wish to define a function-like macro on the command line,
     write its argument list with surrounding parentheses before the
     equals sign (if any).  Parentheses are meaningful to most shells,
     so you will need to quote the option.  With `sh' and `csh',
     `-D'NAME(ARGS...)=DEFINITION'' works.

     `-D' and `-U' options are processed in the order they are given on
     the command line.  All `-imacros FILE' and `-include FILE' options
     are processed after all `-D' and `-U' options.

`-U NAME'
     Cancel any previous definition of NAME, either built in or
     provided with a `-D' option.

`-undef'
     Do not predefine any system-specific or GCC-specific macros.  The
     standard predefined macros remain defined.

`-I DIR'
     Add the directory DIR to the list of directories to be searched
     for header files.  Directories named by `-I' are searched before
     the standard system include directories.  If the directory DIR is
     a standard system include directory, the option is ignored to
     ensure that the default search order for system directories and
     the special treatment of system headers are not defeated .  If DIR
     begins with `=', then the `=' will be replaced by the sysroot
     prefix; see `--sysroot' and `-isysroot'.

`-o FILE'
     Write output to FILE.  This is the same as specifying FILE as the
     second non-option argument to `cpp'.  `gcc' has a different
     interpretation of a second non-option argument, so you must use
     `-o' to specify the output file.

`-Wall'
     Turns on all optional warnings which are desirable for normal code.
     At present this is `-Wcomment', `-Wtrigraphs', `-Wmultichar' and a
     warning about integer promotion causing a change of sign in `#if'
     expressions.  Note that many of the preprocessor's warnings are on
     by default and have no options to control them.

`-Wcomment'
`-Wcomments'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a backslash-newline appears in a `//' comment.
     (Both forms have the same effect.)

`-Wtrigraphs'
     Most trigraphs in comments cannot affect the meaning of the
     program.  However, a trigraph that would form an escaped newline
     (`??/' at the end of a line) can, by changing where the comment
     begins or ends.  Therefore, only trigraphs that would form escaped
     newlines produce warnings inside a comment.

     This option is implied by `-Wall'.  If `-Wall' is not given, this
     option is still enabled unless trigraphs are enabled.  To get
     trigraph conversion without warnings, but get the other `-Wall'
     warnings, use `-trigraphs -Wall -Wno-trigraphs'.

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and problematic constructs which
     should be avoided.

`-Wundef'
     Warn whenever an identifier which is not a macro is encountered in
     an `#if' directive, outside of `defined'.  Such identifiers are
     replaced with zero.

`-Wunused-macros'
     Warn about macros defined in the main file that are unused.  A
     macro is "used" if it is expanded or tested for existence at least
     once.  The preprocessor will also warn if the macro has not been
     used at the time it is redefined or undefined.

     Built-in macros, macros defined on the command line, and macros
     defined in include files are not warned about.

     _Note:_ If a macro is actually used, but only used in skipped
     conditional blocks, then CPP will report it as unused.  To avoid
     the warning in such a case, you might improve the scope of the
     macro's definition by, for example, moving it into the first
     skipped block.  Alternatively, you could provide a dummy use with
     something like:

          #if defined the_macro_causing_the_warning
          #endif

`-Wendif-labels'
     Warn whenever an `#else' or an `#endif' are followed by text.
     This usually happens in code of the form

          #if FOO
          ...
          #else FOO
          ...
          #endif FOO

     The second and third `FOO' should be in comments, but often are not
     in older programs.  This warning is on by default.

`-Werror'
     Make all warnings into hard errors.  Source code which triggers
     warnings will be rejected.

`-Wsystem-headers'
     Issue warnings for code in system headers.  These are normally
     unhelpful in finding bugs in your own code, therefore suppressed.
     If you are responsible for the system library, you may want to see
     them.

`-w'
     Suppress all warnings, including those which GNU CPP issues by
     default.

`-pedantic'
     Issue all the mandatory diagnostics listed in the C standard.
     Some of them are left out by default, since they trigger
     frequently on harmless code.

`-pedantic-errors'
     Issue all the mandatory diagnostics, and make all mandatory
     diagnostics into errors.  This includes mandatory diagnostics that
     GCC issues without `-pedantic' but treats as warnings.

`-M'
     Instead of outputting the result of preprocessing, output a rule
     suitable for `make' describing the dependencies of the main source
     file.  The preprocessor outputs one `make' rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from `-include' or
     `-imacros' command line options.

     Unless specified explicitly (with `-MT' or `-MQ'), the object file
     name consists of the name of the source file with any suffix
     replaced with object file suffix and with any leading directory
     parts removed.  If there are many included files then the rule is
     split into several lines using `\'-newline.  The rule has no
     commands.

     This option does not suppress the preprocessor's debug output,
     such as `-dM'.  To avoid mixing such debug output with the
     dependency rules you should explicitly specify the dependency
     output file with `-MF', or use an environment variable like
     `DEPENDENCIES_OUTPUT' (*note Environment Variables::).  Debug
     output will still be sent to the regular output stream as normal.

     Passing `-M' to the driver implies `-E', and suppresses warnings
     with an implicit `-w'.

`-MM'
     Like `-M' but do not mention header files that are found in system
     header directories, nor header files that are included, directly
     or indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an `#include' directive does not in itself determine whether that
     header will appear in `-MM' dependency output.  This is a slight
     change in semantics from GCC versions 3.0 and earlier.

`-MF FILE'
     When used with `-M' or `-MM', specifies a file to write the
     dependencies to.  If no `-MF' switch is given the preprocessor
     sends the rules to the same place it would have sent preprocessed
     output.

     When used with the driver options `-MD' or `-MMD', `-MF' overrides
     the default dependency output file.

`-MG'
     In conjunction with an option such as `-M' requesting dependency
     generation, `-MG' assumes missing header files are generated files
     and adds them to the dependency list without raising an error.
     The dependency filename is taken directly from the `#include'
     directive without prepending any path.  `-MG' also suppresses
     preprocessed output, as a missing header file renders this useless.

     This feature is used in automatic updating of makefiles.

`-MP'
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors `make' gives if you remove header
     files without updating the `Makefile' to match.

     This is typical output:

          test.o: test.c test.h

          test.h:

`-MT TARGET'
     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, deletes any
     directory components and any file suffix such as `.c', and appends
     the platform's usual object suffix.  The result is the target.

     An `-MT' option will set the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to `-MT', or use multiple `-MT' options.

     For example, `-MT '$(objpfx)foo.o'' might give

          $(objpfx)foo.o: foo.c

`-MQ TARGET'
     Same as `-MT', but it quotes any characters which are special to
     Make.  `-MQ '$(objpfx)foo.o'' gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with `-MQ'.

`-MD'
     `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
     implied.  The driver determines FILE based on whether an `-o'
     option is given.  If it is, the driver uses its argument but with
     a suffix of `.d', otherwise it takes the name of the input file,
     removes any directory components and suffix, and applies a `.d'
     suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (*note -MF:
     dashMF.), but if used without `-E', each `-o' is understood to
     specify a target object file.

     Since `-E' is not implied, `-MD' can be used to generate a
     dependency output file as a side-effect of the compilation process.

`-MMD'
     Like `-MD' except mention only user header files, not system
     header files.

`-fpch-deps'
     When using precompiled headers (*note Precompiled Headers::), this
     flag will cause the dependency-output flags to also list the files
     from the precompiled header's dependencies.  If not specified only
     the precompiled header would be listed and not the files that were
     used to create it because those files are not consulted when a
     precompiled header is used.

`-fpch-preprocess'
     This option allows use of a precompiled header (*note Precompiled
     Headers::) together with `-E'.  It inserts a special `#pragma',
     `#pragma GCC pch_preprocess "<filename>"' in the output to mark
     the place where the precompiled header was found, and its
     filename.  When `-fpreprocessed' is in use, GCC recognizes this
     `#pragma' and loads the PCH.

     This option is off by default, because the resulting preprocessed
     output is only really suitable as input to GCC.  It is switched on
     by `-save-temps'.

     You should not write this `#pragma' in your own code, but it is
     safe to edit the filename if the PCH file is available in a
     different location.  The filename may be absolute or it may be
     relative to GCC's current directory.

`-x c'
`-x c++'
`-x objective-c'
`-x assembler-with-cpp'
     Specify the source language: C, C++, Objective-C, or assembly.
     This has nothing to do with standards conformance or extensions;
     it merely selects which base syntax to expect.  If you give none
     of these options, cpp will deduce the language from the extension
     of the source file: `.c', `.cc', `.m', or `.S'.  Some other common
     extensions for C++ and assembly are also recognized.  If cpp does
     not recognize the extension, it will treat the file as C; this is
     the most generic mode.

     _Note:_ Previous versions of cpp accepted a `-lang' option which
     selected both the language and the standards conformance level.
     This option has been removed, because it conflicts with the `-l'
     option.

`-std=STANDARD'
`-ansi'
     Specify the standard to which the code should conform.  Currently
     CPP knows about C and C++ standards; others may be added in the
     future.

     STANDARD may be one of:
    `iso9899:1990'
    `c89'
          The ISO C standard from 1990.  `c89' is the customary
          shorthand for this version of the standard.

          The `-ansi' option is equivalent to `-std=c89'.

    `iso9899:199409'
          The 1990 C standard, as amended in 1994.

    `iso9899:1999'
    `c99'
    `iso9899:199x'
    `c9x'
          The revised ISO C standard, published in December 1999.
          Before publication, this was known as C9X.

    `gnu89'
          The 1990 C standard plus GNU extensions.  This is the default.

    `gnu99'
    `gnu9x'
          The 1999 C standard plus GNU extensions.

    `c++98'
          The 1998 ISO C++ standard plus amendments.

    `gnu++98'
          The same as `-std=c++98' plus GNU extensions.  This is the
          default for C++ code.

`-I-'
     Split the include path.  Any directories specified with `-I'
     options before `-I-' are searched only for headers requested with
     `#include "FILE"'; they are not searched for `#include <FILE>'.
     If additional directories are specified with `-I' options after
     the `-I-', those directories are searched for all `#include'
     directives.

     In addition, `-I-' inhibits the use of the directory of the current
     file directory as the first search directory for `#include "FILE"'.
     This option has been deprecated.

`-nostdinc'
     Do not search the standard system directories for header files.
     Only the directories you have specified with `-I' options (and the
     directory of the current file, if appropriate) are searched.

`-nostdinc++'
     Do not search for header files in the C++-specific standard
     directories, but do still search the other standard directories.
     (This option is used when building the C++ library.)

`-include FILE'
     Process FILE as if `#include "file"' appeared as the first line of
     the primary source file.  However, the first directory searched
     for FILE is the preprocessor's working directory _instead of_ the
     directory containing the main source file.  If not found there, it
     is searched for in the remainder of the `#include "..."' search
     chain as normal.

     If multiple `-include' options are given, the files are included
     in the order they appear on the command line.

`-imacros FILE'
     Exactly like `-include', except that any output produced by
     scanning FILE is thrown away.  Macros it defines remain defined.
     This allows you to acquire all the macros from a header without
     also processing its declarations.

     All files specified by `-imacros' are processed before all files
     specified by `-include'.

`-idirafter DIR'
     Search DIR for header files, but do it _after_ all directories
     specified with `-I' and the standard system directories have been
     exhausted.  DIR is treated as a system include directory.  If DIR
     begins with `=', then the `=' will be replaced by the sysroot
     prefix; see `--sysroot' and `-isysroot'.

`-iprefix PREFIX'
     Specify PREFIX as the prefix for subsequent `-iwithprefix'
     options.  If the prefix represents a directory, you should include
     the final `/'.

`-iwithprefix DIR'
`-iwithprefixbefore DIR'
     Append DIR to the prefix specified previously with `-iprefix', and
     add the resulting directory to the include search path.
     `-iwithprefixbefore' puts it in the same place `-I' would;
     `-iwithprefix' puts it where `-idirafter' would.

`-isysroot DIR'
     This option is like the `--sysroot' option, but applies only to
     header files.  See the `--sysroot' option for more information.

`-imultilib DIR'
     Use DIR as a subdirectory of the directory containing
     target-specific C++ headers.

`-isystem DIR'
     Search DIR for header files, after all directories specified by
     `-I' but before the standard system directories.  Mark it as a
     system directory, so that it gets the same special treatment as is
     applied to the standard system directories.  If DIR begins with
     `=', then the `=' will be replaced by the sysroot prefix; see
     `--sysroot' and `-isysroot'.

`-iquote DIR'
     Search DIR only for header files requested with `#include "FILE"';
     they are not searched for `#include <FILE>', before all
     directories specified by `-I' and before the standard system
     directories.  If DIR begins with `=', then the `=' will be replaced
     by the sysroot prefix; see `--sysroot' and `-isysroot'.

`-fdirectives-only'
     When preprocessing, handle directives, but do not expand macros.

     The option's behavior depends on the `-E' and `-fpreprocessed'
     options.

     With `-E', preprocessing is limited to the handling of directives
     such as `#define', `#ifdef', and `#error'.  Other preprocessor
     operations, such as macro expansion and trigraph conversion are
     not performed.  In addition, the `-dD' option is implicitly
     enabled.

     With `-fpreprocessed', predefinition of command line and most
     builtin macros is disabled.  Macros such as `__LINE__', which are
     contextually dependent, are handled normally.  This enables
     compilation of files previously preprocessed with `-E
     -fdirectives-only'.

     With both `-E' and `-fpreprocessed', the rules for
     `-fpreprocessed' take precedence.  This enables full preprocessing
     of files previously preprocessed with `-E -fdirectives-only'.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.

`-fextended-identifiers'
     Accept universal character names in identifiers.  This option is
     experimental; in a future version of GCC, it will be enabled by
     default for C99 and C++.

`-fpreprocessed'
     Indicate to the preprocessor that the input file has already been
     preprocessed.  This suppresses things like macro expansion,
     trigraph conversion, escaped newline splicing, and processing of
     most directives.  The preprocessor still recognizes and removes
     comments, so that you can pass a file preprocessed with `-C' to
     the compiler without problems.  In this mode the integrated
     preprocessor is little more than a tokenizer for the front ends.

     `-fpreprocessed' is implicit if the input file has one of the
     extensions `.i', `.ii' or `.mi'.  These are the extensions that
     GCC uses for preprocessed files created by `-save-temps'.

`-ftabstop=WIDTH'
     Set the distance between tab stops.  This helps the preprocessor
     report correct column numbers in warnings or errors, even if tabs
     appear on the line.  If the value is less than 1 or greater than
     100, the option is ignored.  The default is 8.

`-fexec-charset=CHARSET'
     Set the execution character set, used for string and character
     constants.  The default is UTF-8.  CHARSET can be any encoding
     supported by the system's `iconv' library routine.

`-fwide-exec-charset=CHARSET'
     Set the wide execution character set, used for wide string and
     character constants.  The default is UTF-32 or UTF-16, whichever
     corresponds to the width of `wchar_t'.  As with `-fexec-charset',
     CHARSET can be any encoding supported by the system's `iconv'
     library routine; however, you will have problems with encodings
     that do not fit exactly in `wchar_t'.

`-finput-charset=CHARSET'
     Set the input character set, used for translation from the
     character set of the input file to the source character set used
     by GCC.  If the locale does not specify, or GCC cannot get this
     information from the locale, the default is UTF-8.  This can be
     overridden by either the locale or this command line option.
     Currently the command line option takes precedence if there's a
     conflict.  CHARSET can be any encoding supported by the system's
     `iconv' library routine.

`-fworking-directory'
     Enable generation of linemarkers in the preprocessor output that
     will let the compiler know the current working directory at the
     time of preprocessing.  When this option is enabled, the
     preprocessor will emit, after the initial linemarker, a second
     linemarker with the current working directory followed by two
     slashes.  GCC will use this directory, when it's present in the
     preprocessed input, as the directory emitted as the current
     working directory in some debugging information formats.  This
     option is implicitly enabled if debugging information is enabled,
     but this can be inhibited with the negated form
     `-fno-working-directory'.  If the `-P' flag is present in the
     command line, this option has no effect, since no `#line'
     directives are emitted whatsoever.

`-fno-show-column'
     Do not print column numbers in diagnostics.  This may be necessary
     if diagnostics are being scanned by a program that does not
     understand the column numbers, such as `dejagnu'.

`-A PREDICATE=ANSWER'
     Make an assertion with the predicate PREDICATE and answer ANSWER.
     This form is preferred to the older form `-A PREDICATE(ANSWER)',
     which is still supported, because it does not use shell special
     characters.

`-A -PREDICATE=ANSWER'
     Cancel an assertion with the predicate PREDICATE and answer ANSWER.

`-dCHARS'
     CHARS is a sequence of one or more of the following characters,
     and must not be preceded by a space.  Other characters are
     interpreted by the compiler proper, or reserved for future
     versions of GCC, and so are silently ignored.  If you specify
     characters whose behavior conflicts, the result is undefined.

    `M'
          Instead of the normal output, generate a list of `#define'
          directives for all the macros defined during the execution of
          the preprocessor, including predefined macros.  This gives
          you a way of finding out what is predefined in your version
          of the preprocessor.  Assuming you have no file `foo.h', the
          command

               touch foo.h; cpp -dM foo.h

          will show all the predefined macros.

          If you use `-dM' without the `-E' option, `-dM' is
          interpreted as a synonym for `-fdump-rtl-mach'.  *Note
          Debugging Options: (gcc)Debugging Options.

    `D'
          Like `M' except in two respects: it does _not_ include the
          predefined macros, and it outputs _both_ the `#define'
          directives and the result of preprocessing.  Both kinds of
          output go to the standard output file.

    `N'
          Like `D', but emit only the macro names, not their expansions.

    `I'
          Output `#include' directives in addition to the result of
          preprocessing.

    `U'
          Like `D' except that only macros that are expanded, or whose
          definedness is tested in preprocessor directives, are output;
          the output is delayed until the use or test of the macro; and
          `#undef' directives are also output for macros tested but
          undefined at the time.

`-P'
     Inhibit generation of linemarkers in the output from the
     preprocessor.  This might be useful when running the preprocessor
     on something that is not C code, and will be sent to a program
     which might be confused by the linemarkers.

`-C'
     Do not discard comments.  All comments are passed through to the
     output file, except for comments in processed directives, which
     are deleted along with the directive.

     You should be prepared for side effects when using `-C'; it causes
     the preprocessor to treat comments as tokens in their own right.
     For example, comments appearing at the start of what would be a
     directive line have the effect of turning that line into an
     ordinary source line, since the first token on the line is no
     longer a `#'.

`-CC'
     Do not discard comments, including during macro expansion.  This is
     like `-C', except that comments contained within macros are also
     passed through to the output file where the macro is expanded.

     In addition to the side-effects of the `-C' option, the `-CC'
     option causes all C++-style comments inside a macro to be
     converted to C-style comments.  This is to prevent later use of
     that macro from inadvertently commenting out the remainder of the
     source line.

     The `-CC' option is generally used to support lint comments.

`-traditional-cpp'
     Try to imitate the behavior of old-fashioned C preprocessors, as
     opposed to ISO C preprocessors.

`-trigraphs'
     Process trigraph sequences.  These are three-character sequences,
     all starting with `??', that are defined by ISO C to stand for
     single characters.  For example, `??/' stands for `\', so `'??/n''
     is a character constant for a newline.  By default, GCC ignores
     trigraphs, but in standard-conforming modes it converts them.  See
     the `-std' and `-ansi' options.

     The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

`-remap'
     Enable special code to work around file systems which only permit
     very short file names, such as MS-DOS.

`--help'
`--target-help'
     Print text describing all the command line options instead of
     preprocessing anything.

`-v'
     Verbose mode.  Print out GNU CPP's version number at the beginning
     of execution, and report the final form of the include path.

`-H'
     Print the name of each header file used, in addition to other
     normal activities.  Each name is indented to show how deep in the
     `#include' stack it is.  Precompiled header files are also
     printed, even if they are found to be invalid; an invalid
     precompiled header file is printed with `...x' and a valid one
     with `...!' .

`-version'
`--version'
     Print out GNU CPP's version number.  With one dash, proceed to
     preprocess as normal.  With two dashes, exit immediately.

File: gcc.info,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

3.12 Passing Options to the Assembler
=====================================

You can pass options to the assembler.

`-Wa,OPTION'
     Pass OPTION as an option to the assembler.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-Xassembler OPTION'
     Pass OPTION as an option to the assembler.  You can use this to
     supply system-specific assembler options which GCC does not know
     how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xassembler' twice, once for the option and once for the argument.


File: gcc.info,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

3.13 Options for Linking
========================

These options come into play when the compiler links object files into
an executable output file.  They are meaningless if the compiler is not
doing a link step.

`OBJECT-FILE-NAME'
     A file name that does not end in a special recognized suffix is
     considered to name an object file or library.  (Object files are
     distinguished from libraries by the linker according to the file
     contents.)  If linking is done, these object files are used as
     input to the linker.

`-c'
`-S'
`-E'
     If any of these options is used, then the linker is not run, and
     object file names should not be used as arguments.  *Note Overall
     Options::.

`-lLIBRARY'
`-l LIBRARY'
     Search the library named LIBRARY when linking.  (The second
     alternative with the library as a separate argument is only for
     POSIX compliance and is not recommended.)

     It makes a difference where in the command you write this option;
     the linker searches and processes libraries and object files in
     the order they are specified.  Thus, `foo.o -lz bar.o' searches
     library `z' after file `foo.o' but before `bar.o'.  If `bar.o'
     refers to functions in `z', those functions may not be loaded.

     The linker searches a standard list of directories for the library,
     which is actually a file named `libLIBRARY.a'.  The linker then
     uses this file as if it had been specified precisely by name.

     The directories searched include several standard system
     directories plus any that you specify with `-L'.

     Normally the files found this way are library files--archive files
     whose members are object files.  The linker handles an archive
     file by scanning through it for members which define symbols that
     have so far been referenced but not defined.  But if the file that
     is found is an ordinary object file, it is linked in the usual
     fashion.  The only difference between using an `-l' option and
     specifying a file name is that `-l' surrounds LIBRARY with `lib'
     and `.a' and searches several directories.

`-lobjc'
     You need this special case of the `-l' option in order to link an
     Objective-C or Objective-C++ program.

`-nostartfiles'
     Do not use the standard system startup files when linking.  The
     standard system libraries are used normally, unless `-nostdlib' or
     `-nodefaultlibs' is used.

`-nodefaultlibs'
     Do not use the standard system libraries when linking.  Only the
     libraries you specify will be passed to the linker.  The standard
     startup files are used normally, unless `-nostartfiles' is used.
     The compiler may generate calls to `memcmp', `memset', `memcpy'
     and `memmove'.  These entries are usually resolved by entries in
     libc.  These entry points should be supplied through some other
     mechanism when this option is specified.

`-nostdlib'
     Do not use the standard system startup files or libraries when
     linking.  No startup files and only the libraries you specify will
     be passed to the linker.  The compiler may generate calls to
     `memcmp', `memset', `memcpy' and `memmove'.  These entries are
     usually resolved by entries in libc.  These entry points should be
     supplied through some other mechanism when this option is
     specified.

     One of the standard libraries bypassed by `-nostdlib' and
     `-nodefaultlibs' is `libgcc.a', a library of internal subroutines
     that GCC uses to overcome shortcomings of particular machines, or
     special needs for some languages.  (*Note Interfacing to GCC
     Output: (gccint)Interface, for more discussion of `libgcc.a'.)  In
     most cases, you need `libgcc.a' even when you want to avoid other
     standard libraries.  In other words, when you specify `-nostdlib'
     or `-nodefaultlibs' you should usually specify `-lgcc' as well.
     This ensures that you have no unresolved references to internal GCC
     library subroutines.  (For example, `__main', used to ensure C++
     constructors will be called; *note `collect2': (gccint)Collect2.)

`-pie'
     Produce a position independent executable on targets which support
     it.  For predictable results, you must also specify the same set
     of options that were used to generate code (`-fpie', `-fPIE', or
     model suboptions) when you specify this option.

`-rdynamic'
     Pass the flag `-export-dynamic' to the ELF linker, on targets that
     support it. This instructs the linker to add all symbols, not only
     used ones, to the dynamic symbol table. This option is needed for
     some uses of `dlopen' or to allow obtaining backtraces from within
     a program.

`-s'
     Remove all symbol table and relocation information from the
     executable.

`-static'
     On systems that support dynamic linking, this prevents linking
     with the shared libraries.  On other systems, this option has no
     effect.

`-shared'
     Produce a shared object which can then be linked with other
     objects to form an executable.  Not all systems support this
     option.  For predictable results, you must also specify the same
     set of options that were used to generate code (`-fpic', `-fPIC',
     or model suboptions) when you specify this option.(1)

`-shared-libgcc'
`-static-libgcc'
     On systems that provide `libgcc' as a shared library, these options
     force the use of either the shared or static version respectively.
     If no shared version of `libgcc' was built when the compiler was
     configured, these options have no effect.

     There are several situations in which an application should use the
     shared `libgcc' instead of the static version.  The most common of
     these is when the application wishes to throw and catch exceptions
     across different shared libraries.  In that case, each of the
     libraries as well as the application itself should use the shared
     `libgcc'.

     Therefore, the G++ and GCJ drivers automatically add
     `-shared-libgcc' whenever you build a shared library or a main
     executable, because C++ and Java programs typically use
     exceptions, so this is the right thing to do.

     If, instead, you use the GCC driver to create shared libraries,
     you may find that they will not always be linked with the shared
     `libgcc'.  If GCC finds, at its configuration time, that you have
     a non-GNU linker or a GNU linker that does not support option
     `--eh-frame-hdr', it will link the shared version of `libgcc' into
     shared libraries by default.  Otherwise, it will take advantage of
     the linker and optimize away the linking with the shared version
     of `libgcc', linking with the static version of libgcc by default.
     This allows exceptions to propagate through such shared libraries,
     without incurring relocation costs at library load time.

     However, if a library or main executable is supposed to throw or
     catch exceptions, you must link it using the G++ or GCJ driver, as
     appropriate for the languages used in the program, or using the
     option `-shared-libgcc', such that it is linked with the shared
     `libgcc'.

`-symbolic'
     Bind references to global symbols when building a shared object.
     Warn about any unresolved references (unless overridden by the
     link editor option `-Xlinker -z -Xlinker defs').  Only a few
     systems support this option.

`-T SCRIPT'
     Use SCRIPT as the linker script.  This option is supported by most
     systems using the GNU linker.  On some targets, such as bare-board
     targets without an operating system, the `-T' option may be
     required when linking to avoid references to undefined symbols.

`-Xlinker OPTION'
     Pass OPTION as an option to the linker.  You can use this to
     supply system-specific linker options which GCC does not know how
     to recognize.

     If you want to pass an option that takes a separate argument, you
     must use `-Xlinker' twice, once for the option and once for the
     argument.  For example, to pass `-assert definitions', you must
     write `-Xlinker -assert -Xlinker definitions'.  It does not work
     to write `-Xlinker "-assert definitions"', because this passes the
     entire string as a single argument, which is not what the linker
     expects.

     When using the GNU linker, it is usually more convenient to pass
     arguments to linker options using the `OPTION=VALUE' syntax than
     as separate arguments.  For example, you can specify `-Xlinker
     -Map=output.map' rather than `-Xlinker -Map -Xlinker output.map'.
     Other linkers may not support this syntax for command-line options.

`-Wl,OPTION'
     Pass OPTION as an option to the linker.  If OPTION contains
     commas, it is split into multiple options at the commas.  You can
     use this syntax to pass an argument to the option.  For example,
     `-Wl,-Map,output.map' passes `-Map output.map' to the linker.
     When using the GNU linker, you can also get the same effect with
     `-Wl,-Map=output.map'.

`-u SYMBOL'
     Pretend the symbol SYMBOL is undefined, to force linking of
     library modules to define it.  You can use `-u' multiple times with
     different symbols to force loading of additional library modules.

 ---------- Footnotes ----------

 (1) On some systems, `gcc -shared' needs to build supplementary stub
code for constructors to work.  On multi-libbed systems, `gcc -shared'
must select the correct support libraries to link against.  Failing to
supply the correct flags may lead to subtle defects.  Supplying them in
cases where they are not necessary is innocuous.

File: gcc.info,  Node: Directory Options,  Next: Spec Files,  Prev: Link Options,  Up: Invoking GCC

3.14 Options for Directory Search
=================================

These options specify directories to search for header files, for
libraries and for parts of the compiler:

`-IDIR'
     Add the directory DIR to the head of the list of directories to be
     searched for header files.  This can be used to override a system
     header file, substituting your own version, since these
     directories are searched before the system header file
     directories.  However, you should not use this option to add
     directories that contain vendor-supplied system header files (use
     `-isystem' for that).  If you use more than one `-I' option, the
     directories are scanned in left-to-right order; the standard
     system directories come after.

     If a standard system include directory, or a directory specified
     with `-isystem', is also specified with `-I', the `-I' option will
     be ignored.  The directory will still be searched but as a system
     directory at its normal position in the system include chain.
     This is to ensure that GCC's procedure to fix buggy system headers
     and the ordering for the include_next directive are not
     inadvertently changed.  If you really need to change the search
     order for system directories, use the `-nostdinc' and/or
     `-isystem' options.

`-iquoteDIR'
     Add the directory DIR to the head of the list of directories to be
     searched for header files only for the case of `#include "FILE"';
     they are not searched for `#include <FILE>', otherwise just like
     `-I'.

`-LDIR'
     Add directory DIR to the list of directories to be searched for
     `-l'.

`-BPREFIX'
     This option specifies where to find the executables, libraries,
     include files, and data files of the compiler itself.

     The compiler driver program runs one or more of the subprograms
     `cpp', `cc1', `as' and `ld'.  It tries PREFIX as a prefix for each
     program it tries to run, both with and without `MACHINE/VERSION/'
     (*note Target Options::).

     For each subprogram to be run, the compiler driver first tries the
     `-B' prefix, if any.  If that name is not found, or if `-B' was
     not specified, the driver tries two standard prefixes, which are
     `/usr/lib/gcc/' and `/usr/local/lib/gcc/'.  If neither of those
     results in a file name that is found, the unmodified program name
     is searched for using the directories specified in your `PATH'
     environment variable.

     The compiler will check to see if the path provided by the `-B'
     refers to a directory, and if necessary it will add a directory
     separator character at the end of the path.

     `-B' prefixes that effectively specify directory names also apply
     to libraries in the linker, because the compiler translates these
     options into `-L' options for the linker.  They also apply to
     includes files in the preprocessor, because the compiler
     translates these options into `-isystem' options for the
     preprocessor.  In this case, the compiler appends `include' to the
     prefix.

     The run-time support file `libgcc.a' can also be searched for using
     the `-B' prefix, if needed.  If it is not found there, the two
     standard prefixes above are tried, and that is all.  The file is
     left out of the link if it is not found by those means.

     Another way to specify a prefix much like the `-B' prefix is to use
     the environment variable `GCC_EXEC_PREFIX'.  *Note Environment
     Variables::.

     As a special kludge, if the path provided by `-B' is
     `[dir/]stageN/', where N is a number in the range 0 to 9, then it
     will be replaced by `[dir/]include'.  This is to help with
     boot-strapping the compiler.

`-specs=FILE'
     Process FILE after the compiler reads in the standard `specs'
     file, in order to override the defaults that the `gcc' driver
     program uses when determining what switches to pass to `cc1',
     `cc1plus', `as', `ld', etc.  More than one `-specs=FILE' can be
     specified on the command line, and they are processed in order,
     from left to right.

`--sysroot=DIR'
     Use DIR as the logical root directory for headers and libraries.
     For example, if the compiler would normally search for headers in
     `/usr/include' and libraries in `/usr/lib', it will instead search
     `DIR/usr/include' and `DIR/usr/lib'.

     If you use both this option and the `-isysroot' option, then the
     `--sysroot' option will apply to libraries, but the `-isysroot'
     option will apply to header files.

     The GNU linker (beginning with version 2.16) has the necessary
     support for this option.  If your linker does not support this
     option, the header file aspect of `--sysroot' will still work, but
     the library aspect will not.

`-I-'
     This option has been deprecated.  Please use `-iquote' instead for
     `-I' directories before the `-I-' and remove the `-I-'.  Any
     directories you specify with `-I' options before the `-I-' option
     are searched only for the case of `#include "FILE"'; they are not
     searched for `#include <FILE>'.

     If additional directories are specified with `-I' options after
     the `-I-', these directories are searched for all `#include'
     directives.  (Ordinarily _all_ `-I' directories are used this way.)

     In addition, the `-I-' option inhibits the use of the current
     directory (where the current input file came from) as the first
     search directory for `#include "FILE"'.  There is no way to
     override this effect of `-I-'.  With `-I.' you can specify
     searching the directory which was current when the compiler was
     invoked.  That is not exactly the same as what the preprocessor
     does by default, but it is often satisfactory.

     `-I-' does not inhibit the use of the standard system directories
     for header files.  Thus, `-I-' and `-nostdinc' are independent.

File: gcc.info,  Node: Spec Files,  Next: Target Options,  Prev: Directory Options,  Up: Invoking GCC

3.15 Specifying subprocesses and the switches to pass to them
=============================================================

`gcc' is a driver program.  It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it
ought to place on their command lines.  This behavior is controlled by
"spec strings".  In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior.  The spec strings built into GCC can
be overridden by using the `-specs=' command-line switch to specify a
spec file.

 "Spec files" are plaintext files that are used to construct spec
strings.  They consist of a sequence of directives separated by blank
lines.  The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:

`%COMMAND'
     Issues a COMMAND to the spec file processor.  The commands that can
     appear here are:

    `%include <FILE>'
          Search for FILE and insert its text at the current point in
          the specs file.

    `%include_noerr <FILE>'
          Just like `%include', but do not generate an error message if
          the include file cannot be found.

    `%rename OLD_NAME NEW_NAME'
          Rename the spec string OLD_NAME to NEW_NAME.


`*[SPEC_NAME]:'
     This tells the compiler to create, override or delete the named
     spec string.  All lines after this directive up to the next
     directive or blank line are considered to be the text for the spec
     string.  If this results in an empty string then the spec will be
     deleted.  (Or, if the spec did not exist, then nothing will
     happened.)  Otherwise, if the spec does not currently exist a new
     spec will be created.  If the spec does exist then its contents
     will be overridden by the text of this directive, unless the first
     character of that text is the `+' character, in which case the
     text will be appended to the spec.

`[SUFFIX]:'
     Creates a new `[SUFFIX] spec' pair.  All lines after this directive
     and up to the next directive or blank line are considered to make
     up the spec string for the indicated suffix.  When the compiler
     encounters an input file with the named suffix, it will processes
     the spec string in order to work out how to compile that file.
     For example:

          .ZZ:
          z-compile -input %i

     This says that any input file whose name ends in `.ZZ' should be
     passed to the program `z-compile', which should be invoked with the
     command-line switch `-input' and with the result of performing the
     `%i' substitution.  (See below.)

     As an alternative to providing a spec string, the text that
     follows a suffix directive can be one of the following:

    `@LANGUAGE'
          This says that the suffix is an alias for a known LANGUAGE.
          This is similar to using the `-x' command-line switch to GCC
          to specify a language explicitly.  For example:

               .ZZ:
               @c++

          Says that .ZZ files are, in fact, C++ source files.

    `#NAME'
          This causes an error messages saying:

               NAME compiler not installed on this system.

     GCC already has an extensive list of suffixes built into it.  This
     directive will add an entry to the end of the list of suffixes, but
     since the list is searched from the end backwards, it is
     effectively possible to override earlier entries using this
     technique.


 GCC has the following spec strings built into it.  Spec files can
override these strings or create their own.  Note that individual
targets can also add their own spec strings to this list.

     asm          Options to pass to the assembler
     asm_final    Options to pass to the assembler post-processor
     cpp          Options to pass to the C preprocessor
     cc1          Options to pass to the C compiler
     cc1plus      Options to pass to the C++ compiler
     endfile      Object files to include at the end of the link
     link         Options to pass to the linker
     lib          Libraries to include on the command line to the linker
     libgcc       Decides which GCC support library to pass to the linker
     linker       Sets the name of the linker
     predefines   Defines to be passed to the C preprocessor
     signed_char  Defines to pass to CPP to say whether `char' is signed
                  by default
     startfile    Object files to include at the start of the link

 Here is a small example of a spec file:

     %rename lib                 old_lib

     *lib:
     --start-group -lgcc -lc -leval1 --end-group %(old_lib)

 This example renames the spec called `lib' to `old_lib' and then
overrides the previous definition of `lib' with a new one.  The new
definition adds in some extra command-line options before including the
text of the old definition.

 "Spec strings" are a list of command-line options to be passed to their
corresponding program.  In addition, the spec strings can contain
`%'-prefixed sequences to substitute variable text or to conditionally
insert text into the command line.  Using these constructs it is
possible to generate quite complex command lines.

 Here is a table of all defined `%'-sequences for spec strings.  Note
that spaces are not generated automatically around the results of
expanding these sequences.  Therefore you can concatenate them together
or combine them with constant text in a single argument.

`%%'
     Substitute one `%' into the program name or argument.

`%i'
     Substitute the name of the input file being processed.

`%b'
     Substitute the basename of the input file being processed.  This
     is the substring up to (and not including) the last period and not
     including the directory.

`%B'
     This is the same as `%b', but include the file suffix (text after
     the last period).

`%d'
     Marks the argument containing or following the `%d' as a temporary
     file name, so that that file will be deleted if GCC exits
     successfully.  Unlike `%g', this contributes no text to the
     argument.

`%gSUFFIX'
     Substitute a file name that has suffix SUFFIX and is chosen once
     per compilation, and mark the argument in the same way as `%d'.
     To reduce exposure to denial-of-service attacks, the file name is
     now chosen in a way that is hard to predict even when previously
     chosen file names are known.  For example, `%g.s ... %g.o ... %g.s'
     might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'.  SUFFIX
     matches the regexp `[.A-Za-z]*' or the special string `%O', which
     is treated exactly as if `%O' had been preprocessed.  Previously,
     `%g' was simply substituted with a file name chosen once per
     compilation, without regard to any appended suffix (which was
     therefore treated just like ordinary text), making such attacks
     more likely to succeed.

`%uSUFFIX'
     Like `%g', but generates a new temporary file name even if
     `%uSUFFIX' was already seen.

`%USUFFIX'
     Substitutes the last file name generated with `%uSUFFIX',
     generating a new one if there is no such last file name.  In the
     absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
     they don't share the same suffix _space_, so `%g.s ... %U.s ...
     %g.s ... %U.s' would involve the generation of two distinct file
     names, one for each `%g.s' and another for each `%U.s'.
     Previously, `%U' was simply substituted with a file name chosen
     for the previous `%u', without regard to any appended suffix.

`%jSUFFIX'
     Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
     writable, and if save-temps is off; otherwise, substitute the name
     of a temporary file, just like `%u'.  This temporary file is not
     meant for communication between processes, but rather as a junk
     disposal mechanism.

`%|SUFFIX'
`%mSUFFIX'
     Like `%g', except if `-pipe' is in effect.  In that case `%|'
     substitutes a single dash and `%m' substitutes nothing at all.
     These are the two most common ways to instruct a program that it
     should read from standard input or write to standard output.  If
     you need something more elaborate you can use an `%{pipe:`X'}'
     construct: see for example `f/lang-specs.h'.

`%.SUFFIX'
     Substitutes .SUFFIX for the suffixes of a matched switch's args
     when it is subsequently output with `%*'.  SUFFIX is terminated by
     the next space or %.

`%w'
     Marks the argument containing or following the `%w' as the
     designated output file of this compilation.  This puts the argument
     into the sequence of arguments that `%o' will substitute later.

`%o'
     Substitutes the names of all the output files, with spaces
     automatically placed around them.  You should write spaces around
     the `%o' as well or the results are undefined.  `%o' is for use in
     the specs for running the linker.  Input files whose names have no
     recognized suffix are not compiled at all, but they are included
     among the output files, so they will be linked.

`%O'
     Substitutes the suffix for object files.  Note that this is
     handled specially when it immediately follows `%g, %u, or %U',
     because of the need for those to form complete file names.  The
     handling is such that `%O' is treated exactly as if it had already
     been substituted, except that `%g, %u, and %U' do not currently
     support additional SUFFIX characters following `%O' as they would
     following, for example, `.o'.

`%p'
     Substitutes the standard macro predefinitions for the current
     target machine.  Use this when running `cpp'.

`%P'
     Like `%p', but puts `__' before and after the name of each
     predefined macro, except for macros that start with `__' or with
     `_L', where L is an uppercase letter.  This is for ISO C.

`%I'
     Substitute any of `-iprefix' (made from `GCC_EXEC_PREFIX'),
     `-isysroot' (made from `TARGET_SYSTEM_ROOT'), `-isystem' (made
     from `COMPILER_PATH' and `-B' options) and `-imultilib' as
     necessary.

`%s'
     Current argument is the name of a library or startup file of some
     sort.  Search for that file in a standard list of directories and
     substitute the full name found.

`%eSTR'
     Print STR as an error message.  STR is terminated by a newline.
     Use this when inconsistent options are detected.

`%(NAME)'
     Substitute the contents of spec string NAME at this point.

`%[NAME]'
     Like `%(...)' but put `__' around `-D' arguments.

`%x{OPTION}'
     Accumulate an option for `%X'.

`%X'
     Output the accumulated linker options specified by `-Wl' or a `%x'
     spec string.

`%Y'
     Output the accumulated assembler options specified by `-Wa'.

`%Z'
     Output the accumulated preprocessor options specified by `-Wp'.

`%a'
     Process the `asm' spec.  This is used to compute the switches to
     be passed to the assembler.

`%A'
     Process the `asm_final' spec.  This is a spec string for passing
     switches to an assembler post-processor, if such a program is
     needed.

`%l'
     Process the `link' spec.  This is the spec for computing the
     command line passed to the linker.  Typically it will make use of
     the `%L %G %S %D and %E' sequences.

`%D'
     Dump out a `-L' option for each directory that GCC believes might
     contain startup files.  If the target supports multilibs then the
     current multilib directory will be prepended to each of these
     paths.

`%L'
     Process the `lib' spec.  This is a spec string for deciding which
     libraries should be included on the command line to the linker.

`%G'
     Process the `libgcc' spec.  This is a spec string for deciding
     which GCC support library should be included on the command line
     to the linker.

`%S'
     Process the `startfile' spec.  This is a spec for deciding which
     object files should be the first ones passed to the linker.
     Typically this might be a file named `crt0.o'.

`%E'
     Process the `endfile' spec.  This is a spec string that specifies
     the last object files that will be passed to the linker.

`%C'
     Process the `cpp' spec.  This is used to construct the arguments
     to be passed to the C preprocessor.

`%1'
     Process the `cc1' spec.  This is used to construct the options to
     be passed to the actual C compiler (`cc1').

`%2'
     Process the `cc1plus' spec.  This is used to construct the options
     to be passed to the actual C++ compiler (`cc1plus').

`%*'
     Substitute the variable part of a matched option.  See below.
     Note that each comma in the substituted string is replaced by a
     single space.

`%<`S''
     Remove all occurrences of `-S' from the command line.  Note--this
     command is position dependent.  `%' commands in the spec string
     before this one will see `-S', `%' commands in the spec string
     after this one will not.

`%:FUNCTION(ARGS)'
     Call the named function FUNCTION, passing it ARGS.  ARGS is first
     processed as a nested spec string, then split into an argument
     vector in the usual fashion.  The function returns a string which
     is processed as if it had appeared literally as part of the
     current spec.

     The following built-in spec functions are provided:

    ``getenv''
          The `getenv' spec function takes two arguments: an environment
          variable name and a string.  If the environment variable is
          not defined, a fatal error is issued.  Otherwise, the return
          value is the value of the environment variable concatenated
          with the string.  For example, if `TOPDIR' is defined as
          `/path/to/top', then:

               %:getenv(TOPDIR /include)

          expands to `/path/to/top/include'.

    ``if-exists''
          The `if-exists' spec function takes one argument, an absolute
          pathname to a file.  If the file exists, `if-exists' returns
          the pathname.  Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s

    ``if-exists-else''
          The `if-exists-else' spec function is similar to the
          `if-exists' spec function, except that it takes two
          arguments.  The first argument is an absolute pathname to a
          file.  If the file exists, `if-exists-else' returns the
          pathname.  If it does not exist, it returns the second
          argument.  This way, `if-exists-else' can be used to select
          one file or another, based on the existence of the first.
          Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) \
               %:if-exists-else(crtbeginT%O%s crtbegin%O%s)

    ``replace-outfile''
          The `replace-outfile' spec function takes two arguments.  It
          looks for the first argument in the outfiles array and
          replaces it with the second argument.  Here is a small
          example of its usage:

               %{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)}

    ``print-asm-header''
          The `print-asm-header' function takes no arguments and simply
          prints a banner like:

               Assembler options
               =================

               Use "-Wa,OPTION" to pass "OPTION" to the assembler.

          It is used to separate compiler options from assembler options
          in the `--target-help' output.

`%{`S'}'
     Substitutes the `-S' switch, if that switch was given to GCC.  If
     that switch was not specified, this substitutes nothing.  Note that
     the leading dash is omitted when specifying this option, and it is
     automatically inserted if the substitution is performed.  Thus the
     spec string `%{foo}' would match the command-line option `-foo'
     and would output the command line option `-foo'.

`%W{`S'}'
     Like %{`S'} but mark last argument supplied within as a file to be
     deleted on failure.

`%{`S'*}'
     Substitutes all the switches specified to GCC whose names start
     with `-S', but which also take an argument.  This is used for
     switches like `-o', `-D', `-I', etc.  GCC considers `-o foo' as
     being one switch whose names starts with `o'.  %{o*} would
     substitute this text, including the space.  Thus two arguments
     would be generated.

`%{`S'*&`T'*}'
     Like %{`S'*}, but preserve order of `S' and `T' options (the order
     of `S' and `T' in the spec is not significant).  There can be any
     number of ampersand-separated variables; for each the wild card is
     optional.  Useful for CPP as `%{D*&U*&A*}'.

`%{`S':`X'}'
     Substitutes `X', if the `-S' switch was given to GCC.

`%{!`S':`X'}'
     Substitutes `X', if the `-S' switch was _not_ given to GCC.

`%{`S'*:`X'}'
     Substitutes `X' if one or more switches whose names start with
     `-S' are specified to GCC.  Normally `X' is substituted only once,
     no matter how many such switches appeared.  However, if `%*'
     appears somewhere in `X', then `X' will be substituted once for
     each matching switch, with the `%*' replaced by the part of that
     switch that matched the `*'.

`%{.`S':`X'}'
     Substitutes `X', if processing a file with suffix `S'.

`%{!.`S':`X'}'
     Substitutes `X', if _not_ processing a file with suffix `S'.

`%{,`S':`X'}'
     Substitutes `X', if processing a file for language `S'.

`%{!,`S':`X'}'
     Substitutes `X', if not processing a file for language `S'.

`%{`S'|`P':`X'}'
     Substitutes `X' if either `-S' or `-P' was given to GCC.  This may
     be combined with `!', `.', `,', and `*' sequences as well,
     although they have a stronger binding than the `|'.  If `%*'
     appears in `X', all of the alternatives must be starred, and only
     the first matching alternative is substituted.

     For example, a spec string like this:

          %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}

     will output the following command-line options from the following
     input command-line options:

          fred.c        -foo -baz
          jim.d         -bar -boggle
          -d fred.c     -foo -baz -boggle
          -d jim.d      -bar -baz -boggle

`%{S:X; T:Y; :D}'
     If `S' was given to GCC, substitutes `X'; else if `T' was given to
     GCC, substitutes `Y'; else substitutes `D'.  There can be as many
     clauses as you need.  This may be combined with `.', `,', `!',
     `|', and `*' as needed.


 The conditional text `X' in a %{`S':`X'} or similar construct may
contain other nested `%' constructs or spaces, or even newlines.  They
are processed as usual, as described above.  Trailing white space in
`X' is ignored.  White space may also appear anywhere on the left side
of the colon in these constructs, except between `.' or `*' and the
corresponding word.

 The `-O', `-f', `-m', and `-W' switches are handled specifically in
these constructs.  If another value of `-O' or the negated form of a
`-f', `-m', or `-W' switch is found later in the command line, the
earlier switch value is ignored, except with {`S'*} where `S' is just
one letter, which passes all matching options.

 The character `|' at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, but
only if `-pipe' is specified.

 It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments.  But this cannot
be done in a consistent fashion.  GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).

 GCC also knows implicitly that arguments starting in `-l' are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.

File: gcc.info,  Node: Target Options,  Next: Submodel Options,  Prev: Spec Files,  Up: Invoking GCC

3.16 Specifying Target Machine and Compiler Version
===================================================

The usual way to run GCC is to run the executable called `gcc', or
`<machine>-gcc' when cross-compiling, or `<machine>-gcc-<version>' to
run a version other than the one that was installed last.  Sometimes
this is inconvenient, so GCC provides options that will switch to
another cross-compiler or version.

`-b MACHINE'
     The argument MACHINE specifies the target machine for compilation.

     The value to use for MACHINE is the same as was specified as the
     machine type when configuring GCC as a cross-compiler.  For
     example, if a cross-compiler was configured with `configure
     arm-elf', meaning to compile for an arm processor with elf
     binaries, then you would specify `-b arm-elf' to run that cross
     compiler.  Because there are other options beginning with `-b', the
     configuration must contain a hyphen, or `-b' alone should be one
     argument followed by the configuration in the next argument.

`-V VERSION'
     The argument VERSION specifies which version of GCC to run.  This
     is useful when multiple versions are installed.  For example,
     VERSION might be `4.0', meaning to run GCC version 4.0.

 The `-V' and `-b' options work by running the
`<machine>-gcc-<version>' executable, so there's no real reason to use
them if you can just run that directly.

File: gcc.info,  Node: Invoking G++,  Next: C Dialect Options,  Prev: Overall Options,  Up: Invoking GCC

3.3 Compiling C++ Programs
==========================

C++ source files conventionally use one of the suffixes `.C', `.cc',
`.cpp', `.CPP', `.c++', `.cp', or `.cxx'; C++ header files often use
`.hh', `.hpp', `.H', or (for shared template code) `.tcc'; and
preprocessed C++ files use the suffix `.ii'.  GCC recognizes files with
these names and compiles them as C++ programs even if you call the
compiler the same way as for compiling C programs (usually with the
name `gcc').

 However, the use of `gcc' does not add the C++ library.  `g++' is a
program that calls GCC and treats `.c', `.h' and `.i' files as C++
source files instead of C source files unless `-x' is used, and
automatically specifies linking against the C++ library.  This program
is also useful when precompiling a C header file with a `.h' extension
for use in C++ compilations.  On many systems, `g++' is also installed
with the name `c++'.

 When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.  *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C.  *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.

File: gcc.info,  Node: Submodel Options,  Next: Code Gen Options,  Prev: Target Options,  Up: Invoking GCC

3.17 Hardware Models and Configurations
=======================================

Earlier we discussed the standard option `-b' which chooses among
different installed compilers for completely different target machines,
such as VAX vs. 68000 vs. 80386.

 In addition, each of these target machine types can have its own
special options, starting with `-m', to choose among various hardware
models or configurations--for example, 68010 vs 68020, floating
coprocessor or none.  A single installed version of the compiler can
compile for any model or configuration, according to the options
specified.

 Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.

* Menu:

* ARC Options::
* ARM Options::
* AVR Options::
* Blackfin Options::
* CRIS Options::
* CRX Options::
* Darwin Options::
* DEC Alpha Options::
* DEC Alpha/VMS Options::
* FR30 Options::
* FRV Options::
* GNU/Linux Options::
* H8/300 Options::
* HPPA Options::
* i386 and x86-64 Options::
* i386 and x86-64 Windows Options::
* IA-64 Options::
* M32C Options::
* M32R/D Options::
* M680x0 Options::
* M68hc1x Options::
* MCore Options::
* MIPS Options::
* MMIX Options::
* MN10300 Options::
* PDP-11 Options::
* picoChip Options::
* PowerPC Options::
* RS/6000 and PowerPC Options::
* S/390 and zSeries Options::
* Score Options::
* SH Options::
* SPARC Options::
* SPU Options::
* System V Options::
* V850 Options::
* VAX Options::
* VxWorks Options::
* x86-64 Options::
* Xstormy16 Options::
* Xtensa Options::
* zSeries Options::

File: gcc.info,  Node: ARC Options,  Next: ARM Options,  Up: Submodel Options

3.17.1 ARC Options
------------------

These options are defined for ARC implementations:

`-EL'
     Compile code for little endian mode.  This is the default.

`-EB'
     Compile code for big endian mode.

`-mmangle-cpu'
     Prepend the name of the cpu to all public symbol names.  In
     multiple-processor systems, there are many ARC variants with
     different instruction and register set characteristics.  This flag
     prevents code compiled for one cpu to be linked with code compiled
     for another.  No facility exists for handling variants that are
     "almost identical".  This is an all or nothing option.

`-mcpu=CPU'
     Compile code for ARC variant CPU.  Which variants are supported
     depend on the configuration.  All variants support `-mcpu=base',
     this is the default.

`-mtext=TEXT-SECTION'
`-mdata=DATA-SECTION'
`-mrodata=READONLY-DATA-SECTION'
     Put functions, data, and readonly data in TEXT-SECTION,
     DATA-SECTION, and READONLY-DATA-SECTION respectively by default.
     This can be overridden with the `section' attribute.  *Note
     Variable Attributes::.

`-mfix-cortex-m3-ldrd'
     Some Cortex-M3 cores can cause data corruption when `ldrd'
     instructions with overlapping destination and base registers are
     used.  This option avoids generating these instructions.  This
     option is enabled by default when `-mcpu=cortex-m3' is specified.


File: gcc.info,  Node: ARM Options,  Next: AVR Options,  Prev: ARC Options,  Up: Submodel Options

3.17.2 ARM Options
------------------

These `-m' options are defined for Advanced RISC Machines (ARM)
architectures:

`-mabi=NAME'
     Generate code for the specified ABI.  Permissible values are:
     `apcs-gnu', `atpcs', `aapcs', `aapcs-linux' and `iwmmxt'.

`-mapcs-frame'
     Generate a stack frame that is compliant with the ARM Procedure
     Call Standard for all functions, even if this is not strictly
     necessary for correct execution of the code.  Specifying
     `-fomit-frame-pointer' with this option will cause the stack
     frames not to be generated for leaf functions.  The default is
     `-mno-apcs-frame'.

`-mapcs'
     This is a synonym for `-mapcs-frame'.

`-mthumb-interwork'
     Generate code which supports calling between the ARM and Thumb
     instruction sets.  Without this option the two instruction sets
     cannot be reliably used inside one program.  The default is
     `-mno-thumb-interwork', since slightly larger code is generated
     when `-mthumb-interwork' is specified.

`-mno-sched-prolog'
     Prevent the reordering of instructions in the function prolog, or
     the merging of those instruction with the instructions in the
     function's body.  This means that all functions will start with a
     recognizable set of instructions (or in fact one of a choice from
     a small set of different function prologues), and this information
     can be used to locate the start if functions inside an executable
     piece of code.  The default is `-msched-prolog'.

`-mfloat-abi=NAME'
     Specifies which floating-point ABI to use.  Permissible values
     are: `soft', `softfp' and `hard'.

     Specifying `soft' causes GCC to generate output containing library
     calls for floating-point operations.  `softfp' allows the
     generation of code using hardware floating-point instructions, but
     still uses the soft-float calling conventions.  `hard' allows
     generation of floating-point instructions and uses FPU-specific
     calling conventions.

     Using `-mfloat-abi=hard' with VFP coprocessors is not supported.
     Use `-mfloat-abi=softfp' with the appropriate `-mfpu' option to
     allow the compiler to generate code that makes use of the hardware
     floating-point capabilities for these CPUs.

     The default depends on the specific target configuration.  Note
     that the hard-float and soft-float ABIs are not link-compatible;
     you must compile your entire program with the same ABI, and link
     with a compatible set of libraries.

`-mhard-float'
     Equivalent to `-mfloat-abi=hard'.

`-msoft-float'
     Equivalent to `-mfloat-abi=soft'.

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.  This
     is the default for all standard configurations.

`-mbig-endian'
     Generate code for a processor running in big-endian mode; the
     default is to compile code for a little-endian processor.

`-mwords-little-endian'
     This option only applies when generating code for big-endian
     processors.  Generate code for a little-endian word order but a
     big-endian byte order.  That is, a byte order of the form
     `32107654'.  Note: this option should only be used if you require
     compatibility with code for big-endian ARM processors generated by
     versions of the compiler prior to 2.8.

`-mcpu=NAME'
     This specifies the name of the target ARM processor.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  Permissible names are: `arm2', `arm250',
     `arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
     `arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
     `arm700i', `arm710', `arm710c', `arm7100', `arm720', `arm7500',
     `arm7500fe', `arm7tdmi', `arm7tdmi-s', `arm710t', `arm720t',
     `arm740t', `strongarm', `strongarm110', `strongarm1100',
     `strongarm1110', `arm8', `arm810', `arm9', `arm9e', `arm920',
     `arm920t', `arm922t', `arm946e-s', `arm966e-s', `arm968e-s',
     `arm926ej-s', `arm940t', `arm9tdmi', `arm10tdmi', `arm1020t',
     `arm1026ej-s', `arm10e', `arm1020e', `arm1022e', `arm1136j-s',
     `arm1136jf-s', `mpcore', `mpcorenovfp', `arm1156t2-s',
     `arm1176jz-s', `arm1176jzf-s', `cortex-a8', `cortex-a9',
     `cortex-r4', `cortex-r4f', `cortex-m3', `cortex-m1', `xscale',
     `iwmmxt', `iwmmxt2', `ep9312'.

`-mtune=NAME'
     This option is very similar to the `-mcpu=' option, except that
     instead of specifying the actual target processor type, and hence
     restricting which instructions can be used, it specifies that GCC
     should tune the performance of the code as if the target were of
     the type specified in this option, but still choosing the
     instructions that it will generate based on the cpu specified by a
     `-mcpu=' option.  For some ARM implementations better performance
     can be obtained by using this option.

`-march=NAME'
     This specifies the name of the target ARM architecture.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  This option can be used in conjunction
     with or instead of the `-mcpu=' option.  Permissible names are:
     `armv2', `armv2a', `armv3', `armv3m', `armv4', `armv4t', `armv5',
     `armv5t', `armv5e', `armv5te', `armv6', `armv6j', `armv6t2',
     `armv6z', `armv6zk', `armv6-m', `armv7', `armv7-a', `armv7-r',
     `armv7-m', `iwmmxt', `iwmmxt2', `ep9312'.

`-mfpu=NAME'
`-mfpe=NUMBER'
`-mfp=NUMBER'
     This specifies what floating point hardware (or hardware
     emulation) is available on the target.  Permissible names are:
     `fpa', `fpe2', `fpe3', `maverick', `vfp', `vfpv3', `vfpv3-d16' and
     `neon'.  `-mfp' and `-mfpe' are synonyms for `-mfpu'=`fpe'NUMBER,
     for compatibility with older versions of GCC.

     If `-msoft-float' is specified this specifies the format of
     floating point values.

`-mstructure-size-boundary=N'
     The size of all structures and unions will be rounded up to a
     multiple of the number of bits set by this option.  Permissible
     values are 8, 32 and 64.  The default value varies for different
     toolchains.  For the COFF targeted toolchain the default value is
     8.  A value of 64 is only allowed if the underlying ABI supports
     it.

     Specifying the larger number can produce faster, more efficient
     code, but can also increase the size of the program.  Different
     values are potentially incompatible.  Code compiled with one value
     cannot necessarily expect to work with code or libraries compiled
     with another value, if they exchange information using structures
     or unions.

`-mabort-on-noreturn'
     Generate a call to the function `abort' at the end of a `noreturn'
     function.  It will be executed if the function tries to return.

`-mlong-calls'
`-mno-long-calls'
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function will lie outside of the 64 megabyte addressing
     range of the offset based version of subroutine call instruction.

     Even if this switch is enabled, not all function calls will be
     turned into long calls.  The heuristic is that static functions,
     functions which have the `short-call' attribute, functions that
     are inside the scope of a `#pragma no_long_calls' directive and
     functions whose definitions have already been compiled within the
     current compilation unit, will not be turned into long calls.  The
     exception to this rule is that weak function definitions,
     functions with the `long-call' attribute or the `section'
     attribute, and functions that are within the scope of a `#pragma
     long_calls' directive, will always be turned into long calls.

     This feature is not enabled by default.  Specifying
     `-mno-long-calls' will restore the default behavior, as will
     placing the function calls within the scope of a `#pragma
     long_calls_off' directive.  Note these switches have no effect on
     how the compiler generates code to handle function calls via
     function pointers.

`-msingle-pic-base'
     Treat the register used for PIC addressing as read-only, rather
     than loading it in the prologue for each function.  The run-time
     system is responsible for initializing this register with an
     appropriate value before execution begins.

`-mpic-register=REG'
     Specify the register to be used for PIC addressing.  The default
     is R10 unless stack-checking is enabled, when R9 is used.

`-mcirrus-fix-invalid-insns'
     Insert NOPs into the instruction stream to in order to work around
     problems with invalid Maverick instruction combinations.  This
     option is only valid if the `-mcpu=ep9312' option has been used to
     enable generation of instructions for the Cirrus Maverick floating
     point co-processor.  This option is not enabled by default, since
     the problem is only present in older Maverick implementations.
     The default can be re-enabled by use of the
     `-mno-cirrus-fix-invalid-insns' switch.

`-mpoke-function-name'
     Write the name of each function into the text section, directly
     preceding the function prologue.  The generated code is similar to
     this:

               t0
                   .ascii "arm_poke_function_name", 0
                   .align
               t1
                   .word 0xff000000 + (t1 - t0)
               arm_poke_function_name
                   mov     ip, sp
                   stmfd   sp!, {fp, ip, lr, pc}
                   sub     fp, ip, #4

     When performing a stack backtrace, code can inspect the value of
     `pc' stored at `fp + 0'.  If the trace function then looks at
     location `pc - 12' and the top 8 bits are set, then we know that
     there is a function name embedded immediately preceding this
     location and has length `((pc[-3]) & 0xff000000)'.

`-mthumb'
     Generate code for the Thumb instruction set.  The default is to
     use the 32-bit ARM instruction set.  This option automatically
     enables either 16-bit Thumb-1 or mixed 16/32-bit Thumb-2
     instructions based on the `-mcpu=NAME' and `-march=NAME' options.

`-mtpcs-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all non-leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-tpcs-frame'.

`-mtpcs-leaf-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-apcs-leaf-frame'.

`-mcallee-super-interworking'
     Gives all externally visible functions in the file being compiled
     an ARM instruction set header which switches to Thumb mode before
     executing the rest of the function.  This allows these functions
     to be called from non-interworking code.

`-mcaller-super-interworking'
     Allows calls via function pointers (including virtual functions) to
     execute correctly regardless of whether the target code has been
     compiled for interworking or not.  There is a small overhead in
     the cost of executing a function pointer if this option is enabled.

`-mtp=NAME'
     Specify the access model for the thread local storage pointer.
     The valid models are `soft', which generates calls to
     `__aeabi_read_tp', `cp15', which fetches the thread pointer from
     `cp15' directly (supported in the arm6k architecture), and `auto',
     which uses the best available method for the selected processor.
     The default setting is `auto'.

`-mword-relocations'
     Only generate absolute relocations on word sized values (i.e.
     R_ARM_ABS32).  This is enabled by default on targets (uClinux,
     SymbianOS) where the runtime loader imposes this restriction, and
     when `-fpic' or `-fPIC' is specified.


File: gcc.info,  Node: AVR Options,  Next: Blackfin Options,  Prev: ARM Options,  Up: Submodel Options

3.17.3 AVR Options
------------------

These options are defined for AVR implementations:

`-mmcu=MCU'
     Specify ATMEL AVR instruction set or MCU type.

     Instruction set avr1 is for the minimal AVR core, not supported by
     the C compiler, only for assembler programs (MCU types: at90s1200,
     attiny10, attiny11, attiny12, attiny15, attiny28).

     Instruction set avr2 (default) is for the classic AVR core with up
     to 8K program memory space (MCU types: at90s2313, at90s2323,
     attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434,
     at90s8515, at90c8534, at90s8535).

     Instruction set avr3 is for the classic AVR core with up to 128K
     program memory space (MCU types: atmega103, atmega603, at43usb320,
     at76c711).

     Instruction set avr4 is for the enhanced AVR core with up to 8K
     program memory space (MCU types: atmega8, atmega83, atmega85).

     Instruction set avr5 is for the enhanced AVR core with up to 128K
     program memory space (MCU types: atmega16, atmega161, atmega163,
     atmega32, atmega323, atmega64, atmega128, at43usb355, at94k).

`-msize'
     Output instruction sizes to the asm file.

`-mno-interrupts'
     Generated code is not compatible with hardware interrupts.  Code
     size will be smaller.

`-mcall-prologues'
     Functions prologues/epilogues expanded as call to appropriate
     subroutines.  Code size will be smaller.

`-mno-tablejump'
     Do not generate tablejump insns which sometimes increase code size.
     The option is now deprecated in favor of the equivalent
     `-fno-jump-tables'

`-mtiny-stack'
     Change only the low 8 bits of the stack pointer.

`-mint8'
     Assume int to be 8 bit integer.  This affects the sizes of all
     types: A char will be 1 byte, an int will be 1 byte, an long will
     be 2 bytes and long long will be 4 bytes.  Please note that this
     option does not comply to the C standards, but it will provide you
     with smaller code size.

File: gcc.info,  Node: Blackfin Options,  Next: CRIS Options,  Prev: AVR Options,  Up: Submodel Options

3.17.4 Blackfin Options
-----------------------

`-mcpu=CPU[-SIREVISION]'
     Specifies the name of the target Blackfin processor.  Currently,
     CPU can be one of `bf512', `bf514', `bf516', `bf518', `bf522',
     `bf523', `bf524', `bf525', `bf526', `bf527', `bf531', `bf532',
     `bf533', `bf534', `bf536', `bf537', `bf538', `bf539', `bf542',
     `bf544', `bf547', `bf548', `bf549', `bf561'.  The optional
     SIREVISION specifies the silicon revision of the target Blackfin
     processor.  Any workarounds available for the targeted silicon
     revision will be enabled.  If SIREVISION is `none', no workarounds
     are enabled.  If SIREVISION is `any', all workarounds for the
     targeted processor will be enabled.  The `__SILICON_REVISION__'
     macro is defined to two hexadecimal digits representing the major
     and minor numbers in the silicon revision.  If SIREVISION is
     `none', the `__SILICON_REVISION__' is not defined.  If SIREVISION
     is `any', the `__SILICON_REVISION__' is defined to be `0xffff'.
     If this optional SIREVISION is not used, GCC assumes the latest
     known silicon revision of the targeted Blackfin processor.

     Support for `bf561' is incomplete.  For `bf561', Only the
     processor macro is defined.  Without this option, `bf532' is used
     as the processor by default.  The corresponding predefined
     processor macros for CPU is to be defined.  And for `bfin-elf'
     toolchain, this causes the hardware BSP provided by libgloss to be
     linked in if `-msim' is not given.

`-msim'
     Specifies that the program will be run on the simulator.  This
     causes the simulator BSP provided by libgloss to be linked in.
     This option has effect only for `bfin-elf' toolchain.  Certain
     other options, such as `-mid-shared-library' and `-mfdpic', imply
     `-msim'.

`-momit-leaf-frame-pointer'
     Don't keep the frame pointer in a register for leaf functions.
     This avoids the instructions to save, set up and restore frame
     pointers and makes an extra register available in leaf functions.
     The option `-fomit-frame-pointer' removes the frame pointer for
     all functions which might make debugging harder.

`-mspecld-anomaly'
     When enabled, the compiler will ensure that the generated code
     does not contain speculative loads after jump instructions. If
     this option is used, `__WORKAROUND_SPECULATIVE_LOADS' is defined.

`-mno-specld-anomaly'
     Don't generate extra code to prevent speculative loads from
     occurring.

`-mcsync-anomaly'
     When enabled, the compiler will ensure that the generated code
     does not contain CSYNC or SSYNC instructions too soon after
     conditional branches.  If this option is used,
     `__WORKAROUND_SPECULATIVE_SYNCS' is defined.

`-mno-csync-anomaly'
     Don't generate extra code to prevent CSYNC or SSYNC instructions
     from occurring too soon after a conditional branch.

`-mlow-64k'
     When enabled, the compiler is free to take advantage of the
     knowledge that the entire program fits into the low 64k of memory.

`-mno-low-64k'
     Assume that the program is arbitrarily large.  This is the default.

`-mstack-check-l1'
     Do stack checking using information placed into L1 scratchpad
     memory by the uClinux kernel.

`-mid-shared-library'
     Generate code that supports shared libraries via the library ID
     method.  This allows for execute in place and shared libraries in
     an environment without virtual memory management.  This option
     implies `-fPIC'.  With a `bfin-elf' target, this option implies
     `-msim'.

`-mno-id-shared-library'
     Generate code that doesn't assume ID based shared libraries are
     being used.  This is the default.

`-mleaf-id-shared-library'
     Generate code that supports shared libraries via the library ID
     method, but assumes that this library or executable won't link
     against any other ID shared libraries.  That allows the compiler
     to use faster code for jumps and calls.

`-mno-leaf-id-shared-library'
     Do not assume that the code being compiled won't link against any
     ID shared libraries.  Slower code will be generated for jump and
     call insns.

`-mshared-library-id=n'
     Specified the identification number of the ID based shared library
     being compiled.  Specifying a value of 0 will generate more
     compact code, specifying other values will force the allocation of
     that number to the current library but is no more space or time
     efficient than omitting this option.

`-msep-data'
     Generate code that allows the data segment to be located in a
     different area of memory from the text segment.  This allows for
     execute in place in an environment without virtual memory
     management by eliminating relocations against the text section.

`-mno-sep-data'
     Generate code that assumes that the data segment follows the text
     segment.  This is the default.

`-mlong-calls'
`-mno-long-calls'
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function will lie outside of the 24 bit addressing range of
     the offset based version of subroutine call instruction.

     This feature is not enabled by default.  Specifying
     `-mno-long-calls' will restore the default behavior.  Note these
     switches have no effect on how the compiler generates code to
     handle function calls via function pointers.

`-mfast-fp'
     Link with the fast floating-point library. This library relaxes
     some of the IEEE floating-point standard's rules for checking
     inputs against Not-a-Number (NAN), in the interest of performance.

`-minline-plt'
     Enable inlining of PLT entries in function calls to functions that
     are not known to bind locally.  It has no effect without `-mfdpic'.

`-mmulticore'
     Build standalone application for multicore Blackfin processor.
     Proper start files and link scripts will be used to support
     multicore.  This option defines `__BFIN_MULTICORE'. It can only be
     used with `-mcpu=bf561[-SIREVISION]'. It can be used with
     `-mcorea' or `-mcoreb'. If it's used without `-mcorea' or
     `-mcoreb', single application/dual core programming model is used.
     In this model, the main function of Core B should be named as
     coreb_main. If it's used with `-mcorea' or `-mcoreb', one
     application per core programming model is used.  If this option is
     not used, single core application programming model is used.

`-mcorea'
     Build standalone application for Core A of BF561 when using one
     application per core programming model. Proper start files and
     link scripts will be used to support Core A. This option defines
     `__BFIN_COREA'. It must be used with `-mmulticore'.

`-mcoreb'
     Build standalone application for Core B of BF561 when using one
     application per core programming model. Proper start files and
     link scripts will be used to support Core B. This option defines
     `__BFIN_COREB'. When this option is used, coreb_main should be
     used instead of main. It must be used with `-mmulticore'.

`-msdram'
     Build standalone application for SDRAM. Proper start files and
     link scripts will be used to put the application into SDRAM.
     Loader should initialize SDRAM before loading the application into
     SDRAM. This option defines `__BFIN_SDRAM'.

`-micplb'
     Assume that ICPLBs are enabled at runtime.  This has an effect on
     certain anomaly workarounds.  For Linux targets, the default is to
     assume ICPLBs are enabled; for standalone applications the default
     is off.

File: gcc.info,  Node: CRIS Options,  Next: CRX Options,  Prev: Blackfin Options,  Up: Submodel Options

3.17.5 CRIS Options
-------------------

These options are defined specifically for the CRIS ports.

`-march=ARCHITECTURE-TYPE'
`-mcpu=ARCHITECTURE-TYPE'
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are `v3', `v8' and `v10' for respectively
     ETRAX 4, ETRAX 100, and ETRAX 100 LX.  Default is `v0' except for
     cris-axis-linux-gnu, where the default is `v10'.

`-mtune=ARCHITECTURE-TYPE'
     Tune to ARCHITECTURE-TYPE everything applicable about the generated
     code, except for the ABI and the set of available instructions.
     The choices for ARCHITECTURE-TYPE are the same as for
     `-march=ARCHITECTURE-TYPE'.

`-mmax-stack-frame=N'
     Warn when the stack frame of a function exceeds N bytes.

`-metrax4'
`-metrax100'
     The options `-metrax4' and `-metrax100' are synonyms for
     `-march=v3' and `-march=v8' respectively.

`-mmul-bug-workaround'
`-mno-mul-bug-workaround'
     Work around a bug in the `muls' and `mulu' instructions for CPU
     models where it applies.  This option is active by default.

`-mpdebug'
     Enable CRIS-specific verbose debug-related information in the
     assembly code.  This option also has the effect to turn off the
     `#NO_APP' formatted-code indicator to the assembler at the
     beginning of the assembly file.

`-mcc-init'
     Do not use condition-code results from previous instruction;
     always emit compare and test instructions before use of condition
     codes.

`-mno-side-effects'
     Do not emit instructions with side-effects in addressing modes
     other than post-increment.

`-mstack-align'
`-mno-stack-align'
`-mdata-align'
`-mno-data-align'
`-mconst-align'
`-mno-const-align'
     These options (no-options) arranges (eliminate arrangements) for
     the stack-frame, individual data and constants to be aligned for
     the maximum single data access size for the chosen CPU model.  The
     default is to arrange for 32-bit alignment.  ABI details such as
     structure layout are not affected by these options.

`-m32-bit'
`-m16-bit'
`-m8-bit'
     Similar to the stack- data- and const-align options above, these
     options arrange for stack-frame, writable data and constants to
     all be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
     alignment.

`-mno-prologue-epilogue'
`-mprologue-epilogue'
     With `-mno-prologue-epilogue', the normal function prologue and
     epilogue that sets up the stack-frame are omitted and no return
     instructions or return sequences are generated in the code.  Use
     this option only together with visual inspection of the compiled
     code: no warnings or errors are generated when call-saved
     registers must be saved, or storage for local variable needs to be
     allocated.

`-mno-gotplt'
`-mgotplt'
     With `-fpic' and `-fPIC', don't generate (do generate) instruction
     sequences that load addresses for functions from the PLT part of
     the GOT rather than (traditional on other architectures) calls to
     the PLT.  The default is `-mgotplt'.

`-melf'
     Legacy no-op option only recognized with the cris-axis-elf and
     cris-axis-linux-gnu targets.

`-mlinux'
     Legacy no-op option only recognized with the cris-axis-linux-gnu
     target.

`-sim'
     This option, recognized for the cris-axis-elf arranges to link
     with input-output functions from a simulator library.  Code,
     initialized data and zero-initialized data are allocated
     consecutively.

`-sim2'
     Like `-sim', but pass linker options to locate initialized data at
     0x40000000 and zero-initialized data at 0x80000000.

File: gcc.info,  Node: CRX Options,  Next: Darwin Options,  Prev: CRIS Options,  Up: Submodel Options

3.17.6 CRX Options
------------------

These options are defined specifically for the CRX ports.

`-mmac'
     Enable the use of multiply-accumulate instructions. Disabled by
     default.

`-mpush-args'
     Push instructions will be used to pass outgoing arguments when
     functions are called. Enabled by default.

File: gcc.info,  Node: Darwin Options,  Next: DEC Alpha Options,  Prev: CRX Options,  Up: Submodel Options

3.17.7 Darwin Options
---------------------

These options are defined for all architectures running the Darwin
operating system.

 FSF GCC on Darwin does not create "fat" object files; it will create
an object file for the single architecture that it was built to target.
Apple's GCC on Darwin does create "fat" files if multiple `-arch'
options are used; it does so by running the compiler or linker multiple
times and joining the results together with `lipo'.

 The subtype of the file created (like `ppc7400' or `ppc970' or `i686')
is determined by the flags that specify the ISA that GCC is targetting,
like `-mcpu' or `-march'.  The `-force_cpusubtype_ALL' option can be
used to override this.

 The Darwin tools vary in their behavior when presented with an ISA
mismatch.  The assembler, `as', will only permit instructions to be
used that are valid for the subtype of the file it is generating, so
you cannot put 64-bit instructions in an `ppc750' object file.  The
linker for shared libraries, `/usr/bin/libtool', will fail and print an
error if asked to create a shared library with a less restrictive
subtype than its input files (for instance, trying to put a `ppc970'
object file in a `ppc7400' library).  The linker for executables, `ld',
will quietly give the executable the most restrictive subtype of any of
its input files.

`-FDIR'
     Add the framework directory DIR to the head of the list of
     directories to be searched for header files.  These directories are
     interleaved with those specified by `-I' options and are scanned
     in a left-to-right order.

     A framework directory is a directory with frameworks in it.  A
     framework is a directory with a `"Headers"' and/or
     `"PrivateHeaders"' directory contained directly in it that ends in
     `".framework"'.  The name of a framework is the name of this
     directory excluding the `".framework"'.  Headers associated with
     the framework are found in one of those two directories, with
     `"Headers"' being searched first.  A subframework is a framework
     directory that is in a framework's `"Frameworks"' directory.
     Includes of subframework headers can only appear in a header of a
     framework that contains the subframework, or in a sibling
     subframework header.  Two subframeworks are siblings if they occur
     in the same framework.  A subframework should not have the same
     name as a framework, a warning will be issued if this is violated.
     Currently a subframework cannot have subframeworks, in the future,
     the mechanism may be extended to support this.  The standard
     frameworks can be found in `"/System/Library/Frameworks"' and
     `"/Library/Frameworks"'.  An example include looks like `#include
     <Framework/header.h>', where `Framework' denotes the name of the
     framework and header.h is found in the `"PrivateHeaders"' or
     `"Headers"' directory.

`-iframeworkDIR'
     Like `-F' except the directory is a treated as a system directory.
     The main difference between this `-iframework' and `-F' is that
     with `-iframework' the compiler does not warn about constructs
     contained within header files found via DIR.  This option is valid
     only for the C family of languages.

`-gused'
     Emit debugging information for symbols that are used.  For STABS
     debugging format, this enables `-feliminate-unused-debug-symbols'.
     This is by default ON.

`-gfull'
     Emit debugging information for all symbols and types.

`-mmacosx-version-min=VERSION'
     The earliest version of MacOS X that this executable will run on
     is VERSION.  Typical values of VERSION include `10.1', `10.2', and
     `10.3.9'.

     If the compiler was built to use the system's headers by default,
     then the default for this option is the system version on which the
     compiler is running, otherwise the default is to make choices which
     are compatible with as many systems and code bases as possible.

`-mkernel'
     Enable kernel development mode.  The `-mkernel' option sets
     `-static', `-fno-common', `-fno-cxa-atexit', `-fno-exceptions',
     `-fno-non-call-exceptions', `-fapple-kext', `-fno-weak' and
     `-fno-rtti' where applicable.  This mode also sets `-mno-altivec',
     `-msoft-float', `-fno-builtin' and `-mlong-branch' for PowerPC
     targets.

`-mone-byte-bool'
     Override the defaults for `bool' so that `sizeof(bool)==1'.  By
     default `sizeof(bool)' is `4' when compiling for Darwin/PowerPC
     and `1' when compiling for Darwin/x86, so this option has no
     effect on x86.

     *Warning:* The `-mone-byte-bool' switch causes GCC to generate
     code that is not binary compatible with code generated without
     that switch.  Using this switch may require recompiling all other
     modules in a program, including system libraries.  Use this switch
     to conform to a non-default data model.

`-mfix-and-continue'
`-ffix-and-continue'
`-findirect-data'
     Generate code suitable for fast turn around development.  Needed to
     enable gdb to dynamically load `.o' files into already running
     programs.  `-findirect-data' and `-ffix-and-continue' are provided
     for backwards compatibility.

`-all_load'
     Loads all members of static archive libraries.  See man ld(1) for
     more information.

`-arch_errors_fatal'
     Cause the errors having to do with files that have the wrong
     architecture to be fatal.

`-bind_at_load'
     Causes the output file to be marked such that the dynamic linker
     will bind all undefined references when the file is loaded or
     launched.

`-bundle'
     Produce a Mach-o bundle format file.  See man ld(1) for more
     information.

`-bundle_loader EXECUTABLE'
     This option specifies the EXECUTABLE that will be loading the build
     output file being linked.  See man ld(1) for more information.

`-dynamiclib'
     When passed this option, GCC will produce a dynamic library
     instead of an executable when linking, using the Darwin `libtool'
     command.

`-force_cpusubtype_ALL'
     This causes GCC's output file to have the ALL subtype, instead of
     one controlled by the `-mcpu' or `-march' option.

`-allowable_client  CLIENT_NAME'
`-client_name'
`-compatibility_version'
`-current_version'
`-dead_strip'
`-dependency-file'
`-dylib_file'
`-dylinker_install_name'
`-dynamic'
`-exported_symbols_list'
`-filelist'
`-flat_namespace'
`-force_flat_namespace'
`-headerpad_max_install_names'
`-image_base'
`-init'
`-install_name'
`-keep_private_externs'
`-multi_module'
`-multiply_defined'
`-multiply_defined_unused'
`-noall_load'
`-no_dead_strip_inits_and_terms'
`-nofixprebinding'
`-nomultidefs'
`-noprebind'
`-noseglinkedit'
`-pagezero_size'
`-prebind'
`-prebind_all_twolevel_modules'
`-private_bundle'
`-read_only_relocs'
`-sectalign'
`-sectobjectsymbols'
`-whyload'
`-seg1addr'
`-sectcreate'
`-sectobjectsymbols'
`-sectorder'
`-segaddr'
`-segs_read_only_addr'
`-segs_read_write_addr'
`-seg_addr_table'
`-seg_addr_table_filename'
`-seglinkedit'
`-segprot'
`-segs_read_only_addr'
`-segs_read_write_addr'
`-single_module'
`-static'
`-sub_library'
`-sub_umbrella'
`-twolevel_namespace'
`-umbrella'
`-undefined'
`-unexported_symbols_list'
`-weak_reference_mismatches'
`-whatsloaded'
     These options are passed to the Darwin linker.  The Darwin linker
     man page describes them in detail.

File: gcc.info,  Node: DEC Alpha Options,  Next: DEC Alpha/VMS Options,  Prev: Darwin Options,  Up: Submodel Options

3.17.8 DEC Alpha Options
------------------------

These `-m' options are defined for the DEC Alpha implementations:

`-mno-soft-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions for
     floating-point operations.  When `-msoft-float' is specified,
     functions in `libgcc.a' will be used to perform floating-point
     operations.  Unless they are replaced by routines that emulate the
     floating-point operations, or compiled in such a way as to call
     such emulations routines, these routines will issue floating-point
     operations.   If you are compiling for an Alpha without
     floating-point operations, you must ensure that the library is
     built so as not to call them.

     Note that Alpha implementations without floating-point operations
     are required to have floating-point registers.

`-mfp-reg'
`-mno-fp-regs'
     Generate code that uses (does not use) the floating-point register
     set.  `-mno-fp-regs' implies `-msoft-float'.  If the floating-point
     register set is not used, floating point operands are passed in
     integer registers as if they were integers and floating-point
     results are passed in `$0' instead of `$f0'.  This is a
     non-standard calling sequence, so any function with a
     floating-point argument or return value called by code compiled
     with `-mno-fp-regs' must also be compiled with that option.

     A typical use of this option is building a kernel that does not
     use, and hence need not save and restore, any floating-point
     registers.

`-mieee'
     The Alpha architecture implements floating-point hardware
     optimized for maximum performance.  It is mostly compliant with
     the IEEE floating point standard.  However, for full compliance,
     software assistance is required.  This option generates code fully
     IEEE compliant code _except_ that the INEXACT-FLAG is not
     maintained (see below).  If this option is turned on, the
     preprocessor macro `_IEEE_FP' is defined during compilation.  The
     resulting code is less efficient but is able to correctly support
     denormalized numbers and exceptional IEEE values such as
     not-a-number and plus/minus infinity.  Other Alpha compilers call
     this option `-ieee_with_no_inexact'.

`-mieee-with-inexact'
     This is like `-mieee' except the generated code also maintains the
     IEEE INEXACT-FLAG.  Turning on this option causes the generated
     code to implement fully-compliant IEEE math.  In addition to
     `_IEEE_FP', `_IEEE_FP_EXACT' is defined as a preprocessor macro.
     On some Alpha implementations the resulting code may execute
     significantly slower than the code generated by default.  Since
     there is very little code that depends on the INEXACT-FLAG, you
     should normally not specify this option.  Other Alpha compilers
     call this option `-ieee_with_inexact'.

`-mfp-trap-mode=TRAP-MODE'
     This option controls what floating-point related traps are enabled.
     Other Alpha compilers call this option `-fptm TRAP-MODE'.  The
     trap mode can be set to one of four values:

    `n'
          This is the default (normal) setting.  The only traps that
          are enabled are the ones that cannot be disabled in software
          (e.g., division by zero trap).

    `u'
          In addition to the traps enabled by `n', underflow traps are
          enabled as well.

    `su'
          Like `u', but the instructions are marked to be safe for
          software completion (see Alpha architecture manual for
          details).

    `sui'
          Like `su', but inexact traps are enabled as well.

`-mfp-rounding-mode=ROUNDING-MODE'
     Selects the IEEE rounding mode.  Other Alpha compilers call this
     option `-fprm ROUNDING-MODE'.  The ROUNDING-MODE can be one of:

    `n'
          Normal IEEE rounding mode.  Floating point numbers are
          rounded towards the nearest machine number or towards the
          even machine number in case of a tie.

    `m'
          Round towards minus infinity.

    `c'
          Chopped rounding mode.  Floating point numbers are rounded
          towards zero.

    `d'
          Dynamic rounding mode.  A field in the floating point control
          register (FPCR, see Alpha architecture reference manual)
          controls the rounding mode in effect.  The C library
          initializes this register for rounding towards plus infinity.
          Thus, unless your program modifies the FPCR, `d' corresponds
          to round towards plus infinity.

`-mtrap-precision=TRAP-PRECISION'
     In the Alpha architecture, floating point traps are imprecise.
     This means without software assistance it is impossible to recover
     from a floating trap and program execution normally needs to be
     terminated.  GCC can generate code that can assist operating
     system trap handlers in determining the exact location that caused
     a floating point trap.  Depending on the requirements of an
     application, different levels of precisions can be selected:

    `p'
          Program precision.  This option is the default and means a
          trap handler can only identify which program caused a
          floating point exception.

    `f'
          Function precision.  The trap handler can determine the
          function that caused a floating point exception.

    `i'
          Instruction precision.  The trap handler can determine the
          exact instruction that caused a floating point exception.

     Other Alpha compilers provide the equivalent options called
     `-scope_safe' and `-resumption_safe'.

`-mieee-conformant'
     This option marks the generated code as IEEE conformant.  You must
     not use this option unless you also specify `-mtrap-precision=i'
     and either `-mfp-trap-mode=su' or `-mfp-trap-mode=sui'.  Its only
     effect is to emit the line `.eflag 48' in the function prologue of
     the generated assembly file.  Under DEC Unix, this has the effect
     that IEEE-conformant math library routines will be linked in.

`-mbuild-constants'
     Normally GCC examines a 32- or 64-bit integer constant to see if
     it can construct it from smaller constants in two or three
     instructions.  If it cannot, it will output the constant as a
     literal and generate code to load it from the data segment at
     runtime.

     Use this option to require GCC to construct _all_ integer constants
     using code, even if it takes more instructions (the maximum is
     six).

     You would typically use this option to build a shared library
     dynamic loader.  Itself a shared library, it must relocate itself
     in memory before it can find the variables and constants in its
     own data segment.

`-malpha-as'
`-mgas'
     Select whether to generate code to be assembled by the
     vendor-supplied assembler (`-malpha-as') or by the GNU assembler
     `-mgas'.

`-mbwx'
`-mno-bwx'
`-mcix'
`-mno-cix'
`-mfix'
`-mno-fix'
`-mmax'
`-mno-max'
     Indicate whether GCC should generate code to use the optional BWX,
     CIX, FIX and MAX instruction sets.  The default is to use the
     instruction sets supported by the CPU type specified via `-mcpu='
     option or that of the CPU on which GCC was built if none was
     specified.

`-mfloat-vax'
`-mfloat-ieee'
     Generate code that uses (does not use) VAX F and G floating point
     arithmetic instead of IEEE single and double precision.

`-mexplicit-relocs'
`-mno-explicit-relocs'
     Older Alpha assemblers provided no way to generate symbol
     relocations except via assembler macros.  Use of these macros does
     not allow optimal instruction scheduling.  GNU binutils as of
     version 2.12 supports a new syntax that allows the compiler to
     explicitly mark which relocations should apply to which
     instructions.  This option is mostly useful for debugging, as GCC
     detects the capabilities of the assembler when it is built and
     sets the default accordingly.

`-msmall-data'
`-mlarge-data'
     When `-mexplicit-relocs' is in effect, static data is accessed via
     "gp-relative" relocations.  When `-msmall-data' is used, objects 8
     bytes long or smaller are placed in a "small data area" (the
     `.sdata' and `.sbss' sections) and are accessed via 16-bit
     relocations off of the `$gp' register.  This limits the size of
     the small data area to 64KB, but allows the variables to be
     directly accessed via a single instruction.

     The default is `-mlarge-data'.  With this option the data area is
     limited to just below 2GB.  Programs that require more than 2GB of
     data must use `malloc' or `mmap' to allocate the data in the heap
     instead of in the program's data segment.

     When generating code for shared libraries, `-fpic' implies
     `-msmall-data' and `-fPIC' implies `-mlarge-data'.

`-msmall-text'
`-mlarge-text'
     When `-msmall-text' is used, the compiler assumes that the code of
     the entire program (or shared library) fits in 4MB, and is thus
     reachable with a branch instruction.  When `-msmall-data' is used,
     the compiler can assume that all local symbols share the same
     `$gp' value, and thus reduce the number of instructions required
     for a function call from 4 to 1.

     The default is `-mlarge-text'.

`-mcpu=CPU_TYPE'
     Set the instruction set and instruction scheduling parameters for
     machine type CPU_TYPE.  You can specify either the `EV' style name
     or the corresponding chip number.  GCC supports scheduling
     parameters for the EV4, EV5 and EV6 family of processors and will
     choose the default values for the instruction set from the
     processor you specify.  If you do not specify a processor type,
     GCC will default to the processor on which the compiler was built.

     Supported values for CPU_TYPE are

    `ev4'
    `ev45'
    `21064'
          Schedules as an EV4 and has no instruction set extensions.

    `ev5'
    `21164'
          Schedules as an EV5 and has no instruction set extensions.

    `ev56'
    `21164a'
          Schedules as an EV5 and supports the BWX extension.

    `pca56'
    `21164pc'
    `21164PC'
          Schedules as an EV5 and supports the BWX and MAX extensions.

    `ev6'
    `21264'
          Schedules as an EV6 and supports the BWX, FIX, and MAX
          extensions.

    `ev67'
    `21264a'
          Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
          extensions.

     Native Linux/GNU toolchains also support the value `native', which
     selects the best architecture option for the host processor.
     `-mcpu=native' has no effect if GCC does not recognize the
     processor.

`-mtune=CPU_TYPE'
     Set only the instruction scheduling parameters for machine type
     CPU_TYPE.  The instruction set is not changed.

     Native Linux/GNU toolchains also support the value `native', which
     selects the best architecture option for the host processor.
     `-mtune=native' has no effect if GCC does not recognize the
     processor.

`-mmemory-latency=TIME'
     Sets the latency the scheduler should assume for typical memory
     references as seen by the application.  This number is highly
     dependent on the memory access patterns used by the application
     and the size of the external cache on the machine.

     Valid options for TIME are

    `NUMBER'
          A decimal number representing clock cycles.

    `L1'
    `L2'
    `L3'
    `main'
          The compiler contains estimates of the number of clock cycles
          for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
          (also called Dcache, Scache, and Bcache), as well as to main
          memory.  Note that L3 is only valid for EV5.


File: gcc.info,  Node: DEC Alpha/VMS Options,  Next: FR30 Options,  Prev: DEC Alpha Options,  Up: Submodel Options

3.17.9 DEC Alpha/VMS Options
----------------------------

These `-m' options are defined for the DEC Alpha/VMS implementations:

`-mvms-return-codes'
     Return VMS condition codes from main.  The default is to return
     POSIX style condition (e.g. error) codes.

File: gcc.info,  Node: FR30 Options,  Next: FRV Options,  Prev: DEC Alpha/VMS Options,  Up: Submodel Options

3.17.10 FR30 Options
--------------------

These options are defined specifically for the FR30 port.

`-msmall-model'
     Use the small address space model.  This can produce smaller code,
     but it does assume that all symbolic values and addresses will fit
     into a 20-bit range.

`-mno-lsim'
     Assume that run-time support has been provided and so there is no
     need to include the simulator library (`libsim.a') on the linker
     command line.


File: gcc.info,  Node: FRV Options,  Next: GNU/Linux Options,  Prev: FR30 Options,  Up: Submodel Options

3.17.11 FRV Options
-------------------

`-mgpr-32'
     Only use the first 32 general purpose registers.

`-mgpr-64'
     Use all 64 general purpose registers.

`-mfpr-32'
     Use only the first 32 floating point registers.

`-mfpr-64'
     Use all 64 floating point registers

`-mhard-float'
     Use hardware instructions for floating point operations.

`-msoft-float'
     Use library routines for floating point operations.

`-malloc-cc'
     Dynamically allocate condition code registers.

`-mfixed-cc'
     Do not try to dynamically allocate condition code registers, only
     use `icc0' and `fcc0'.

`-mdword'
     Change ABI to use double word insns.

`-mno-dword'
     Do not use double word instructions.

`-mdouble'
     Use floating point double instructions.

`-mno-double'
     Do not use floating point double instructions.

`-mmedia'
     Use media instructions.

`-mno-media'
     Do not use media instructions.

`-mmuladd'
     Use multiply and add/subtract instructions.

`-mno-muladd'
     Do not use multiply and add/subtract instructions.

`-mfdpic'
     Select the FDPIC ABI, that uses function descriptors to represent
     pointers to functions.  Without any PIC/PIE-related options, it
     implies `-fPIE'.  With `-fpic' or `-fpie', it assumes GOT entries
     and small data are within a 12-bit range from the GOT base
     address; with `-fPIC' or `-fPIE', GOT offsets are computed with 32
     bits.  With a `bfin-elf' target, this option implies `-msim'.

`-minline-plt'
     Enable inlining of PLT entries in function calls to functions that
     are not known to bind locally.  It has no effect without `-mfdpic'.
     It's enabled by default if optimizing for speed and compiling for
     shared libraries (i.e., `-fPIC' or `-fpic'), or when an
     optimization option such as `-O3' or above is present in the
     command line.

`-mTLS'
     Assume a large TLS segment when generating thread-local code.

`-mtls'
     Do not assume a large TLS segment when generating thread-local
     code.

`-mgprel-ro'
     Enable the use of `GPREL' relocations in the FDPIC ABI for data
     that is known to be in read-only sections.  It's enabled by
     default, except for `-fpic' or `-fpie': even though it may help
     make the global offset table smaller, it trades 1 instruction for
     4.  With `-fPIC' or `-fPIE', it trades 3 instructions for 4, one
     of which may be shared by multiple symbols, and it avoids the need
     for a GOT entry for the referenced symbol, so it's more likely to
     be a win.  If it is not, `-mno-gprel-ro' can be used to disable it.

`-multilib-library-pic'
     Link with the (library, not FD) pic libraries.  It's implied by
     `-mlibrary-pic', as well as by `-fPIC' and `-fpic' without
     `-mfdpic'.  You should never have to use it explicitly.

`-mlinked-fp'
     Follow the EABI requirement of always creating a frame pointer
     whenever a stack frame is allocated.  This option is enabled by
     default and can be disabled with `-mno-linked-fp'.

`-mlong-calls'
     Use indirect addressing to call functions outside the current
     compilation unit.  This allows the functions to be placed anywhere
     within the 32-bit address space.

`-malign-labels'
     Try to align labels to an 8-byte boundary by inserting nops into
     the previous packet.  This option only has an effect when VLIW
     packing is enabled.  It doesn't create new packets; it merely adds
     nops to existing ones.

`-mlibrary-pic'
     Generate position-independent EABI code.

`-macc-4'
     Use only the first four media accumulator registers.

`-macc-8'
     Use all eight media accumulator registers.

`-mpack'
     Pack VLIW instructions.

`-mno-pack'
     Do not pack VLIW instructions.

`-mno-eflags'
     Do not mark ABI switches in e_flags.

`-mcond-move'
     Enable the use of conditional-move instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-cond-move'
     Disable the use of conditional-move instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mscc'
     Enable the use of conditional set instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-scc'
     Disable the use of conditional set instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mcond-exec'
     Enable the use of conditional execution (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-cond-exec'
     Disable the use of conditional execution.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mvliw-branch'
     Run a pass to pack branches into VLIW instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-vliw-branch'
     Do not run a pass to pack branches into VLIW instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mmulti-cond-exec'
     Enable optimization of `&&' and `||' in conditional execution
     (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-multi-cond-exec'
     Disable optimization of `&&' and `||' in conditional execution.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mnested-cond-exec'
     Enable nested conditional execution optimizations (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-nested-cond-exec'
     Disable nested conditional execution optimizations.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-moptimize-membar'
     This switch removes redundant `membar' instructions from the
     compiler generated code.  It is enabled by default.

`-mno-optimize-membar'
     This switch disables the automatic removal of redundant `membar'
     instructions from the generated code.

`-mtomcat-stats'
     Cause gas to print out tomcat statistics.

`-mcpu=CPU'
     Select the processor type for which to generate code.  Possible
     values are `frv', `fr550', `tomcat', `fr500', `fr450', `fr405',
     `fr400', `fr300' and `simple'.


File: gcc.info,  Node: GNU/Linux Options,  Next: H8/300 Options,  Prev: FRV Options,  Up: Submodel Options

3.17.12 GNU/Linux Options
-------------------------

These `-m' options are defined for GNU/Linux targets:

`-mglibc'
     Use the GNU C library instead of uClibc.  This is the default
     except on `*-*-linux-*uclibc*' targets.

`-muclibc'
     Use uClibc instead of the GNU C library.  This is the default on
     `*-*-linux-*uclibc*' targets.

File: gcc.info,  Node: H8/300 Options,  Next: HPPA Options,  Prev: GNU/Linux Options,  Up: Submodel Options

3.17.13 H8/300 Options
----------------------

These `-m' options are defined for the H8/300 implementations:

`-mrelax'
     Shorten some address references at link time, when possible; uses
     the linker option `-relax'.  *Note `ld' and the H8/300:
     (ld)H8/300, for a fuller description.

`-mh'
     Generate code for the H8/300H.

`-ms'
     Generate code for the H8S.

`-mn'
     Generate code for the H8S and H8/300H in the normal mode.  This
     switch must be used either with `-mh' or `-ms'.

`-ms2600'
     Generate code for the H8S/2600.  This switch must be used with
     `-ms'.

`-mint32'
     Make `int' data 32 bits by default.

`-malign-300'
     On the H8/300H and H8S, use the same alignment rules as for the
     H8/300.  The default for the H8/300H and H8S is to align longs and
     floats on 4 byte boundaries.  `-malign-300' causes them to be
     aligned on 2 byte boundaries.  This option has no effect on the
     H8/300.

File: gcc.info,  Node: HPPA Options,  Next: i386 and x86-64 Options,  Prev: H8/300 Options,  Up: Submodel Options

3.17.14 HPPA Options
--------------------

These `-m' options are defined for the HPPA family of computers:

`-march=ARCHITECTURE-TYPE'
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are `1.0' for PA 1.0, `1.1' for PA 1.1, and
     `2.0' for PA 2.0 processors.  Refer to `/usr/lib/sched.models' on
     an HP-UX system to determine the proper architecture option for
     your machine.  Code compiled for lower numbered architectures will
     run on higher numbered architectures, but not the other way around.

`-mpa-risc-1-0'
`-mpa-risc-1-1'
`-mpa-risc-2-0'
     Synonyms for `-march=1.0', `-march=1.1', and `-march=2.0'
     respectively.

`-mbig-switch'
     Generate code suitable for big switch tables.  Use this option
     only if the assembler/linker complain about out of range branches
     within a switch table.

`-mjump-in-delay'
     Fill delay slots of function calls with unconditional jump
     instructions by modifying the return pointer for the function call
     to be the target of the conditional jump.

`-mdisable-fpregs'
     Prevent floating point registers from being used in any manner.
     This is necessary for compiling kernels which perform lazy context
     switching of floating point registers.  If you use this option and
     attempt to perform floating point operations, the compiler will
     abort.

`-mdisable-indexing'
     Prevent the compiler from using indexing address modes.  This
     avoids some rather obscure problems when compiling MIG generated
     code under MACH.

`-mno-space-regs'
     Generate code that assumes the target has no space registers.
     This allows GCC to generate faster indirect calls and use unscaled
     index address modes.

     Such code is suitable for level 0 PA systems and kernels.

`-mfast-indirect-calls'
     Generate code that assumes calls never cross space boundaries.
     This allows GCC to emit code which performs faster indirect calls.

     This option will not work in the presence of shared libraries or
     nested functions.

`-mfixed-range=REGISTER-RANGE'
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator can not use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

`-mlong-load-store'
     Generate 3-instruction load and store sequences as sometimes
     required by the HP-UX 10 linker.  This is equivalent to the `+k'
     option to the HP compilers.

`-mportable-runtime'
     Use the portable calling conventions proposed by HP for ELF
     systems.

`-mgas'
     Enable the use of assembler directives only GAS understands.

`-mschedule=CPU-TYPE'
     Schedule code according to the constraints for the machine type
     CPU-TYPE.  The choices for CPU-TYPE are `700' `7100', `7100LC',
     `7200', `7300' and `8000'.  Refer to `/usr/lib/sched.models' on an
     HP-UX system to determine the proper scheduling option for your
     machine.  The default scheduling is `8000'.

`-mlinker-opt'
     Enable the optimization pass in the HP-UX linker.  Note this makes
     symbolic debugging impossible.  It also triggers a bug in the
     HP-UX 8 and HP-UX 9 linkers in which they give bogus error
     messages when linking some programs.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all HPPA
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this cannot be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GCC, with `-msoft-float' in order for this
     to work.

`-msio'
     Generate the predefine, `_SIO', for server IO.  The default is
     `-mwsio'.  This generates the predefines, `__hp9000s700',
     `__hp9000s700__' and `_WSIO', for workstation IO.  These options
     are available under HP-UX and HI-UX.

`-mgnu-ld'
     Use GNU ld specific options.  This passes `-shared' to ld when
     building a shared library.  It is the default when GCC is
     configured, explicitly or implicitly, with the GNU linker.  This
     option does not have any affect on which ld is called, it only
     changes what parameters are passed to that ld.  The ld that is
     called is determined by the `--with-ld' configure option, GCC's
     program search path, and finally by the user's `PATH'.  The linker
     used by GCC can be printed using `which `gcc
     -print-prog-name=ld`'.  This option is only available on the 64
     bit HP-UX GCC, i.e. configured with `hppa*64*-*-hpux*'.

`-mhp-ld'
     Use HP ld specific options.  This passes `-b' to ld when building
     a shared library and passes `+Accept TypeMismatch' to ld on all
     links.  It is the default when GCC is configured, explicitly or
     implicitly, with the HP linker.  This option does not have any
     affect on which ld is called, it only changes what parameters are
     passed to that ld.  The ld that is called is determined by the
     `--with-ld' configure option, GCC's program search path, and
     finally by the user's `PATH'.  The linker used by GCC can be
     printed using `which `gcc -print-prog-name=ld`'.  This option is
     only available on the 64 bit HP-UX GCC, i.e. configured with
     `hppa*64*-*-hpux*'.

`-mlong-calls'
     Generate code that uses long call sequences.  This ensures that a
     call is always able to reach linker generated stubs.  The default
     is to generate long calls only when the distance from the call
     site to the beginning of the function or translation unit, as the
     case may be, exceeds a predefined limit set by the branch type
     being used.  The limits for normal calls are 7,600,000 and 240,000
     bytes, respectively for the PA 2.0 and PA 1.X architectures.
     Sibcalls are always limited at 240,000 bytes.

     Distances are measured from the beginning of functions when using
     the `-ffunction-sections' option, or when using the `-mgas' and
     `-mno-portable-runtime' options together under HP-UX with the SOM
     linker.

     It is normally not desirable to use this option as it will degrade
     performance.  However, it may be useful in large applications,
     particularly when partial linking is used to build the application.

     The types of long calls used depends on the capabilities of the
     assembler and linker, and the type of code being generated.  The
     impact on systems that support long absolute calls, and long pic
     symbol-difference or pc-relative calls should be relatively small.
     However, an indirect call is used on 32-bit ELF systems in pic code
     and it is quite long.

`-munix=UNIX-STD'
     Generate compiler predefines and select a startfile for the
     specified UNIX standard.  The choices for UNIX-STD are `93', `95'
     and `98'.  `93' is supported on all HP-UX versions.  `95' is
     available on HP-UX 10.10 and later.  `98' is available on HP-UX
     11.11 and later.  The default values are `93' for HP-UX 10.00,
     `95' for HP-UX 10.10 though to 11.00, and `98' for HP-UX 11.11 and
     later.

     `-munix=93' provides the same predefines as GCC 3.3 and 3.4.
     `-munix=95' provides additional predefines for `XOPEN_UNIX' and
     `_XOPEN_SOURCE_EXTENDED', and the startfile `unix95.o'.
     `-munix=98' provides additional predefines for `_XOPEN_UNIX',
     `_XOPEN_SOURCE_EXTENDED', `_INCLUDE__STDC_A1_SOURCE' and
     `_INCLUDE_XOPEN_SOURCE_500', and the startfile `unix98.o'.

     It is _important_ to note that this option changes the interfaces
     for various library routines.  It also affects the operational
     behavior of the C library.  Thus, _extreme_ care is needed in
     using this option.

     Library code that is intended to operate with more than one UNIX
     standard must test, set and restore the variable
     __XPG4_EXTENDED_MASK as appropriate.  Most GNU software doesn't
     provide this capability.

`-nolibdld'
     Suppress the generation of link options to search libdld.sl when
     the `-static' option is specified on HP-UX 10 and later.

`-static'
     The HP-UX implementation of setlocale in libc has a dependency on
     libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
     when the `-static' option is specified, special link options are
     needed to resolve this dependency.

     On HP-UX 10 and later, the GCC driver adds the necessary options to
     link with libdld.sl when the `-static' option is specified.  This
     causes the resulting binary to be dynamic.  On the 64-bit port,
     the linkers generate dynamic binaries by default in any case.  The
     `-nolibdld' option can be used to prevent the GCC driver from
     adding these link options.

`-threads'
     Add support for multithreading with the "dce thread" library under
     HP-UX.  This option sets flags for both the preprocessor and
     linker.

File: gcc.info,  Node: i386 and x86-64 Options,  Next: i386 and x86-64 Windows Options,  Prev: HPPA Options,  Up: Submodel Options

3.17.15 Intel 386 and AMD x86-64 Options
----------------------------------------

These `-m' options are defined for the i386 and x86-64 family of
computers:

`-mtune=CPU-TYPE'
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  The
     choices for CPU-TYPE are:
    _generic_
          Produce code optimized for the most common IA32/AMD64/EM64T
          processors.  If you know the CPU on which your code will run,
          then you should use the corresponding `-mtune' option instead
          of `-mtune=generic'.  But, if you do not know exactly what
          CPU users of your application will have, then you should use
          this option.

          As new processors are deployed in the marketplace, the
          behavior of this option will change.  Therefore, if you
          upgrade to a newer version of GCC, the code generated option
          will change to reflect the processors that were most common
          when that version of GCC was released.

          There is no `-march=generic' option because `-march'
          indicates the instruction set the compiler can use, and there
          is no generic instruction set applicable to all processors.
          In contrast, `-mtune' indicates the processor (or, in this
          case, collection of processors) for which the code is
          optimized.

    _native_
          This selects the CPU to tune for at compilation time by
          determining the processor type of the compiling machine.
          Using `-mtune=native' will produce code optimized for the
          local machine under the constraints of the selected
          instruction set.  Using `-march=native' will enable all
          instruction subsets supported by the local machine (hence the
          result might not run on different machines).

    _i386_
          Original Intel's i386 CPU.

    _i486_
          Intel's i486 CPU.  (No scheduling is implemented for this
          chip.)

    _i586, pentium_
          Intel Pentium CPU with no MMX support.

    _pentium-mmx_
          Intel PentiumMMX CPU based on Pentium core with MMX
          instruction set support.

    _pentiumpro_
          Intel PentiumPro CPU.

    _i686_
          Same as `generic', but when used as `march' option, PentiumPro
          instruction set will be used, so the code will run on all
          i686 family chips.

    _pentium2_
          Intel Pentium2 CPU based on PentiumPro core with MMX
          instruction set support.

    _pentium3, pentium3m_
          Intel Pentium3 CPU based on PentiumPro core with MMX and SSE
          instruction set support.

    _pentium-m_
          Low power version of Intel Pentium3 CPU with MMX, SSE and
          SSE2 instruction set support.  Used by Centrino notebooks.

    _pentium4, pentium4m_
          Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set
          support.

    _prescott_
          Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2
          and SSE3 instruction set support.

    _nocona_
          Improved version of Intel Pentium4 CPU with 64-bit
          extensions, MMX, SSE, SSE2 and SSE3 instruction set support.

    _core2_
          Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3
          and SSSE3 instruction set support.

    _k6_
          AMD K6 CPU with MMX instruction set support.

    _k6-2, k6-3_
          Improved versions of AMD K6 CPU with MMX and 3dNOW!
          instruction set support.

    _athlon, athlon-tbird_
          AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE
          prefetch instructions support.

    _athlon-4, athlon-xp, athlon-mp_
          Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and
          full SSE instruction set support.

    _k8, opteron, athlon64, athlon-fx_
          AMD K8 core based CPUs with x86-64 instruction set support.
          (This supersets MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and
          64-bit instruction set extensions.)

    _k8-sse3, opteron-sse3, athlon64-sse3_
          Improved versions of k8, opteron and athlon64 with SSE3
          instruction set support.

    _amdfam10, barcelona_
          AMD Family 10h core based CPUs with x86-64 instruction set
          support.  (This supersets MMX, SSE, SSE2, SSE3, SSE4A,
          3dNOW!, enhanced 3dNOW!, ABM and 64-bit instruction set
          extensions.)

    _winchip-c6_
          IDT Winchip C6 CPU, dealt in same way as i486 with additional
          MMX instruction set support.

    _winchip2_
          IDT Winchip2 CPU, dealt in same way as i486 with additional
          MMX and 3dNOW!  instruction set support.

    _c3_
          Via C3 CPU with MMX and 3dNOW! instruction set support.  (No
          scheduling is implemented for this chip.)

    _c3-2_
          Via C3-2 CPU with MMX and SSE instruction set support.  (No
          scheduling is implemented for this chip.)

    _geode_
          Embedded AMD CPU with MMX and 3dNOW! instruction set support.

     While picking a specific CPU-TYPE will schedule things
     appropriately for that particular chip, the compiler will not
     generate any code that does not run on the i386 without the
     `-march=CPU-TYPE' option being used.

`-march=CPU-TYPE'
     Generate instructions for the machine type CPU-TYPE.  The choices
     for CPU-TYPE are the same as for `-mtune'.  Moreover, specifying
     `-march=CPU-TYPE' implies `-mtune=CPU-TYPE'.

`-mcpu=CPU-TYPE'
     A deprecated synonym for `-mtune'.

`-mfpmath=UNIT'
     Generate floating point arithmetics for selected unit UNIT.  The
     choices for UNIT are:

    `387'
          Use the standard 387 floating point coprocessor present
          majority of chips and emulated otherwise.  Code compiled with
          this option will run almost everywhere.  The temporary
          results are computed in 80bit precision instead of precision
          specified by the type resulting in slightly different results
          compared to most of other chips.  See `-ffloat-store' for
          more detailed description.

          This is the default choice for i386 compiler.

    `sse'
          Use scalar floating point instructions present in the SSE
          instruction set.  This instruction set is supported by
          Pentium3 and newer chips, in the AMD line by Athlon-4,
          Athlon-xp and Athlon-mp chips.  The earlier version of SSE
          instruction set supports only single precision arithmetics,
          thus the double and extended precision arithmetics is still
          done using 387.  Later version, present only in Pentium4 and
          the future AMD x86-64 chips supports double precision
          arithmetics too.

          For the i386 compiler, you need to use `-march=CPU-TYPE',
          `-msse' or `-msse2' switches to enable SSE extensions and
          make this option effective.  For the x86-64 compiler, these
          extensions are enabled by default.

          The resulting code should be considerably faster in the
          majority of cases and avoid the numerical instability
          problems of 387 code, but may break some existing code that
          expects temporaries to be 80bit.

          This is the default choice for the x86-64 compiler.

    `sse,387'
    `sse+387'
    `both'
          Attempt to utilize both instruction sets at once.  This
          effectively double the amount of available registers and on
          chips with separate execution units for 387 and SSE the
          execution resources too.  Use this option with care, as it is
          still experimental, because the GCC register allocator does
          not model separate functional units well resulting in
          instable performance.

`-masm=DIALECT'
     Output asm instructions using selected DIALECT.  Supported choices
     are `intel' or `att' (the default one).  Darwin does not support
     `intel'.

`-mieee-fp'
`-mno-ieee-fp'
     Control whether or not the compiler uses IEEE floating point
     comparisons.  These handle correctly the case where the result of a
     comparison is unordered.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GCC.  Normally
     the facilities of the machine's usual C compiler are used, but
     this can't be done directly in cross-compilation.  You must make
     your own arrangements to provide suitable library functions for
     cross-compilation.

     On machines where a function returns floating point results in the
     80387 register stack, some floating point opcodes may be emitted
     even if `-msoft-float' is used.

`-mno-fp-ret-in-387'
     Do not use the FPU registers for return values of functions.

     The usual calling convention has functions return values of types
     `float' and `double' in an FPU register, even if there is no FPU.
     The idea is that the operating system should emulate an FPU.

     The option `-mno-fp-ret-in-387' causes such values to be returned
     in ordinary CPU registers instead.

`-mno-fancy-math-387'
     Some 387 emulators do not support the `sin', `cos' and `sqrt'
     instructions for the 387.  Specify this option to avoid generating
     those instructions.  This option is the default on FreeBSD,
     OpenBSD and NetBSD.  This option is overridden when `-march'
     indicates that the target cpu will always have an FPU and so the
     instruction will not need emulation.  As of revision 2.6.1, these
     instructions are not generated unless you also use the
     `-funsafe-math-optimizations' switch.

`-malign-double'
`-mno-align-double'
     Control whether GCC aligns `double', `long double', and `long
     long' variables on a two word boundary or a one word boundary.
     Aligning `double' variables on a two word boundary will produce
     code that runs somewhat faster on a `Pentium' at the expense of
     more memory.

     On x86-64, `-malign-double' is enabled by default.

     *Warning:* if you use the `-malign-double' switch, structures
     containing the above types will be aligned differently than the
     published application binary interface specifications for the 386
     and will not be binary compatible with structures in code compiled
     without that switch.

`-m96bit-long-double'
`-m128bit-long-double'
     These switches control the size of `long double' type.  The i386
     application binary interface specifies the size to be 96 bits, so
     `-m96bit-long-double' is the default in 32 bit mode.

     Modern architectures (Pentium and newer) would prefer `long double'
     to be aligned to an 8 or 16 byte boundary.  In arrays or structures
     conforming to the ABI, this would not be possible.  So specifying a
     `-m128bit-long-double' will align `long double' to a 16 byte
     boundary by padding the `long double' with an additional 32 bit
     zero.

     In the x86-64 compiler, `-m128bit-long-double' is the default
     choice as its ABI specifies that `long double' is to be aligned on
     16 byte boundary.

     Notice that neither of these options enable any extra precision
     over the x87 standard of 80 bits for a `long double'.

     *Warning:* if you override the default value for your target ABI,
     the structures and arrays containing `long double' variables will
     change their size as well as function calling convention for
     function taking `long double' will be modified.  Hence they will
     not be binary compatible with arrays or structures in code
     compiled without that switch.

`-mlarge-data-threshold=NUMBER'
     When `-mcmodel=medium' is specified, the data greater than
     THRESHOLD are placed in large data section.  This value must be the
     same across all object linked into the binary and defaults to
     65535.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the `ret' NUM
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     You can specify that an individual function is called with this
     calling sequence with the function attribute `stdcall'.  You can
     also override the `-mrtd' option by using the function attribute
     `cdecl'.  *Note Function Attributes::.

     *Warning:* this calling convention is incompatible with the one
     normally used on Unix, so you cannot use it if you need to call
     libraries compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

`-mregparm=NUM'
     Control how many registers are used to pass integer arguments.  By
     default, no registers are used to pass arguments, and at most 3
     registers can be used.  You can control this behavior for a
     specific function by using the function attribute `regparm'.
     *Note Function Attributes::.

     *Warning:* if you use this switch, and NUM is nonzero, then you
     must build all modules with the same value, including any
     libraries.  This includes the system libraries and startup modules.

`-msseregparm'
     Use SSE register passing conventions for float and double arguments
     and return values.  You can control this behavior for a specific
     function by using the function attribute `sseregparm'.  *Note
     Function Attributes::.

     *Warning:* if you use this switch then you must build all modules
     with the same value, including any libraries.  This includes the
     system libraries and startup modules.

`-mpc32'
`-mpc64'
`-mpc80'
     Set 80387 floating-point precision to 32, 64 or 80 bits.  When
     `-mpc32' is specified, the significands of results of
     floating-point operations are rounded to 24 bits (single
     precision); `-mpc64' rounds the significands of results of
     floating-point operations to 53 bits (double precision) and
     `-mpc80' rounds the significands of results of floating-point
     operations to 64 bits (extended double precision), which is the
     default.  When this option is used, floating-point operations in
     higher precisions are not available to the programmer without
     setting the FPU control word explicitly.

     Setting the rounding of floating-point operations to less than the
     default 80 bits can speed some programs by 2% or more.  Note that
     some mathematical libraries assume that extended precision (80
     bit) floating-point operations are enabled by default; routines in
     such libraries could suffer significant loss of accuracy,
     typically through so-called "catastrophic cancellation", when this
     option is used to set the precision to less than extended
     precision.

`-mstackrealign'
     Realign the stack at entry.  On the Intel x86, the `-mstackrealign'
     option will generate an alternate prologue and epilogue that
     realigns the runtime stack if necessary.  This supports mixing
     legacy codes that keep a 4-byte aligned stack with modern codes
     that keep a 16-byte stack for SSE compatibility.  See also the
     attribute `force_align_arg_pointer', applicable to individual
     functions.

`-mpreferred-stack-boundary=NUM'
     Attempt to keep the stack boundary aligned to a 2 raised to NUM
     byte boundary.  If `-mpreferred-stack-boundary' is not specified,
     the default is 4 (16 bytes or 128 bits).

`-mincoming-stack-boundary=NUM'
     Assume the incoming stack is aligned to a 2 raised to NUM byte
     boundary.  If `-mincoming-stack-boundary' is not specified, the
     one specified by `-mpreferred-stack-boundary' will be used.

     On Pentium and PentiumPro, `double' and `long double' values
     should be aligned to an 8 byte boundary (see `-malign-double') or
     suffer significant run time performance penalties.  On Pentium
     III, the Streaming SIMD Extension (SSE) data type `__m128' may not
     work properly if it is not 16 byte aligned.

     To ensure proper alignment of this values on the stack, the stack
     boundary must be as aligned as that required by any value stored
     on the stack.  Further, every function must be generated such that
     it keeps the stack aligned.  Thus calling a function compiled with
     a higher preferred stack boundary from a function compiled with a
     lower preferred stack boundary will most likely misalign the
     stack.  It is recommended that libraries that use callbacks always
     use the default setting.

     This extra alignment does consume extra stack space, and generally
     increases code size.  Code that is sensitive to stack space usage,
     such as embedded systems and operating system kernels, may want to
     reduce the preferred alignment to `-mpreferred-stack-boundary=2'.

`-mmmx'
`-mno-mmx'
`-msse'
`-mno-sse'
`-msse2'
`-mno-sse2'
`-msse3'
`-mno-sse3'
`-mssse3'
`-mno-ssse3'
`-msse4.1'
`-mno-sse4.1'
`-msse4.2'
`-mno-sse4.2'
`-msse4'
`-mno-sse4'
`-mavx'
`-mno-avx'
`-maes'
`-mno-aes'
`-mpclmul'
`-mno-pclmul'
`-mfsgsbase'
`-mno-fsgsbase'
`-mrdrnd'
`-mno-rdrnd'
`-mf16c'
`-mno-f16c'
`-msse4a'
`-mno-sse4a'
`-mfma4'
`-mno-fma4'
`-mxop'
`-mno-xop'
`-mlwp'
`-mno-lwp'
`-m3dnow'
`-mno-3dnow'
`-mpopcnt'
`-mno-popcnt'
`-mabm'
`-mno-abm'
`-mbmi'
`-mno-bmi'
`-mtbm'
`-mno-tbm'
     These switches enable or disable the use of instructions in the
     MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1, AVX, AES, PCLMUL, FSGSBASE,
     RDRND, F16C, SSE4A, FMA4, XOP, LWP, ABM, BMI, or 3DNow! extended
     instruction sets.  These extensions are also available as built-in
     functions: see *note X86 Built-in Functions::, for details of the
     functions enabled and disabled by these switches.

     To have SSE/SSE2 instructions generated automatically from
     floating-point code (as opposed to 387 instructions), see
     `-mfpmath=sse'.

     GCC depresses SSEx instructions when `-mavx' is used. Instead, it
     generates new AVX instructions or AVX equivalence for all SSEx
     instructions when needed.

     These options will enable GCC to use these extended instructions in
     generated code, even without `-mfpmath=sse'.  Applications which
     perform runtime CPU detection must compile separate files for each
     supported architecture, using the appropriate flags.  In
     particular, the file containing the CPU detection code should be
     compiled without these options.

`-mfused-madd'
`-mno-fused-madd'
     Do (don't) generate code that uses the fused multiply/add or
     multiply/subtract instructions.  The default is to use these
     instructions.

`-mcld'
     This option instructs GCC to emit a `cld' instruction in the
     prologue of functions that use string instructions.  String
     instructions depend on the DF flag to select between autoincrement
     or autodecrement mode.  While the ABI specifies the DF flag to be
     cleared on function entry, some operating systems violate this
     specification by not clearing the DF flag in their exception
     dispatchers.  The exception handler can be invoked with the DF flag
     set which leads to wrong direction mode, when string instructions
     are used.  This option can be enabled by default on 32-bit x86
     targets by configuring GCC with the `--enable-cld' configure
     option.  Generation of `cld' instructions can be suppressed with
     the `-mno-cld' compiler option in this case.

`-mcx16'
     This option will enable GCC to use CMPXCHG16B instruction in
     generated code.  CMPXCHG16B allows for atomic operations on
     128-bit double quadword (or oword) data types.  This is useful for
     high resolution counters that could be updated by multiple
     processors (or cores).  This instruction is generated as part of
     atomic built-in functions: see *note Atomic Builtins:: for details.

`-msahf'
     This option will enable GCC to use SAHF instruction in generated
     64-bit code.  Early Intel CPUs with Intel 64 lacked LAHF and SAHF
     instructions supported by AMD64 until introduction of Pentium 4 G1
     step in December 2005.  LAHF and SAHF are load and store
     instructions, respectively, for certain status flags.  In 64-bit
     mode, SAHF instruction is used to optimize `fmod', `drem' or
     `remainder' built-in functions: see *note Other Builtins:: for
     details.

`-mmovbe'
     This option will enable GCC to use movbe instruction to implement
     `__builtin_bswap32' and `__builtin_bswap64'.

`-mcrc32'
     This option will enable built-in functions,
     `__builtin_ia32_crc32qi', `__builtin_ia32_crc32hi'.
     `__builtin_ia32_crc32si' and `__builtin_ia32_crc32di' to generate
     the crc32 machine instruction.

`-mrecip'
     This option will enable GCC to use RCPSS and RSQRTSS instructions
     (and their vectorized variants RCPPS and RSQRTPS) with an
     additional Newton-Raphson step to increase precision instead of
     DIVSS and SQRTSS (and their vectorized variants) for single
     precision floating point arguments.  These instructions are
     generated only when `-funsafe-math-optimizations' is enabled
     together with `-finite-math-only' and `-fno-trapping-math'.  Note
     that while the throughput of the sequence is higher than the
     throughput of the non-reciprocal instruction, the precision of the
     sequence can be decreased by up to 2 ulp (i.e. the inverse of 1.0
     equals 0.99999994).

`-mveclibabi=TYPE'
     Specifies the ABI type to use for vectorizing intrinsics using an
     external library.  Supported types are `svml' for the Intel short
     vector math library and `acml' for the AMD math core library style
     of interfacing.  GCC will currently emit calls to `vmldExp2',
     `vmldLn2', `vmldLog102', `vmldLog102', `vmldPow2', `vmldTanh2',
     `vmldTan2', `vmldAtan2', `vmldAtanh2', `vmldCbrt2', `vmldSinh2',
     `vmldSin2', `vmldAsinh2', `vmldAsin2', `vmldCosh2', `vmldCos2',
     `vmldAcosh2', `vmldAcos2', `vmlsExp4', `vmlsLn4', `vmlsLog104',
     `vmlsLog104', `vmlsPow4', `vmlsTanh4', `vmlsTan4', `vmlsAtan4',
     `vmlsAtanh4', `vmlsCbrt4', `vmlsSinh4', `vmlsSin4', `vmlsAsinh4',
     `vmlsAsin4', `vmlsCosh4', `vmlsCos4', `vmlsAcosh4' and `vmlsAcos4'
     for corresponding function type when `-mveclibabi=svml' is used
     and `__vrd2_sin', `__vrd2_cos', `__vrd2_exp', `__vrd2_log',
     `__vrd2_log2', `__vrd2_log10', `__vrs4_sinf', `__vrs4_cosf',
     `__vrs4_expf', `__vrs4_logf', `__vrs4_log2f', `__vrs4_log10f' and
     `__vrs4_powf' for corresponding function type when
     `-mveclibabi=acml' is used. Both `-ftree-vectorize' and
     `-funsafe-math-optimizations' have to be enabled. A SVML or ACML
     ABI compatible library will have to be specified at link time.

`-mpush-args'
`-mno-push-args'
     Use PUSH operations to store outgoing parameters.  This method is
     shorter and usually equally fast as method using SUB/MOV
     operations and is enabled by default.  In some cases disabling it
     may improve performance because of improved scheduling and reduced
     dependencies.

`-maccumulate-outgoing-args'
     If enabled, the maximum amount of space required for outgoing
     arguments will be computed in the function prologue.  This is
     faster on most modern CPUs because of reduced dependencies,
     improved scheduling and reduced stack usage when preferred stack
     boundary is not equal to 2.  The drawback is a notable increase in
     code size.  This switch implies `-mno-push-args'.

`-mthreads'
     Support thread-safe exception handling on `Mingw32'.  Code that
     relies on thread-safe exception handling must compile and link all
     code with the `-mthreads' option.  When compiling, `-mthreads'
     defines `-D_MT'; when linking, it links in a special thread helper
     library `-lmingwthrd' which cleans up per thread exception
     handling data.

`-mno-align-stringops'
     Do not align destination of inlined string operations.  This
     switch reduces code size and improves performance in case the
     destination is already aligned, but GCC doesn't know about it.

`-minline-all-stringops'
     By default GCC inlines string operations only when destination is
     known to be aligned at least to 4 byte boundary.  This enables
     more inlining, increase code size, but may improve performance of
     code that depends on fast memcpy, strlen and memset for short
     lengths.

`-minline-stringops-dynamically'
     For string operation of unknown size, inline runtime checks so for
     small blocks inline code is used, while for large blocks library
     call is used.

`-mstringop-strategy=ALG'
     Overwrite internal decision heuristic about particular algorithm
     to inline string operation with.  The allowed values are
     `rep_byte', `rep_4byte', `rep_8byte' for expanding using i386
     `rep' prefix of specified size, `byte_loop', `loop',
     `unrolled_loop' for expanding inline loop, `libcall' for always
     expanding library call.

`-momit-leaf-frame-pointer'
     Don't keep the frame pointer in a register for leaf functions.
     This avoids the instructions to save, set up and restore frame
     pointers and makes an extra register available in leaf functions.
     The option `-fomit-frame-pointer' removes the frame pointer for
     all functions which might make debugging harder.

`-mtls-direct-seg-refs'
`-mno-tls-direct-seg-refs'
     Controls whether TLS variables may be accessed with offsets from
     the TLS segment register (`%gs' for 32-bit, `%fs' for 64-bit), or
     whether the thread base pointer must be added.  Whether or not this
     is legal depends on the operating system, and whether it maps the
     segment to cover the entire TLS area.

     For systems that use GNU libc, the default is on.

`-msse2avx'
`-mno-sse2avx'
     Specify that the assembler should encode SSE instructions with VEX
     prefix.  The option `-mavx' turns this on by default.

 These `-m' switches are supported in addition to the above on AMD
x86-64 processors in 64-bit environments.

`-m32'
`-m64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits and generates
     code that runs on any i386 system.  The 64-bit environment sets
     int to 32 bits and long and pointer to 64 bits and generates code
     for AMD's x86-64 architecture. For darwin only the -m64 option
     turns off the `-fno-pic' and `-mdynamic-no-pic' options.

`-mno-red-zone'
     Do not use a so called red zone for x86-64 code.  The red zone is
     mandated by the x86-64 ABI, it is a 128-byte area beyond the
     location of the stack pointer that will not be modified by signal
     or interrupt handlers and therefore can be used for temporary data
     without adjusting the stack pointer.  The flag `-mno-red-zone'
     disables this red zone.

`-mcmodel=small'
     Generate code for the small code model: the program and its
     symbols must be linked in the lower 2 GB of the address space.
     Pointers are 64 bits.  Programs can be statically or dynamically
     linked.  This is the default code model.

`-mcmodel=kernel'
     Generate code for the kernel code model.  The kernel runs in the
     negative 2 GB of the address space.  This model has to be used for
     Linux kernel code.

`-mcmodel=medium'
     Generate code for the medium model: The program is linked in the
     lower 2 GB of the address space.  Small symbols are also placed
     there.  Symbols with sizes larger than `-mlarge-data-threshold'
     are put into large data or bss sections and can be located above
     2GB.  Programs can be statically or dynamically linked.

`-mcmodel=large'
     Generate code for the large model: This model makes no assumptions
     about addresses and sizes of sections.

File: gcc.info,  Node: i386 and x86-64 Windows Options,  Next: IA-64 Options,  Prev: i386 and x86-64 Options,  Up: Submodel Options

3.17.16 i386 and x86-64 Windows Options
---------------------------------------

These additional options are available for Windows targets:

`-mconsole'
     This option is available for Cygwin and MinGW targets.  It
     specifies that a console application is to be generated, by
     instructing the linker to set the PE header subsystem type
     required for console applications.  This is the default behaviour
     for Cygwin and MinGW targets.

`-mcygwin'
     This option is available for Cygwin targets.  It specifies that
     the Cygwin internal interface is to be used for predefined
     preprocessor macros, C runtime libraries and related linker paths
     and options.  For Cygwin targets this is the default behaviour.
     This option is deprecated and will be removed in a future release.

`-mno-cygwin'
     This option is available for Cygwin targets.  It specifies that
     the MinGW internal interface is to be used instead of Cygwin's, by
     setting MinGW-related predefined macros and linker paths and
     default library options.  This option is deprecated and will be
     removed in a future release.

`-mdll'
     This option is available for Cygwin and MinGW targets.  It
     specifies that a DLL - a dynamic link library - is to be
     generated, enabling the selection of the required runtime startup
     object and entry point.

`-mnop-fun-dllimport'
     This option is available for Cygwin and MinGW targets.  It
     specifies that the dllimport attribute should be ignored.

`-mthread'
     This option is available for MinGW targets. It specifies that
     MinGW-specific thread support is to be used.

`-mwin32'
     This option is available for Cygwin and MinGW targets.  It
     specifies that the typical Windows pre-defined macros are to be
     set in the pre-processor, but does not influence the choice of
     runtime library/startup code.

`-mwindows'
     This option is available for Cygwin and MinGW targets.  It
     specifies that a GUI application is to be generated by instructing
     the linker to set the PE header subsystem type appropriately.

 See also under *note i386 and x86-64 Options:: for standard options.

File: gcc.info,  Node: IA-64 Options,  Next: M32C Options,  Prev: i386 and x86-64 Windows Options,  Up: Submodel Options

3.17.17 IA-64 Options
---------------------

These are the `-m' options defined for the Intel IA-64 architecture.

`-mbig-endian'
     Generate code for a big endian target.  This is the default for
     HP-UX.

`-mlittle-endian'
     Generate code for a little endian target.  This is the default for
     AIX5 and GNU/Linux.

`-mgnu-as'
`-mno-gnu-as'
     Generate (or don't) code for the GNU assembler.  This is the
     default.

`-mgnu-ld'
`-mno-gnu-ld'
     Generate (or don't) code for the GNU linker.  This is the default.

`-mno-pic'
     Generate code that does not use a global pointer register.  The
     result is not position independent code, and violates the IA-64
     ABI.

`-mvolatile-asm-stop'
`-mno-volatile-asm-stop'
     Generate (or don't) a stop bit immediately before and after
     volatile asm statements.

`-mregister-names'
`-mno-register-names'
     Generate (or don't) `in', `loc', and `out' register names for the
     stacked registers.  This may make assembler output more readable.

`-mno-sdata'
`-msdata'
     Disable (or enable) optimizations that use the small data section.
     This may be useful for working around optimizer bugs.

`-mconstant-gp'
     Generate code that uses a single constant global pointer value.
     This is useful when compiling kernel code.

`-mauto-pic'
     Generate code that is self-relocatable.  This implies
     `-mconstant-gp'.  This is useful when compiling firmware code.

`-minline-float-divide-min-latency'
     Generate code for inline divides of floating point values using
     the minimum latency algorithm.

`-minline-float-divide-max-throughput'
     Generate code for inline divides of floating point values using
     the maximum throughput algorithm.

`-minline-int-divide-min-latency'
     Generate code for inline divides of integer values using the
     minimum latency algorithm.

`-minline-int-divide-max-throughput'
     Generate code for inline divides of integer values using the
     maximum throughput algorithm.

`-minline-sqrt-min-latency'
     Generate code for inline square roots using the minimum latency
     algorithm.

`-minline-sqrt-max-throughput'
     Generate code for inline square roots using the maximum throughput
     algorithm.

`-mno-dwarf2-asm'
`-mdwarf2-asm'
     Don't (or do) generate assembler code for the DWARF2 line number
     debugging info.  This may be useful when not using the GNU
     assembler.

`-mearly-stop-bits'
`-mno-early-stop-bits'
     Allow stop bits to be placed earlier than immediately preceding the
     instruction that triggered the stop bit.  This can improve
     instruction scheduling, but does not always do so.

`-mfixed-range=REGISTER-RANGE'
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator can not use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

`-mtls-size=TLS-SIZE'
     Specify bit size of immediate TLS offsets.  Valid values are 14,
     22, and 64.

`-mtune=CPU-TYPE'
     Tune the instruction scheduling for a particular CPU, Valid values
     are itanium, itanium1, merced, itanium2, and mckinley.

`-mt'
`-pthread'
     Add support for multithreading using the POSIX threads library.
     This option sets flags for both the preprocessor and linker.  It
     does not affect the thread safety of object code produced by the
     compiler or that of libraries supplied with it.  These are HP-UX
     specific flags.

`-milp32'
`-mlp64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.
     These are HP-UX specific flags.

`-mno-sched-br-data-spec'
`-msched-br-data-spec'
     (Dis/En)able data speculative scheduling before reload.  This will
     result in generation of the ld.a instructions and the
     corresponding check instructions (ld.c / chk.a).  The default is
     'disable'.

`-msched-ar-data-spec'
`-mno-sched-ar-data-spec'
     (En/Dis)able data speculative scheduling after reload.  This will
     result in generation of the ld.a instructions and the
     corresponding check instructions (ld.c / chk.a).  The default is
     'enable'.

`-mno-sched-control-spec'
`-msched-control-spec'
     (Dis/En)able control speculative scheduling.  This feature is
     available only during region scheduling (i.e. before reload).
     This will result in generation of the ld.s instructions and the
     corresponding check instructions chk.s .  The default is 'disable'.

`-msched-br-in-data-spec'
`-mno-sched-br-in-data-spec'
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the data speculative loads before reload.  This is
     effective only with `-msched-br-data-spec' enabled.  The default
     is 'enable'.

`-msched-ar-in-data-spec'
`-mno-sched-ar-in-data-spec'
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the data speculative loads after reload.  This is
     effective only with `-msched-ar-data-spec' enabled.  The default
     is 'enable'.

`-msched-in-control-spec'
`-mno-sched-in-control-spec'
     (En/Dis)able speculative scheduling of the instructions that are
     dependent on the control speculative loads.  This is effective
     only with `-msched-control-spec' enabled.  The default is 'enable'.

`-msched-ldc'
`-mno-sched-ldc'
     (En/Dis)able use of simple data speculation checks ld.c .  If
     disabled, only chk.a instructions will be emitted to check data
     speculative loads.  The default is 'enable'.

`-mno-sched-control-ldc'
`-msched-control-ldc'
     (Dis/En)able use of ld.c instructions to check control speculative
     loads.  If enabled, in case of control speculative load with no
     speculatively scheduled dependent instructions this load will be
     emitted as ld.sa and ld.c will be used to check it.  The default
     is 'disable'.

`-mno-sched-spec-verbose'
`-msched-spec-verbose'
     (Dis/En)able printing of the information about speculative motions.

`-mno-sched-prefer-non-data-spec-insns'
`-msched-prefer-non-data-spec-insns'
     If enabled, data speculative instructions will be chosen for
     schedule only if there are no other choices at the moment.  This
     will make the use of the data speculation much more conservative.
     The default is 'disable'.

`-mno-sched-prefer-non-control-spec-insns'
`-msched-prefer-non-control-spec-insns'
     If enabled, control speculative instructions will be chosen for
     schedule only if there are no other choices at the moment.  This
     will make the use of the control speculation much more
     conservative.  The default is 'disable'.

`-mno-sched-count-spec-in-critical-path'
`-msched-count-spec-in-critical-path'
     If enabled, speculative dependencies will be considered during
     computation of the instructions priorities.  This will make the
     use of the speculation a bit more conservative.  The default is
     'disable'.


File: gcc.info,  Node: M32C Options,  Next: M32R/D Options,  Prev: IA-64 Options,  Up: Submodel Options

3.17.18 M32C Options
--------------------

`-mcpu=NAME'
     Select the CPU for which code is generated.  NAME may be one of
     `r8c' for the R8C/Tiny series, `m16c' for the M16C (up to /60)
     series, `m32cm' for the M16C/80 series, or `m32c' for the M32C/80
     series.

`-msim'
     Specifies that the program will be run on the simulator.  This
     causes an alternate runtime library to be linked in which
     supports, for example, file I/O.  You must not use this option
     when generating programs that will run on real hardware; you must
     provide your own runtime library for whatever I/O functions are
     needed.

`-memregs=NUMBER'
     Specifies the number of memory-based pseudo-registers GCC will use
     during code generation.  These pseudo-registers will be used like
     real registers, so there is a tradeoff between GCC's ability to
     fit the code into available registers, and the performance penalty
     of using memory instead of registers.  Note that all modules in a
     program must be compiled with the same value for this option.
     Because of that, you must not use this option with the default
     runtime libraries gcc builds.


File: gcc.info,  Node: M32R/D Options,  Next: M680x0 Options,  Prev: M32C Options,  Up: Submodel Options

3.17.19 M32R/D Options
----------------------

These `-m' options are defined for Renesas M32R/D architectures:

`-m32r2'
     Generate code for the M32R/2.

`-m32rx'
     Generate code for the M32R/X.

`-m32r'
     Generate code for the M32R.  This is the default.

`-mmodel=small'
     Assume all objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction), and assume
     all subroutines are reachable with the `bl' instruction.  This is
     the default.

     The addressability of a particular object can be set with the
     `model' attribute.

`-mmodel=medium'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume all subroutines are reachable with the `bl'
     instruction.

`-mmodel=large'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume subroutines may not be reachable with the
     `bl' instruction (the compiler will generate the much slower
     `seth/add3/jl' instruction sequence).

`-msdata=none'
     Disable use of the small data area.  Variables will be put into
     one of `.data', `bss', or `.rodata' (unless the `section'
     attribute has been specified).  This is the default.

     The small data area consists of sections `.sdata' and `.sbss'.
     Objects may be explicitly put in the small data area with the
     `section' attribute using one of these sections.

`-msdata=sdata'
     Put small global and static data in the small data area, but do not
     generate special code to reference them.

`-msdata=use'
     Put small global and static data in the small data area, and
     generate special instructions to reference them.

`-G NUM'
     Put global and static objects less than or equal to NUM bytes into
     the small data or bss sections instead of the normal data or bss
     sections.  The default value of NUM is 8.  The `-msdata' option
     must be set to one of `sdata' or `use' for this option to have any
     effect.

     All modules should be compiled with the same `-G NUM' value.
     Compiling with different values of NUM may or may not work; if it
     doesn't the linker will give an error message--incorrect code will
     not be generated.

`-mdebug'
     Makes the M32R specific code in the compiler display some
     statistics that might help in debugging programs.

`-malign-loops'
     Align all loops to a 32-byte boundary.

`-mno-align-loops'
     Do not enforce a 32-byte alignment for loops.  This is the default.

`-missue-rate=NUMBER'
     Issue NUMBER instructions per cycle.  NUMBER can only be 1 or 2.

`-mbranch-cost=NUMBER'
     NUMBER can only be 1 or 2.  If it is 1 then branches will be
     preferred over conditional code, if it is 2, then the opposite will
     apply.

`-mflush-trap=NUMBER'
     Specifies the trap number to use to flush the cache.  The default
     is 12.  Valid numbers are between 0 and 15 inclusive.

`-mno-flush-trap'
     Specifies that the cache cannot be flushed by using a trap.

`-mflush-func=NAME'
     Specifies the name of the operating system function to call to
     flush the cache.  The default is __flush_cache_, but a function
     call will only be used if a trap is not available.

`-mno-flush-func'
     Indicates that there is no OS function for flushing the cache.


File: gcc.info,  Node: M680x0 Options,  Next: M68hc1x Options,  Prev: M32R/D Options,  Up: Submodel Options

3.17.20 M680x0 Options
----------------------

These are the `-m' options defined for M680x0 and ColdFire processors.
The default settings depend on which architecture was selected when the
compiler was configured; the defaults for the most common choices are
given below.

`-march=ARCH'
     Generate code for a specific M680x0 or ColdFire instruction set
     architecture.  Permissible values of ARCH for M680x0 architectures
     are: `68000', `68010', `68020', `68030', `68040', `68060' and
     `cpu32'.  ColdFire architectures are selected according to
     Freescale's ISA classification and the permissible values are:
     `isaa', `isaaplus', `isab' and `isac'.

     gcc defines a macro `__mcfARCH__' whenever it is generating code
     for a ColdFire target.  The ARCH in this macro is one of the
     `-march' arguments given above.

     When used together, `-march' and `-mtune' select code that runs on
     a family of similar processors but that is optimized for a
     particular microarchitecture.

`-mcpu=CPU'
     Generate code for a specific M680x0 or ColdFire processor.  The
     M680x0 CPUs are: `68000', `68010', `68020', `68030', `68040',
     `68060', `68302', `68332' and `cpu32'.  The ColdFire CPUs are
     given by the table below, which also classifies the CPUs into
     families:

     *Family*      *`-mcpu' arguments*
     `51qe'        `51qe'
     `5206'        `5202' `5204' `5206'
     `5206e'       `5206e'
     `5208'        `5207' `5208'
     `5211a'       `5210a' `5211a'
     `5213'        `5211' `5212' `5213'
     `5216'        `5214' `5216'
     `52235'       `52230' `52231' `52232' `52233' `52234' `52235'
     `5225'        `5224' `5225'
     `5235'        `5232' `5233' `5234' `5235' `523x'
     `5249'        `5249'
     `5250'        `5250'
     `5271'        `5270' `5271'
     `5272'        `5272'
     `5275'        `5274' `5275'
     `5282'        `5280' `5281' `5282' `528x'
     `5307'        `5307'
     `5329'        `5327' `5328' `5329' `532x'
     `5373'        `5372' `5373' `537x'
     `5407'        `5407'
     `5475'        `5470' `5471' `5472' `5473' `5474' `5475' `547x'
                   `5480' `5481' `5482' `5483' `5484' `5485'

     `-mcpu=CPU' overrides `-march=ARCH' if ARCH is compatible with
     CPU.  Other combinations of `-mcpu' and `-march' are rejected.

     gcc defines the macro `__mcf_cpu_CPU' when ColdFire target CPU is
     selected.  It also defines `__mcf_family_FAMILY', where the value
     of FAMILY is given by the table above.

`-mtune=TUNE'
     Tune the code for a particular microarchitecture, within the
     constraints set by `-march' and `-mcpu'.  The M680x0
     microarchitectures are: `68000', `68010', `68020', `68030',
     `68040', `68060' and `cpu32'.  The ColdFire microarchitectures
     are: `cfv1', `cfv2', `cfv3', `cfv4' and `cfv4e'.

     You can also use `-mtune=68020-40' for code that needs to run
     relatively well on 68020, 68030 and 68040 targets.
     `-mtune=68020-60' is similar but includes 68060 targets as well.
     These two options select the same tuning decisions as `-m68020-40'
     and `-m68020-60' respectively.

     gcc defines the macros `__mcARCH' and `__mcARCH__' when tuning for
     680x0 architecture ARCH.  It also defines `mcARCH' unless either
     `-ansi' or a non-GNU `-std' option is used.  If gcc is tuning for
     a range of architectures, as selected by `-mtune=68020-40' or
     `-mtune=68020-60', it defines the macros for every architecture in
     the range.

     gcc also defines the macro `__mUARCH__' when tuning for ColdFire
     microarchitecture UARCH, where UARCH is one of the arguments given
     above.

`-m68000'
`-mc68000'
     Generate output for a 68000.  This is the default when the
     compiler is configured for 68000-based systems.  It is equivalent
     to `-march=68000'.

     Use this option for microcontrollers with a 68000 or EC000 core,
     including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

`-m68010'
     Generate output for a 68010.  This is the default when the
     compiler is configured for 68010-based systems.  It is equivalent
     to `-march=68010'.

`-m68020'
`-mc68020'
     Generate output for a 68020.  This is the default when the
     compiler is configured for 68020-based systems.  It is equivalent
     to `-march=68020'.

`-m68030'
     Generate output for a 68030.  This is the default when the
     compiler is configured for 68030-based systems.  It is equivalent
     to `-march=68030'.

`-m68040'
     Generate output for a 68040.  This is the default when the
     compiler is configured for 68040-based systems.  It is equivalent
     to `-march=68040'.

     This option inhibits the use of 68881/68882 instructions that have
     to be emulated by software on the 68040.  Use this option if your
     68040 does not have code to emulate those instructions.

`-m68060'
     Generate output for a 68060.  This is the default when the
     compiler is configured for 68060-based systems.  It is equivalent
     to `-march=68060'.

     This option inhibits the use of 68020 and 68881/68882 instructions
     that have to be emulated by software on the 68060.  Use this
     option if your 68060 does not have code to emulate those
     instructions.

`-mcpu32'
     Generate output for a CPU32.  This is the default when the
     compiler is configured for CPU32-based systems.  It is equivalent
     to `-march=cpu32'.

     Use this option for microcontrollers with a CPU32 or CPU32+ core,
     including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
     68341, 68349 and 68360.

`-m5200'
     Generate output for a 520X ColdFire CPU.  This is the default when
     the compiler is configured for 520X-based systems.  It is
     equivalent to `-mcpu=5206', and is now deprecated in favor of that
     option.

     Use this option for microcontroller with a 5200 core, including
     the MCF5202, MCF5203, MCF5204 and MCF5206.

`-m5206e'
     Generate output for a 5206e ColdFire CPU.  The option is now
     deprecated in favor of the equivalent `-mcpu=5206e'.

`-m528x'
     Generate output for a member of the ColdFire 528X family.  The
     option is now deprecated in favor of the equivalent `-mcpu=528x'.

`-m5307'
     Generate output for a ColdFire 5307 CPU.  The option is now
     deprecated in favor of the equivalent `-mcpu=5307'.

`-m5407'
     Generate output for a ColdFire 5407 CPU.  The option is now
     deprecated in favor of the equivalent `-mcpu=5407'.

`-mcfv4e'
     Generate output for a ColdFire V4e family CPU (e.g. 547x/548x).
     This includes use of hardware floating point instructions.  The
     option is equivalent to `-mcpu=547x', and is now deprecated in
     favor of that option.

`-m68020-40'
     Generate output for a 68040, without using any of the new
     instructions.  This results in code which can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated
     on the 68040.

     The option is equivalent to `-march=68020' `-mtune=68020-40'.

`-m68020-60'
     Generate output for a 68060, without using any of the new
     instructions.  This results in code which can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated
     on the 68060.

     The option is equivalent to `-march=68020' `-mtune=68020-60'.

`-mhard-float'
`-m68881'
     Generate floating-point instructions.  This is the default for
     68020 and above, and for ColdFire devices that have an FPU.  It
     defines the macro `__HAVE_68881__' on M680x0 targets and
     `__mcffpu__' on ColdFire targets.

`-msoft-float'
     Do not generate floating-point instructions; use library calls
     instead.  This is the default for 68000, 68010, and 68832 targets.
     It is also the default for ColdFire devices that have no FPU.

`-mdiv'
`-mno-div'
     Generate (do not generate) ColdFire hardware divide and remainder
     instructions.  If `-march' is used without `-mcpu', the default is
     "on" for ColdFire architectures and "off" for M680x0
     architectures.  Otherwise, the default is taken from the target CPU
     (either the default CPU, or the one specified by `-mcpu').  For
     example, the default is "off" for `-mcpu=5206' and "on" for
     `-mcpu=5206e'.

     gcc defines the macro `__mcfhwdiv__' when this option is enabled.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.
     Additionally, parameters passed on the stack are also aligned to a
     16-bit boundary even on targets whose API mandates promotion to
     32-bit.

`-mno-short'
     Do not consider type `int' to be 16 bits wide.  This is the
     default.

`-mnobitfield'
`-mno-bitfield'
     Do not use the bit-field instructions.  The `-m68000', `-mcpu32'
     and `-m5200' options imply `-mnobitfield'.

`-mbitfield'
     Do use the bit-field instructions.  The `-m68020' option implies
     `-mbitfield'.  This is the default if you use a configuration
     designed for a 68020.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the `rtd'
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

     The `rtd' instruction is supported by the 68010, 68020, 68030,
     68040, 68060 and CPU32 processors, but not by the 68000 or 5200.

`-mno-rtd'
     Do not use the calling conventions selected by `-mrtd'.  This is
     the default.

`-malign-int'
`-mno-align-int'
     Control whether GCC aligns `int', `long', `long long', `float',
     `double', and `long double' variables on a 32-bit boundary
     (`-malign-int') or a 16-bit boundary (`-mno-align-int').  Aligning
     variables on 32-bit boundaries produces code that runs somewhat
     faster on processors with 32-bit busses at the expense of more
     memory.

     *Warning:* if you use the `-malign-int' switch, GCC will align
     structures containing the above types  differently than most
     published application binary interface specifications for the m68k.

`-mpcrel'
     Use the pc-relative addressing mode of the 68000 directly, instead
     of using a global offset table.  At present, this option implies
     `-fpic', allowing at most a 16-bit offset for pc-relative
     addressing.  `-fPIC' is not presently supported with `-mpcrel',
     though this could be supported for 68020 and higher processors.

`-mno-strict-align'
`-mstrict-align'
     Do not (do) assume that unaligned memory references will be
     handled by the system.

`-msep-data'
     Generate code that allows the data segment to be located in a
     different area of memory from the text segment.  This allows for
     execute in place in an environment without virtual memory
     management.  This option implies `-fPIC'.

`-mno-sep-data'
     Generate code that assumes that the data segment follows the text
     segment.  This is the default.

`-mid-shared-library'
     Generate code that supports shared libraries via the library ID
     method.  This allows for execute in place and shared libraries in
     an environment without virtual memory management.  This option
     implies `-fPIC'.

`-mno-id-shared-library'
     Generate code that doesn't assume ID based shared libraries are
     being used.  This is the default.

`-mshared-library-id=n'
     Specified the identification number of the ID based shared library
     being compiled.  Specifying a value of 0 will generate more
     compact code, specifying other values will force the allocation of
     that number to the current library but is no more space or time
     efficient than omitting this option.

`-mxgot'
`-mno-xgot'
     When generating position-independent code for ColdFire, generate
     code that works if the GOT has more than 8192 entries.  This code
     is larger and slower than code generated without this option.  On
     M680x0 processors, this option is not needed; `-fPIC' suffices.

     GCC normally uses a single instruction to load values from the GOT.
     While this is relatively efficient, it only works if the GOT is
     smaller than about 64k.  Anything larger causes the linker to
     report an error such as:

          relocation truncated to fit: R_68K_GOT16O foobar

     If this happens, you should recompile your code with `-mxgot'.  It
     should then work with very large GOTs.  However, code generated
     with `-mxgot' is less efficient, since it takes 4 instructions to
     fetch the value of a global symbol.

     Note that some linkers, including newer versions of the GNU linker,
     can create multiple GOTs and sort GOT entries.  If you have such a
     linker, you should only need to use `-mxgot' when compiling a
     single object file that accesses more than 8192 GOT entries.  Very
     few do.

     These options have no effect unless GCC is generating
     position-independent code.


File: gcc.info,  Node: M68hc1x Options,  Next: MCore Options,  Prev: M680x0 Options,  Up: Submodel Options

3.17.21 M68hc1x Options
-----------------------

These are the `-m' options defined for the 68hc11 and 68hc12
microcontrollers.  The default values for these options depends on
which style of microcontroller was selected when the compiler was
configured; the defaults for the most common choices are given below.

`-m6811'
`-m68hc11'
     Generate output for a 68HC11.  This is the default when the
     compiler is configured for 68HC11-based systems.

`-m6812'
`-m68hc12'
     Generate output for a 68HC12.  This is the default when the
     compiler is configured for 68HC12-based systems.

`-m68S12'
`-m68hcs12'
     Generate output for a 68HCS12.

`-mauto-incdec'
     Enable the use of 68HC12 pre and post auto-increment and
     auto-decrement addressing modes.

`-minmax'
`-nominmax'
     Enable the use of 68HC12 min and max instructions.

`-mlong-calls'
`-mno-long-calls'
     Treat all calls as being far away (near).  If calls are assumed to
     be far away, the compiler will use the `call' instruction to call
     a function and the `rtc' instruction for returning.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.

`-msoft-reg-count=COUNT'
     Specify the number of pseudo-soft registers which are used for the
     code generation.  The maximum number is 32.  Using more pseudo-soft
     register may or may not result in better code depending on the
     program.  The default is 4 for 68HC11 and 2 for 68HC12.


File: gcc.info,  Node: MCore Options,  Next: MIPS Options,  Prev: M68hc1x Options,  Up: Submodel Options

3.17.22 MCore Options
---------------------

These are the `-m' options defined for the Motorola M*Core processors.

`-mhardlit'
`-mno-hardlit'
     Inline constants into the code stream if it can be done in two
     instructions or less.

`-mdiv'
`-mno-div'
     Use the divide instruction.  (Enabled by default).

`-mrelax-immediate'
`-mno-relax-immediate'
     Allow arbitrary sized immediates in bit operations.

`-mwide-bitfields'
`-mno-wide-bitfields'
     Always treat bit-fields as int-sized.

`-m4byte-functions'
`-mno-4byte-functions'
     Force all functions to be aligned to a four byte boundary.

`-mcallgraph-data'
`-mno-callgraph-data'
     Emit callgraph information.

`-mslow-bytes'
`-mno-slow-bytes'
     Prefer word access when reading byte quantities.

`-mlittle-endian'
`-mbig-endian'
     Generate code for a little endian target.

`-m210'
`-m340'
     Generate code for the 210 processor.

`-mno-lsim'
     Assume that run-time support has been provided and so omit the
     simulator library (`libsim.a)' from the linker command line.

`-mstack-increment=SIZE'
     Set the maximum amount for a single stack increment operation.
     Large values can increase the speed of programs which contain
     functions that need a large amount of stack space, but they can
     also trigger a segmentation fault if the stack is extended too
     much.  The default value is 0x1000.


File: gcc.info,  Node: MIPS Options,  Next: MMIX Options,  Prev: MCore Options,  Up: Submodel Options

3.17.23 MIPS Options
--------------------

`-EB'
     Generate big-endian code.

`-EL'
     Generate little-endian code.  This is the default for `mips*el-*-*'
     configurations.

`-march=ARCH'
     Generate code that will run on ARCH, which can be the name of a
     generic MIPS ISA, or the name of a particular processor.  The ISA
     names are: `mips1', `mips2', `mips3', `mips4', `mips32',
     `mips32r2', `mips64' and `mips64r2'.  The processor names are:
     `4kc', `4km', `4kp', `4ksc', `4kec', `4kem', `4kep', `4ksd',
     `5kc', `5kf', `20kc', `24kc', `24kf2_1', `24kf1_1', `24kec',
     `24kef2_1', `24kef1_1', `34kc', `34kf2_1', `34kf1_1', `74kc',
     `74kf2_1', `74kf1_1', `74kf3_2', `loongson2e', `loongson2f', `m4k',
     `octeon', `orion', `r2000', `r3000', `r3900', `r4000', `r4400',
     `r4600', `r4650', `r6000', `r8000', `rm7000', `rm9000', `r10000',
     `r12000', `r14000', `r16000', `sb1', `sr71000', `vr4100',
     `vr4111', `vr4120', `vr4130', `vr4300', `vr5000', `vr5400',
     `vr5500' and `xlr'.  The special value `from-abi' selects the most
     compatible architecture for the selected ABI (that is, `mips1' for
     32-bit ABIs and `mips3' for 64-bit ABIs).

     Native Linux/GNU toolchains also support the value `native', which
     selects the best architecture option for the host processor.
     `-march=native' has no effect if GCC does not recognize the
     processor.

     In processor names, a final `000' can be abbreviated as `k' (for
     example, `-march=r2k').  Prefixes are optional, and `vr' may be
     written `r'.

     Names of the form `Nf2_1' refer to processors with FPUs clocked at
     half the rate of the core, names of the form `Nf1_1' refer to
     processors with FPUs clocked at the same rate as the core, and
     names of the form `Nf3_2' refer to processors with FPUs clocked a
     ratio of 3:2 with respect to the core.  For compatibility reasons,
     `Nf' is accepted as a synonym for `Nf2_1' while `Nx' and `Bfx' are
     accepted as synonyms for `Nf1_1'.

     GCC defines two macros based on the value of this option.  The
     first is `_MIPS_ARCH', which gives the name of target
     architecture, as a string.  The second has the form
     `_MIPS_ARCH_FOO', where FOO is the capitalized value of
     `_MIPS_ARCH'.  For example, `-march=r2000' will set `_MIPS_ARCH'
     to `"r2000"' and define the macro `_MIPS_ARCH_R2000'.

     Note that the `_MIPS_ARCH' macro uses the processor names given
     above.  In other words, it will have the full prefix and will not
     abbreviate `000' as `k'.  In the case of `from-abi', the macro
     names the resolved architecture (either `"mips1"' or `"mips3"').
     It names the default architecture when no `-march' option is given.

`-mtune=ARCH'
     Optimize for ARCH.  Among other things, this option controls the
     way instructions are scheduled, and the perceived cost of
     arithmetic operations.  The list of ARCH values is the same as for
     `-march'.

     When this option is not used, GCC will optimize for the processor
     specified by `-march'.  By using `-march' and `-mtune' together,
     it is possible to generate code that will run on a family of
     processors, but optimize the code for one particular member of
     that family.

     `-mtune' defines the macros `_MIPS_TUNE' and `_MIPS_TUNE_FOO',
     which work in the same way as the `-march' ones described above.

`-mips1'
     Equivalent to `-march=mips1'.

`-mips2'
     Equivalent to `-march=mips2'.

`-mips3'
     Equivalent to `-march=mips3'.

`-mips4'
     Equivalent to `-march=mips4'.

`-mips32'
     Equivalent to `-march=mips32'.

`-mips32r2'
     Equivalent to `-march=mips32r2'.

`-mips64'
     Equivalent to `-march=mips64'.

`-mips64r2'
     Equivalent to `-march=mips64r2'.

`-mips16'
`-mno-mips16'
     Generate (do not generate) MIPS16 code.  If GCC is targetting a
     MIPS32 or MIPS64 architecture, it will make use of the MIPS16e ASE.

     MIPS16 code generation can also be controlled on a per-function
     basis by means of `mips16' and `nomips16' attributes.  *Note
     Function Attributes::, for more information.

`-mflip-mips16'
     Generate MIPS16 code on alternating functions.  This option is
     provided for regression testing of mixed MIPS16/non-MIPS16 code
     generation, and is not intended for ordinary use in compiling user
     code.

`-minterlink-mips16'
`-mno-interlink-mips16'
     Require (do not require) that non-MIPS16 code be link-compatible
     with MIPS16 code.

     For example, non-MIPS16 code cannot jump directly to MIPS16 code;
     it must either use a call or an indirect jump.
     `-minterlink-mips16' therefore disables direct jumps unless GCC
     knows that the target of the jump is not MIPS16.

`-mabi=32'
`-mabi=o64'
`-mabi=n32'
`-mabi=64'
`-mabi=eabi'
     Generate code for the given ABI.

     Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
     generates 64-bit code when you select a 64-bit architecture, but
     you can use `-mgp32' to get 32-bit code instead.

     For information about the O64 ABI, see
     `http://gcc.gnu.org/projects/mipso64-abi.html'.

     GCC supports a variant of the o32 ABI in which floating-point
     registers are 64 rather than 32 bits wide.  You can select this
     combination with `-mabi=32' `-mfp64'.  This ABI relies on the
     `mthc1' and `mfhc1' instructions and is therefore only supported
     for MIPS32R2 processors.

     The register assignments for arguments and return values remain the
     same, but each scalar value is passed in a single 64-bit register
     rather than a pair of 32-bit registers.  For example, scalar
     floating-point values are returned in `$f0' only, not a
     `$f0'/`$f1' pair.  The set of call-saved registers also remains
     the same, but all 64 bits are saved.

`-mabicalls'
`-mno-abicalls'
     Generate (do not generate) code that is suitable for SVR4-style
     dynamic objects.  `-mabicalls' is the default for SVR4-based
     systems.

`-mshared'
`-mno-shared'
     Generate (do not generate) code that is fully position-independent,
     and that can therefore be linked into shared libraries.  This
     option only affects `-mabicalls'.

     All `-mabicalls' code has traditionally been position-independent,
     regardless of options like `-fPIC' and `-fpic'.  However, as an
     extension, the GNU toolchain allows executables to use absolute
     accesses for locally-binding symbols.  It can also use shorter GP
     initialization sequences and generate direct calls to
     locally-defined functions.  This mode is selected by `-mno-shared'.

     `-mno-shared' depends on binutils 2.16 or higher and generates
     objects that can only be linked by the GNU linker.  However, the
     option does not affect the ABI of the final executable; it only
     affects the ABI of relocatable objects.  Using `-mno-shared' will
     generally make executables both smaller and quicker.

     `-mshared' is the default.

`-mplt'
`-mno-plt'
     Assume (do not assume) that the static and dynamic linkers support
     PLTs and copy relocations.  This option only affects `-mno-shared
     -mabicalls'.  For the n64 ABI, this option has no effect without
     `-msym32'.

     You can make `-mplt' the default by configuring GCC with
     `--with-mips-plt'.  The default is `-mno-plt' otherwise.

`-mxgot'
`-mno-xgot'
     Lift (do not lift) the usual restrictions on the size of the global
     offset table.

     GCC normally uses a single instruction to load values from the GOT.
     While this is relatively efficient, it will only work if the GOT
     is smaller than about 64k.  Anything larger will cause the linker
     to report an error such as:

          relocation truncated to fit: R_MIPS_GOT16 foobar

     If this happens, you should recompile your code with `-mxgot'.  It
     should then work with very large GOTs, although it will also be
     less efficient, since it will take three instructions to fetch the
     value of a global symbol.

     Note that some linkers can create multiple GOTs.  If you have such
     a linker, you should only need to use `-mxgot' when a single object
     file accesses more than 64k's worth of GOT entries.  Very few do.

     These options have no effect unless GCC is generating position
     independent code.

`-mgp32'
     Assume that general-purpose registers are 32 bits wide.

`-mgp64'
     Assume that general-purpose registers are 64 bits wide.

`-mfp32'
     Assume that floating-point registers are 32 bits wide.

`-mfp64'
     Assume that floating-point registers are 64 bits wide.

`-mhard-float'
     Use floating-point coprocessor instructions.

`-msoft-float'
     Do not use floating-point coprocessor instructions.  Implement
     floating-point calculations using library calls instead.

`-msingle-float'
     Assume that the floating-point coprocessor only supports
     single-precision operations.

`-mdouble-float'
     Assume that the floating-point coprocessor supports
     double-precision operations.  This is the default.

`-mllsc'
`-mno-llsc'
     Use (do not use) `ll', `sc', and `sync' instructions to implement
     atomic memory built-in functions.  When neither option is
     specified, GCC will use the instructions if the target architecture
     supports them.

     `-mllsc' is useful if the runtime environment can emulate the
     instructions and `-mno-llsc' can be useful when compiling for
     nonstandard ISAs.  You can make either option the default by
     configuring GCC with `--with-llsc' and `--without-llsc'
     respectively.  `--with-llsc' is the default for some
     configurations; see the installation documentation for details.

`-mdsp'
`-mno-dsp'
     Use (do not use) revision 1 of the MIPS DSP ASE.  *Note MIPS DSP
     Built-in Functions::.  This option defines the preprocessor macro
     `__mips_dsp'.  It also defines `__mips_dsp_rev' to 1.

`-mdspr2'
`-mno-dspr2'
     Use (do not use) revision 2 of the MIPS DSP ASE.  *Note MIPS DSP
     Built-in Functions::.  This option defines the preprocessor macros
     `__mips_dsp' and `__mips_dspr2'.  It also defines `__mips_dsp_rev'
     to 2.

`-msmartmips'
`-mno-smartmips'
     Use (do not use) the MIPS SmartMIPS ASE.

`-mpaired-single'
`-mno-paired-single'
     Use (do not use) paired-single floating-point instructions.  *Note
     MIPS Paired-Single Support::.  This option requires hardware
     floating-point support to be enabled.

`-mdmx'
`-mno-mdmx'
     Use (do not use) MIPS Digital Media Extension instructions.  This
     option can only be used when generating 64-bit code and requires
     hardware floating-point support to be enabled.

`-mips3d'
`-mno-mips3d'
     Use (do not use) the MIPS-3D ASE.  *Note MIPS-3D Built-in
     Functions::.  The option `-mips3d' implies `-mpaired-single'.

`-mmt'
`-mno-mt'
     Use (do not use) MT Multithreading instructions.

`-mlong64'
     Force `long' types to be 64 bits wide.  See `-mlong32' for an
     explanation of the default and the way that the pointer size is
     determined.

`-mlong32'
     Force `long', `int', and pointer types to be 32 bits wide.

     The default size of `int's, `long's and pointers depends on the
     ABI.  All the supported ABIs use 32-bit `int's.  The n64 ABI uses
     64-bit `long's, as does the 64-bit EABI; the others use 32-bit
     `long's.  Pointers are the same size as `long's, or the same size
     as integer registers, whichever is smaller.

`-msym32'
`-mno-sym32'
     Assume (do not assume) that all symbols have 32-bit values,
     regardless of the selected ABI.  This option is useful in
     combination with `-mabi=64' and `-mno-abicalls' because it allows
     GCC to generate shorter and faster references to symbolic
     addresses.

`-G NUM'
     Put definitions of externally-visible data in a small data section
     if that data is no bigger than NUM bytes.  GCC can then access the
     data more efficiently; see `-mgpopt' for details.

     The default `-G' option depends on the configuration.

`-mlocal-sdata'
`-mno-local-sdata'
     Extend (do not extend) the `-G' behavior to local data too, such
     as to static variables in C.  `-mlocal-sdata' is the default for
     all configurations.

     If the linker complains that an application is using too much
     small data, you might want to try rebuilding the less
     performance-critical parts with `-mno-local-sdata'.  You might
     also want to build large libraries with `-mno-local-sdata', so
     that the libraries leave more room for the main program.

`-mextern-sdata'
`-mno-extern-sdata'
     Assume (do not assume) that externally-defined data will be in a
     small data section if that data is within the `-G' limit.
     `-mextern-sdata' is the default for all configurations.

     If you compile a module MOD with `-mextern-sdata' `-G NUM'
     `-mgpopt', and MOD references a variable VAR that is no bigger
     than NUM bytes, you must make sure that VAR is placed in a small
     data section.  If VAR is defined by another module, you must
     either compile that module with a high-enough `-G' setting or
     attach a `section' attribute to VAR's definition.  If VAR is
     common, you must link the application with a high-enough `-G'
     setting.

     The easiest way of satisfying these restrictions is to compile and
     link every module with the same `-G' option.  However, you may
     wish to build a library that supports several different small data
     limits.  You can do this by compiling the library with the highest
     supported `-G' setting and additionally using `-mno-extern-sdata'
     to stop the library from making assumptions about
     externally-defined data.

`-mgpopt'
`-mno-gpopt'
     Use (do not use) GP-relative accesses for symbols that are known
     to be in a small data section; see `-G', `-mlocal-sdata' and
     `-mextern-sdata'.  `-mgpopt' is the default for all configurations.

     `-mno-gpopt' is useful for cases where the `$gp' register might
     not hold the value of `_gp'.  For example, if the code is part of
     a library that might be used in a boot monitor, programs that call
     boot monitor routines will pass an unknown value in `$gp'.  (In
     such situations, the boot monitor itself would usually be compiled
     with `-G0'.)

     `-mno-gpopt' implies `-mno-local-sdata' and `-mno-extern-sdata'.

`-membedded-data'
`-mno-embedded-data'
     Allocate variables to the read-only data section first if
     possible, then next in the small data section if possible,
     otherwise in data.  This gives slightly slower code than the
     default, but reduces the amount of RAM required when executing,
     and thus may be preferred for some embedded systems.

`-muninit-const-in-rodata'
`-mno-uninit-const-in-rodata'
     Put uninitialized `const' variables in the read-only data section.
     This option is only meaningful in conjunction with
     `-membedded-data'.

`-mcode-readable=SETTING'
     Specify whether GCC may generate code that reads from executable
     sections.  There are three possible settings:

    `-mcode-readable=yes'
          Instructions may freely access executable sections.  This is
          the default setting.

    `-mcode-readable=pcrel'
          MIPS16 PC-relative load instructions can access executable
          sections, but other instructions must not do so.  This option
          is useful on 4KSc and 4KSd processors when the code TLBs have
          the Read Inhibit bit set.  It is also useful on processors
          that can be configured to have a dual instruction/data SRAM
          interface and that, like the M4K, automatically redirect
          PC-relative loads to the instruction RAM.

    `-mcode-readable=no'
          Instructions must not access executable sections.  This
          option can be useful on targets that are configured to have a
          dual instruction/data SRAM interface but that (unlike the
          M4K) do not automatically redirect PC-relative loads to the
          instruction RAM.

`-msplit-addresses'
`-mno-split-addresses'
     Enable (disable) use of the `%hi()' and `%lo()' assembler
     relocation operators.  This option has been superseded by
     `-mexplicit-relocs' but is retained for backwards compatibility.

`-mexplicit-relocs'
`-mno-explicit-relocs'
     Use (do not use) assembler relocation operators when dealing with
     symbolic addresses.  The alternative, selected by
     `-mno-explicit-relocs', is to use assembler macros instead.

     `-mexplicit-relocs' is the default if GCC was configured to use an
     assembler that supports relocation operators.

`-mcheck-zero-division'
`-mno-check-zero-division'
     Trap (do not trap) on integer division by zero.

     The default is `-mcheck-zero-division'.

`-mdivide-traps'
`-mdivide-breaks'
     MIPS systems check for division by zero by generating either a
     conditional trap or a break instruction.  Using traps results in
     smaller code, but is only supported on MIPS II and later.  Also,
     some versions of the Linux kernel have a bug that prevents trap
     from generating the proper signal (`SIGFPE').  Use
     `-mdivide-traps' to allow conditional traps on architectures that
     support them and `-mdivide-breaks' to force the use of breaks.

     The default is usually `-mdivide-traps', but this can be
     overridden at configure time using `--with-divide=breaks'.
     Divide-by-zero checks can be completely disabled using
     `-mno-check-zero-division'.

`-mmemcpy'
`-mno-memcpy'
     Force (do not force) the use of `memcpy()' for non-trivial block
     moves.  The default is `-mno-memcpy', which allows GCC to inline
     most constant-sized copies.

`-mlong-calls'
`-mno-long-calls'
     Disable (do not disable) use of the `jal' instruction.  Calling
     functions using `jal' is more efficient but requires the caller
     and callee to be in the same 256 megabyte segment.

     This option has no effect on abicalls code.  The default is
     `-mno-long-calls'.

`-mmad'
`-mno-mad'
     Enable (disable) use of the `mad', `madu' and `mul' instructions,
     as provided by the R4650 ISA.

`-mfused-madd'
`-mno-fused-madd'
     Enable (disable) use of the floating point multiply-accumulate
     instructions, when they are available.  The default is
     `-mfused-madd'.

     When multiply-accumulate instructions are used, the intermediate
     product is calculated to infinite precision and is not subject to
     the FCSR Flush to Zero bit.  This may be undesirable in some
     circumstances.

`-nocpp'
     Tell the MIPS assembler to not run its preprocessor over user
     assembler files (with a `.s' suffix) when assembling them.

`-mfix-r4000'
`-mno-fix-r4000'
     Work around certain R4000 CPU errata:
        - A double-word or a variable shift may give an incorrect
          result if executed immediately after starting an integer
          division.

        - A double-word or a variable shift may give an incorrect
          result if executed while an integer multiplication is in
          progress.

        - An integer division may give an incorrect result if started
          in a delay slot of a taken branch or a jump.

`-mfix-r4400'
`-mno-fix-r4400'
     Work around certain R4400 CPU errata:
        - A double-word or a variable shift may give an incorrect
          result if executed immediately after starting an integer
          division.

`-mfix-r10000'
`-mno-fix-r10000'
     Work around certain R10000 errata:
        - `ll'/`sc' sequences may not behave atomically on revisions
          prior to 3.0.  They may deadlock on revisions 2.6 and earlier.

     This option can only be used if the target architecture supports
     branch-likely instructions.  `-mfix-r10000' is the default when
     `-march=r10000' is used; `-mno-fix-r10000' is the default
     otherwise.

`-mfix-vr4120'
`-mno-fix-vr4120'
     Work around certain VR4120 errata:
        - `dmultu' does not always produce the correct result.

        - `div' and `ddiv' do not always produce the correct result if
          one of the operands is negative.
     The workarounds for the division errata rely on special functions
     in `libgcc.a'.  At present, these functions are only provided by
     the `mips64vr*-elf' configurations.

     Other VR4120 errata require a nop to be inserted between certain
     pairs of instructions.  These errata are handled by the assembler,
     not by GCC itself.

`-mfix-vr4130'
     Work around the VR4130 `mflo'/`mfhi' errata.  The workarounds are
     implemented by the assembler rather than by GCC, although GCC will
     avoid using `mflo' and `mfhi' if the VR4130 `macc', `macchi',
     `dmacc' and `dmacchi' instructions are available instead.

`-mfix-sb1'
`-mno-fix-sb1'
     Work around certain SB-1 CPU core errata.  (This flag currently
     works around the SB-1 revision 2 "F1" and "F2" floating point
     errata.)

`-mr10k-cache-barrier=SETTING'
     Specify whether GCC should insert cache barriers to avoid the
     side-effects of speculation on R10K processors.

     In common with many processors, the R10K tries to predict the
     outcome of a conditional branch and speculatively executes
     instructions from the "taken" branch.  It later aborts these
     instructions if the predicted outcome was wrong.  However, on the
     R10K, even aborted instructions can have side effects.

     This problem only affects kernel stores and, depending on the
     system, kernel loads.  As an example, a speculatively-executed
     store may load the target memory into cache and mark the cache
     line as dirty, even if the store itself is later aborted.  If a
     DMA operation writes to the same area of memory before the "dirty"
     line is flushed, the cached data will overwrite the DMA-ed data.
     See the R10K processor manual for a full description, including
     other potential problems.

     One workaround is to insert cache barrier instructions before
     every memory access that might be speculatively executed and that
     might have side effects even if aborted.
     `-mr10k-cache-barrier=SETTING' controls GCC's implementation of
     this workaround.  It assumes that aborted accesses to any byte in
     the following regions will not have side effects:

       1. the memory occupied by the current function's stack frame;

       2. the memory occupied by an incoming stack argument;

       3. the memory occupied by an object with a link-time-constant
          address.

     It is the kernel's responsibility to ensure that speculative
     accesses to these regions are indeed safe.

     If the input program contains a function declaration such as:

          void foo (void);

     then the implementation of `foo' must allow `j foo' and `jal foo'
     to be executed speculatively.  GCC honors this restriction for
     functions it compiles itself.  It expects non-GCC functions (such
     as hand-written assembly code) to do the same.

     The option has three forms:

    `-mr10k-cache-barrier=load-store'
          Insert a cache barrier before a load or store that might be
          speculatively executed and that might have side effects even
          if aborted.

    `-mr10k-cache-barrier=store'
          Insert a cache barrier before a store that might be
          speculatively executed and that might have side effects even
          if aborted.

    `-mr10k-cache-barrier=none'
          Disable the insertion of cache barriers.  This is the default
          setting.

`-mflush-func=FUNC'
`-mno-flush-func'
     Specifies the function to call to flush the I and D caches, or to
     not call any such function.  If called, the function must take the
     same arguments as the common `_flush_func()', that is, the address
     of the memory range for which the cache is being flushed, the size
     of the memory range, and the number 3 (to flush both caches).  The
     default depends on the target GCC was configured for, but commonly
     is either `_flush_func' or `__cpu_flush'.

`mbranch-cost=NUM'
     Set the cost of branches to roughly NUM "simple" instructions.
     This cost is only a heuristic and is not guaranteed to produce
     consistent results across releases.  A zero cost redundantly
     selects the default, which is based on the `-mtune' setting.

`-mbranch-likely'
`-mno-branch-likely'
     Enable or disable use of Branch Likely instructions, regardless of
     the default for the selected architecture.  By default, Branch
     Likely instructions may be generated if they are supported by the
     selected architecture.  An exception is for the MIPS32 and MIPS64
     architectures and processors which implement those architectures;
     for those, Branch Likely instructions will not be generated by
     default because the MIPS32 and MIPS64 architectures specifically
     deprecate their use.

`-mfp-exceptions'
`-mno-fp-exceptions'
     Specifies whether FP exceptions are enabled.  This affects how we
     schedule FP instructions for some processors.  The default is that
     FP exceptions are enabled.

     For instance, on the SB-1, if FP exceptions are disabled, and we
     are emitting 64-bit code, then we can use both FP pipes.
     Otherwise, we can only use one FP pipe.

`-mvr4130-align'
`-mno-vr4130-align'
     The VR4130 pipeline is two-way superscalar, but can only issue two
     instructions together if the first one is 8-byte aligned.  When
     this option is enabled, GCC will align pairs of instructions that
     it thinks should execute in parallel.

     This option only has an effect when optimizing for the VR4130.  It
     normally makes code faster, but at the expense of making it bigger.
     It is enabled by default at optimization level `-O3'.

File: gcc.info,  Node: MMIX Options,  Next: MN10300 Options,  Prev: MIPS Options,  Up: Submodel Options

3.17.24 MMIX Options
--------------------

These options are defined for the MMIX:

`-mlibfuncs'
`-mno-libfuncs'
     Specify that intrinsic library functions are being compiled,
     passing all values in registers, no matter the size.

`-mepsilon'
`-mno-epsilon'
     Generate floating-point comparison instructions that compare with
     respect to the `rE' epsilon register.

`-mabi=mmixware'
`-mabi=gnu'
     Generate code that passes function parameters and return values
     that (in the called function) are seen as registers `$0' and up,
     as opposed to the GNU ABI which uses global registers `$231' and
     up.

`-mzero-extend'
`-mno-zero-extend'
     When reading data from memory in sizes shorter than 64 bits, use
     (do not use) zero-extending load instructions by default, rather
     than sign-extending ones.

`-mknuthdiv'
`-mno-knuthdiv'
     Make the result of a division yielding a remainder have the same
     sign as the divisor.  With the default, `-mno-knuthdiv', the sign
     of the remainder follows the sign of the dividend.  Both methods
     are arithmetically valid, the latter being almost exclusively used.

`-mtoplevel-symbols'
`-mno-toplevel-symbols'
     Prepend (do not prepend) a `:' to all global symbols, so the
     assembly code can be used with the `PREFIX' assembly directive.

`-melf'
     Generate an executable in the ELF format, rather than the default
     `mmo' format used by the `mmix' simulator.

`-mbranch-predict'
`-mno-branch-predict'
     Use (do not use) the probable-branch instructions, when static
     branch prediction indicates a probable branch.

`-mbase-addresses'
`-mno-base-addresses'
     Generate (do not generate) code that uses _base addresses_.  Using
     a base address automatically generates a request (handled by the
     assembler and the linker) for a constant to be set up in a global
     register.  The register is used for one or more base address
     requests within the range 0 to 255 from the value held in the
     register.  The generally leads to short and fast code, but the
     number of different data items that can be addressed is limited.
     This means that a program that uses lots of static data may
     require `-mno-base-addresses'.

`-msingle-exit'
`-mno-single-exit'
     Force (do not force) generated code to have a single exit point in
     each function.

File: gcc.info,  Node: MN10300 Options,  Next: PDP-11 Options,  Prev: MMIX Options,  Up: Submodel Options

3.17.25 MN10300 Options
-----------------------

These `-m' options are defined for Matsushita MN10300 architectures:

`-mmult-bug'
     Generate code to avoid bugs in the multiply instructions for the
     MN10300 processors.  This is the default.

`-mno-mult-bug'
     Do not generate code to avoid bugs in the multiply instructions
     for the MN10300 processors.

`-mam33'
     Generate code which uses features specific to the AM33 processor.

`-mno-am33'
     Do not generate code which uses features specific to the AM33
     processor.  This is the default.

`-mreturn-pointer-on-d0'
     When generating a function which returns a pointer, return the
     pointer in both `a0' and `d0'.  Otherwise, the pointer is returned
     only in a0, and attempts to call such functions without a prototype
     would result in errors.  Note that this option is on by default;
     use `-mno-return-pointer-on-d0' to disable it.

`-mno-crt0'
     Do not link in the C run-time initialization object file.

`-mrelax'
     Indicate to the linker that it should perform a relaxation
     optimization pass to shorten branches, calls and absolute memory
     addresses.  This option only has an effect when used on the
     command line for the final link step.

     This option makes symbolic debugging impossible.

File: gcc.info,  Node: PDP-11 Options,  Next: picoChip Options,  Prev: MN10300 Options,  Up: Submodel Options

3.17.26 PDP-11 Options
----------------------

These options are defined for the PDP-11:

`-mfpu'
     Use hardware FPP floating point.  This is the default.  (FIS
     floating point on the PDP-11/40 is not supported.)

`-msoft-float'
     Do not use hardware floating point.

`-mac0'
     Return floating-point results in ac0 (fr0 in Unix assembler
     syntax).

`-mno-ac0'
     Return floating-point results in memory.  This is the default.

`-m40'
     Generate code for a PDP-11/40.

`-m45'
     Generate code for a PDP-11/45.  This is the default.

`-m10'
     Generate code for a PDP-11/10.

`-mbcopy-builtin'
     Use inline `movmemhi' patterns for copying memory.  This is the
     default.

`-mbcopy'
     Do not use inline `movmemhi' patterns for copying memory.

`-mint16'
`-mno-int32'
     Use 16-bit `int'.  This is the default.

`-mint32'
`-mno-int16'
     Use 32-bit `int'.

`-mfloat64'
`-mno-float32'
     Use 64-bit `float'.  This is the default.

`-mfloat32'
`-mno-float64'
     Use 32-bit `float'.

`-mabshi'
     Use `abshi2' pattern.  This is the default.

`-mno-abshi'
     Do not use `abshi2' pattern.

`-mbranch-expensive'
     Pretend that branches are expensive.  This is for experimenting
     with code generation only.

`-mbranch-cheap'
     Do not pretend that branches are expensive.  This is the default.

`-msplit'
     Generate code for a system with split I&D.

`-mno-split'
     Generate code for a system without split I&D.  This is the default.

`-munix-asm'
     Use Unix assembler syntax.  This is the default when configured for
     `pdp11-*-bsd'.

`-mdec-asm'
     Use DEC assembler syntax.  This is the default when configured for
     any PDP-11 target other than `pdp11-*-bsd'.

File: gcc.info,  Node: picoChip Options,  Next: PowerPC Options,  Prev: PDP-11 Options,  Up: Submodel Options

3.17.27 picoChip Options
------------------------

These `-m' options are defined for picoChip implementations:

`-mae=AE_TYPE'
     Set the instruction set, register set, and instruction scheduling
     parameters for array element type AE_TYPE.  Supported values for
     AE_TYPE are `ANY', `MUL', and `MAC'.

     `-mae=ANY' selects a completely generic AE type.  Code generated
     with this option will run on any of the other AE types.  The code
     will not be as efficient as it would be if compiled for a specific
     AE type, and some types of operation (e.g., multiplication) will
     not work properly on all types of AE.

     `-mae=MUL' selects a MUL AE type.  This is the most useful AE type
     for compiled code, and is the default.

     `-mae=MAC' selects a DSP-style MAC AE.  Code compiled with this
     option may suffer from poor performance of byte (char)
     manipulation, since the DSP AE does not provide hardware support
     for byte load/stores.

`-msymbol-as-address'
     Enable the compiler to directly use a symbol name as an address in
     a load/store instruction, without first loading it into a
     register.  Typically, the use of this option will generate larger
     programs, which run faster than when the option isn't used.
     However, the results vary from program to program, so it is left
     as a user option, rather than being permanently enabled.

`-mno-inefficient-warnings'
     Disables warnings about the generation of inefficient code.  These
     warnings can be generated, for example, when compiling code which
     performs byte-level memory operations on the MAC AE type.  The MAC
     AE has no hardware support for byte-level memory operations, so
     all byte load/stores must be synthesized from word load/store
     operations.  This is inefficient and a warning will be generated
     indicating to the programmer that they should rewrite the code to
     avoid byte operations, or to target an AE type which has the
     necessary hardware support.  This option enables the warning to be
     turned off.


File: gcc.info,  Node: PowerPC Options,  Next: RS/6000 and PowerPC Options,  Prev: picoChip Options,  Up: Submodel Options

3.17.28 PowerPC Options
-----------------------

These are listed under *Note RS/6000 and PowerPC Options::.

File: gcc.info,  Node: RS/6000 and PowerPC Options,  Next: S/390 and zSeries Options,  Prev: PowerPC Options,  Up: Submodel Options

3.17.29 IBM RS/6000 and PowerPC Options
---------------------------------------

These `-m' options are defined for the IBM RS/6000 and PowerPC:
`-mpower'
`-mno-power'
`-mpower2'
`-mno-power2'
`-mpowerpc'
`-mno-powerpc'
`-mpowerpc-gpopt'
`-mno-powerpc-gpopt'
`-mpowerpc-gfxopt'
`-mno-powerpc-gfxopt'
`-mpowerpc64'
`-mno-powerpc64'
`-mmfcrf'
`-mno-mfcrf'
`-mpopcntb'
`-mno-popcntb'
`-mpopcntd'
`-mno-popcntd'
`-mfprnd'
`-mno-fprnd'
`-mcmpb'
`-mno-cmpb'
`-mmfpgpr'
`-mno-mfpgpr'
`-mhard-dfp'
`-mno-hard-dfp'
     GCC supports two related instruction set architectures for the
     RS/6000 and PowerPC.  The "POWER" instruction set are those
     instructions supported by the `rios' chip set used in the original
     RS/6000 systems and the "PowerPC" instruction set is the
     architecture of the Freescale MPC5xx, MPC6xx, MPC8xx
     microprocessors, and the IBM 4xx, 6xx, and follow-on
     microprocessors.

     Neither architecture is a subset of the other.  However there is a
     large common subset of instructions supported by both.  An MQ
     register is included in processors supporting the POWER
     architecture.

     You use these options to specify which instructions are available
     on the processor you are using.  The default value of these
     options is determined when configuring GCC.  Specifying the
     `-mcpu=CPU_TYPE' overrides the specification of these options.  We
     recommend you use the `-mcpu=CPU_TYPE' option rather than the
     options listed above.

     The `-mpower' option allows GCC to generate instructions that are
     found only in the POWER architecture and to use the MQ register.
     Specifying `-mpower2' implies `-power' and also allows GCC to
     generate instructions that are present in the POWER2 architecture
     but not the original POWER architecture.

     The `-mpowerpc' option allows GCC to generate instructions that
     are found only in the 32-bit subset of the PowerPC architecture.
     Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
     GCC to use the optional PowerPC architecture instructions in the
     General Purpose group, including floating-point square root.
     Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows
     GCC to use the optional PowerPC architecture instructions in the
     Graphics group, including floating-point select.

     The `-mmfcrf' option allows GCC to generate the move from
     condition register field instruction implemented on the POWER4
     processor and other processors that support the PowerPC V2.01
     architecture.  The `-mpopcntb' option allows GCC to generate the
     popcount and double precision FP reciprocal estimate instruction
     implemented on the POWER5 processor and other processors that
     support the PowerPC V2.02 architecture.  The `-mpopcntd' option
     allows GCC to generate the popcount instruction implemented on the
     POWER7 processor and other processors that support the PowerPC
     V2.06 architecture.  The `-mfprnd' option allows GCC to generate
     the FP round to integer instructions implemented on the POWER5+
     processor and other processors that support the PowerPC V2.03
     architecture.  The `-mcmpb' option allows GCC to generate the
     compare bytes instruction implemented on the POWER6 processor and
     other processors that support the PowerPC V2.05 architecture.  The
     `-mmfpgpr' option allows GCC to generate the FP move to/from
     general purpose register instructions implemented on the POWER6X
     processor and other processors that support the extended PowerPC
     V2.05 architecture.  The `-mhard-dfp' option allows GCC to
     generate the decimal floating point instructions implemented on
     some POWER processors.

     The `-mpowerpc64' option allows GCC to generate the additional
     64-bit instructions that are found in the full PowerPC64
     architecture and to treat GPRs as 64-bit, doubleword quantities.
     GCC defaults to `-mno-powerpc64'.

     If you specify both `-mno-power' and `-mno-powerpc', GCC will use
     only the instructions in the common subset of both architectures
     plus some special AIX common-mode calls, and will not use the MQ
     register.  Specifying both `-mpower' and `-mpowerpc' permits GCC
     to use any instruction from either architecture and to allow use
     of the MQ register; specify this for the Motorola MPC601.

`-mnew-mnemonics'
`-mold-mnemonics'
     Select which mnemonics to use in the generated assembler code.
     With `-mnew-mnemonics', GCC uses the assembler mnemonics defined
     for the PowerPC architecture.  With `-mold-mnemonics' it uses the
     assembler mnemonics defined for the POWER architecture.
     Instructions defined in only one architecture have only one
     mnemonic; GCC uses that mnemonic irrespective of which of these
     options is specified.

     GCC defaults to the mnemonics appropriate for the architecture in
     use.  Specifying `-mcpu=CPU_TYPE' sometimes overrides the value of
     these option.  Unless you are building a cross-compiler, you
     should normally not specify either `-mnew-mnemonics' or
     `-mold-mnemonics', but should instead accept the default.

`-mcpu=CPU_TYPE'
     Set architecture type, register usage, choice of mnemonics, and
     instruction scheduling parameters for machine type CPU_TYPE.
     Supported values for CPU_TYPE are `401', `403', `405', `405fp',
     `440', `440fp', `464', `464fp', `505', `601', `602', `603',
     `603e', `604', `604e', `620', `630', `740', `7400', `7450', `750',
     `801', `821', `823', `860', `970', `8540', `e300c2', `e300c3',
     `e500mc', `ec603e', `G3', `G4', `G5', `power', `power2', `power3',
     `power4', `power5', `power5+', `power6', `power6x', `power7',
     `common', `powerpc', `powerpc64', `rios', `rios1', `rios2', `rsc',
     and `rs64'.

     `-mcpu=common' selects a completely generic processor.  Code
     generated under this option will run on any POWER or PowerPC
     processor.  GCC will use only the instructions in the common
     subset of both architectures, and will not use the MQ register.
     GCC assumes a generic processor model for scheduling purposes.

     `-mcpu=power', `-mcpu=power2', `-mcpu=powerpc', and
     `-mcpu=powerpc64' specify generic POWER, POWER2, pure 32-bit
     PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
     types, with an appropriate, generic processor model assumed for
     scheduling purposes.

     The other options specify a specific processor.  Code generated
     under those options will run best on that processor, and may not
     run at all on others.

     The `-mcpu' options automatically enable or disable the following
     options:

          -maltivec  -mfprnd  -mhard-float  -mmfcrf  -mmultiple
          -mnew-mnemonics  -mpopcntb -mpopcntd  -mpower  -mpower2  -mpowerpc64
          -mpowerpc-gpopt  -mpowerpc-gfxopt  -msingle-float -mdouble-float
          -msimple-fpu -mstring  -mmulhw  -mdlmzb  -mmfpgpr -mvsx

     The particular options set for any particular CPU will vary between
     compiler versions, depending on what setting seems to produce
     optimal code for that CPU; it doesn't necessarily reflect the
     actual hardware's capabilities.  If you wish to set an individual
     option to a particular value, you may specify it after the `-mcpu'
     option, like `-mcpu=970 -mno-altivec'.

     On AIX, the `-maltivec' and `-mpowerpc64' options are not enabled
     or disabled by the `-mcpu' option at present because AIX does not
     have full support for these options.  You may still enable or
     disable them individually if you're sure it'll work in your
     environment.

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the architecture type, register usage, or
     choice of mnemonics, as `-mcpu=CPU_TYPE' would.  The same values
     for CPU_TYPE are used for `-mtune' as for `-mcpu'.  If both are
     specified, the code generated will use the architecture,
     registers, and mnemonics set by `-mcpu', but the scheduling
     parameters set by `-mtune'.

`-mcmodel=small'
     Generate PowerPC64 code for the small model: The TOC is limited to
     64k.

`-mcmodel=medium'
     Generate PowerPC64 code for the medium model: The TOC and other
     static data may be up to a total of 4G in size.

`-mcmodel=large'
     Generate PowerPC64 code for the large model: The TOC may be up to
     4G in size.  Other data and code is only limited by the 64-bit
     address space.

`-mswdiv'
`-mno-swdiv'
     Generate code to compute division as reciprocal estimate and
     iterative refinement, creating opportunities for increased
     throughput.  This feature requires: optional PowerPC Graphics
     instruction set for single precision and FRE instruction for
     double precision, assuming divides cannot generate user-visible
     traps, and the domain values not include Infinities, denormals or
     zero denominator.

`-maltivec'
`-mno-altivec'
     Generate code that uses (does not use) AltiVec instructions, and
     also enable the use of built-in functions that allow more direct
     access to the AltiVec instruction set.  You may also need to set
     `-mabi=altivec' to adjust the current ABI with AltiVec ABI
     enhancements.

`-mvrsave'
`-mno-vrsave'
     Generate VRSAVE instructions when generating AltiVec code.

`-mgen-cell-microcode'
     Generate Cell microcode instructions

`-mwarn-cell-microcode'
     Warning when a Cell microcode instruction is going to emitted.  An
     example of a Cell microcode instruction is a variable shift.

`-msecure-plt'
     Generate code that allows ld and ld.so to build executables and
     shared libraries with non-exec .plt and .got sections.  This is a
     PowerPC 32-bit SYSV ABI option.

`-mbss-plt'
     Generate code that uses a BSS .plt section that ld.so fills in, and
     requires .plt and .got sections that are both writable and
     executable.  This is a PowerPC 32-bit SYSV ABI option.

`-misel'
`-mno-isel'
     This switch enables or disables the generation of ISEL
     instructions.

`-misel=YES/NO'
     This switch has been deprecated.  Use `-misel' and `-mno-isel'
     instead.

`-mspe'
`-mno-spe'
     This switch enables or disables the generation of SPE simd
     instructions.

`-mpaired'
`-mno-paired'
     This switch enables or disables the generation of PAIRED simd
     instructions.

`-mspe=YES/NO'
     This option has been deprecated.  Use `-mspe' and `-mno-spe'
     instead.

`-mvsx'
`-mno-vsx'
     Generate code that uses (does not use) vector/scalar (VSX)
     instructions, and also enable the use of built-in functions that
     allow more direct access to the VSX instruction set.

`-mfloat-gprs=YES/SINGLE/DOUBLE/NO'
`-mfloat-gprs'
     This switch enables or disables the generation of floating point
     operations on the general purpose registers for architectures that
     support it.

     The argument YES or SINGLE enables the use of single-precision
     floating point operations.

     The argument DOUBLE enables the use of single and double-precision
     floating point operations.

     The argument NO disables floating point operations on the general
     purpose registers.

     This option is currently only available on the MPC854x.

`-m32'
`-m64'
     Generate code for 32-bit or 64-bit environments of Darwin and SVR4
     targets (including GNU/Linux).  The 32-bit environment sets int,
     long and pointer to 32 bits and generates code that runs on any
     PowerPC variant.  The 64-bit environment sets int to 32 bits and
     long and pointer to 64 bits, and generates code for PowerPC64, as
     for `-mpowerpc64'.

`-mfull-toc'
`-mno-fp-in-toc'
`-mno-sum-in-toc'
`-mminimal-toc'
     Modify generation of the TOC (Table Of Contents), which is created
     for every executable file.  The `-mfull-toc' option is selected by
     default.  In that case, GCC will allocate at least one TOC entry
     for each unique non-automatic variable reference in your program.
     GCC will also place floating-point constants in the TOC.  However,
     only 16,384 entries are available in the TOC.

     If you receive a linker error message that saying you have
     overflowed the available TOC space, you can reduce the amount of
     TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc'
     options.  `-mno-fp-in-toc' prevents GCC from putting floating-point
     constants in the TOC and `-mno-sum-in-toc' forces GCC to generate
     code to calculate the sum of an address and a constant at run-time
     instead of putting that sum into the TOC.  You may specify one or
     both of these options.  Each causes GCC to produce very slightly
     slower and larger code at the expense of conserving TOC space.

     If you still run out of space in the TOC even when you specify
     both of these options, specify `-mminimal-toc' instead.  This
     option causes GCC to make only one TOC entry for every file.  When
     you specify this option, GCC will produce code that is slower and
     larger but which uses extremely little TOC space.  You may wish to
     use this option only on files that contain less frequently
     executed code.

`-maix64'
`-maix32'
     Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
     64-bit `long' type, and the infrastructure needed to support them.
     Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while
     `-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'.
     GCC defaults to `-maix32'.

`-mxl-compat'
`-mno-xl-compat'
     Produce code that conforms more closely to IBM XL compiler
     semantics when using AIX-compatible ABI.  Pass floating-point
     arguments to prototyped functions beyond the register save area
     (RSA) on the stack in addition to argument FPRs.  Do not assume
     that most significant double in 128-bit long double value is
     properly rounded when comparing values and converting to double.
     Use XL symbol names for long double support routines.

     The AIX calling convention was extended but not initially
     documented to handle an obscure K&R C case of calling a function
     that takes the address of its arguments with fewer arguments than
     declared.  IBM XL compilers access floating point arguments which
     do not fit in the RSA from the stack when a subroutine is compiled
     without optimization.  Because always storing floating-point
     arguments on the stack is inefficient and rarely needed, this
     option is not enabled by default and only is necessary when
     calling subroutines compiled by IBM XL compilers without
     optimization.

`-mpe'
     Support "IBM RS/6000 SP" "Parallel Environment" (PE).  Link an
     application written to use message passing with special startup
     code to enable the application to run.  The system must have PE
     installed in the standard location (`/usr/lpp/ppe.poe/'), or the
     `specs' file must be overridden with the `-specs=' option to
     specify the appropriate directory location.  The Parallel
     Environment does not support threads, so the `-mpe' option and the
     `-pthread' option are incompatible.

`-malign-natural'
`-malign-power'
     On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option
     `-malign-natural' overrides the ABI-defined alignment of larger
     types, such as floating-point doubles, on their natural size-based
     boundary.  The option `-malign-power' instructs GCC to follow the
     ABI-specified alignment rules.  GCC defaults to the standard
     alignment defined in the ABI.

     On 64-bit Darwin, natural alignment is the default, and
     `-malign-power' is not supported.

`-msoft-float'
`-mhard-float'
     Generate code that does not use (uses) the floating-point register
     set.  Software floating point emulation is provided if you use the
     `-msoft-float' option, and pass the option to GCC when linking.

`-msingle-float'
`-mdouble-float'
     Generate code for single or double-precision floating point
     operations.  `-mdouble-float' implies `-msingle-float'.

`-msimple-fpu'
     Do not generate sqrt and div instructions for hardware floating
     point unit.

`-mfpu'
     Specify type of floating point unit.  Valid values are SP_LITE
     (equivalent to -msingle-float -msimple-fpu), DP_LITE (equivalent
     to -mdouble-float -msimple-fpu), SP_FULL (equivalent to
     -msingle-float), and DP_FULL (equivalent to -mdouble-float).

`-mxilinx-fpu'
     Perform optimizations for floating point unit on Xilinx PPC
     405/440.

`-mmultiple'
`-mno-multiple'
     Generate code that uses (does not use) the load multiple word
     instructions and the store multiple word instructions.  These
     instructions are generated by default on POWER systems, and not
     generated on PowerPC systems.  Do not use `-mmultiple' on little
     endian PowerPC systems, since those instructions do not work when
     the processor is in little endian mode.  The exceptions are PPC740
     and PPC750 which permit the instructions usage in little endian
     mode.

`-mstring'
`-mno-string'
     Generate code that uses (does not use) the load string instructions
     and the store string word instructions to save multiple registers
     and do small block moves.  These instructions are generated by
     default on POWER systems, and not generated on PowerPC systems.
     Do not use `-mstring' on little endian PowerPC systems, since those
     instructions do not work when the processor is in little endian
     mode.  The exceptions are PPC740 and PPC750 which permit the
     instructions usage in little endian mode.

`-mupdate'
`-mno-update'
     Generate code that uses (does not use) the load or store
     instructions that update the base register to the address of the
     calculated memory location.  These instructions are generated by
     default.  If you use `-mno-update', there is a small window
     between the time that the stack pointer is updated and the address
     of the previous frame is stored, which means code that walks the
     stack frame across interrupts or signals may get corrupted data.

`-mavoid-indexed-addresses'

`-mno-avoid-indexed-addresses'
     Generate code that tries to avoid (not avoid) the use of indexed
     load or store instructions. These instructions can incur a
     performance penalty on Power6 processors in certain situations,
     such as when stepping through large arrays that cross a 16M
     boundary.  This option is enabled by default when targetting
     Power6 and disabled otherwise.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating is used.

`-mmulhw'
`-mno-mulhw'
     Generate code that uses (does not use) the half-word multiply and
     multiply-accumulate instructions on the IBM 405, 440 and 464
     processors.  These instructions are generated by default when
     targetting those processors.

`-mdlmzb'
`-mno-dlmzb'
     Generate code that uses (does not use) the string-search `dlmzb'
     instruction on the IBM 405, 440 and 464 processors.  This
     instruction is generated by default when targetting those
     processors.

`-mno-bit-align'
`-mbit-align'
     On System V.4 and embedded PowerPC systems do not (do) force
     structures and unions that contain bit-fields to be aligned to the
     base type of the bit-field.

     For example, by default a structure containing nothing but 8
     `unsigned' bit-fields of length 1 would be aligned to a 4 byte
     boundary and have a size of 4 bytes.  By using `-mno-bit-align',
     the structure would be aligned to a 1 byte boundary and be one
     byte in size.

`-mno-strict-align'
`-mstrict-align'
     On System V.4 and embedded PowerPC systems do not (do) assume that
     unaligned memory references will be handled by the system.

`-mrelocatable'
`-mno-relocatable'
     On embedded PowerPC systems generate code that allows (does not
     allow) the program to be relocated to a different address at
     runtime.  If you use `-mrelocatable' on any module, all objects
     linked together must be compiled with `-mrelocatable' or
     `-mrelocatable-lib'.

`-mrelocatable-lib'
`-mno-relocatable-lib'
     On embedded PowerPC systems generate code that allows (does not
     allow) the program to be relocated to a different address at
     runtime.  Modules compiled with `-mrelocatable-lib' can be linked
     with either modules compiled without `-mrelocatable' and
     `-mrelocatable-lib' or with modules compiled with the
     `-mrelocatable' options.

`-mno-toc'
`-mtoc'
     On System V.4 and embedded PowerPC systems do not (do) assume that
     register 2 contains a pointer to a global area pointing to the
     addresses used in the program.

`-mlittle'
`-mlittle-endian'
     On System V.4 and embedded PowerPC systems compile code for the
     processor in little endian mode.  The `-mlittle-endian' option is
     the same as `-mlittle'.

`-mbig'
`-mbig-endian'
     On System V.4 and embedded PowerPC systems compile code for the
     processor in big endian mode.  The `-mbig-endian' option is the
     same as `-mbig'.

`-mdynamic-no-pic'
     On Darwin and Mac OS X systems, compile code so that it is not
     relocatable, but that its external references are relocatable.  The
     resulting code is suitable for applications, but not shared
     libraries.

`-mprioritize-restricted-insns=PRIORITY'
     This option controls the priority that is assigned to
     dispatch-slot restricted instructions during the second scheduling
     pass.  The argument PRIORITY takes the value 0/1/2 to assign
     NO/HIGHEST/SECOND-HIGHEST priority to dispatch slot restricted
     instructions.

`-msched-costly-dep=DEPENDENCE_TYPE'
     This option controls which dependences are considered costly by
     the target during instruction scheduling.  The argument
     DEPENDENCE_TYPE takes one of the following values: NO: no
     dependence is costly, ALL: all dependences are costly,
     TRUE_STORE_TO_LOAD: a true dependence from store to load is costly,
     STORE_TO_LOAD: any dependence from store to load is costly,
     NUMBER: any dependence which latency >= NUMBER is costly.

`-minsert-sched-nops=SCHEME'
     This option controls which nop insertion scheme will be used during
     the second scheduling pass.  The argument SCHEME takes one of the
     following values: NO: Don't insert nops.  PAD: Pad with nops any
     dispatch group which has vacant issue slots, according to the
     scheduler's grouping.  REGROUP_EXACT: Insert nops to force costly
     dependent insns into separate groups.  Insert exactly as many nops
     as needed to force an insn to a new group, according to the
     estimated processor grouping.  NUMBER: Insert nops to force costly
     dependent insns into separate groups.  Insert NUMBER nops to force
     an insn to a new group.

`-mcall-sysv'
     On System V.4 and embedded PowerPC systems compile code using
     calling conventions that adheres to the March 1995 draft of the
     System V Application Binary Interface, PowerPC processor
     supplement.  This is the default unless you configured GCC using
     `powerpc-*-eabiaix'.

`-mcall-sysv-eabi'
     Specify both `-mcall-sysv' and `-meabi' options.

`-mcall-sysv-noeabi'
     Specify both `-mcall-sysv' and `-mno-eabi' options.

`-mcall-solaris'
     On System V.4 and embedded PowerPC systems compile code for the
     Solaris operating system.

`-mcall-linux'
     On System V.4 and embedded PowerPC systems compile code for the
     Linux-based GNU system.

`-mcall-gnu'
     On System V.4 and embedded PowerPC systems compile code for the
     Hurd-based GNU system.

`-mcall-netbsd'
     On System V.4 and embedded PowerPC systems compile code for the
     NetBSD operating system.

`-maix-struct-return'
     Return all structures in memory (as specified by the AIX ABI).

`-msvr4-struct-return'
     Return structures smaller than 8 bytes in registers (as specified
     by the SVR4 ABI).

`-mabi=ABI-TYPE'
     Extend the current ABI with a particular extension, or remove such
     extension.  Valid values are ALTIVEC, NO-ALTIVEC, SPE, NO-SPE,
     IBMLONGDOUBLE, IEEELONGDOUBLE.

`-mabi=spe'
     Extend the current ABI with SPE ABI extensions.  This does not
     change the default ABI, instead it adds the SPE ABI extensions to
     the current ABI.

`-mabi=no-spe'
     Disable Booke SPE ABI extensions for the current ABI.

`-mabi=ibmlongdouble'
     Change the current ABI to use IBM extended precision long double.
     This is a PowerPC 32-bit SYSV ABI option.

`-mabi=ieeelongdouble'
     Change the current ABI to use IEEE extended precision long double.
     This is a PowerPC 32-bit Linux ABI option.

`-mprototype'
`-mno-prototype'
     On System V.4 and embedded PowerPC systems assume that all calls to
     variable argument functions are properly prototyped.  Otherwise,
     the compiler must insert an instruction before every non
     prototyped call to set or clear bit 6 of the condition code
     register (CR) to indicate whether floating point values were
     passed in the floating point registers in case the function takes
     a variable arguments.  With `-mprototype', only calls to
     prototyped variable argument functions will set or clear the bit.

`-msim'
     On embedded PowerPC systems, assume that the startup module is
     called `sim-crt0.o' and that the standard C libraries are
     `libsim.a' and `libc.a'.  This is the default for
     `powerpc-*-eabisim' configurations.

`-mmvme'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libmvme.a' and
     `libc.a'.

`-mads'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libads.a' and
     `libc.a'.

`-myellowknife'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libyk.a' and
     `libc.a'.

`-mvxworks'
     On System V.4 and embedded PowerPC systems, specify that you are
     compiling for a VxWorks system.

`-memb'
     On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
     header to indicate that `eabi' extended relocations are used.

`-meabi'
`-mno-eabi'
     On System V.4 and embedded PowerPC systems do (do not) adhere to
     the Embedded Applications Binary Interface (eabi) which is a set of
     modifications to the System V.4 specifications.  Selecting `-meabi'
     means that the stack is aligned to an 8 byte boundary, a function
     `__eabi' is called to from `main' to set up the eabi environment,
     and the `-msdata' option can use both `r2' and `r13' to point to
     two separate small data areas.  Selecting `-mno-eabi' means that
     the stack is aligned to a 16 byte boundary, do not call an
     initialization function from `main', and the `-msdata' option will
     only use `r13' to point to a single small data area.  The `-meabi'
     option is on by default if you configured GCC using one of the
     `powerpc*-*-eabi*' options.

`-msdata=eabi'
     On System V.4 and embedded PowerPC systems, put small initialized
     `const' global and static data in the `.sdata2' section, which is
     pointed to by register `r2'.  Put small initialized non-`const'
     global and static data in the `.sdata' section, which is pointed
     to by register `r13'.  Put small uninitialized global and static
     data in the `.sbss' section, which is adjacent to the `.sdata'
     section.  The `-msdata=eabi' option is incompatible with the
     `-mrelocatable' option.  The `-msdata=eabi' option also sets the
     `-memb' option.

`-msdata=sysv'
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the `.sdata' section, which is pointed to by
     register `r13'.  Put small uninitialized global and static data in
     the `.sbss' section, which is adjacent to the `.sdata' section.
     The `-msdata=sysv' option is incompatible with the `-mrelocatable'
     option.

`-msdata=default'
`-msdata'
     On System V.4 and embedded PowerPC systems, if `-meabi' is used,
     compile code the same as `-msdata=eabi', otherwise compile code the
     same as `-msdata=sysv'.

`-msdata=data'
     On System V.4 and embedded PowerPC systems, put small global data
     in the `.sdata' section.  Put small uninitialized global data in
     the `.sbss' section.  Do not use register `r13' to address small
     data however.  This is the default behavior unless other `-msdata'
     options are used.

`-msdata=none'
`-mno-sdata'
     On embedded PowerPC systems, put all initialized global and static
     data in the `.data' section, and all uninitialized data in the
     `.bss' section.

`-G NUM'
     On embedded PowerPC systems, put global and static items less than
     or equal to NUM bytes into the small data or bss sections instead
     of the normal data or bss section.  By default, NUM is 8.  The `-G
     NUM' switch is also passed to the linker.  All modules should be
     compiled with the same `-G NUM' value.

`-mregnames'
`-mno-regnames'
     On System V.4 and embedded PowerPC systems do (do not) emit
     register names in the assembly language output using symbolic
     forms.

`-mlongcall'
`-mno-longcall'
     By default assume that all calls are far away so that a longer more
     expensive calling sequence is required.  This is required for calls
     further than 32 megabytes (33,554,432 bytes) from the current
     location.  A short call will be generated if the compiler knows
     the call cannot be that far away.  This setting can be overridden
     by the `shortcall' function attribute, or by `#pragma longcall(0)'.

     Some linkers are capable of detecting out-of-range calls and
     generating glue code on the fly.  On these systems, long calls are
     unnecessary and generate slower code.  As of this writing, the AIX
     linker can do this, as can the GNU linker for PowerPC/64.  It is
     planned to add this feature to the GNU linker for 32-bit PowerPC
     systems as well.

     On Darwin/PPC systems, `#pragma longcall' will generate "jbsr
     callee, L42", plus a "branch island" (glue code).  The two target
     addresses represent the callee and the "branch island".  The
     Darwin/PPC linker will prefer the first address and generate a "bl
     callee" if the PPC "bl" instruction will reach the callee directly;
     otherwise, the linker will generate "bl L42" to call the "branch
     island".  The "branch island" is appended to the body of the
     calling function; it computes the full 32-bit address of the callee
     and jumps to it.

     On Mach-O (Darwin) systems, this option directs the compiler emit
     to the glue for every direct call, and the Darwin linker decides
     whether to use or discard it.

     In the future, we may cause GCC to ignore all longcall
     specifications when the linker is known to generate glue.

`-pthread'
     Adds support for multithreading with the "pthreads" library.  This
     option sets flags for both the preprocessor and linker.


File: gcc.info,  Node: S/390 and zSeries Options,  Next: Score Options,  Prev: RS/6000 and PowerPC Options,  Up: Submodel Options

3.17.30 S/390 and zSeries Options
---------------------------------

These are the `-m' options defined for the S/390 and zSeries
architecture.

`-mhard-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions and
     registers for floating-point operations.  When `-msoft-float' is
     specified, functions in `libgcc.a' will be used to perform
     floating-point operations.  When `-mhard-float' is specified, the
     compiler generates IEEE floating-point instructions.  This is the
     default.

`-mhard-dfp'
`-mno-hard-dfp'
     Use (do not use) the hardware decimal-floating-point instructions
     for decimal-floating-point operations.  When `-mno-hard-dfp' is
     specified, functions in `libgcc.a' will be used to perform
     decimal-floating-point operations.  When `-mhard-dfp' is
     specified, the compiler generates decimal-floating-point hardware
     instructions.  This is the default for `-march=z9-ec' or higher.

`-mlong-double-64'
`-mlong-double-128'
     These switches control the size of `long double' type. A size of
     64bit makes the `long double' type equivalent to the `double'
     type. This is the default.

`-mbackchain'
`-mno-backchain'
     Store (do not store) the address of the caller's frame as
     backchain pointer into the callee's stack frame.  A backchain may
     be needed to allow debugging using tools that do not understand
     DWARF-2 call frame information.  When `-mno-packed-stack' is in
     effect, the backchain pointer is stored at the bottom of the stack
     frame; when `-mpacked-stack' is in effect, the backchain is placed
     into the topmost word of the 96/160 byte register save area.

     In general, code compiled with `-mbackchain' is call-compatible
     with code compiled with `-mmo-backchain'; however, use of the
     backchain for debugging purposes usually requires that the whole
     binary is built with `-mbackchain'.  Note that the combination of
     `-mbackchain', `-mpacked-stack' and `-mhard-float' is not
     supported.  In order to build a linux kernel use `-msoft-float'.

     The default is to not maintain the backchain.

`-mpacked-stack'
`-mno-packed-stack'
     Use (do not use) the packed stack layout.  When
     `-mno-packed-stack' is specified, the compiler uses the all fields
     of the 96/160 byte register save area only for their default
     purpose; unused fields still take up stack space.  When
     `-mpacked-stack' is specified, register save slots are densely
     packed at the top of the register save area; unused space is
     reused for other purposes, allowing for more efficient use of the
     available stack space.  However, when `-mbackchain' is also in
     effect, the topmost word of the save area is always used to store
     the backchain, and the return address register is always saved two
     words below the backchain.

     As long as the stack frame backchain is not used, code generated
     with `-mpacked-stack' is call-compatible with code generated with
     `-mno-packed-stack'.  Note that some non-FSF releases of GCC 2.95
     for S/390 or zSeries generated code that uses the stack frame
     backchain at run time, not just for debugging purposes.  Such code
     is not call-compatible with code compiled with `-mpacked-stack'.
     Also, note that the combination of `-mbackchain', `-mpacked-stack'
     and `-mhard-float' is not supported.  In order to build a linux
     kernel use `-msoft-float'.

     The default is to not use the packed stack layout.

`-msmall-exec'
`-mno-small-exec'
     Generate (or do not generate) code using the `bras' instruction to
     do subroutine calls.  This only works reliably if the total
     executable size does not exceed 64k.  The default is to use the
     `basr' instruction instead, which does not have this limitation.

`-m64'
`-m31'
     When `-m31' is specified, generate code compliant to the GNU/Linux
     for S/390 ABI.  When `-m64' is specified, generate code compliant
     to the GNU/Linux for zSeries ABI.  This allows GCC in particular
     to generate 64-bit instructions.  For the `s390' targets, the
     default is `-m31', while the `s390x' targets default to `-m64'.

`-mzarch'
`-mesa'
     When `-mzarch' is specified, generate code using the instructions
     available on z/Architecture.  When `-mesa' is specified, generate
     code using the instructions available on ESA/390.  Note that
     `-mesa' is not possible with `-m64'.  When generating code
     compliant to the GNU/Linux for S/390 ABI, the default is `-mesa'.
     When generating code compliant to the GNU/Linux for zSeries ABI,
     the default is `-mzarch'.

`-mmvcle'
`-mno-mvcle'
     Generate (or do not generate) code using the `mvcle' instruction
     to perform block moves.  When `-mno-mvcle' is specified, use a
     `mvc' loop instead.  This is the default unless optimizing for
     size.

`-mdebug'
`-mno-debug'
     Print (or do not print) additional debug information when
     compiling.  The default is to not print debug information.

`-march=CPU-TYPE'
     Generate code that will run on CPU-TYPE, which is the name of a
     system representing a certain processor type.  Possible values for
     CPU-TYPE are `g5', `g6', `z900', `z990', `z9-109', `z9-ec' and
     `z10'.  When generating code using the instructions available on
     z/Architecture, the default is `-march=z900'.  Otherwise, the
     default is `-march=g5'.

`-mtune=CPU-TYPE'
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  The
     list of CPU-TYPE values is the same as for `-march'.  The default
     is the value used for `-march'.

`-mtpf-trace'
`-mno-tpf-trace'
     Generate code that adds (does not add) in TPF OS specific branches
     to trace routines in the operating system.  This option is off by
     default, even when compiling for the TPF OS.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating point is used.

`-mwarn-framesize=FRAMESIZE'
     Emit a warning if the current function exceeds the given frame
     size.  Because this is a compile time check it doesn't need to be
     a real problem when the program runs.  It is intended to identify
     functions which most probably cause a stack overflow.  It is
     useful to be used in an environment with limited stack size e.g.
     the linux kernel.

`-mwarn-dynamicstack'
     Emit a warning if the function calls alloca or uses dynamically
     sized arrays.  This is generally a bad idea with a limited stack
     size.

`-mstack-guard=STACK-GUARD'
`-mstack-size=STACK-SIZE'
     If these options are provided the s390 back end emits additional
     instructions in the function prologue which trigger a trap if the
     stack size is STACK-GUARD bytes above the STACK-SIZE (remember
     that the stack on s390 grows downward).  If the STACK-GUARD option
     is omitted the smallest power of 2 larger than the frame size of
     the compiled function is chosen.  These options are intended to be
     used to help debugging stack overflow problems.  The additionally
     emitted code causes only little overhead and hence can also be
     used in production like systems without greater performance
     degradation.  The given values have to be exact powers of 2 and
     STACK-SIZE has to be greater than STACK-GUARD without exceeding
     64k.  In order to be efficient the extra code makes the assumption
     that the stack starts at an address aligned to the value given by
     STACK-SIZE.  The STACK-GUARD option can only be used in
     conjunction with STACK-SIZE.

`-mhotpatch=PRE-HALFWORDS,POST-HALFWORDS'
     If the hotpatch option is enabled, a "hot-patching" function
     prologue is generated for all functions in the compilation unit.
     The funtion label is prepended with the given number of two-byte
     NOP instructions (PRE-HALFWORDS, maximum 1000000).  After the
     label, 2 * POST-HALFWORDS bytes are appended, using the largest
     NOP like instructions the architecture allows (maximum 1000000).

     If both arguments are zero, hotpatching is disabled.

     This option can be overridden for individual functions with the
     `hotpatch' attribute.

File: gcc.info,  Node: Score Options,  Next: SH Options,  Prev: S/390 and zSeries Options,  Up: Submodel Options

3.17.31 Score Options
---------------------

These options are defined for Score implementations:

`-meb'
     Compile code for big endian mode.  This is the default.

`-mel'
     Compile code for little endian mode.

`-mnhwloop'
     Disable generate bcnz instruction.

`-muls'
     Enable generate unaligned load and store instruction.

`-mmac'
     Enable the use of multiply-accumulate instructions. Disabled by
     default.

`-mscore5'
     Specify the SCORE5 as the target architecture.

`-mscore5u'
     Specify the SCORE5U of the target architecture.

`-mscore7'
     Specify the SCORE7 as the target architecture. This is the default.

`-mscore7d'
     Specify the SCORE7D as the target architecture.

File: gcc.info,  Node: SH Options,  Next: SPARC Options,  Prev: Score Options,  Up: Submodel Options

3.17.32 SH Options
------------------

These `-m' options are defined for the SH implementations:

`-m1'
     Generate code for the SH1.

`-m2'
     Generate code for the SH2.

`-m2e'
     Generate code for the SH2e.

`-m3'
     Generate code for the SH3.

`-m3e'
     Generate code for the SH3e.

`-m4-nofpu'
     Generate code for the SH4 without a floating-point unit.

`-m4-single-only'
     Generate code for the SH4 with a floating-point unit that only
     supports single-precision arithmetic.

`-m4-single'
     Generate code for the SH4 assuming the floating-point unit is in
     single-precision mode by default.

`-m4'
     Generate code for the SH4.

`-m4a-nofpu'
     Generate code for the SH4al-dsp, or for a SH4a in such a way that
     the floating-point unit is not used.

`-m4a-single-only'
     Generate code for the SH4a, in such a way that no double-precision
     floating point operations are used.

`-m4a-single'
     Generate code for the SH4a assuming the floating-point unit is in
     single-precision mode by default.

`-m4a'
     Generate code for the SH4a.

`-m4al'
     Same as `-m4a-nofpu', except that it implicitly passes `-dsp' to
     the assembler.  GCC doesn't generate any DSP instructions at the
     moment.

`-mb'
     Compile code for the processor in big endian mode.

`-ml'
     Compile code for the processor in little endian mode.

`-mdalign'
     Align doubles at 64-bit boundaries.  Note that this changes the
     calling conventions, and thus some functions from the standard C
     library will not work unless you recompile it first with
     `-mdalign'.

`-mrelax'
     Shorten some address references at link time, when possible; uses
     the linker option `-relax'.

`-mbigtable'
     Use 32-bit offsets in `switch' tables.  The default is to use
     16-bit offsets.

`-mbitops'
     Enable the use of bit manipulation instructions on SH2A.

`-mfmovd'
     Enable the use of the instruction `fmovd'.

`-mhitachi'
     Comply with the calling conventions defined by Renesas.

`-mrenesas'
     Comply with the calling conventions defined by Renesas.

`-mno-renesas'
     Comply with the calling conventions defined for GCC before the
     Renesas conventions were available.  This option is the default
     for all targets of the SH toolchain except for `sh-symbianelf'.

`-mnomacsave'
     Mark the `MAC' register as call-clobbered, even if `-mhitachi' is
     given.

`-mieee'
     Increase IEEE-compliance of floating-point code.  At the moment,
     this is equivalent to `-fno-finite-math-only'.  When generating 16
     bit SH opcodes, getting IEEE-conforming results for comparisons of
     NANs / infinities incurs extra overhead in every floating point
     comparison, therefore the default is set to `-ffinite-math-only'.

`-minline-ic_invalidate'
     Inline code to invalidate instruction cache entries after setting
     up nested function trampolines.  This option has no effect if
     -musermode is in effect and the selected code generation option
     (e.g. -m4) does not allow the use of the icbi instruction.  If the
     selected code generation option does not allow the use of the icbi
     instruction, and -musermode is not in effect, the inlined code will
     manipulate the instruction cache address array directly with an
     associative write.  This not only requires privileged mode, but it
     will also fail if the cache line had been mapped via the TLB and
     has become unmapped.

`-misize'
     Dump instruction size and location in the assembly code.

`-mpadstruct'
     This option is deprecated.  It pads structures to multiple of 4
     bytes, which is incompatible with the SH ABI.

`-mspace'
     Optimize for space instead of speed.  Implied by `-Os'.

`-mprefergot'
     When generating position-independent code, emit function calls
     using the Global Offset Table instead of the Procedure Linkage
     Table.

`-musermode'
     Don't generate privileged mode only code; implies
     -mno-inline-ic_invalidate if the inlined code would not work in
     user mode.  This is the default when the target is `sh-*-linux*'.

`-multcost=NUMBER'
     Set the cost to assume for a multiply insn.

`-mdiv=STRATEGY'
     Set the division strategy to use for SHmedia code.  STRATEGY must
     be one of: call, call2, fp, inv, inv:minlat, inv20u, inv20l,
     inv:call, inv:call2, inv:fp .  "fp" performs the operation in
     floating point.  This has a very high latency, but needs only a
     few instructions, so it might be a good choice if your code has
     enough easily exploitable ILP to allow the compiler to schedule
     the floating point instructions together with other instructions.
     Division by zero causes a floating point exception.  "inv" uses
     integer operations to calculate the inverse of the divisor, and
     then multiplies the dividend with the inverse.  This strategy
     allows cse and hoisting of the inverse calculation.  Division by
     zero calculates an unspecified result, but does not trap.
     "inv:minlat" is a variant of "inv" where if no cse / hoisting
     opportunities have been found, or if the entire operation has been
     hoisted to the same place, the last stages of the inverse
     calculation are intertwined with the final multiply to reduce the
     overall latency, at the expense of using a few more instructions,
     and thus offering fewer scheduling opportunities with other code.
     "call" calls a library function that usually implements the
     inv:minlat strategy.  This gives high code density for
     m5-*media-nofpu compilations.  "call2" uses a different entry
     point of the same library function, where it assumes that a
     pointer to a lookup table has already been set up, which exposes
     the pointer load to cse / code hoisting optimizations.
     "inv:call", "inv:call2" and "inv:fp" all use the "inv" algorithm
     for initial code generation, but if the code stays unoptimized,
     revert to the "call", "call2", or "fp" strategies, respectively.
     Note that the potentially-trapping side effect of division by zero
     is carried by a separate instruction, so it is possible that all
     the integer instructions are hoisted out, but the marker for the
     side effect stays where it is.  A recombination to fp operations
     or a call is not possible in that case.  "inv20u" and "inv20l" are
     variants of the "inv:minlat" strategy.  In the case that the
     inverse calculation was nor separated from the multiply, they speed
     up division where the dividend fits into 20 bits (plus sign where
     applicable), by inserting a test to skip a number of operations in
     this case; this test slows down the case of larger dividends.
     inv20u assumes the case of a such a small dividend to be unlikely,
     and inv20l assumes it to be likely.

`-mdivsi3_libfunc=NAME'
     Set the name of the library function used for 32 bit signed
     division to NAME.  This only affect the name used in the call and
     inv:call division strategies, and the compiler will still expect
     the same sets of input/output/clobbered registers as if this
     option was not present.

`-mfixed-range=REGISTER-RANGE'
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator can not use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

`-madjust-unroll'
     Throttle unrolling to avoid thrashing target registers.  This
     option only has an effect if the gcc code base supports the
     TARGET_ADJUST_UNROLL_MAX target hook.

`-mindexed-addressing'
     Enable the use of the indexed addressing mode for
     SHmedia32/SHcompact.  This is only safe if the hardware and/or OS
     implement 32 bit wrap-around semantics for the indexed addressing
     mode.  The architecture allows the implementation of processors
     with 64 bit MMU, which the OS could use to get 32 bit addressing,
     but since no current hardware implementation supports this or any
     other way to make the indexed addressing mode safe to use in the
     32 bit ABI, the default is -mno-indexed-addressing.

`-mgettrcost=NUMBER'
     Set the cost assumed for the gettr instruction to NUMBER.  The
     default is 2 if `-mpt-fixed' is in effect, 100 otherwise.

`-mpt-fixed'
     Assume pt* instructions won't trap.  This will generally generate
     better scheduled code, but is unsafe on current hardware.  The
     current architecture definition says that ptabs and ptrel trap
     when the target anded with 3 is 3.  This has the unintentional
     effect of making it unsafe to schedule ptabs / ptrel before a
     branch, or hoist it out of a loop.  For example,
     __do_global_ctors, a part of libgcc that runs constructors at
     program startup, calls functions in a list which is delimited by
     -1.  With the -mpt-fixed option, the ptabs will be done before
     testing against -1.  That means that all the constructors will be
     run a bit quicker, but when the loop comes to the end of the list,
     the program crashes because ptabs loads -1 into a target register.
     Since this option is unsafe for any hardware implementing the
     current architecture specification, the default is -mno-pt-fixed.
     Unless the user specifies a specific cost with `-mgettrcost',
     -mno-pt-fixed also implies `-mgettrcost=100'; this deters register
     allocation using target registers for storing ordinary integers.

`-minvalid-symbols'
     Assume symbols might be invalid.  Ordinary function symbols
     generated by the compiler will always be valid to load with
     movi/shori/ptabs or movi/shori/ptrel, but with assembler and/or
     linker tricks it is possible to generate symbols that will cause
     ptabs / ptrel to trap.  This option is only meaningful when
     `-mno-pt-fixed' is in effect.  It will then prevent
     cross-basic-block cse, hoisting and most scheduling of symbol
     loads.  The default is `-mno-invalid-symbols'.

File: gcc.info,  Node: SPARC Options,  Next: SPU Options,  Prev: SH Options,  Up: Submodel Options

3.17.33 SPARC Options
---------------------

These `-m' options are supported on the SPARC:

`-mno-app-regs'
`-mapp-regs'
     Specify `-mapp-regs' to generate output using the global registers
     2 through 4, which the SPARC SVR4 ABI reserves for applications.
     This is the default.

     To be fully SVR4 ABI compliant at the cost of some performance
     loss, specify `-mno-app-regs'.  You should compile libraries and
     system software with this option.

`-mfpu'
`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default.

`-mno-fpu'
`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all SPARC
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this cannot be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.  The embedded
     targets `sparc-*-aout' and `sparclite-*-*' do provide software
     floating point support.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GCC, with `-msoft-float' in order for this
     to work.

`-mhard-quad-float'
     Generate output containing quad-word (long double) floating point
     instructions.

`-msoft-quad-float'
     Generate output containing library calls for quad-word (long
     double) floating point instructions.  The functions called are
     those specified in the SPARC ABI.  This is the default.

     As of this writing, there are no SPARC implementations that have
     hardware support for the quad-word floating point instructions.
     They all invoke a trap handler for one of these instructions, and
     then the trap handler emulates the effect of the instruction.
     Because of the trap handler overhead, this is much slower than
     calling the ABI library routines.  Thus the `-msoft-quad-float'
     option is the default.

`-mno-unaligned-doubles'
`-munaligned-doubles'
     Assume that doubles have 8 byte alignment.  This is the default.

     With `-munaligned-doubles', GCC assumes that doubles have 8 byte
     alignment only if they are contained in another type, or if they
     have an absolute address.  Otherwise, it assumes they have 4 byte
     alignment.  Specifying this option avoids some rare compatibility
     problems with code generated by other compilers.  It is not the
     default because it results in a performance loss, especially for
     floating point code.

`-mno-faster-structs'
`-mfaster-structs'
     With `-mfaster-structs', the compiler assumes that structures
     should have 8 byte alignment.  This enables the use of pairs of
     `ldd' and `std' instructions for copies in structure assignment,
     in place of twice as many `ld' and `st' pairs.  However, the use
     of this changed alignment directly violates the SPARC ABI.  Thus,
     it's intended only for use on targets where the developer
     acknowledges that their resulting code will not be directly in
     line with the rules of the ABI.

`-mimpure-text'
     `-mimpure-text', used in addition to `-shared', tells the compiler
     to not pass `-z text' to the linker when linking a shared object.
     Using this option, you can link position-dependent code into a
     shared object.

     `-mimpure-text' suppresses the "relocations remain against
     allocatable but non-writable sections" linker error message.
     However, the necessary relocations will trigger copy-on-write, and
     the shared object is not actually shared across processes.
     Instead of using `-mimpure-text', you should compile all source
     code with `-fpic' or `-fPIC'.

     This option is only available on SunOS and Solaris.

`-mcpu=CPU_TYPE'
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are `v7', `cypress', `v8', `supersparc', `sparclite',
     `f930', `f934', `hypersparc', `sparclite86x', `sparclet',
     `tsc701', `v9', `ultrasparc', `ultrasparc3', `niagara' and
     `niagara2'.

     Default instruction scheduling parameters are used for values that
     select an architecture and not an implementation.  These are `v7',
     `v8', `sparclite', `sparclet', `v9'.

     Here is a list of each supported architecture and their supported
     implementations.

              v7:             cypress
              v8:             supersparc, hypersparc
              sparclite:      f930, f934, sparclite86x
              sparclet:       tsc701
              v9:             ultrasparc, ultrasparc3, niagara, niagara2

     By default (unless configured otherwise), GCC generates code for
     the V7 variant of the SPARC architecture.  With `-mcpu=cypress',
     the compiler additionally optimizes it for the Cypress CY7C602
     chip, as used in the SPARCStation/SPARCServer 3xx series.  This is
     also appropriate for the older SPARCStation 1, 2, IPX etc.

     With `-mcpu=v8', GCC generates code for the V8 variant of the SPARC
     architecture.  The only difference from V7 code is that the
     compiler emits the integer multiply and integer divide
     instructions which exist in SPARC-V8 but not in SPARC-V7.  With
     `-mcpu=supersparc', the compiler additionally optimizes it for the
     SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
     series.

     With `-mcpu=sparclite', GCC generates code for the SPARClite
     variant of the SPARC architecture.  This adds the integer
     multiply, integer divide step and scan (`ffs') instructions which
     exist in SPARClite but not in SPARC-V7.  With `-mcpu=f930', the
     compiler additionally optimizes it for the Fujitsu MB86930 chip,
     which is the original SPARClite, with no FPU.  With `-mcpu=f934',
     the compiler additionally optimizes it for the Fujitsu MB86934
     chip, which is the more recent SPARClite with FPU.

     With `-mcpu=sparclet', GCC generates code for the SPARClet variant
     of the SPARC architecture.  This adds the integer multiply,
     multiply/accumulate, integer divide step and scan (`ffs')
     instructions which exist in SPARClet but not in SPARC-V7.  With
     `-mcpu=tsc701', the compiler additionally optimizes it for the
     TEMIC SPARClet chip.

     With `-mcpu=v9', GCC generates code for the V9 variant of the SPARC
     architecture.  This adds 64-bit integer and floating-point move
     instructions, 3 additional floating-point condition code registers
     and conditional move instructions.  With `-mcpu=ultrasparc', the
     compiler additionally optimizes it for the Sun UltraSPARC I/II/IIi
     chips.  With `-mcpu=ultrasparc3', the compiler additionally
     optimizes it for the Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+
     chips.  With `-mcpu=niagara', the compiler additionally optimizes
     it for Sun UltraSPARC T1 chips.  With `-mcpu=niagara2', the
     compiler additionally optimizes it for Sun UltraSPARC T2 chips.

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the instruction set or register set that
     the option `-mcpu=CPU_TYPE' would.

     The same values for `-mcpu=CPU_TYPE' can be used for
     `-mtune=CPU_TYPE', but the only useful values are those that
     select a particular cpu implementation.  Those are `cypress',
     `supersparc', `hypersparc', `f930', `f934', `sparclite86x',
     `tsc701', `ultrasparc', `ultrasparc3', `niagara', and `niagara2'.

`-mv8plus'
`-mno-v8plus'
     With `-mv8plus', GCC generates code for the SPARC-V8+ ABI.  The
     difference from the V8 ABI is that the global and out registers are
     considered 64-bit wide.  This is enabled by default on Solaris in
     32-bit mode for all SPARC-V9 processors.

`-mvis'
`-mno-vis'
     With `-mvis', GCC generates code that takes advantage of the
     UltraSPARC Visual Instruction Set extensions.  The default is
     `-mno-vis'.

 These `-m' options are supported in addition to the above on SPARC-V9
processors in 64-bit environments:

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.  It
     is only available for a few configurations and most notably not on
     Solaris and Linux.

`-m32'
`-m64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.

`-mcmodel=medlow'
     Generate code for the Medium/Low code model: 64-bit addresses,
     programs must be linked in the low 32 bits of memory.  Programs
     can be statically or dynamically linked.

`-mcmodel=medmid'
     Generate code for the Medium/Middle code model: 64-bit addresses,
     programs must be linked in the low 44 bits of memory, the text and
     data segments must be less than 2GB in size and the data segment
     must be located within 2GB of the text segment.

`-mcmodel=medany'
     Generate code for the Medium/Anywhere code model: 64-bit
     addresses, programs may be linked anywhere in memory, the text and
     data segments must be less than 2GB in size and the data segment
     must be located within 2GB of the text segment.

`-mcmodel=embmedany'
     Generate code for the Medium/Anywhere code model for embedded
     systems: 64-bit addresses, the text and data segments must be less
     than 2GB in size, both starting anywhere in memory (determined at
     link time).  The global register %g4 points to the base of the
     data segment.  Programs are statically linked and PIC is not
     supported.

`-mstack-bias'
`-mno-stack-bias'
     With `-mstack-bias', GCC assumes that the stack pointer, and frame
     pointer if present, are offset by -2047 which must be added back
     when making stack frame references.  This is the default in 64-bit
     mode.  Otherwise, assume no such offset is present.

 These switches are supported in addition to the above on Solaris:

`-threads'
     Add support for multithreading using the Solaris threads library.
     This option sets flags for both the preprocessor and linker.  This
     option does not affect the thread safety of object code produced
     by the compiler or that of libraries supplied with it.

`-pthreads'
     Add support for multithreading using the POSIX threads library.
     This option sets flags for both the preprocessor and linker.  This
     option does not affect the thread safety of object code produced
     by the compiler or that of libraries supplied with it.

`-pthread'
     This is a synonym for `-pthreads'.

File: gcc.info,  Node: SPU Options,  Next: System V Options,  Prev: SPARC Options,  Up: Submodel Options

3.17.34 SPU Options
-------------------

These `-m' options are supported on the SPU:

`-mwarn-reloc'
`-merror-reloc'
     The loader for SPU does not handle dynamic relocations.  By
     default, GCC will give an error when it generates code that
     requires a dynamic relocation.  `-mno-error-reloc' disables the
     error, `-mwarn-reloc' will generate a warning instead.

`-msafe-dma'
`-munsafe-dma'
     Instructions which initiate or test completion of DMA must not be
     reordered with respect to loads and stores of the memory which is
     being accessed.  Users typically address this problem using the
     volatile keyword, but that can lead to inefficient code in places
     where the memory is known to not change.  Rather than mark the
     memory as volatile we treat the DMA instructions as potentially
     effecting all memory.  With `-munsafe-dma' users must use the
     volatile keyword to protect memory accesses.

`-mbranch-hints'
     By default, GCC will generate a branch hint instruction to avoid
     pipeline stalls for always taken or probably taken branches.  A
     hint will not be generated closer than 8 instructions away from
     its branch.  There is little reason to disable them, except for
     debugging purposes, or to make an object a little bit smaller.

`-msmall-mem'
`-mlarge-mem'
     By default, GCC generates code assuming that addresses are never
     larger than 18 bits.  With `-mlarge-mem' code is generated that
     assumes a full 32 bit address.

`-mstdmain'
     By default, GCC links against startup code that assumes the
     SPU-style main function interface (which has an unconventional
     parameter list).  With `-mstdmain', GCC will link your program
     against startup code that assumes a C99-style interface to `main',
     including a local copy of `argv' strings.

`-mfixed-range=REGISTER-RANGE'
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator can not use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

`-mdual-nops'
`-mdual-nops=N'
     By default, GCC will insert nops to increase dual issue when it
     expects it to increase performance.  N can be a value from 0 to
     10.  A smaller N will insert fewer nops.  10 is the default, 0 is
     the same as `-mno-dual-nops'.  Disabled with `-Os'.

`-mhint-max-nops=N'
     Maximum number of nops to insert for a branch hint.  A branch hint
     must be at least 8 instructions away from the branch it is
     effecting.  GCC will insert up to N nops to enforce this,
     otherwise it will not generate the branch hint.

`-mhint-max-distance=N'
     The encoding of the branch hint instruction limits the hint to be
     within 256 instructions of the branch it is effecting.  By
     default, GCC makes sure it is within 125.

`-msafe-hints'
     Work around a hardware bug which causes the SPU to stall
     indefinitely.  By default, GCC will insert the `hbrp' instruction
     to make sure this stall won't happen.


File: gcc.info,  Node: System V Options,  Next: V850 Options,  Prev: SPU Options,  Up: Submodel Options

3.17.35 Options for System V
----------------------------

These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:

`-G'
     Create a shared object.  It is recommended that `-symbolic' or
     `-shared' be used instead.

`-Qy'
     Identify the versions of each tool used by the compiler, in a
     `.ident' assembler directive in the output.

`-Qn'
     Refrain from adding `.ident' directives to the output file (this is
     the default).

`-YP,DIRS'
     Search the directories DIRS, and no others, for libraries
     specified with `-l'.

`-Ym,DIR'
     Look in the directory DIR to find the M4 preprocessor.  The
     assembler uses this option.

File: gcc.info,  Node: V850 Options,  Next: VAX Options,  Prev: System V Options,  Up: Submodel Options

3.17.36 V850 Options
--------------------

These `-m' options are defined for V850 implementations:

`-mlong-calls'
`-mno-long-calls'
     Treat all calls as being far away (near).  If calls are assumed to
     be far away, the compiler will always load the functions address
     up into a register, and call indirect through the pointer.

`-mno-ep'
`-mep'
     Do not optimize (do optimize) basic blocks that use the same index
     pointer 4 or more times to copy pointer into the `ep' register, and
     use the shorter `sld' and `sst' instructions.  The `-mep' option
     is on by default if you optimize.

`-mno-prolog-function'
`-mprolog-function'
     Do not use (do use) external functions to save and restore
     registers at the prologue and epilogue of a function.  The
     external functions are slower, but use less code space if more
     than one function saves the same number of registers.  The
     `-mprolog-function' option is on by default if you optimize.

`-mspace'
     Try to make the code as small as possible.  At present, this just
     turns on the `-mep' and `-mprolog-function' options.

`-mtda=N'
     Put static or global variables whose size is N bytes or less into
     the tiny data area that register `ep' points to.  The tiny data
     area can hold up to 256 bytes in total (128 bytes for byte
     references).

`-msda=N'
     Put static or global variables whose size is N bytes or less into
     the small data area that register `gp' points to.  The small data
     area can hold up to 64 kilobytes.

`-mzda=N'
     Put static or global variables whose size is N bytes or less into
     the first 32 kilobytes of memory.

`-mv850'
     Specify that the target processor is the V850.

`-mbig-switch'
     Generate code suitable for big switch tables.  Use this option
     only if the assembler/linker complain about out of range branches
     within a switch table.

`-mapp-regs'
     This option will cause r2 and r5 to be used in the code generated
     by the compiler.  This setting is the default.

`-mno-app-regs'
     This option will cause r2 and r5 to be treated as fixed registers.

`-mv850e1'
     Specify that the target processor is the V850E1.  The preprocessor
     constants `__v850e1__' and `__v850e__' will be defined if this
     option is used.

`-mv850e'
     Specify that the target processor is the V850E.  The preprocessor
     constant `__v850e__' will be defined if this option is used.

     If neither `-mv850' nor `-mv850e' nor `-mv850e1' are defined then
     a default target processor will be chosen and the relevant
     `__v850*__' preprocessor constant will be defined.

     The preprocessor constants `__v850' and `__v851__' are always
     defined, regardless of which processor variant is the target.

`-mdisable-callt'
     This option will suppress generation of the CALLT instruction for
     the v850e and v850e1 flavors of the v850 architecture.  The
     default is `-mno-disable-callt' which allows the CALLT instruction
     to be used.


File: gcc.info,  Node: VAX Options,  Next: VxWorks Options,  Prev: V850 Options,  Up: Submodel Options

3.17.37 VAX Options
-------------------

These `-m' options are defined for the VAX:

`-munix'
     Do not output certain jump instructions (`aobleq' and so on) that
     the Unix assembler for the VAX cannot handle across long ranges.

`-mgnu'
     Do output those jump instructions, on the assumption that you will
     assemble with the GNU assembler.

`-mg'
     Output code for g-format floating point numbers instead of
     d-format.

File: gcc.info,  Node: VxWorks Options,  Next: x86-64 Options,  Prev: VAX Options,  Up: Submodel Options

3.17.38 VxWorks Options
-----------------------

The options in this section are defined for all VxWorks targets.
Options specific to the target hardware are listed with the other
options for that target.

`-mrtp'
     GCC can generate code for both VxWorks kernels and real time
     processes (RTPs).  This option switches from the former to the
     latter.  It also defines the preprocessor macro `__RTP__'.

`-non-static'
     Link an RTP executable against shared libraries rather than static
     libraries.  The options `-static' and `-shared' can also be used
     for RTPs (*note Link Options::); `-static' is the default.

`-Bstatic'
`-Bdynamic'
     These options are passed down to the linker.  They are defined for
     compatibility with Diab.

`-Xbind-lazy'
     Enable lazy binding of function calls.  This option is equivalent
     to `-Wl,-z,now' and is defined for compatibility with Diab.

`-Xbind-now'
     Disable lazy binding of function calls.  This option is the
     default and is defined for compatibility with Diab.

File: gcc.info,  Node: x86-64 Options,  Next: Xstormy16 Options,  Prev: VxWorks Options,  Up: Submodel Options

3.17.39 x86-64 Options
----------------------

These are listed under *Note i386 and x86-64 Options::.

File: gcc.info,  Node: Xstormy16 Options,  Next: Xtensa Options,  Prev: x86-64 Options,  Up: Submodel Options

3.17.40 Xstormy16 Options
-------------------------

These options are defined for Xstormy16:

`-msim'
     Choose startup files and linker script suitable for the simulator.

File: gcc.info,  Node: Xtensa Options,  Next: zSeries Options,  Prev: Xstormy16 Options,  Up: Submodel Options

3.17.41 Xtensa Options
----------------------

These options are supported for Xtensa targets:

`-mconst16'
`-mno-const16'
     Enable or disable use of `CONST16' instructions for loading
     constant values.  The `CONST16' instruction is currently not a
     standard option from Tensilica.  When enabled, `CONST16'
     instructions are always used in place of the standard `L32R'
     instructions.  The use of `CONST16' is enabled by default only if
     the `L32R' instruction is not available.

`-mfused-madd'
`-mno-fused-madd'
     Enable or disable use of fused multiply/add and multiply/subtract
     instructions in the floating-point option.  This has no effect if
     the floating-point option is not also enabled.  Disabling fused
     multiply/add and multiply/subtract instructions forces the
     compiler to use separate instructions for the multiply and
     add/subtract operations.  This may be desirable in some cases
     where strict IEEE 754-compliant results are required: the fused
     multiply add/subtract instructions do not round the intermediate
     result, thereby producing results with _more_ bits of precision
     than specified by the IEEE standard.  Disabling fused multiply
     add/subtract instructions also ensures that the program output is
     not sensitive to the compiler's ability to combine multiply and
     add/subtract operations.

`-mserialize-volatile'
`-mno-serialize-volatile'
     When this option is enabled, GCC inserts `MEMW' instructions before
     `volatile' memory references to guarantee sequential consistency.
     The default is `-mserialize-volatile'.  Use
     `-mno-serialize-volatile' to omit the `MEMW' instructions.

`-mtext-section-literals'
`-mno-text-section-literals'
     Control the treatment of literal pools.  The default is
     `-mno-text-section-literals', which places literals in a separate
     section in the output file.  This allows the literal pool to be
     placed in a data RAM/ROM, and it also allows the linker to combine
     literal pools from separate object files to remove redundant
     literals and improve code size.  With `-mtext-section-literals',
     the literals are interspersed in the text section in order to keep
     them as close as possible to their references.  This may be
     necessary for large assembly files.

`-mtarget-align'
`-mno-target-align'
     When this option is enabled, GCC instructs the assembler to
     automatically align instructions to reduce branch penalties at the
     expense of some code density.  The assembler attempts to widen
     density instructions to align branch targets and the instructions
     following call instructions.  If there are not enough preceding
     safe density instructions to align a target, no widening will be
     performed.  The default is `-mtarget-align'.  These options do not
     affect the treatment of auto-aligned instructions like `LOOP',
     which the assembler will always align, either by widening density
     instructions or by inserting no-op instructions.

`-mlongcalls'
`-mno-longcalls'
     When this option is enabled, GCC instructs the assembler to
     translate direct calls to indirect calls unless it can determine
     that the target of a direct call is in the range allowed by the
     call instruction.  This translation typically occurs for calls to
     functions in other source files.  Specifically, the assembler
     translates a direct `CALL' instruction into an `L32R' followed by
     a `CALLX' instruction.  The default is `-mno-longcalls'.  This
     option should be used in programs where the call target can
     potentially be out of range.  This option is implemented in the
     assembler, not the compiler, so the assembly code generated by GCC
     will still show direct call instructions--look at the disassembled
     object code to see the actual instructions.  Note that the
     assembler will use an indirect call for every cross-file call, not
     just those that really will be out of range.

File: gcc.info,  Node: zSeries Options,  Prev: Xtensa Options,  Up: Submodel Options

3.17.42 zSeries Options
-----------------------

These are listed under *Note S/390 and zSeries Options::.

File: gcc.info,  Node: Code Gen Options,  Next: Environment Variables,  Prev: Submodel Options,  Up: Invoking GCC

3.18 Options for Code Generation Conventions
============================================

These machine-independent options control the interface conventions
used in code generation.

 Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  In the table below, only one of the
forms is listed--the one which is not the default.  You can figure out
the other form by either removing `no-' or adding it.

`-fbounds-check'
     For front-ends that support it, generate additional code to check
     that indices used to access arrays are within the declared range.
     This is currently only supported by the Java and Fortran
     front-ends, where this option defaults to true and false
     respectively.

`-ftrapv'
     This option generates traps for signed overflow on addition,
     subtraction, multiplication operations.

`-fwrapv'
     This option instructs the compiler to assume that signed arithmetic
     overflow of addition, subtraction and multiplication wraps around
     using twos-complement representation.  This flag enables some
     optimizations and disables others.  This option is enabled by
     default for the Java front-end, as required by the Java language
     specification.

`-fexceptions'
     Enable exception handling.  Generates extra code needed to
     propagate exceptions.  For some targets, this implies GCC will
     generate frame unwind information for all functions, which can
     produce significant data size overhead, although it does not
     affect execution.  If you do not specify this option, GCC will
     enable it by default for languages like C++ which normally require
     exception handling, and disable it for languages like C that do
     not normally require it.  However, you may need to enable this
     option when compiling C code that needs to interoperate properly
     with exception handlers written in C++.  You may also wish to
     disable this option if you are compiling older C++ programs that
     don't use exception handling.

`-fnon-call-exceptions'
     Generate code that allows trapping instructions to throw
     exceptions.  Note that this requires platform-specific runtime
     support that does not exist everywhere.  Moreover, it only allows
     _trapping_ instructions to throw exceptions, i.e. memory
     references or floating point instructions.  It does not allow
     exceptions to be thrown from arbitrary signal handlers such as
     `SIGALRM'.

`-funwind-tables'
     Similar to `-fexceptions', except that it will just generate any
     needed static data, but will not affect the generated code in any
     other way.  You will normally not enable this option; instead, a
     language processor that needs this handling would enable it on
     your behalf.

`-fasynchronous-unwind-tables'
     Generate unwind table in dwarf2 format, if supported by target
     machine.  The table is exact at each instruction boundary, so it
     can be used for stack unwinding from asynchronous events (such as
     debugger or garbage collector).

`-fpcc-struct-return'
     Return "short" `struct' and `union' values in memory like longer
     ones, rather than in registers.  This convention is less
     efficient, but it has the advantage of allowing intercallability
     between GCC-compiled files and files compiled with other
     compilers, particularly the Portable C Compiler (pcc).

     The precise convention for returning structures in memory depends
     on the target configuration macros.

     Short structures and unions are those whose size and alignment
     match that of some integer type.

     *Warning:* code compiled with the `-fpcc-struct-return' switch is
     not binary compatible with code compiled with the
     `-freg-struct-return' switch.  Use it to conform to a non-default
     application binary interface.

`-freg-struct-return'
     Return `struct' and `union' values in registers when possible.
     This is more efficient for small structures than
     `-fpcc-struct-return'.

     If you specify neither `-fpcc-struct-return' nor
     `-freg-struct-return', GCC defaults to whichever convention is
     standard for the target.  If there is no standard convention, GCC
     defaults to `-fpcc-struct-return', except on targets where GCC is
     the principal compiler.  In those cases, we can choose the
     standard, and we chose the more efficient register return
     alternative.

     *Warning:* code compiled with the `-freg-struct-return' switch is
     not binary compatible with code compiled with the
     `-fpcc-struct-return' switch.  Use it to conform to a non-default
     application binary interface.

`-fshort-enums'
     Allocate to an `enum' type only as many bytes as it needs for the
     declared range of possible values.  Specifically, the `enum' type
     will be equivalent to the smallest integer type which has enough
     room.

     *Warning:* the `-fshort-enums' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fshort-double'
     Use the same size for `double' as for `float'.

     *Warning:* the `-fshort-double' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fshort-wchar'
     Override the underlying type for `wchar_t' to be `short unsigned
     int' instead of the default for the target.  This option is useful
     for building programs to run under WINE.

     *Warning:* the `-fshort-wchar' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fno-common'
     In C code, controls the placement of uninitialized global
     variables.  Unix C compilers have traditionally permitted multiple
     definitions of such variables in different compilation units by
     placing the variables in a common block.  This is the behavior
     specified by `-fcommon', and is the default for GCC on most
     targets.  On the other hand, this behavior is not required by ISO
     C, and on some targets may carry a speed or code size penalty on
     variable references.  The `-fno-common' option specifies that the
     compiler should place uninitialized global variables in the data
     section of the object file, rather than generating them as common
     blocks.  This has the effect that if the same variable is declared
     (without `extern') in two different compilations, you will get a
     multiple-definition error when you link them.  In this case, you
     must compile with `-fcommon' instead.  Compiling with
     `-fno-common' is useful on targets for which it provides better
     performance, or if you wish to verify that the program will work
     on other systems which always treat uninitialized variable
     declarations this way.

`-fno-ident'
     Ignore the `#ident' directive.

`-finhibit-size-directive'
     Don't output a `.size' assembler directive, or anything else that
     would cause trouble if the function is split in the middle, and the
     two halves are placed at locations far apart in memory.  This
     option is used when compiling `crtstuff.c'; you should not need to
     use it for anything else.

`-fverbose-asm'
     Put extra commentary information in the generated assembly code to
     make it more readable.  This option is generally only of use to
     those who actually need to read the generated assembly code
     (perhaps while debugging the compiler itself).

     `-fno-verbose-asm', the default, causes the extra information to
     be omitted and is useful when comparing two assembler files.

`-frecord-gcc-switches'
     This switch causes the command line that was used to invoke the
     compiler to be recorded into the object file that is being created.
     This switch is only implemented on some targets and the exact
     format of the recording is target and binary file format
     dependent, but it usually takes the form of a section containing
     ASCII text.  This switch is related to the `-fverbose-asm' switch,
     but that switch only records information in the assembler output
     file as comments, so it never reaches the object file.

`-fpic'
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  The dynamic loader resolves the GOT entries when the
     program starts (the dynamic loader is not part of GCC; it is part
     of the operating system).  If the GOT size for the linked
     executable exceeds a machine-specific maximum size, you get an
     error message from the linker indicating that `-fpic' does not
     work; in that case, recompile with `-fPIC' instead.  (These
     maximums are 8k on the SPARC and 32k on the m68k and RS/6000.  The
     386 has no such limit.)

     Position-independent code requires special support, and therefore
     works only on certain machines.  For the 386, GCC supports PIC for
     System V but not for the Sun 386i.  Code generated for the IBM
     RS/6000 is always position-independent.

     When this flag is set, the macros `__pic__' and `__PIC__' are
     defined to 1.

`-fPIC'
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference
     on the m68k, PowerPC and SPARC.

     Position-independent code requires special support, and therefore
     works only on certain machines.

     When this flag is set, the macros `__pic__' and `__PIC__' are
     defined to 2.

`-fpie'
`-fPIE'
     These options are similar to `-fpic' and `-fPIC', but generated
     position independent code can be only linked into executables.
     Usually these options are used when `-pie' GCC option will be used
     during linking.

     `-fpie' and `-fPIE' both define the macros `__pie__' and
     `__PIE__'.  The macros have the value 1 for `-fpie' and 2 for
     `-fPIE'.

`-fno-jump-tables'
     Do not use jump tables for switch statements even where it would be
     more efficient than other code generation strategies.  This option
     is of use in conjunction with `-fpic' or `-fPIC' for building code
     which forms part of a dynamic linker and cannot reference the
     address of a jump table.  On some targets, jump tables do not
     require a GOT and this option is not needed.

`-ffixed-REG'
     Treat the register named REG as a fixed register; generated code
     should never refer to it (except perhaps as a stack pointer, frame
     pointer or in some other fixed role).

     REG must be the name of a register.  The register names accepted
     are machine-specific and are defined in the `REGISTER_NAMES' macro
     in the machine description macro file.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-used-REG'
     Treat the register named REG as an allocable register that is
     clobbered by function calls.  It may be allocated for temporaries
     or variables that do not live across a call.  Functions compiled
     this way will not save and restore the register REG.

     It is an error to used this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model will produce
     disastrous results.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-saved-REG'
     Treat the register named REG as an allocable register saved by
     functions.  It may be allocated even for temporaries or variables
     that live across a call.  Functions compiled this way will save
     and restore the register REG if they use it.

     It is an error to used this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model will produce
     disastrous results.

     A different sort of disaster will result from the use of this flag
     for a register in which function values may be returned.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fpack-struct[=N]'
     Without a value specified, pack all structure members together
     without holes.  When a value is specified (which must be a small
     power of two), pack structure members according to this value,
     representing the maximum alignment (that is, objects with default
     alignment requirements larger than this will be output potentially
     unaligned at the next fitting location.

     *Warning:* the `-fpack-struct' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Additionally, it makes the code suboptimal.  Use it to
     conform to a non-default application binary interface.

`-finstrument-functions'
     Generate instrumentation calls for entry and exit to functions.
     Just after function entry and just before function exit, the
     following profiling functions will be called with the address of
     the current function and its call site.  (On some platforms,
     `__builtin_return_address' does not work beyond the current
     function, so the call site information may not be available to the
     profiling functions otherwise.)

          void __cyg_profile_func_enter (void *this_fn,
                                         void *call_site);
          void __cyg_profile_func_exit  (void *this_fn,
                                         void *call_site);

     The first argument is the address of the start of the current
     function, which may be looked up exactly in the symbol table.

     This instrumentation is also done for functions expanded inline in
     other functions.  The profiling calls will indicate where,
     conceptually, the inline function is entered and exited.  This
     means that addressable versions of such functions must be
     available.  If all your uses of a function are expanded inline,
     this may mean an additional expansion of code size.  If you use
     `extern inline' in your C code, an addressable version of such
     functions must be provided.  (This is normally the case anyways,
     but if you get lucky and the optimizer always expands the
     functions inline, you might have gotten away without providing
     static copies.)

     A function may be given the attribute `no_instrument_function', in
     which case this instrumentation will not be done.  This can be
     used, for example, for the profiling functions listed above,
     high-priority interrupt routines, and any functions from which the
     profiling functions cannot safely be called (perhaps signal
     handlers, if the profiling routines generate output or allocate
     memory).

`-finstrument-functions-exclude-file-list=FILE,FILE,...'
     Set the list of functions that are excluded from instrumentation
     (see the description of `-finstrument-functions').  If the file
     that contains a function definition matches with one of FILE, then
     that function is not instrumented.  The match is done on
     substrings: if the FILE parameter is a substring of the file name,
     it is considered to be a match.

     For example,
     `-finstrument-functions-exclude-file-list=/bits/stl,include/sys'
     will exclude any inline function defined in files whose pathnames
     contain `/bits/stl' or `include/sys'.

     If, for some reason, you want to include letter `','' in one of
     SYM, write `'\,''. For example,
     `-finstrument-functions-exclude-file-list='\,\,tmp'' (note the
     single quote surrounding the option).

`-finstrument-functions-exclude-function-list=SYM,SYM,...'
     This is similar to `-finstrument-functions-exclude-file-list', but
     this option sets the list of function names to be excluded from
     instrumentation.  The function name to be matched is its
     user-visible name, such as `vector<int> blah(const vector<int>
     &)', not the internal mangled name (e.g.,
     `_Z4blahRSt6vectorIiSaIiEE').  The match is done on substrings: if
     the SYM parameter is a substring of the function name, it is
     considered to be a match.

`-fstack-check'
     Generate code to verify that you do not go beyond the boundary of
     the stack.  You should specify this flag if you are running in an
     environment with multiple threads, but only rarely need to specify
     it in a single-threaded environment since stack overflow is
     automatically detected on nearly all systems if there is only one
     stack.

     Note that this switch does not actually cause checking to be done;
     the operating system or the language runtime must do that.  The
     switch causes generation of code to ensure that they see the stack
     being extended.

     You can additionally specify a string parameter: `no' means no
     checking, `generic' means force the use of old-style checking,
     `specific' means use the best checking method and is equivalent to
     bare `-fstack-check'.

     Old-style checking is a generic mechanism that requires no specific
     target support in the compiler but comes with the following
     drawbacks:

       1. Modified allocation strategy for large objects: they will
          always be allocated dynamically if their size exceeds a fixed
          threshold.

       2. Fixed limit on the size of the static frame of functions:
          when it is topped by a particular function, stack checking is
          not reliable and a warning is issued by the compiler.

       3. Inefficiency: because of both the modified allocation
          strategy and the generic implementation, the performances of
          the code are hampered.

     Note that old-style stack checking is also the fallback method for
     `specific' if no target support has been added in the compiler.

`-fstack-limit-register=REG'
`-fstack-limit-symbol=SYM'
`-fno-stack-limit'
     Generate code to ensure that the stack does not grow beyond a
     certain value, either the value of a register or the address of a
     symbol.  If the stack would grow beyond the value, a signal is
     raised.  For most targets, the signal is raised before the stack
     overruns the boundary, so it is possible to catch the signal
     without taking special precautions.

     For instance, if the stack starts at absolute address `0x80000000'
     and grows downwards, you can use the flags
     `-fstack-limit-symbol=__stack_limit' and
     `-Wl,--defsym,__stack_limit=0x7ffe0000' to enforce a stack limit
     of 128KB.  Note that this may only work with the GNU linker.

`-fargument-alias'
`-fargument-noalias'
`-fargument-noalias-global'
`-fargument-noalias-anything'
     Specify the possible relationships among parameters and between
     parameters and global data.

     `-fargument-alias' specifies that arguments (parameters) may alias
     each other and may alias global storage.
     `-fargument-noalias' specifies that arguments do not alias each
     other, but may alias global storage.
     `-fargument-noalias-global' specifies that arguments do not alias
     each other and do not alias global storage.
     `-fargument-noalias-anything' specifies that arguments do not
     alias any other storage.

     Each language will automatically use whatever option is required by
     the language standard.  You should not need to use these options
     yourself.

`-fleading-underscore'
     This option and its counterpart, `-fno-leading-underscore',
     forcibly change the way C symbols are represented in the object
     file.  One use is to help link with legacy assembly code.

     *Warning:* the `-fleading-underscore' switch causes GCC to
     generate code that is not binary compatible with code generated
     without that switch.  Use it to conform to a non-default
     application binary interface.  Not all targets provide complete
     support for this switch.

`-ftls-model=MODEL'
     Alter the thread-local storage model to be used (*note
     Thread-Local::).  The MODEL argument should be one of
     `global-dynamic', `local-dynamic', `initial-exec' or `local-exec'.

     The default without `-fpic' is `initial-exec'; with `-fpic' the
     default is `global-dynamic'.

`-fvisibility=DEFAULT|INTERNAL|HIDDEN|PROTECTED'
     Set the default ELF image symbol visibility to the specified
     option--all symbols will be marked with this unless overridden
     within the code.  Using this feature can very substantially
     improve linking and load times of shared object libraries, produce
     more optimized code, provide near-perfect API export and prevent
     symbol clashes.  It is *strongly* recommended that you use this in
     any shared objects you distribute.

     Despite the nomenclature, `default' always means public ie;
     available to be linked against from outside the shared object.
     `protected' and `internal' are pretty useless in real-world usage
     so the only other commonly used option will be `hidden'.  The
     default if `-fvisibility' isn't specified is `default', i.e., make
     every symbol public--this causes the same behavior as previous
     versions of GCC.

     A good explanation of the benefits offered by ensuring ELF symbols
     have the correct visibility is given by "How To Write Shared
     Libraries" by Ulrich Drepper (which can be found at
     `http://people.redhat.com/~drepper/')--however a superior solution
     made possible by this option to marking things hidden when the
     default is public is to make the default hidden and mark things
     public.  This is the norm with DLL's on Windows and with
     `-fvisibility=hidden' and `__attribute__
     ((visibility("default")))' instead of `__declspec(dllexport)' you
     get almost identical semantics with identical syntax.  This is a
     great boon to those working with cross-platform projects.

     For those adding visibility support to existing code, you may find
     `#pragma GCC visibility' of use.  This works by you enclosing the
     declarations you wish to set visibility for with (for example)
     `#pragma GCC visibility push(hidden)' and `#pragma GCC visibility
     pop'.  Bear in mind that symbol visibility should be viewed *as
     part of the API interface contract* and thus all new code should
     always specify visibility when it is not the default ie;
     declarations only for use within the local DSO should *always* be
     marked explicitly as hidden as so to avoid PLT indirection
     overheads--making this abundantly clear also aids readability and
     self-documentation of the code.  Note that due to ISO C++
     specification requirements, operator new and operator delete must
     always be of default visibility.

     Be aware that headers from outside your project, in particular
     system headers and headers from any other library you use, may not
     be expecting to be compiled with visibility other than the
     default.  You may need to explicitly say `#pragma GCC visibility
     push(default)' before including any such headers.

     `extern' declarations are not affected by `-fvisibility', so a lot
     of code can be recompiled with `-fvisibility=hidden' with no
     modifications.  However, this means that calls to `extern'
     functions with no explicit visibility will use the PLT, so it is
     more effective to use `__attribute ((visibility))' and/or `#pragma
     GCC visibility' to tell the compiler which `extern' declarations
     should be treated as hidden.

     Note that `-fvisibility' does affect C++ vague linkage entities.
     This means that, for instance, an exception class that will be
     thrown between DSOs must be explicitly marked with default
     visibility so that the `type_info' nodes will be unified between
     the DSOs.

     An overview of these techniques, their benefits and how to use them
     is at `http://gcc.gnu.org/wiki/Visibility'.


File: gcc.info,  Node: Environment Variables,  Next: Precompiled Headers,  Prev: Code Gen Options,  Up: Invoking GCC

3.19 Environment Variables Affecting GCC
========================================

This section describes several environment variables that affect how GCC
operates.  Some of them work by specifying directories or prefixes to
use when searching for various kinds of files.  Some are used to
specify other aspects of the compilation environment.

 Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (*note Directory Options::).  These take precedence
over places specified using environment variables, which in turn take
precedence over those specified by the configuration of GCC.  *Note
Controlling the Compilation Driver `gcc': (gccint)Driver.

`LANG'
`LC_CTYPE'
`LC_MESSAGES'
`LC_ALL'
     These environment variables control the way that GCC uses
     localization information that allow GCC to work with different
     national conventions.  GCC inspects the locale categories
     `LC_CTYPE' and `LC_MESSAGES' if it has been configured to do so.
     These locale categories can be set to any value supported by your
     installation.  A typical value is `en_GB.UTF-8' for English in the
     United Kingdom encoded in UTF-8.

     The `LC_CTYPE' environment variable specifies character
     classification.  GCC uses it to determine the character boundaries
     in a string; this is needed for some multibyte encodings that
     contain quote and escape characters that would otherwise be
     interpreted as a string end or escape.

     The `LC_MESSAGES' environment variable specifies the language to
     use in diagnostic messages.

     If the `LC_ALL' environment variable is set, it overrides the value
     of `LC_CTYPE' and `LC_MESSAGES'; otherwise, `LC_CTYPE' and
     `LC_MESSAGES' default to the value of the `LANG' environment
     variable.  If none of these variables are set, GCC defaults to
     traditional C English behavior.

`TMPDIR'
     If `TMPDIR' is set, it specifies the directory to use for temporary
     files.  GCC uses temporary files to hold the output of one stage of
     compilation which is to be used as input to the next stage: for
     example, the output of the preprocessor, which is the input to the
     compiler proper.

`GCC_EXEC_PREFIX'
     If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
     names of the subprograms executed by the compiler.  No slash is
     added when this prefix is combined with the name of a subprogram,
     but you can specify a prefix that ends with a slash if you wish.

     If `GCC_EXEC_PREFIX' is not set, GCC will attempt to figure out an
     appropriate prefix to use based on the pathname it was invoked
     with.

     If GCC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.

     The default value of `GCC_EXEC_PREFIX' is `PREFIX/lib/gcc/' where
     PREFIX is the prefix to the installed compiler. In many cases
     PREFIX is the value of `prefix' when you ran the `configure'
     script.

     Other prefixes specified with `-B' take precedence over this
     prefix.

     This prefix is also used for finding files such as `crt0.o' that
     are used for linking.

     In addition, the prefix is used in an unusual way in finding the
     directories to search for header files.  For each of the standard
     directories whose name normally begins with `/usr/local/lib/gcc'
     (more precisely, with the value of `GCC_INCLUDE_DIR'), GCC tries
     replacing that beginning with the specified prefix to produce an
     alternate directory name.  Thus, with `-Bfoo/', GCC will search
     `foo/bar' where it would normally search `/usr/local/lib/bar'.
     These alternate directories are searched first; the standard
     directories come next. If a standard directory begins with the
     configured PREFIX then the value of PREFIX is replaced by
     `GCC_EXEC_PREFIX' when looking for header files.

`COMPILER_PATH'
     The value of `COMPILER_PATH' is a colon-separated list of
     directories, much like `PATH'.  GCC tries the directories thus
     specified when searching for subprograms, if it can't find the
     subprograms using `GCC_EXEC_PREFIX'.

`LIBRARY_PATH'
     The value of `LIBRARY_PATH' is a colon-separated list of
     directories, much like `PATH'.  When configured as a native
     compiler, GCC tries the directories thus specified when searching
     for special linker files, if it can't find them using
     `GCC_EXEC_PREFIX'.  Linking using GCC also uses these directories
     when searching for ordinary libraries for the `-l' option (but
     directories specified with `-L' come first).

`LANG'
     This variable is used to pass locale information to the compiler.
     One way in which this information is used is to determine the
     character set to be used when character literals, string literals
     and comments are parsed in C and C++.  When the compiler is
     configured to allow multibyte characters, the following values for
     `LANG' are recognized:

    `C-JIS'
          Recognize JIS characters.

    `C-SJIS'
          Recognize SJIS characters.

    `C-EUCJP'
          Recognize EUCJP characters.

     If `LANG' is not defined, or if it has some other value, then the
     compiler will use mblen and mbtowc as defined by the default
     locale to recognize and translate multibyte characters.

Some additional environments variables affect the behavior of the
preprocessor.

`CPATH'
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
     Each variable's value is a list of directories separated by a
     special character, much like `PATH', in which to look for header
     files.  The special character, `PATH_SEPARATOR', is
     target-dependent and determined at GCC build time.  For Microsoft
     Windows-based targets it is a semicolon, and for almost all other
     targets it is a colon.

     `CPATH' specifies a list of directories to be searched as if
     specified with `-I', but after any paths given with `-I' options
     on the command line.  This environment variable is used regardless
     of which language is being preprocessed.

     The remaining environment variables apply only when preprocessing
     the particular language indicated.  Each specifies a list of
     directories to be searched as if specified with `-isystem', but
     after any paths given with `-isystem' options on the command line.

     In all these variables, an empty element instructs the compiler to
     search its current working directory.  Empty elements can appear
     at the beginning or end of a path.  For instance, if the value of
     `CPATH' is `:/special/include', that has the same effect as
     `-I. -I/special/include'.

`DEPENDENCIES_OUTPUT'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the non-system header files
     processed by the compiler.  System header files are ignored in the
     dependency output.

     The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form `FILE TARGET', in which case the rules are written to file
     FILE using TARGET as the target name.

     In other words, this environment variable is equivalent to
     combining the options `-MM' and `-MF' (*note Preprocessor
     Options::), with an optional `-MT' switch too.

`SUNPRO_DEPENDENCIES'
     This variable is the same as `DEPENDENCIES_OUTPUT' (see above),
     except that system header files are not ignored, so it implies
     `-M' rather than `-MM'.  However, the dependence on the main input
     file is omitted.  *Note Preprocessor Options::.

File: gcc.info,  Node: Precompiled Headers,  Next: Running Protoize,  Prev: Environment Variables,  Up: Invoking GCC

3.20 Using Precompiled Headers
==============================

Often large projects have many header files that are included in every
source file.  The time the compiler takes to process these header files
over and over again can account for nearly all of the time required to
build the project.  To make builds faster, GCC allows users to
`precompile' a header file; then, if builds can use the precompiled
header file they will be much faster.

 To create a precompiled header file, simply compile it as you would any
other file, if necessary using the `-x' option to make the driver treat
it as a C or C++ header file.  You will probably want to use a tool
like `make' to keep the precompiled header up-to-date when the headers
it contains change.

 A precompiled header file will be searched for when `#include' is seen
in the compilation.  As it searches for the included file (*note Search
Path: (cpp)Search Path.) the compiler looks for a precompiled header in
each directory just before it looks for the include file in that
directory.  The name searched for is the name specified in the
`#include' with `.gch' appended.  If the precompiled header file can't
be used, it is ignored.

 For instance, if you have `#include "all.h"', and you have `all.h.gch'
in the same directory as `all.h', then the precompiled header file will
be used if possible, and the original header will be used otherwise.

 Alternatively, you might decide to put the precompiled header file in a
directory and use `-I' to ensure that directory is searched before (or
instead of) the directory containing the original header.  Then, if you
want to check that the precompiled header file is always used, you can
put a file of the same name as the original header in this directory
containing an `#error' command.

 This also works with `-include'.  So yet another way to use
precompiled headers, good for projects not designed with precompiled
header files in mind, is to simply take most of the header files used by
a project, include them from another header file, precompile that header
file, and `-include' the precompiled header.  If the header files have
guards against multiple inclusion, they will be skipped because they've
already been included (in the precompiled header).

 If you need to precompile the same header file for different
languages, targets, or compiler options, you can instead make a
_directory_ named like `all.h.gch', and put each precompiled header in
the directory, perhaps using `-o'.  It doesn't matter what you call the
files in the directory, every precompiled header in the directory will
be considered.  The first precompiled header encountered in the
directory that is valid for this compilation will be used; they're
searched in no particular order.

 There are many other possibilities, limited only by your imagination,
good sense, and the constraints of your build system.

 A precompiled header file can be used only when these conditions apply:

   * Only one precompiled header can be used in a particular
     compilation.

   * A precompiled header can't be used once the first C token is seen.
     You can have preprocessor directives before a precompiled header;
     you cannot include a precompiled header from inside another header.

   * The precompiled header file must be produced for the same language
     as the current compilation.  You can't use a C precompiled header
     for a C++ compilation.

   * The precompiled header file must have been produced by the same
     compiler binary as the current compilation is using.

   * Any macros defined before the precompiled header is included must
     either be defined in the same way as when the precompiled header
     was generated, or must not affect the precompiled header, which
     usually means that they don't appear in the precompiled header at
     all.

     The `-D' option is one way to define a macro before a precompiled
     header is included; using a `#define' can also do it.  There are
     also some options that define macros implicitly, like `-O' and
     `-Wdeprecated'; the same rule applies to macros defined this way.

   * If debugging information is output when using the precompiled
     header, using `-g' or similar, the same kind of debugging
     information must have been output when building the precompiled
     header.  However, a precompiled header built using `-g' can be
     used in a compilation when no debugging information is being
     output.

   * The same `-m' options must generally be used when building and
     using the precompiled header.  *Note Submodel Options::, for any
     cases where this rule is relaxed.

   * Each of the following options must be the same when building and
     using the precompiled header:

          -fexceptions

   * Some other command-line options starting with `-f', `-p', or `-O'
     must be defined in the same way as when the precompiled header was
     generated.  At present, it's not clear which options are safe to
     change and which are not; the safest choice is to use exactly the
     same options when generating and using the precompiled header.
     The following are known to be safe:

          -fmessage-length=  -fpreprocessed  -fsched-interblock
          -fsched-spec  -fsched-spec-load  -fsched-spec-load-dangerous
          -fsched-verbose=<number>  -fschedule-insns  -fvisibility=
          -pedantic-errors


 For all of these except the last, the compiler will automatically
ignore the precompiled header if the conditions aren't met.  If you
find an option combination that doesn't work and doesn't cause the
precompiled header to be ignored, please consider filing a bug report,
see *note Bugs::.

 If you do use differing options when generating and using the
precompiled header, the actual behavior will be a mixture of the
behavior for the options.  For instance, if you use `-g' to generate
the precompiled header but not when using it, you may or may not get
debugging information for routines in the precompiled header.

File: gcc.info,  Node: Running Protoize,  Prev: Precompiled Headers,  Up: Invoking GCC

3.21 Running Protoize
=====================

The program `protoize' is an optional part of GCC.  You can use it to
add prototypes to a program, thus converting the program to ISO C in
one respect.  The companion program `unprotoize' does the reverse: it
removes argument types from any prototypes that are found.

 When you run these programs, you must specify a set of source files as
command line arguments.  The conversion programs start out by compiling
these files to see what functions they define.  The information gathered
about a file FOO is saved in a file named `FOO.X'.

 After scanning comes actual conversion.  The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.

 But not all the eligible files are converted.  By default, `protoize'
and `unprotoize' convert only source and header files in the current
directory.  You can specify additional directories whose files should
be converted with the `-d DIRECTORY' option.  You can also specify
particular files to exclude with the `-x FILE' option.  A file is
converted if it is eligible, its directory name matches one of the
specified directory names, and its name within the directory has not
been excluded.

 Basic conversion with `protoize' consists of rewriting most function
definitions and function declarations to specify the types of the
arguments.  The only ones not rewritten are those for varargs functions.

 `protoize' optionally inserts prototype declarations at the beginning
of the source file, to make them available for any calls that precede
the function's definition.  Or it can insert prototype declarations
with block scope in the blocks where undeclared functions are called.

 Basic conversion with `unprotoize' consists of rewriting most function
declarations to remove any argument types, and rewriting function
definitions to the old-style pre-ISO form.

 Both conversion programs print a warning for any function declaration
or definition that they can't convert.  You can suppress these warnings
with `-q'.

 The output from `protoize' or `unprotoize' replaces the original
source file.  The original file is renamed to a name ending with
`.save' (for DOS, the saved filename ends in `.sav' without the
original `.c' suffix).  If the `.save' (`.sav' for DOS) file already
exists, then the source file is simply discarded.

 `protoize' and `unprotoize' both depend on GCC itself to scan the
program and collect information about the functions it uses.  So
neither of these programs will work until GCC is installed.

 Here is a table of the options you can use with `protoize' and
`unprotoize'.  Each option works with both programs unless otherwise
stated.

`-B DIRECTORY'
     Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the
     usual directory (normally `/usr/local/lib').  This file contains
     prototype information about standard system functions.  This option
     applies only to `protoize'.

`-c COMPILATION-OPTIONS'
     Use COMPILATION-OPTIONS as the options when running `gcc' to
     produce the `.X' files.  The special option `-aux-info' is always
     passed in addition, to tell `gcc' to write a `.X' file.

     Note that the compilation options must be given as a single
     argument to `protoize' or `unprotoize'.  If you want to specify
     several `gcc' options, you must quote the entire set of
     compilation options to make them a single word in the shell.

     There are certain `gcc' arguments that you cannot use, because they
     would produce the wrong kind of output.  These include `-g', `-O',
     `-c', `-S', and `-o' If you include these in the
     COMPILATION-OPTIONS, they are ignored.

`-C'
     Rename files to end in `.C' (`.cc' for DOS-based file systems)
     instead of `.c'.  This is convenient if you are converting a C
     program to C++.  This option applies only to `protoize'.

`-g'
     Add explicit global declarations.  This means inserting explicit
     declarations at the beginning of each source file for each function
     that is called in the file and was not declared.  These
     declarations precede the first function definition that contains a
     call to an undeclared function.  This option applies only to
     `protoize'.

`-i STRING'
     Indent old-style parameter declarations with the string STRING.
     This option applies only to `protoize'.

     `unprotoize' converts prototyped function definitions to old-style
     function definitions, where the arguments are declared between the
     argument list and the initial `{'.  By default, `unprotoize' uses
     five spaces as the indentation.  If you want to indent with just
     one space instead, use `-i " "'.

`-k'
     Keep the `.X' files.  Normally, they are deleted after conversion
     is finished.

`-l'
     Add explicit local declarations.  `protoize' with `-l' inserts a
     prototype declaration for each function in each block which calls
     the function without any declaration.  This option applies only to
     `protoize'.

`-n'
     Make no real changes.  This mode just prints information about the
     conversions that would have been done without `-n'.

`-N'
     Make no `.save' files.  The original files are simply deleted.
     Use this option with caution.

`-p PROGRAM'
     Use the program PROGRAM as the compiler.  Normally, the name `gcc'
     is used.

`-q'
     Work quietly.  Most warnings are suppressed.

`-v'
     Print the version number, just like `-v' for `gcc'.

 If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file specially,
by running `gcc' on that source file with the appropriate options and
the option `-aux-info'.  Then run `protoize' on the entire set of
files.  `protoize' will use the existing `.X' file because it is newer
than the source file.  For example:

     gcc -Dfoo=bar file1.c -aux-info file1.X
     protoize *.c

You need to include the special files along with the rest in the
`protoize' command, even though their `.X' files already exist, because
otherwise they won't get converted.

 *Note Protoize Caveats::, for more information on how to use
`protoize' successfully.

File: gcc.info,  Node: C Implementation,  Next: C Extensions,  Prev: Invoking GCC,  Up: Top

4 C Implementation-defined behavior
***********************************

A conforming implementation of ISO C is required to document its choice
of behavior in each of the areas that are designated "implementation
defined".  The following lists all such areas, along with the section
numbers from the ISO/IEC 9899:1990 and ISO/IEC 9899:1999 standards.
Some areas are only implementation-defined in one version of the
standard.

 Some choices depend on the externally determined ABI for the platform
(including standard character encodings) which GCC follows; these are
listed as "determined by ABI" below.  *Note Binary Compatibility:
Compatibility, and `http://gcc.gnu.org/readings.html'.  Some choices
are documented in the preprocessor manual.  *Note
Implementation-defined behavior: (cpp)Implementation-defined behavior.
Some choices are made by the library and operating system (or other
environment when compiling for a freestanding environment); refer to
their documentation for details.

* Menu:

* Translation implementation::
* Environment implementation::
* Identifiers implementation::
* Characters implementation::
* Integers implementation::
* Floating point implementation::
* Arrays and pointers implementation::
* Hints implementation::
* Structures unions enumerations and bit-fields implementation::
* Qualifiers implementation::
* Declarators implementation::
* Statements implementation::
* Preprocessing directives implementation::
* Library functions implementation::
* Architecture implementation::
* Locale-specific behavior implementation::

File: gcc.info,  Node: Translation implementation,  Next: Environment implementation,  Up: C Implementation

4.1 Translation
===============

   * `How a diagnostic is identified (C90 3.7, C99 3.10, C90 and C99
     5.1.1.3).'

     Diagnostics consist of all the output sent to stderr by GCC.

   * `Whether each nonempty sequence of white-space characters other
     than new-line is retained or replaced by one space character in
     translation phase 3 (C90 and C99 5.1.1.2).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.


File: gcc.info,  Node: Environment implementation,  Next: Identifiers implementation,  Prev: Translation implementation,  Up: C Implementation

4.2 Environment
===============

The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.

   * `The mapping between physical source file multibyte characters and
     the source character set in translation phase 1 (C90 and C99
     5.1.1.2).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.


File: gcc.info,  Node: Identifiers implementation,  Next: Characters implementation,  Prev: Environment implementation,  Up: C Implementation

4.3 Identifiers
===============

   * `Which additional multibyte characters may appear in identifiers
     and their correspondence to universal character names (C99 6.4.2).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   * `The number of significant initial characters in an identifier
     (C90 6.1.2, C90 and C99 5.2.4.1, C99 6.4.2).'

     For internal names, all characters are significant.  For external
     names, the number of significant characters are defined by the
     linker; for almost all targets, all characters are significant.

   * `Whether case distinctions are significant in an identifier with
     external linkage (C90 6.1.2).'

     This is a property of the linker.  C99 requires that case
     distinctions are always significant in identifiers with external
     linkage and systems without this property are not supported by GCC.


File: gcc.info,  Node: Characters implementation,  Next: Integers implementation,  Prev: Identifiers implementation,  Up: C Implementation

4.4 Characters
==============

   * `The number of bits in a byte (C90 3.4, C99 3.6).'

     Determined by ABI.

   * `The values of the members of the execution character set (C90 and
     C99 5.2.1).'

     Determined by ABI.

   * `The unique value of the member of the execution character set
     produced for each of the standard alphabetic escape sequences (C90
     and C99 5.2.2).'

     Determined by ABI.

   * `The value of a `char' object into which has been stored any
     character other than a member of the basic execution character set
     (C90 6.1.2.5, C99 6.2.5).'

     Determined by ABI.

   * `Which of `signed char' or `unsigned char' has the same range,
     representation, and behavior as "plain" `char' (C90 6.1.2.5, C90
     6.2.1.1, C99 6.2.5, C99 6.3.1.1).'

     Determined by ABI.  The options `-funsigned-char' and
     `-fsigned-char' change the default.  *Note Options Controlling C
     Dialect: C Dialect Options.

   * `The mapping of members of the source character set (in character
     constants and string literals) to members of the execution
     character set (C90 6.1.3.4, C99 6.4.4.4, C90 and C99 5.1.1.2).'

     Determined by ABI.

   * `The value of an integer character constant containing more than
     one character or containing a character or escape sequence that
     does not map to a single-byte execution character (C90 6.1.3.4,
     C99 6.4.4.4).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   * `The value of a wide character constant containing more than one
     multibyte character, or containing a multibyte character or escape
     sequence not represented in the extended execution character set
     (C90 6.1.3.4, C99 6.4.4.4).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   * `The current locale used to convert a wide character constant
     consisting of a single multibyte character that maps to a member
     of the extended execution character set into a corresponding wide
     character code (C90 6.1.3.4, C99 6.4.4.4).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   * `The current locale used to convert a wide string literal into
     corresponding wide character codes (C90 6.1.4, C99 6.4.5).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

   * `The value of a string literal containing a multibyte character or
     escape sequence not represented in the execution character set
     (C90 6.1.4, C99 6.4.5).'

     *Note Implementation-defined behavior: (cpp)Implementation-defined
     behavior.

File: gcc.info,  Node: Integers implementation,  Next: Floating point implementation,  Prev: Characters implementation,  Up: C Implementation

4.5 Integers
============

   * `Any extended integer types that exist in the implementation (C99
     6.2.5).'

     GCC does not support any extended integer types.

   * `Whether signed integer types are represented using sign and
     magnitude, two's complement, or one's complement, and whether the
     extraordinary value is a trap representation or an ordinary value
     (C99 6.2.6.2).'

     GCC supports only two's complement integer types, and all bit
     patterns are ordinary values.

   * `The rank of any extended integer type relative to another extended
     integer type with the same precision (C99 6.3.1.1).'

     GCC does not support any extended integer types.

   * `The result of, or the signal raised by, converting an integer to a
     signed integer type when the value cannot be represented in an
     object of that type (C90 6.2.1.2, C99 6.3.1.3).'

     For conversion to a type of width N, the value is reduced modulo
     2^N to be within range of the type; no signal is raised.

   * `The results of some bitwise operations on signed integers (C90
     6.3, C99 6.5).'

     Bitwise operators act on the representation of the value including
     both the sign and value bits, where the sign bit is considered
     immediately above the highest-value value bit.  Signed `>>' acts
     on negative numbers by sign extension.

     GCC does not use the latitude given in C99 only to treat certain
     aspects of signed `<<' as undefined, but this is subject to change.

   * `The sign of the remainder on integer division (C90 6.3.5).'

     GCC always follows the C99 requirement that the result of division
     is truncated towards zero.


File: gcc.info,  Node: Floating point implementation,  Next: Arrays and pointers implementation,  Prev: Integers implementation,  Up: C Implementation

4.6 Floating point
==================

   * `The accuracy of the floating-point operations and of the library
     functions in `<math.h>' and `<complex.h>' that return
     floating-point results (C90 and C99 5.2.4.2.2).'

     The accuracy is unknown.

   * `The rounding behaviors characterized by non-standard values of
     `FLT_ROUNDS'  (C90 and C99 5.2.4.2.2).'

     GCC does not use such values.

   * `The evaluation methods characterized by non-standard negative
     values of `FLT_EVAL_METHOD' (C99 5.2.4.2.2).'

     GCC does not use such values.

   * `The direction of rounding when an integer is converted to a
     floating-point number that cannot exactly represent the original
     value (C90 6.2.1.3, C99 6.3.1.4).'

     C99 Annex F is followed.

   * `The direction of rounding when a floating-point number is
     converted to a narrower floating-point number (C90 6.2.1.4, C99
     6.3.1.5).'

     C99 Annex F is followed.

   * `How the nearest representable value or the larger or smaller
     representable value immediately adjacent to the nearest
     representable value is chosen for certain floating constants (C90
     6.1.3.1, C99 6.4.4.2).'

     C99 Annex F is followed.

   * `Whether and how floating expressions are contracted when not
     disallowed by the `FP_CONTRACT' pragma (C99 6.5).'

     Expressions are currently only contracted if
     `-funsafe-math-optimizations' or `-ffast-math' are used.  This is
     subject to change.

   * `The default state for the `FENV_ACCESS' pragma (C99 7.6.1).'

     This pragma is not implemented, but the default is to "off" unless
     `-frounding-math' is used in which case it is "on".

   * `Additional floating-point exceptions, rounding modes,
     environments, and classifications, and their macro names (C99 7.6,
     C99 7.12).'

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.

   * `The default state for the `FP_CONTRACT' pragma (C99 7.12.2).'

     This pragma is not implemented.  Expressions are currently only
     contracted if `-funsafe-math-optimizations' or `-ffast-math' are
     used.  This is subject to change.

   * `Whether the "inexact" floating-point exception can be raised when
     the rounded result actually does equal the mathematical result in
     an IEC 60559 conformant implementation (C99 F.9).'

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.

   * `Whether the "underflow" (and "inexact") floating-point exception
     can be raised when a result is tiny but not inexact in an IEC
     60559 conformant implementation (C99 F.9).'

     This is dependent on the implementation of the C library, and is
     not defined by GCC itself.


File: gcc.info,  Node: Arrays and pointers implementation,  Next: Hints implementation,  Prev: Floating point implementation,  Up: C Implementation

4.7 Arrays and pointers
=======================

   * `The result of converting a pointer to an integer or vice versa
     (C90 6.3.4, C99 6.3.2.3).'

     A cast from pointer to integer discards most-significant bits if
     the pointer representation is larger than the integer type,
     sign-extends(1) if the pointer representation is smaller than the
     integer type, otherwise the bits are unchanged.

     A cast from integer to pointer discards most-significant bits if
     the pointer representation is smaller than the integer type,
     extends according to the signedness of the integer type if the
     pointer representation is larger than the integer type, otherwise
     the bits are unchanged.

     When casting from pointer to integer and back again, the resulting
     pointer must reference the same object as the original pointer,
     otherwise the behavior is undefined.  That is, one may not use
     integer arithmetic to avoid the undefined behavior of pointer
     arithmetic as proscribed in C99 6.5.6/8.

   * `The size of the result of subtracting two pointers to elements of
     the same array (C90 6.3.6, C99 6.5.6).'

     The value is as specified in the standard and the type is
     determined by the ABI.


 ---------- Footnotes ----------

 (1) Future versions of GCC may zero-extend, or use a target-defined
`ptr_extend' pattern.  Do not rely on sign extension.

File: gcc.info,  Node: Hints implementation,  Next: Structures unions enumerations and bit-fields implementation,  Prev: Arrays and pointers implementation,  Up: C Implementation

4.8 Hints
=========

   * `The extent to which suggestions made by using the `register'
     storage-class specifier are effective (C90 6.5.1, C99 6.7.1).'

     The `register' specifier affects code generation only in these
     ways:

        * When used as part of the register variable extension, see
          *note Explicit Reg Vars::.

        * When `-O0' is in use, the compiler allocates distinct stack
          memory for all variables that do not have the `register'
          storage-class specifier; if `register' is specified, the
          variable may have a shorter lifespan than the code would
          indicate and may never be placed in memory.

        * On some rare x86 targets, `setjmp' doesn't save the registers
          in all circumstances.  In those cases, GCC doesn't allocate
          any variables in registers unless they are marked `register'.


   * `The extent to which suggestions made by using the inline function
     specifier are effective (C99 6.7.4).'

     GCC will not inline any functions if the `-fno-inline' option is
     used or if `-O0' is used.  Otherwise, GCC may still be unable to
     inline a function for many reasons; the `-Winline' option may be
     used to determine if a function has not been inlined and why not.


File: gcc.info,  Node: Structures unions enumerations and bit-fields implementation,  Next: Qualifiers implementation,  Prev: Hints implementation,  Up: C Implementation

4.9 Structures, unions, enumerations, and bit-fields
====================================================

   * `A member of a union object is accessed using a member of a
     different type (C90 6.3.2.3).'

     The relevant bytes of the representation of the object are treated
     as an object of the type used for the access.  *Note
     Type-punning::.  This may be a trap representation.

   * `Whether a "plain" `int' bit-field is treated as a `signed int'
     bit-field or as an `unsigned int' bit-field (C90 6.5.2, C90
     6.5.2.1, C99 6.7.2, C99 6.7.2.1).'

     By default it is treated as `signed int' but this may be changed
     by the `-funsigned-bitfields' option.

   * `Allowable bit-field types other than `_Bool', `signed int', and
     `unsigned int' (C99 6.7.2.1).'

     No other types are permitted in strictly conforming mode.

   * `Whether a bit-field can straddle a storage-unit boundary (C90
     6.5.2.1, C99 6.7.2.1).'

     Determined by ABI.

   * `The order of allocation of bit-fields within a unit (C90 6.5.2.1,
     C99 6.7.2.1).'

     Determined by ABI.

   * `The alignment of non-bit-field members of structures (C90
     6.5.2.1, C99 6.7.2.1).'

     Determined by ABI.

   * `The integer type compatible with each enumerated type (C90
     6.5.2.2, C99 6.7.2.2).'

     Normally, the type is `unsigned int' if there are no negative
     values in the enumeration, otherwise `int'.  If `-fshort-enums' is
     specified, then if there are negative values it is the first of
     `signed char', `short' and `int' that can represent all the
     values, otherwise it is the first of `unsigned char', `unsigned
     short' and `unsigned int' that can represent all the values.

     On some targets, `-fshort-enums' is the default; this is
     determined by the ABI.


File: gcc.info,  Node: Qualifiers implementation,  Next: Declarators implementation,  Prev: Structures unions enumerations and bit-fields implementation,  Up: C Implementation

4.10 Qualifiers
===============

   * `What constitutes an access to an object that has
     volatile-qualified type (C90 6.5.3, C99 6.7.3).'

     Such an object is normally accessed by pointers and used for
     accessing hardware.  In most expressions, it is intuitively
     obvious what is a read and what is a write.  For example

          volatile int *dst = SOMEVALUE;
          volatile int *src = SOMEOTHERVALUE;
          *dst = *src;

     will cause a read of the volatile object pointed to by SRC and
     store the value into the volatile object pointed to by DST.  There
     is no guarantee that these reads and writes are atomic, especially
     for objects larger than `int'.

     However, if the volatile storage is not being modified, and the
     value of the volatile storage is not used, then the situation is
     less obvious.  For example

          volatile int *src = SOMEVALUE;
          *src;

     According to the C standard, such an expression is an rvalue whose
     type is the unqualified version of its original type, i.e. `int'.
     Whether GCC interprets this as a read of the volatile object being
     pointed to or only as a request to evaluate the expression for its
     side-effects depends on this type.

     If it is a scalar type, or on most targets an aggregate type whose
     only member object is of a scalar type, or a union type whose
     member objects are of scalar types, the expression is interpreted
     by GCC as a read of the volatile object; in the other cases, the
     expression is only evaluated for its side-effects.


File: gcc.info,  Node: Declarators implementation,  Next: Statements implementation,  Prev: Qualifiers implementation,  Up: C Implementation

4.11 Declarators
================

   * `The maximum number of declarators that may modify an arithmetic,
     structure or union type (C90 6.5.4).'

     GCC is only limited by available memory.


File: gcc.info,  Node: Statements implementation,  Next: Preprocessing directives implementation,  Prev: Declarators implementation,  Up: C Implementation

4.12 Statements
===============

   * `The maximum number of `case' values in a `switch' statement (C90
     6.6.4.2).'

     GCC is only limited by available memory.


File: gcc.info,  Node: Preprocessing directives implementation,  Next: Library functions implementation,  Prev: Statements implementation,  Up: C Implementation

4.13 Preprocessing directives
=============================

*Note Implementation-defined behavior: (cpp)Implementation-defined
behavior, for details of these aspects of implementation-defined
behavior.

   * `How sequences in both forms of header names are mapped to headers
     or external source file names (C90 6.1.7, C99 6.4.7).'

   * `Whether the value of a character constant in a constant expression
     that controls conditional inclusion matches the value of the same
     character constant in the execution character set (C90 6.8.1, C99
     6.10.1).'

   * `Whether the value of a single-character character constant in a
     constant expression that controls conditional inclusion may have a
     negative value (C90 6.8.1, C99 6.10.1).'

   * `The places that are searched for an included `<>' delimited
     header, and how the places are specified or the header is
     identified (C90 6.8.2, C99 6.10.2).'

   * `How the named source file is searched for in an included `""'
     delimited header (C90 6.8.2, C99 6.10.2).'

   * `The method by which preprocessing tokens (possibly resulting from
     macro expansion) in a `#include' directive are combined into a
     header name (C90 6.8.2, C99 6.10.2).'

   * `The nesting limit for `#include' processing (C90 6.8.2, C99
     6.10.2).'

   * `Whether the `#' operator inserts a `\' character before the `\'
     character that begins a universal character name in a character
     constant or string literal (C99 6.10.3.2).'

   * `The behavior on each recognized non-`STDC #pragma' directive (C90
     6.8.6, C99 6.10.6).'

     *Note Pragmas: (cpp)Pragmas, for details of pragmas accepted by
     GCC on all targets.  *Note Pragmas Accepted by GCC: Pragmas, for
     details of target-specific pragmas.

   * `The definitions for `__DATE__' and `__TIME__' when respectively,
     the date and time of translation are not available (C90 6.8.8, C99
     6.10.8).'


File: gcc.info,  Node: Library functions implementation,  Next: Architecture implementation,  Prev: Preprocessing directives implementation,  Up: C Implementation

4.14 Library functions
======================

The behavior of most of these points are dependent on the implementation
of the C library, and are not defined by GCC itself.

   * `The null pointer constant to which the macro `NULL' expands (C90
     7.1.6, C99 7.17).'

     In `<stddef.h>', `NULL' expands to `((void *)0)'.  GCC does not
     provide the other headers which define `NULL' and some library
     implementations may use other definitions in those headers.


File: gcc.info,  Node: Architecture implementation,  Next: Locale-specific behavior implementation,  Prev: Library functions implementation,  Up: C Implementation

4.15 Architecture
=================

   * `The values or expressions assigned to the macros specified in the
     headers `<float.h>', `<limits.h>', and `<stdint.h>' (C90 and C99
     5.2.4.2, C99 7.18.2, C99 7.18.3).'

     Determined by ABI.

   * `The number, order, and encoding of bytes in any object (when not
     explicitly specified in this International Standard) (C99
     6.2.6.1).'

     Determined by ABI.

   * `The value of the result of the `sizeof' operator (C90 6.3.3.4,
     C99 6.5.3.4).'

     Determined by ABI.


File: gcc.info,  Node: Locale-specific behavior implementation,  Prev: Architecture implementation,  Up: C Implementation

4.16 Locale-specific behavior
=============================

The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.

File: gcc.info,  Node: C Extensions,  Next: C++ Extensions,  Prev: C Implementation,  Up: Top

5 Extensions to the C Language Family
*************************************

GNU C provides several language features not found in ISO standard C.
(The `-pedantic' option directs GCC to print a warning message if any
of these features is used.)  To test for the availability of these
features in conditional compilation, check for a predefined macro
`__GNUC__', which is always defined under GCC.

 These extensions are available in C and Objective-C.  Most of them are
also available in C++.  *Note Extensions to the C++ Language: C++
Extensions, for extensions that apply _only_ to C++.

 Some features that are in ISO C99 but not C89 or C++ are also, as
extensions, accepted by GCC in C89 mode and in C++.

* Menu:

* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a block.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls::  Dispatching a call to another function.
* Typeof::              `typeof': referring to the type of an expression.
* Conditionals::        Omitting the middle operand of a `?:' expression.
* Long Long::           Double-word integers---`long long int'.
* Complex::             Data types for complex numbers.
* Floating Types::      Additional Floating Types.
* Decimal Float::       Decimal Floating Types.
* Hex Floats::          Hexadecimal floating-point constants.
* Fixed-Point::         Fixed-Point Types.
* Zero Length::         Zero-length arrays.
* Variable Length::     Arrays whose length is computed at run time.
* Empty Structures::    Structures with no members.
* Variadic Macros::     Macros with a variable number of arguments.
* Escaped Newlines::    Slightly looser rules for escaped newlines.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on `void'-pointers and function pointers.
* Initializers::        Non-constant initializers.
* Compound Literals::   Compound literals give structures, unions
                        or arrays as values.
* Designated Inits::    Labeling elements of initializers.
* Cast to Union::       Casting to union type from any member of the union.
* Case Ranges::         `case 1 ... 9' and such.
* Mixed Declarations::  Mixing declarations and code.
* Function Attributes:: Declaring that functions have no side effects,
                        or that they can never return.
* Attribute Syntax::    Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments::        C++ comments are recognized.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   `\e' stands for the character <ESC>.
* Variable Attributes:: Specifying attributes of variables.
* Type Attributes::     Specifying attributes of types.
* Alignment::           Inquiring about the alignment of a type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Extended Asm::        Assembler instructions with C expressions as operands.
                        (With them you can define ``built-in'' functions.)
* Constraints::         Constraints for asm operands
* Asm Labels::          Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars::   Defining variables residing in specified registers.
* Alternate Keywords::  `__const__', `__asm__', etc., for header files.
* Incomplete Enums::    `enum foo;', with details to follow.
* Function Names::      Printable strings which are the name of the current
                        function.
* Return Address::      Getting the return or frame address of a function.
* Vector Extensions::   Using vector instructions through built-in functions.
* Offsetof::            Special syntax for implementing `offsetof'.
* Atomic Builtins::     Built-in functions for atomic memory access.
* Object Size Checking:: Built-in functions for limited buffer overflow
                        checking.
* Other Builtins::      Other built-in functions.
* Target Builtins::     Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
* Pragmas::             Pragmas accepted by GCC.
* Unnamed Fields::      Unnamed struct/union fields within structs/unions.
* Thread-Local::        Per-thread variables.
* Binary constants::    Binary constants using the `0b' prefix.

File: gcc.info,  Node: Statement Exprs,  Next: Local Labels,  Up: C Extensions

5.1 Statements and Declarations in Expressions
==============================================

A compound statement enclosed in parentheses may appear as an expression
in GNU C.  This allows you to use loops, switches, and local variables
within an expression.

 Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces.  For
example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for
the absolute value of `foo ()'.

 The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type `void', and thus
effectively no value.)

 This feature is especially useful in making macro definitions "safe"
(so that they evaluate each operand exactly once).  For example, the
"maximum" function is commonly defined as a macro in standard C as
follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if
the operand has side effects.  In GNU C, if you know the type of the
operands (here taken as `int'), you can define the macro safely as
follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

 Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or the
initial value of a static variable.

 If you don't know the type of the operand, you can still do this, but
you must use `typeof' (*note Typeof::).

 In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression.  For instance, if `A' is a class, then

             A a;

             ({a;}).Foo ()

will construct a temporary `A' object to hold the result of the
statement expression, and that will be used to invoke `Foo'.  Therefore
the `this' pointer observed by `Foo' will not be the address of `a'.

 Any temporaries created within a statement within a statement
expression will be destroyed at the statement's end.  This makes
statement expressions inside macros slightly different from function
calls.  In the latter case temporaries introduced during argument
evaluation will be destroyed at the end of the statement that includes
the function call.  In the statement expression case they will be
destroyed during the statement expression.  For instance,

     #define macro(a)  ({__typeof__(a) b = (a); b + 3; })
     template<typename T> T function(T a) { T b = a; return b + 3; }

     void foo ()
     {
       macro (X ());
       function (X ());
     }

will have different places where temporaries are destroyed.  For the
`macro' case, the temporary `X' will be destroyed just after the
initialization of `b'.  In the `function' case that temporary will be
destroyed when the function returns.

 These considerations mean that it is probably a bad idea to use
statement-expressions of this form in header files that are designed to
work with C++.  (Note that some versions of the GNU C Library contained
header files using statement-expression that lead to precisely this
bug.)

 Jumping into a statement expression with `goto' or using a `switch'
statement outside the statement expression with a `case' or `default'
label inside the statement expression is not permitted.  Jumping into a
statement expression with a computed `goto' (*note Labels as Values::)
yields undefined behavior.  Jumping out of a statement expression is
permitted, but if the statement expression is part of a larger
expression then it is unspecified which other subexpressions of that
expression have been evaluated except where the language definition
requires certain subexpressions to be evaluated before or after the
statement expression.  In any case, as with a function call the
evaluation of a statement expression is not interleaved with the
evaluation of other parts of the containing expression.  For example,

       foo (), (({ bar1 (); goto a; 0; }) + bar2 ()), baz();

will call `foo' and `bar1' and will not call `baz' but may or may not
call `bar2'.  If `bar2' is called, it will be called after `foo' and
before `bar1'

File: gcc.info,  Node: Local Labels,  Next: Labels as Values,  Prev: Statement Exprs,  Up: C Extensions

5.2 Locally Declared Labels
===========================

GCC allows you to declare "local labels" in any nested block scope.  A
local label is just like an ordinary label, but you can only reference
it (with a `goto' statement, or by taking its address) within the block
in which it was declared.

 A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, /* ... */;

 Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

 The label declaration defines the label _name_, but does not define
the label itself.  You must do this in the usual way, with `LABEL:',
within the statements of the statement expression.

 The local label feature is useful for complex macros.  If a macro
contains nested loops, a `goto' can be useful for breaking out of them.
However, an ordinary label whose scope is the whole function cannot be
used: if the macro can be expanded several times in one function, the
label will be multiply defined in that function.  A local label avoids
this problem.  For example:

     #define SEARCH(value, array, target)              \
     do {                                              \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { (value) = i; goto found; }              \
       (value) = -1;                                   \
      found:;                                          \
     } while (0)

 This could also be written using a statement-expression:

     #define SEARCH(array, target)                     \
     ({                                                \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }                \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })

 Local label declarations also make the labels they declare visible to
nested functions, if there are any.  *Note Nested Functions::, for
details.

File: gcc.info,  Node: Labels as Values,  Next: Nested Functions,  Prev: Local Labels,  Up: C Extensions

5.3 Labels as Values
====================

You can get the address of a label defined in the current function (or
a containing function) with the unary operator `&&'.  The value has
type `void *'.  This value is a constant and can be used wherever a
constant of that type is valid.  For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

 To use these values, you need to be able to jump to one.  This is done
with the computed goto statement(1), `goto *EXP;'.  For example,

     goto *ptr;

Any expression of type `void *' is allowed.

 One way of using these constants is in initializing a static array that
will serve as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

 Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds--array
indexing in C never does that.

 Such an array of label values serves a purpose much like that of the
`switch' statement.  The `switch' statement is cleaner, so use that
rather than an array unless the problem does not fit a `switch'
statement very well.

 Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.

 You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things will happen.  The best way
to avoid this is to store the label address only in automatic variables
and never pass it as an argument.

 An alternate way to write the above example is

     static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                  &&hack - &&foo };
     goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.

 The `&&foo' expressions for the same label might have different values
if the containing function is inlined or cloned.  If a program relies on
them being always the same, `__attribute__((__noinline__))' should be
used to prevent inlining.  If `&&foo' is used in a static variable
initializer, inlining is forbidden.

 ---------- Footnotes ----------

 (1) The analogous feature in Fortran is called an assigned goto, but
that name seems inappropriate in C, where one can do more than simply
store label addresses in label variables.

File: gcc.info,  Node: Nested Functions,  Next: Constructing Calls,  Prev: Labels as Values,  Up: C Extensions

5.4 Nested Functions
====================

A "nested function" is a function defined inside another function.
(Nested functions are not supported for GNU C++.)  The nested function's
name is local to the block where it is defined.  For example, here we
define a nested function named `square', and call it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

 The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called "lexical scoping".  For example, here we show a nested function
which uses an inherited variable named `offset':

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
     }

 Nested function definitions are permitted within functions in the
places where variable definitions are allowed; that is, in any block,
mixed with the other declarations and statements in the block.

 It is possible to call the nested function from outside the scope of
its name by storing its address or passing the address to another
function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

 Here, the function `intermediate' receives the address of `store' as
an argument.  If `intermediate' calls `store', the arguments given to
`store' are used to store into `array'.  But this technique works only
so long as the containing function (`hack', in this example) does not
exit.

 If you try to call the nested function through its address after the
containing function has exited, all hell will break loose.  If you try
to call it after a containing scope level has exited, and if it refers
to some of the variables that are no longer in scope, you may be lucky,
but it's not wise to take the risk.  If, however, the nested function
does not refer to anything that has gone out of scope, you should be
safe.

 GCC implements taking the address of a nested function using a
technique called "trampolines".  A paper describing them is available as

`http://people.debian.org/~aaronl/Usenix88-lexic.pdf'.

 A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (*note Local Labels::).  Such a jump returns instantly to the
containing function, exiting the nested function which did the `goto'
and any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
       /* ... */
       return 0;

      /* Control comes here from `access'
         if it detects an error.  */
      failure:
       return -1;
     }

 A nested function always has no linkage.  Declaring one with `extern'
or `static' is erroneous.  If you need to declare the nested function
before its definition, use `auto' (which is otherwise meaningless for
function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       /* ... */
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       /* ... */
     }

File: gcc.info,  Node: Constructing Calls,  Next: Typeof,  Prev: Nested Functions,  Up: C Extensions

5.5 Constructing Function Calls
===============================

Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.

 You can also record the return value of that function call, and later
return that value, without knowing what data type the function tried to
return (as long as your caller expects that data type).

 However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language.  It is,
therefore, not recommended to use them outside very simple functions
acting as mere forwarders for their arguments.

 -- Built-in Function: void * __builtin_apply_args ()
     This built-in function returns a pointer to data describing how to
     perform a call with the same arguments as were passed to the
     current function.

     The function saves the arg pointer register, structure value
     address, and all registers that might be used to pass arguments to
     a function into a block of memory allocated on the stack.  Then it
     returns the address of that block.

 -- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void
          *ARGUMENTS, size_t SIZE)
     This built-in function invokes FUNCTION with a copy of the
     parameters described by ARGUMENTS and SIZE.

     The value of ARGUMENTS should be the value returned by
     `__builtin_apply_args'.  The argument SIZE specifies the size of
     the stack argument data, in bytes.

     This function returns a pointer to data describing how to return
     whatever value was returned by FUNCTION.  The data is saved in a
     block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The
     value is used by `__builtin_apply' to compute the amount of data
     that should be pushed on the stack and copied from the incoming
     argument area.

 -- Built-in Function: void __builtin_return (void *RESULT)
     This built-in function returns the value described by RESULT from
     the containing function.  You should specify, for RESULT, a value
     returned by `__builtin_apply'.

 -- Built-in Function: __builtin_va_arg_pack ()
     This built-in function represents all anonymous arguments of an
     inline function.  It can be used only in inline functions which
     will be always inlined, never compiled as a separate function,
     such as those using `__attribute__ ((__always_inline__))' or
     `__attribute__ ((__gnu_inline__))' extern inline functions.  It
     must be only passed as last argument to some other function with
     variable arguments.  This is useful for writing small wrapper
     inlines for variable argument functions, when using preprocessor
     macros is undesirable.  For example:
          extern int myprintf (FILE *f, const char *format, ...);
          extern inline __attribute__ ((__gnu_inline__)) int
          myprintf (FILE *f, const char *format, ...)
          {
            int r = fprintf (f, "myprintf: ");
            if (r < 0)
              return r;
            int s = fprintf (f, format, __builtin_va_arg_pack ());
            if (s < 0)
              return s;
            return r + s;
          }

 -- Built-in Function: __builtin_va_arg_pack_len ()
     This built-in function returns the number of anonymous arguments of
     an inline function.  It can be used only in inline functions which
     will be always inlined, never compiled as a separate function, such
     as those using `__attribute__ ((__always_inline__))' or
     `__attribute__ ((__gnu_inline__))' extern inline functions.  For
     example following will do link or runtime checking of open
     arguments for optimized code:
          #ifdef __OPTIMIZE__
          extern inline __attribute__((__gnu_inline__)) int
          myopen (const char *path, int oflag, ...)
          {
            if (__builtin_va_arg_pack_len () > 1)
              warn_open_too_many_arguments ();

            if (__builtin_constant_p (oflag))
              {
                if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
                  {
                    warn_open_missing_mode ();
                    return __open_2 (path, oflag);
                  }
                return open (path, oflag, __builtin_va_arg_pack ());
              }

            if (__builtin_va_arg_pack_len () < 1)
              return __open_2 (path, oflag);

            return open (path, oflag, __builtin_va_arg_pack ());
          }
          #endif

File: gcc.info,  Node: Typeof,  Next: Conditionals,  Prev: Constructing Calls,  Up: C Extensions

5.6 Referring to a Type with `typeof'
=====================================

Another way to refer to the type of an expression is with `typeof'.
The syntax of using of this keyword looks like `sizeof', but the
construct acts semantically like a type name defined with `typedef'.

 There are two ways of writing the argument to `typeof': with an
expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that `x' is an array of pointers to functions; the type
described is that of the values of the functions.

 Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to `int'.

 If you are writing a header file that must work when included in ISO C
programs, write `__typeof__' instead of `typeof'.  *Note Alternate
Keywords::.

 A `typeof'-construct can be used anywhere a typedef name could be
used.  For example, you can use it in a declaration, in a cast, or
inside of `sizeof' or `typeof'.

 `typeof' is often useful in conjunction with the
statements-within-expressions feature.  Here is how the two together can
be used to define a safe "maximum" macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:

     #define max(a,b) \
       ({ typeof (a) _a = (a); \
           typeof (b) _b = (b); \
         _a > _b ? _a : _b; })

 The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within
the expressions that are substituted for `a' and `b'.  Eventually we
hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers;
this will be a more reliable way to prevent such conflicts.

Some more examples of the use of `typeof':

   * This declares `y' with the type of what `x' points to.

          typeof (*x) y;

   * This declares `y' as an array of such values.

          typeof (*x) y[4];

   * This declares `y' as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using `typeof', and why it
     might be a useful way to write, rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, `array (pointer (char), 4)' is the type of arrays of 4
     pointers to `char'.

 _Compatibility Note:_ In addition to `typeof', GCC 2 supported a more
limited extension which permitted one to write

     typedef T = EXPR;

with the effect of declaring T to have the type of the expression EXPR.
This extension does not work with GCC 3 (versions between 3.0 and 3.2
will crash; 3.2.1 and later give an error).  Code which relies on it
should be rewritten to use `typeof':

     typedef typeof(EXPR) T;

This will work with all versions of GCC.

File: gcc.info,  Node: Conditionals,  Next: Long Long,  Prev: Typeof,  Up: C Extensions

5.7 Conditionals with Omitted Operands
======================================

The middle operand in a conditional expression may be omitted.  Then if
the first operand is nonzero, its value is the value of the conditional
expression.

 Therefore, the expression

     x ? : y

has the value of `x' if that is nonzero; otherwise, the value of `y'.

 This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect.  Then
repeating the operand in the middle would perform the side effect
twice.  Omitting the middle operand uses the value already computed
without the undesirable effects of recomputing it.

File: gcc.info,  Node: Long Long,  Next: Complex,  Prev: Conditionals,  Up: C Extensions

5.8 Double-Word Integers
========================

ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C89 mode and in C++.  Simply
write `long long int' for a signed integer, or `unsigned long long int'
for an unsigned integer.  To make an integer constant of type `long
long int', add the suffix `LL' to the integer.  To make an integer
constant of type `unsigned long long int', add the suffix `ULL' to the
integer.

 You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports fullword-to-doubleword a widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC.

 There may be pitfalls when you use `long long' types for function
arguments, unless you declare function prototypes.  If a function
expects type `int' for its argument, and you pass a value of type `long
long int', confusion will result because the caller and the subroutine
will disagree about the number of bytes for the argument.  Likewise, if
the function expects `long long int' and you pass `int'.  The best way
to avoid such problems is to use prototypes.

File: gcc.info,  Node: Complex,  Next: Floating Types,  Prev: Long Long,  Up: C Extensions

5.9 Complex Numbers
===================

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99.  You can declare complex types
using the keyword `_Complex'.  As an extension, the older GNU keyword
`__complex__' is also supported.

 For example, `_Complex double x;' declares `x' as a variable whose
real part and imaginary part are both of type `double'.  `_Complex
short int y;' declares `y' to have real and imaginary parts of type
`short int'; this is not likely to be useful, but it shows that the set
of complex types is complete.

 To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent).  For example, `2.5fi' has type
`_Complex float' and `3i' has type `_Complex int'.  Such a constant
always has a pure imaginary value, but you can form any complex value
you like by adding one to a real constant.  This is a GNU extension; if
you have an ISO C99 conforming C library (such as GNU libc), and want
to construct complex constants of floating type, you should include
`<complex.h>' and use the macros `I' or `_Complex_I' instead.

 To extract the real part of a complex-valued expression EXP, write
`__real__ EXP'.  Likewise, use `__imag__' to extract the imaginary
part.  This is a GNU extension; for values of floating type, you should
use the ISO C99 functions `crealf', `creal', `creall', `cimagf',
`cimag' and `cimagl', declared in `<complex.h>' and also provided as
built-in functions by GCC.

 The operator `~' performs complex conjugation when used on a value
with a complex type.  This is a GNU extension; for values of floating
type, you should use the ISO C99 functions `conjf', `conj' and `conjl',
declared in `<complex.h>' and also provided as built-in functions by
GCC.

 GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa).  Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a
noncontiguous complex variable as if it were two separate variables of
noncomplex type.  If the variable's actual name is `foo', the two
fictitious variables are named `foo$real' and `foo$imag'.  You can
examine and set these two fictitious variables with your debugger.

File: gcc.info,  Node: Floating Types,  Next: Decimal Float,  Prev: Complex,  Up: C Extensions

5.10 Additional Floating Types
==============================

As an extension, the GNU C compiler supports additional floating types,
`__float80' and `__float128' to support 80bit (`XFmode') and 128 bit
(`TFmode') floating types.  Support for additional types includes the
arithmetic operators: add, subtract, multiply, divide; unary arithmetic
operators; relational operators; equality operators; and conversions to
and from integer and other floating types.  Use a suffix `w' or `W' in
a literal constant of type `__float80' and `q' or `Q' for `_float128'.
You can declare complex types using the corresponding internal complex
type, `XCmode' for `__float80' type and `TCmode' for `__float128' type:

     typedef _Complex float __attribute__((mode(TC))) _Complex128;
     typedef _Complex float __attribute__((mode(XC))) _Complex80;

 Not all targets support additional floating point types.  `__float80'
and `__float128' types are supported on i386, x86_64 and ia64 targets.

File: gcc.info,  Node: Decimal Float,  Next: Hex Floats,  Prev: Floating Types,  Up: C Extensions

5.11 Decimal Floating Types
===========================

As an extension, the GNU C compiler supports decimal floating types as
defined in the N1312 draft of ISO/IEC WDTR24732.  Support for decimal
floating types in GCC will evolve as the draft technical report changes.
Calling conventions for any target might also change.  Not all targets
support decimal floating types.

 The decimal floating types are `_Decimal32', `_Decimal64', and
`_Decimal128'.  They use a radix of ten, unlike the floating types
`float', `double', and `long double' whose radix is not specified by
the C standard but is usually two.

 Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators; relational
operators; equality operators; and conversions to and from integer and
other floating types.  Use a suffix `df' or `DF' in a literal constant
of type `_Decimal32', `dd' or `DD' for `_Decimal64', and `dl' or `DL'
for `_Decimal128'.

 GCC support of decimal float as specified by the draft technical report
is incomplete:

   * Pragma `FLOAT_CONST_DECIMAL64' is not supported, nor is the `d'
     suffix for literal constants of type `double'.

   * When the value of a decimal floating type cannot be represented in
     the integer type to which it is being converted, the result is
     undefined rather than the result value specified by the draft
     technical report.

   * GCC does not provide the C library functionality associated with
     `math.h', `fenv.h', `stdio.h', `stdlib.h', and `wchar.h', which
     must come from a separate C library implementation.  Because of
     this the GNU C compiler does not define macro `__STDC_DEC_FP__' to
     indicate that the implementation conforms to the technical report.

 Types `_Decimal32', `_Decimal64', and `_Decimal128' are supported by
the DWARF2 debug information format.

File: gcc.info,  Node: Hex Floats,  Next: Fixed-Point,  Prev: Decimal Float,  Up: C Extensions

5.12 Hex Floats
===============

ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as `1.55e1', but also numbers such as `0x1.fp3'
written in hexadecimal format.  As a GNU extension, GCC supports this
in C89 mode (except in some cases when strictly conforming) and in C++.
In that format the `0x' hex introducer and the `p' or `P' exponent
field are mandatory.  The exponent is a decimal number that indicates
the power of 2 by which the significant part will be multiplied.  Thus
`0x1.f' is 1 15/16, `p3' multiplies it by 8, and the value of `0x1.fp3'
is the same as `1.55e1'.

 Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., `0x1.f'.  This
could mean `1.0f' or `1.9375' since `f' is also the extension for
floating-point constants of type `float'.

File: gcc.info,  Node: Fixed-Point,  Next: Zero Length,  Prev: Hex Floats,  Up: C Extensions

5.13 Fixed-Point Types
======================

As an extension, the GNU C compiler supports fixed-point types as
defined in the N1169 draft of ISO/IEC DTR 18037.  Support for
fixed-point types in GCC will evolve as the draft technical report
changes.  Calling conventions for any target might also change.  Not
all targets support fixed-point types.

 The fixed-point types are `short _Fract', `_Fract', `long _Fract',
`long long _Fract', `unsigned short _Fract', `unsigned _Fract',
`unsigned long _Fract', `unsigned long long _Fract', `_Sat short
_Fract', `_Sat _Fract', `_Sat long _Fract', `_Sat long long _Fract',
`_Sat unsigned short _Fract', `_Sat unsigned _Fract', `_Sat unsigned
long _Fract', `_Sat unsigned long long _Fract', `short _Accum',
`_Accum', `long _Accum', `long long _Accum', `unsigned short _Accum',
`unsigned _Accum', `unsigned long _Accum', `unsigned long long _Accum',
`_Sat short _Accum', `_Sat _Accum', `_Sat long _Accum', `_Sat long long
_Accum', `_Sat unsigned short _Accum', `_Sat unsigned _Accum', `_Sat
unsigned long _Accum', `_Sat unsigned long long _Accum'.

 Fixed-point data values contain fractional and optional integral parts.
The format of fixed-point data varies and depends on the target machine.

 Support for fixed-point types includes:
   * prefix and postfix increment and decrement operators (`++', `--')

   * unary arithmetic operators (`+', `-', `!')

   * binary arithmetic operators (`+', `-', `*', `/')

   * binary shift operators (`<<', `>>')

   * relational operators (`<', `<=', `>=', `>')

   * equality operators (`==', `!=')

   * assignment operators (`+=', `-=', `*=', `/=', `<<=', `>>=')

   * conversions to and from integer, floating-point, or fixed-point
     types

 Use a suffix in a fixed-point literal constant:
   * `hr' or `HR' for `short _Fract' and `_Sat short _Fract'

   * `r' or `R' for `_Fract' and `_Sat _Fract'

   * `lr' or `LR' for `long _Fract' and `_Sat long _Fract'

   * `llr' or `LLR' for `long long _Fract' and `_Sat long long _Fract'

   * `uhr' or `UHR' for `unsigned short _Fract' and `_Sat unsigned
     short _Fract'

   * `ur' or `UR' for `unsigned _Fract' and `_Sat unsigned _Fract'

   * `ulr' or `ULR' for `unsigned long _Fract' and `_Sat unsigned long
     _Fract'

   * `ullr' or `ULLR' for `unsigned long long _Fract' and `_Sat
     unsigned long long _Fract'

   * `hk' or `HK' for `short _Accum' and `_Sat short _Accum'

   * `k' or `K' for `_Accum' and `_Sat _Accum'

   * `lk' or `LK' for `long _Accum' and `_Sat long _Accum'

   * `llk' or `LLK' for `long long _Accum' and `_Sat long long _Accum'

   * `uhk' or `UHK' for `unsigned short _Accum' and `_Sat unsigned
     short _Accum'

   * `uk' or `UK' for `unsigned _Accum' and `_Sat unsigned _Accum'

   * `ulk' or `ULK' for `unsigned long _Accum' and `_Sat unsigned long
     _Accum'

   * `ullk' or `ULLK' for `unsigned long long _Accum' and `_Sat
     unsigned long long _Accum'

 GCC support of fixed-point types as specified by the draft technical
report is incomplete:

   * Pragmas to control overflow and rounding behaviors are not
     implemented.

 Fixed-point types are supported by the DWARF2 debug information format.

File: gcc.info,  Node: Zero Length,  Next: Variable Length,  Prev: Fixed-Point,  Up: C Extensions

5.14 Arrays of Length Zero
==========================

Zero-length arrays are allowed in GNU C.  They are very useful as the
last element of a structure which is really a header for a
variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     struct line *thisline = (struct line *)
       malloc (sizeof (struct line) + this_length);
     thisline->length = this_length;

 In ISO C90, you would have to give `contents' a length of 1, which
means either you waste space or complicate the argument to `malloc'.

 In ISO C99, you would use a "flexible array member", which is slightly
different in syntax and semantics:

   * Flexible array members are written as `contents[]' without the `0'.

   * Flexible array members have incomplete type, and so the `sizeof'
     operator may not be applied.  As a quirk of the original
     implementation of zero-length arrays, `sizeof' evaluates to zero.

   * Flexible array members may only appear as the last member of a
     `struct' that is otherwise non-empty.

   * A structure containing a flexible array member, or a union
     containing such a structure (possibly recursively), may not be a
     member of a structure or an element of an array.  (However, these
     uses are permitted by GCC as extensions.)

 GCC versions before 3.0 allowed zero-length arrays to be statically
initialized, as if they were flexible arrays.  In addition to those
cases that were useful, it also allowed initializations in situations
that would corrupt later data.  Non-empty initialization of zero-length
arrays is now treated like any case where there are more initializer
elements than the array holds, in that a suitable warning about "excess
elements in array" is given, and the excess elements (all of them, in
this case) are ignored.

 Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
I.e. in the following, `f1' is constructed as if it were declared like
`f2'.

     struct f1 {
       int x; int y[];
     } f1 = { 1, { 2, 3, 4 } };

     struct f2 {
       struct f1 f1; int data[3];
     } f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that `f1' has the desired type,
eliminating the need to consistently refer to `f2.f1'.

 This has symmetry with normal static arrays, in that an array of
unknown size is also written with `[]'.

 Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting
data at subsequent offsets.  To avoid undue complication and confusion
with initialization of deeply nested arrays, we simply disallow any
non-empty initialization except when the structure is the top-level
object.  For example:

     struct foo { int x; int y[]; };
     struct bar { struct foo z; };

     struct foo a = { 1, { 2, 3, 4 } };        // Valid.
     struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
     struct bar c = { { 1, { } } };            // Valid.
     struct foo d[1] = { { 1 { 2, 3, 4 } } };  // Invalid.

File: gcc.info,  Node: Variable Length,  Next: Empty Structures,  Prev: Zero Length,  Up: C Extensions

5.16 Arrays of Variable Length
==============================

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C89 mode and in C++.  (However, GCC's
implementation of variable-length arrays does not yet conform in detail
to the ISO C99 standard.)  These arrays are declared like any other
automatic arrays, but with a length that is not a constant expression.
The storage is allocated at the point of declaration and deallocated
when the brace-level is exited.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

 Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

 You can use the function `alloca' to get an effect much like
variable-length arrays.  The function `alloca' is available in many
other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

 There are other differences between these two methods.  Space allocated
with `alloca' exists until the containing _function_ returns.  The
space for a variable-length array is deallocated as soon as the array
name's scope ends.  (If you use both variable-length arrays and
`alloca' in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with `alloca'.)

 You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       /* ... */
     }

 The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
`sizeof'.

 If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list--another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       /* ... */
     }

 The `int len' before the semicolon is a "parameter forward
declaration", and it serves the purpose of making the name `len' known
when the declaration of `data' is parsed.

 You can write any number of such parameter forward declarations in the
parameter list.  They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the "real"
parameter declarations.  Each forward declaration must match a "real"
declaration in parameter name and data type.  ISO C99 does not support
parameter forward declarations.

File: gcc.info,  Node: Empty Structures,  Next: Variadic Macros,  Prev: Variable Length,  Up: C Extensions

5.15 Structures With No Members
===============================

GCC permits a C structure to have no members:

     struct empty {
     };

 The structure will have size zero.  In C++, empty structures are part
of the language.  G++ treats empty structures as if they had a single
member of type `char'.

File: gcc.info,  Node: Variadic Macros,  Next: Escaped Newlines,  Prev: Empty Structures,  Up: C Extensions

5.17 Macros with a Variable Number of Arguments.
================================================

In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can.  The syntax for
defining the macro is similar to that of a function.  Here is an
example:

     #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

 Here `...' is a "variable argument".  In the invocation of such a
macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas.  This set of
tokens replaces the identifier `__VA_ARGS__' in the macro body wherever
it appears.  See the CPP manual for more information.

 GCC has long supported variadic macros, and used a different syntax
that allowed you to give a name to the variable arguments just like any
other argument.  Here is an example:

     #define debug(format, args...) fprintf (stderr, format, args)

 This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.

 GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.

 In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument.  For example,
this invocation is invalid in ISO C, because there is no comma after
the string:

     debug ("A message")

 GNU CPP permits you to completely omit the variable arguments in this
way.  In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.

 To help solve this problem, CPP behaves specially for variable
arguments used with the token paste operator, `##'.  If instead you
write

     #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

 and if the variable arguments are omitted or empty, the `##' operator
causes the preprocessor to remove the comma before it.  If you do
provide some variable arguments in your macro invocation, GNU CPP does
not complain about the paste operation and instead places the variable
arguments after the comma.  Just like any other pasted macro argument,
these arguments are not macro expanded.

File: gcc.info,  Node: Escaped Newlines,  Next: Subscripting,  Prev: Variadic Macros,  Up: C Extensions

5.18 Slightly Looser Rules for Escaped Newlines
===============================================

Recently, the preprocessor has relaxed its treatment of escaped
newlines.  Previously, the newline had to immediately follow a
backslash.  The current implementation allows whitespace in the form of
spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline.  The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line.  This works within comments and
tokens, as well as between tokens.  Comments are _not_ treated as
whitespace for the purposes of this relaxation, since they have not yet
been replaced with spaces.

File: gcc.info,  Node: Subscripting,  Next: Pointer Arith,  Prev: Escaped Newlines,  Up: C Extensions

5.19 Non-Lvalue Arrays May Have Subscripts
==========================================

In ISO C99, arrays that are not lvalues still decay to pointers, and
may be subscripted, although they may not be modified or used after the
next sequence point and the unary `&' operator may not be applied to
them.  As an extension, GCC allows such arrays to be subscripted in C89
mode, though otherwise they do not decay to pointers outside C99 mode.
For example, this is valid in GNU C though not valid in C89:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }

File: gcc.info,  Node: Pointer Arith,  Next: Initializers,  Prev: Subscripting,  Up: C Extensions

5.20 Arithmetic on `void'- and Function-Pointers
================================================

In GNU C, addition and subtraction operations are supported on pointers
to `void' and on pointers to functions.  This is done by treating the
size of a `void' or of a function as 1.

 A consequence of this is that `sizeof' is also allowed on `void' and
on function types, and returns 1.

 The option `-Wpointer-arith' requests a warning if these extensions
are used.

File: gcc.info,  Node: Initializers,  Next: Compound Literals,  Prev: Pointer Arith,  Up: C Extensions

5.21 Non-Constant Initializers
==============================

As in standard C++ and ISO C99, the elements of an aggregate
initializer for an automatic variable are not required to be constant
expressions in GNU C.  Here is an example of an initializer with
run-time varying elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       /* ... */
     }

File: gcc.info,  Node: Compound Literals,  Next: Designated Inits,  Prev: Initializers,  Up: C Extensions

5.22 Compound Literals
======================

ISO C99 supports compound literals.  A compound literal looks like a
cast containing an initializer.  Its value is an object of the type
specified in the cast, containing the elements specified in the
initializer; it is an lvalue.  As an extension, GCC supports compound
literals in C89 mode and in C++.

 Usually, the specified type is a structure.  Assume that `struct foo'
and `structure' are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a `struct foo' with a compound
literal:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

 You can also construct an array.  If all the elements of the compound
literal are (made up of) simple constant expressions, suitable for use
in initializers of objects of static storage duration, then the compound
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

 Compound literals for scalar types and union types are is also
allowed, but then the compound literal is equivalent to a cast.

 As a GNU extension, GCC allows initialization of objects with static
storage duration by compound literals (which is not possible in ISO
C99, because the initializer is not a constant).  It is handled as if
the object was initialized only with the bracket enclosed list if the
types of the compound literal and the object match.  The initializer
list of the compound literal must be constant.  If the object being
initialized has array type of unknown size, the size is determined by
compound literal size.

     static struct foo x = (struct foo) {1, 'a', 'b'};
     static int y[] = (int []) {1, 2, 3};
     static int z[] = (int [3]) {1};

The above lines are equivalent to the following:
     static struct foo x = {1, 'a', 'b'};
     static int y[] = {1, 2, 3};
     static int z[] = {1, 0, 0};

File: gcc.info,  Node: Designated Inits,  Next: Cast to Union,  Prev: Compound Literals,  Up: C Extensions

5.23 Designated Initializers
============================

Standard C89 requires the elements of an initializer to appear in a
fixed order, the same as the order of the elements in the array or
structure being initialized.

 In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C89 mode as well.  This extension is not implemented in
GNU C++.

 To specify an array index, write `[INDEX] =' before the element value.
For example,

     int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being
initialized is automatic.

 An alternative syntax for this which has been obsolete since GCC 2.5
but GCC still accepts is to write `[INDEX]' before the element value,
with no `='.

 To initialize a range of elements to the same value, write `[FIRST ...
LAST] = VALUE'.  This is a GNU extension.  For example,

     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side-effects, the side-effects will happen only
once, not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus
one.

 In a structure initializer, specify the name of a field to initialize
with `.FIELDNAME =' before the element value.  For example, given the
following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

 Another syntax which has the same meaning, obsolete since GCC 2.5, is
`FIELDNAME:', as shown here:

     struct point p = { y: yvalue, x: xvalue };

 The `[INDEX]' or `.FIELDNAME' is known as a "designator".  You can
also use a designator (or the obsolete colon syntax) when initializing
a union, to specify which element of the union should be used.  For
example,

     union foo { int i; double d; };

     union foo f = { .d = 4 };

will convert 4 to a `double' to store it in the union using the second
element.  By contrast, casting 4 to type `union foo' would store it
into the union as the integer `i', since it is an integer.  (*Note Cast
to Union::.)

 You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a designator applies to the next consecutive element of
the array or structure.  For example,

     int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

 Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an `enum' type.  For
example:

     int whitespace[256]
       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

 You can also write a series of `.FIELDNAME' and `[INDEX]' designators
before an `=' to specify a nested subobject to initialize; the list is
taken relative to the subobject corresponding to the closest
surrounding brace pair.  For example, with the `struct point'
declaration above:

     struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it will have value from
the last initialization.  If any such overridden initialization has
side-effect, it is unspecified whether the side-effect happens or not.
Currently, GCC will discard them and issue a warning.

File: gcc.info,  Node: Cast to Union,  Next: Case Ranges,  Prev: Designated Inits,  Up: C Extensions

5.25 Cast to a Union Type
=========================

A cast to union type is similar to other casts, except that the type
specified is a union type.  You can specify the type either with `union
TAG' or with a typedef name.  A cast to union is actually a constructor
though, not a cast, and hence does not yield an lvalue like normal
casts.  (*Note Compound Literals::.)

 The types that may be cast to the union type are those of the members
of the union.  Thus, given the following union and variables:

     union foo { int i; double d; };
     int x;
     double y;

both `x' and `y' can be cast to type `union foo'.

 Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:

     union foo u;
     /* ... */
     u = (union foo) x  ==  u.i = x
     u = (union foo) y  ==  u.d = y

 You can also use the union cast as a function argument:

     void hack (union foo);
     /* ... */
     hack ((union foo) x);

File: gcc.info,  Node: Case Ranges,  Next: Mixed Declarations,  Prev: Cast to Union,  Up: C Extensions

5.24 Case Ranges
================

You can specify a range of consecutive values in a single `case' label,
like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual `case'
labels, one for each integer value from LOW to HIGH, inclusive.

 This feature is especially useful for ranges of ASCII character codes:

     case 'A' ... 'Z':

 *Be careful:* Write spaces around the `...', for otherwise it may be
parsed wrong when you use it with integer values.  For example, write
this:

     case 1 ... 5:

rather than this:

     case 1...5:

File: gcc.info,  Node: Mixed Declarations,  Next: Function Attributes,  Prev: Case Ranges,  Up: C Extensions

5.26 Mixed Declarations and Code
================================

ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements.  As an extension, GCC also allows this in
C89 mode.  For example, you could do:

     int i;
     /* ... */
     i++;
     int j = i + 2;

 Each identifier is visible from where it is declared until the end of
the enclosing block.

File: gcc.info,  Node: Function Attributes,  Next: Attribute Syntax,  Prev: Mixed Declarations,  Up: C Extensions

5.27 Declaring Attributes of Functions
======================================

In GNU C, you declare certain things about functions called in your
program which help the compiler optimize function calls and check your
code more carefully.

 The keyword `__attribute__' allows you to specify special attributes
when making a declaration.  This keyword is followed by an attribute
specification inside double parentheses.  The following attributes are
currently defined for functions on all targets: `aligned',
`alloc_size', `noreturn', `returns_twice', `noinline', `always_inline',
`flatten', `pure', `const', `nothrow', `sentinel', `format',
`format_arg', `no_instrument_function', `section', `constructor',
`destructor', `used', `unused', `deprecated', `weak', `malloc',
`alias', `warn_unused_result', `nonnull', `gnu_inline',
`externally_visible', `hot', `cold', `artificial', `error' and
`warning'.  Several other attributes are defined for functions on
particular target systems.  Other attributes, including `section' are
supported for variables declarations (*note Variable Attributes::) and
for types (*note Type Attributes::).

 You may also specify attributes with `__' preceding and following each
keyword.  This allows you to use them in header files without being
concerned about a possible macro of the same name.  For example, you
may use `__noreturn__' instead of `noreturn'.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`alias ("TARGET")'
     The `alias' attribute causes the declaration to be emitted as an
     alias for another symbol, which must be specified.  For instance,

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

     defines `f' to be a weak alias for `__f'.  In C++, the mangled
     name for the target must be used.  It is an error if `__f' is not
     defined in the same translation unit.

     Not all target machines support this attribute.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment for the function,
     measured in bytes.

     You cannot use this attribute to decrease the alignment of a
     function, only to increase it.  However, when you explicitly
     specify a function alignment this will override the effect of the
     `-falign-functions' (*note Optimize Options::) option for this
     function.

     Note that the effectiveness of `aligned' attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for functions to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  See your linker
     documentation for further information.

     The `aligned' attribute can also be used for variables and fields
     (*note Variable Attributes::.)

`alloc_size'
     The `alloc_size' attribute is used to tell the compiler that the
     function return value points to memory, where the size is given by
     one or two of the functions parameters.  GCC uses this information
     to improve the correctness of `__builtin_object_size'.

     The function parameter(s) denoting the allocated size are
     specified by one or two integer arguments supplied to the
     attribute.  The allocated size is either the value of the single
     function argument specified or the product of the two function
     arguments specified.  Argument numbering starts at one.

     For instance,

          void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
          void my_realloc(void*, size_t) __attribute__((alloc_size(2)))

     declares that my_calloc will return memory of the size given by
     the product of parameter 1 and 2 and that my_realloc will return
     memory of the size given by parameter 2.

`always_inline'
     Generally, functions are not inlined unless optimization is
     specified.  For functions declared inline, this attribute inlines
     the function even if no optimization level was specified.

`gnu_inline'
     This attribute should be used with a function which is also
     declared with the `inline' keyword.  It directs GCC to treat the
     function as if it were defined in gnu89 mode even when compiling
     in C99 or gnu99 mode.

     If the function is declared `extern', then this definition of the
     function is used only for inlining.  In no case is the function
     compiled as a standalone function, not even if you take its address
     explicitly.  Such an address becomes an external reference, as if
     you had only declared the function, and had not defined it.  This
     has almost the effect of a macro.  The way to use this is to put a
     function definition in a header file with this attribute, and put
     another copy of the function, without `extern', in a library file.
     The definition in the header file will cause most calls to the
     function to be inlined.  If any uses of the function remain, they
     will refer to the single copy in the library.  Note that the two
     definitions of the functions need not be precisely the same,
     although if they do not have the same effect your program may
     behave oddly.

     In C, if the function is neither `extern' nor `static', then the
     function is compiled as a standalone function, as well as being
     inlined where possible.

     This is how GCC traditionally handled functions declared `inline'.
     Since ISO C99 specifies a different semantics for `inline', this
     function attribute is provided as a transition measure and as a
     useful feature in its own right.  This attribute is available in
     GCC 4.1.3 and later.  It is available if either of the
     preprocessor macros `__GNUC_GNU_INLINE__' or
     `__GNUC_STDC_INLINE__' are defined.  *Note An Inline Function is
     As Fast As a Macro: Inline.

     In C++, this attribute does not depend on `extern' in any way, but
     it still requires the `inline' keyword to enable its special
     behavior.

`artificial'
     This attribute is useful for small inline wrappers which if
     possible should appear during debugging as a unit, depending on
     the debug info format it will either mean marking the function as
     artificial or using the caller location for all instructions
     within the inlined body.

`flatten'
     Generally, inlining into a function is limited.  For a function
     marked with this attribute, every call inside this function will
     be inlined, if possible.  Whether the function itself is
     considered for inlining depends on its size and the current
     inlining parameters.

`error ("MESSAGE")'
     If this attribute is used on a function declaration and a call to
     such a function is not eliminated through dead code elimination or
     other optimizations, an error which will include MESSAGE will be
     diagnosed.  This is useful for compile time checking, especially
     together with `__builtin_constant_p' and inline functions where
     checking the inline function arguments is not possible through
     `extern char [(condition) ? 1 : -1];' tricks.  While it is
     possible to leave the function undefined and thus invoke a link
     failure, when using this attribute the problem will be diagnosed
     earlier and with exact location of the call even in presence of
     inline functions or when not emitting debugging information.

`warning ("MESSAGE")'
     If this attribute is used on a function declaration and a call to
     such a function is not eliminated through dead code elimination or
     other optimizations, a warning which will include MESSAGE will be
     diagnosed.  This is useful for compile time checking, especially
     together with `__builtin_constant_p' and inline functions.  While
     it is possible to define the function with a message in
     `.gnu.warning*' section, when using this attribute the problem
     will be diagnosed earlier and with exact location of the call even
     in presence of inline functions or when not emitting debugging
     information.

`cdecl'
     On the Intel 386, the `cdecl' attribute causes the compiler to
     assume that the calling function will pop off the stack space used
     to pass arguments.  This is useful to override the effects of the
     `-mrtd' switch.

`const'
     Many functions do not examine any values except their arguments,
     and have no effects except the return value.  Basically this is
     just slightly more strict class than the `pure' attribute below,
     since function is not allowed to read global memory.

     Note that a function that has pointer arguments and examines the
     data pointed to must _not_ be declared `const'.  Likewise, a
     function that calls a non-`const' function usually must not be
     `const'.  It does not make sense for a `const' function to return
     `void'.

     The attribute `const' is not implemented in GCC versions earlier
     than 2.5.  An alternative way to declare that a function has no
     side effects, which works in the current version and in some older
     versions, is as follows:

          typedef int intfn ();

          extern const intfn square;

     This approach does not work in GNU C++ from 2.6.0 on, since the
     language specifies that the `const' must be attached to the return
     value.

`constructor'
`destructor'
`constructor (PRIORITY)'
`destructor (PRIORITY)'
     The `constructor' attribute causes the function to be called
     automatically before execution enters `main ()'.  Similarly, the
     `destructor' attribute causes the function to be called
     automatically after `main ()' has completed or `exit ()' has been
     called.  Functions with these attributes are useful for
     initializing data that will be used implicitly during the
     execution of the program.

     You may provide an optional integer priority to control the order
     in which constructor and destructor functions are run.  A
     constructor with a smaller priority number runs before a
     constructor with a larger priority number; the opposite
     relationship holds for destructors.  So, if you have a constructor
     that allocates a resource and a destructor that deallocates the
     same resource, both functions typically have the same priority.
     The priorities for constructor and destructor functions are the
     same as those specified for namespace-scope C++ objects (*note C++
     Attributes::).

     These attributes are not currently implemented for Objective-C.

`deprecated'
     The `deprecated' attribute results in a warning if the function is
     used anywhere in the source file.  This is useful when identifying
     functions that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated function, to enable users to easily find further
     information about why the function is deprecated, or what they
     should do instead.  Note that the warnings only occurs for uses:

          int old_fn () __attribute__ ((deprecated));
          int old_fn ();
          int (*fn_ptr)() = old_fn;

     results in a warning on line 3 but not line 2.

     The `deprecated' attribute can also be used for variables and
     types (*note Variable Attributes::, *note Type Attributes::.)

`dllexport'
     On Microsoft Windows targets and Symbian OS targets the
     `dllexport' attribute causes the compiler to provide a global
     pointer to a pointer in a DLL, so that it can be referenced with
     the `dllimport' attribute.  On Microsoft Windows targets, the
     pointer name is formed by combining `_imp__' and the function or
     variable name.

     You can use `__declspec(dllexport)' as a synonym for
     `__attribute__ ((dllexport))' for compatibility with other
     compilers.

     On systems that support the `visibility' attribute, this attribute
     also implies "default" visibility.  It is an error to explicitly
     specify any other visibility.

     Currently, the `dllexport' attribute is ignored for inlined
     functions, unless the `-fkeep-inline-functions' flag has been
     used.  The attribute is also ignored for undefined symbols.

     When applied to C++ classes, the attribute marks defined
     non-inlined member functions and static data members as exports.
     Static consts initialized in-class are not marked unless they are
     also defined out-of-class.

     For Microsoft Windows targets there are alternative methods for
     including the symbol in the DLL's export table such as using a
     `.def' file with an `EXPORTS' section or, with GNU ld, using the
     `--export-all' linker flag.

`dllimport'
     On Microsoft Windows and Symbian OS targets, the `dllimport'
     attribute causes the compiler to reference a function or variable
     via a global pointer to a pointer that is set up by the DLL
     exporting the symbol.  The attribute implies `extern'.  On
     Microsoft Windows targets, the pointer name is formed by combining
     `_imp__' and the function or variable name.

     You can use `__declspec(dllimport)' as a synonym for
     `__attribute__ ((dllimport))' for compatibility with other
     compilers.

     On systems that support the `visibility' attribute, this attribute
     also implies "default" visibility.  It is an error to explicitly
     specify any other visibility.

     Currently, the attribute is ignored for inlined functions.  If the
     attribute is applied to a symbol _definition_, an error is
     reported.  If a symbol previously declared `dllimport' is later
     defined, the attribute is ignored in subsequent references, and a
     warning is emitted.  The attribute is also overridden by a
     subsequent declaration as `dllexport'.

     When applied to C++ classes, the attribute marks non-inlined
     member functions and static data members as imports.  However, the
     attribute is ignored for virtual methods to allow creation of
     vtables using thunks.

     On the SH Symbian OS target the `dllimport' attribute also has
     another affect--it can cause the vtable and run-time type
     information for a class to be exported.  This happens when the
     class has a dllimport'ed constructor or a non-inline, non-pure
     virtual function and, for either of those two conditions, the
     class also has a inline constructor or destructor and has a key
     function that is defined in the current translation unit.

     For Microsoft Windows based targets the use of the `dllimport'
     attribute on functions is not necessary, but provides a small
     performance benefit by eliminating a thunk in the DLL.  The use of
     the `dllimport' attribute on imported variables was required on
     older versions of the GNU linker, but can now be avoided by
     passing the `--enable-auto-import' switch to the GNU linker.  As
     with functions, using the attribute for a variable eliminates a
     thunk in the DLL.

     One drawback to using this attribute is that a pointer to a
     _variable_ marked as `dllimport' cannot be used as a constant
     address. However, a pointer to a _function_ with the `dllimport'
     attribute can be used as a constant initializer; in this case, the
     address of a stub function in the import lib is referenced.  On
     Microsoft Windows targets, the attribute can be disabled for
     functions by setting the `-mnop-fun-dllimport' flag.

`eightbit_data'
     Use this attribute on the H8/300, H8/300H, and H8S to indicate
     that the specified variable should be placed into the eight bit
     data section.  The compiler will generate more efficient code for
     certain operations on data in the eight bit data area.  Note the
     eight bit data area is limited to 256 bytes of data.

     You must use GAS and GLD from GNU binutils version 2.7 or later for
     this attribute to work correctly.

`exception_handler'
     Use this attribute on the Blackfin to indicate that the specified
     function is an exception handler.  The compiler will generate
     function entry and exit sequences suitable for use in an exception
     handler when this attribute is present.

`externally_visible'
     This attribute, attached to a global variable or function,
     nullifies the effect of the `-fwhole-program' command-line option,
     so the object remains visible outside the current compilation unit.

`far'
     On 68HC11 and 68HC12 the `far' attribute causes the compiler to
     use a calling convention that takes care of switching memory banks
     when entering and leaving a function.  This calling convention is
     also the default when using the `-mlong-calls' option.

     On 68HC12 the compiler will use the `call' and `rtc' instructions
     to call and return from a function.

     On 68HC11 the compiler will generate a sequence of instructions to
     invoke a board-specific routine to switch the memory bank and call
     the real function.  The board-specific routine simulates a `call'.
     At the end of a function, it will jump to a board-specific routine
     instead of using `rts'.  The board-specific return routine
     simulates the `rtc'.

`fastcall'
     On the Intel 386, the `fastcall' attribute causes the compiler to
     pass the first argument (if of integral type) in the register ECX
     and the second argument (if of integral type) in the register EDX.
     Subsequent and other typed arguments are passed on the stack.  The
     called function will pop the arguments off the stack.  If the
     number of arguments is variable all arguments are pushed on the
     stack.

`format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
     The `format' attribute specifies that a function takes `printf',
     `scanf', `strftime' or `strfmon' style arguments which should be
     type-checked against a format string.  For example, the
     declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to `my_printf'
     for consistency with the `printf' style format string argument
     `my_format'.

     The parameter ARCHETYPE determines how the format string is
     interpreted, and should be `printf', `scanf', `strftime',
     `gnu_printf', `gnu_scanf', `gnu_strftime' or `strfmon'.  (You can
     also use `__printf__', `__scanf__', `__strftime__' or
     `__strfmon__'.)  On MinGW targets, `ms_printf', `ms_scanf', and
     `ms_strftime' are also present.  ARCHTYPE values such as `printf'
     refer to the formats accepted by the system's C run-time library,
     while `gnu_' values always refer to the formats accepted by the
     GNU C Library.  On Microsoft Windows targets, `ms_' values refer
     to the formats accepted by the `msvcrt.dll' library.  The
     parameter STRING-INDEX specifies which argument is the format
     string argument (starting from 1), while FIRST-TO-CHECK is the
     number of the first argument to check against the format string.
     For functions where the arguments are not available to be checked
     (such as `vprintf'), specify the third parameter as zero.  In this
     case the compiler only checks the format string for consistency.
     For `strftime' formats, the third parameter is required to be zero.
     Since non-static C++ methods have an implicit `this' argument, the
     arguments of such methods should be counted from two, not one, when
     giving values for STRING-INDEX and FIRST-TO-CHECK.

     In the example above, the format string (`my_format') is the second
     argument of the function `my_print', and the arguments to check
     start with the third argument, so the correct parameters for the
     format attribute are 2 and 3.

     The `format' attribute allows you to identify your own functions
     which take format strings as arguments, so that GCC can check the
     calls to these functions for errors.  The compiler always (unless
     `-ffreestanding' or `-fno-builtin' is used) checks formats for the
     standard library functions `printf', `fprintf', `sprintf',
     `scanf', `fscanf', `sscanf', `strftime', `vprintf', `vfprintf' and
     `vsprintf' whenever such warnings are requested (using
     `-Wformat'), so there is no need to modify the header file
     `stdio.h'.  In C99 mode, the functions `snprintf', `vsnprintf',
     `vscanf', `vfscanf' and `vsscanf' are also checked.  Except in
     strictly conforming C standard modes, the X/Open function
     `strfmon' is also checked as are `printf_unlocked' and
     `fprintf_unlocked'.  *Note Options Controlling C Dialect: C
     Dialect Options.

     The target may provide additional types of format checks.  *Note
     Format Checks Specific to Particular Target Machines: Target
     Format Checks.

`format_arg (STRING-INDEX)'
     The `format_arg' attribute specifies that a function takes a format
     string for a `printf', `scanf', `strftime' or `strfmon' style
     function and modifies it (for example, to translate it into
     another language), so the result can be passed to a `printf',
     `scanf', `strftime' or `strfmon' style function (with the
     remaining arguments to the format function the same as they would
     have been for the unmodified string).  For example, the
     declaration:

          extern char *
          my_dgettext (char *my_domain, const char *my_format)
                __attribute__ ((format_arg (2)));

     causes the compiler to check the arguments in calls to a `printf',
     `scanf', `strftime' or `strfmon' type function, whose format
     string argument is a call to the `my_dgettext' function, for
     consistency with the format string argument `my_format'.  If the
     `format_arg' attribute had not been specified, all the compiler
     could tell in such calls to format functions would be that the
     format string argument is not constant; this would generate a
     warning when `-Wformat-nonliteral' is used, but the calls could
     not be checked without the attribute.

     The parameter STRING-INDEX specifies which argument is the format
     string argument (starting from one).  Since non-static C++ methods
     have an implicit `this' argument, the arguments of such methods
     should be counted from two.

     The `format-arg' attribute allows you to identify your own
     functions which modify format strings, so that GCC can check the
     calls to `printf', `scanf', `strftime' or `strfmon' type function
     whose operands are a call to one of your own function.  The
     compiler always treats `gettext', `dgettext', and `dcgettext' in
     this manner except when strict ISO C support is requested by
     `-ansi' or an appropriate `-std' option, or `-ffreestanding' or
     `-fno-builtin' is used.  *Note Options Controlling C Dialect: C
     Dialect Options.

`function_vector'
     Use this attribute on the H8/300, H8/300H, and H8S to indicate
     that the specified function should be called through the function
     vector.  Calling a function through the function vector will
     reduce code size, however; the function vector has a limited size
     (maximum 128 entries on the H8/300 and 64 entries on the H8/300H
     and H8S) and shares space with the interrupt vector.

     In SH2A target, this attribute declares a function to be called
     using the TBR relative addressing mode.  The argument to this
     attribute is the entry number of the same function in a vector
     table containing all the TBR relative addressable functions.  For
     the successful jump, register TBR should contain the start address
     of this TBR relative vector table.  In the startup routine of the
     user application, user needs to care of this TBR register
     initialization.  The TBR relative vector table can have at max 256
     function entries.  The jumps to these functions will be generated
     using a SH2A specific, non delayed branch instruction JSR/N
     @(disp8,TBR).  You must use GAS and GLD from GNU binutils version
     2.7 or later for this attribute to work correctly.

     Please refer the example of M16C target, to see the use of this
     attribute while declaring a function,

     In an application, for a function being called once, this
     attribute will save at least 8 bytes of code; and if other
     successive calls are being made to the same function, it will save
     2 bytes of code per each of these calls.

     On M16C/M32C targets, the `function_vector' attribute declares a
     special page subroutine call function. Use of this attribute
     reduces the code size by 2 bytes for each call generated to the
     subroutine. The argument to the attribute is the vector number
     entry from the special page vector table which contains the 16
     low-order bits of the subroutine's entry address. Each vector
     table has special page number (18 to 255) which are used in `jsrs'
     instruction.  Jump addresses of the routines are generated by
     adding 0x0F0000 (in case of M16C targets) or 0xFF0000 (in case of
     M32C targets), to the 2 byte addresses set in the vector table.
     Therefore you need to ensure that all the special page vector
     routines should get mapped within the address range 0x0F0000 to
     0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF (for M32C).

     In the following example 2 bytes will be saved for each call to
     function `foo'.

          void foo (void) __attribute__((function_vector(0x18)));
          void foo (void)
          {
          }

          void bar (void)
          {
              foo();
          }

     If functions are defined in one file and are called in another
     file, then be sure to write this declaration in both files.

     This attribute is ignored for R8C target.

`hotpatch (HALFWORDS-BEFORE-FUNCTION-LABEL,HALFWORDS-AFTER-FUNCTION-LABEL)'
     On S/390 System z targets, you can use this function attribute to
     make GCC generate a "hot-patching" function prologue.  If the
     `-mhotpatch=' command-line option is used at the same time, the
     `hotpatch' attribute takes precedence.  The first of the two
     arguments specifies the number of halfwords to be added before the
     function label.  A second argument can be used to specify the
     number of halfwords to be added after the function label.  For
     both arguments the maximum allowed value is 1000000.

     If both arguments are zero, hotpatching is disabled.

`interrupt'
     Use this attribute on the ARM, AVR, CRX, M32C, M32R/D, m68k, and
     Xstormy16 ports to indicate that the specified function is an
     interrupt handler.  The compiler will generate function entry and
     exit sequences suitable for use in an interrupt handler when this
     attribute is present.

     Note, interrupt handlers for the Blackfin, H8/300, H8/300H, H8S,
     and SH processors can be specified via the `interrupt_handler'
     attribute.

     Note, on the AVR, interrupts will be enabled inside the function.

     Note, for the ARM, you can specify the kind of interrupt to be
     handled by adding an optional parameter to the interrupt attribute
     like this:

          void f () __attribute__ ((interrupt ("IRQ")));

     Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT
     and UNDEF.

     On ARMv7-M the interrupt type is ignored, and the attribute means
     the function may be called with a word aligned stack pointer.

`interrupt_handler'
     Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S,
     and SH to indicate that the specified function is an interrupt
     handler.  The compiler will generate function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

`interrupt_thread'
     Use this attribute on fido, a subarchitecture of the m68k, to
     indicate that the specified function is an interrupt handler that
     is designed to run as a thread.  The compiler omits generate
     prologue/epilogue sequences and replaces the return instruction
     with a `sleep' instruction.  This attribute is available only on
     fido.

`isr'
     Use this attribute on ARM to write Interrupt Service Routines.
     This is an alias to the `interrupt' attribute above.

`kspisusp'
     When used together with `interrupt_handler', `exception_handler'
     or `nmi_handler', code will be generated to load the stack pointer
     from the USP register in the function prologue.

`l1_text'
     This attribute specifies a function to be placed into L1
     Instruction SRAM. The function will be put into a specific section
     named `.l1.text'.  With `-mfdpic', function calls with a such
     function as the callee or caller will use inlined PLT.

`long_call/short_call'
     This attribute specifies how a particular function is called on
     ARM.  Both attributes override the `-mlong-calls' (*note ARM
     Options::) command line switch and `#pragma long_calls' settings.
     The `long_call' attribute indicates that the function might be far
     away from the call site and require a different (more expensive)
     calling sequence.   The `short_call' attribute always places the
     offset to the function from the call site into the `BL'
     instruction directly.

`longcall/shortcall'
     On the Blackfin, RS/6000 and PowerPC, the `longcall' attribute
     indicates that the function might be far away from the call site
     and require a different (more expensive) calling sequence.  The
     `shortcall' attribute indicates that the function is always close
     enough for the shorter calling sequence to be used.  These
     attributes override both the `-mlongcall' switch and, on the
     RS/6000 and PowerPC, the `#pragma longcall' setting.

     *Note RS/6000 and PowerPC Options::, for more information on
     whether long calls are necessary.

`long_call/near/far'
     These attributes specify how a particular function is called on
     MIPS.  The attributes override the `-mlong-calls' (*note MIPS
     Options::) command-line switch.  The `long_call' and `far'
     attributes are synonyms, and cause the compiler to always call the
     function by first loading its address into a register, and then
     using the contents of that register.  The `near' attribute has the
     opposite effect; it specifies that non-PIC calls should be made
     using the more efficient `jal' instruction.

`malloc'
     The `malloc' attribute is used to tell the compiler that a function
     may be treated as if any non-`NULL' pointer it returns cannot
     alias any other pointer valid when the function returns.  This
     will often improve optimization.  Standard functions with this
     property include `malloc' and `calloc'.  `realloc'-like functions
     have this property as long as the old pointer is never referred to
     (including comparing it to the new pointer) after the function
     returns a non-`NULL' value.

`mips16/nomips16'
     On MIPS targets, you can use the `mips16' and `nomips16' function
     attributes to locally select or turn off MIPS16 code generation.
     A function with the `mips16' attribute is emitted as MIPS16 code,
     while MIPS16 code generation is disabled for functions with the
     `nomips16' attribute.  These attributes override the `-mips16' and
     `-mno-mips16' options on the command line (*note MIPS Options::).

     When compiling files containing mixed MIPS16 and non-MIPS16 code,
     the preprocessor symbol `__mips16' reflects the setting on the
     command line, not that within individual functions.  Mixed MIPS16
     and non-MIPS16 code may interact badly with some GCC extensions
     such as `__builtin_apply' (*note Constructing Calls::).

`model (MODEL-NAME)'
     On the M32R/D, use this attribute to set the addressability of an
     object, and of the code generated for a function.  The identifier
     MODEL-NAME is one of `small', `medium', or `large', representing
     each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction), and are
     callable with the `bl' instruction.

     Medium model objects may live anywhere in the 32-bit address space
     (the compiler will generate `seth/add3' instructions to load their
     addresses), and are callable with the `bl' instruction.

     Large model objects may live anywhere in the 32-bit address space
     (the compiler will generate `seth/add3' instructions to load their
     addresses), and may not be reachable with the `bl' instruction
     (the compiler will generate the much slower `seth/add3/jl'
     instruction sequence).

     On IA-64, use this attribute to set the addressability of an
     object.  At present, the only supported identifier for MODEL-NAME
     is `small', indicating addressability via "small" (22-bit)
     addresses (so that their addresses can be loaded with the `addl'
     instruction).  Caveat: such addressing is by definition not
     position independent and hence this attribute must not be used for
     objects defined by shared libraries.

`ms_abi/sysv_abi'
     On 64-bit x86_64-*-* targets, you can use an ABI attribute to
     indicate which calling convention should be used for a function.
     The `ms_abi' attribute tells the compiler to use the Microsoft
     ABI, while the `sysv_abi' attribute tells the compiler to use the
     ABI used on GNU/Linux and other systems.  The default is to use
     the Microsoft ABI when targeting Windows.  On all other systems,
     the default is the AMD ABI.

     Note, This feature is currently sorried out for Windows targets
     trying to

`naked'
     Use this attribute on the ARM, AVR, IP2K and SPU ports to indicate
     that the specified function does not need prologue/epilogue
     sequences generated by the compiler.  It is up to the programmer
     to provide these sequences. The only statements that can be safely
     included in naked functions are `asm' statements that do not have
     operands.  All other statements, including declarations of local
     variables, `if' statements, and so forth, should be avoided.
     Naked functions should be used to implement the body of an
     assembly function, while allowing the compiler to construct the
     requisite function declaration for the assembler.

`near'
     On 68HC11 and 68HC12 the `near' attribute causes the compiler to
     use the normal calling convention based on `jsr' and `rts'.  This
     attribute can be used to cancel the effect of the `-mlong-calls'
     option.

`nesting'
     Use this attribute together with `interrupt_handler',
     `exception_handler' or `nmi_handler' to indicate that the function
     entry code should enable nested interrupts or exceptions.

`nmi_handler'
     Use this attribute on the Blackfin to indicate that the specified
     function is an NMI handler.  The compiler will generate function
     entry and exit sequences suitable for use in an NMI handler when
     this attribute is present.

`no_instrument_function'
     If `-finstrument-functions' is given, profiling function calls will
     be generated at entry and exit of most user-compiled functions.
     Functions with this attribute will not be so instrumented.

`noinline'
     This function attribute prevents a function from being considered
     for inlining.  If the function does not have side-effects, there
     are optimizations other than inlining that causes function calls
     to be optimized away, although the function call is live.  To keep
     such calls from being optimized away, put
          asm ("");
     (*note Extended Asm::) in the called function, to serve as a
     special side-effect.

`nonnull (ARG-INDEX, ...)'
     The `nonnull' attribute specifies that some function parameters
     should be non-null pointers.  For instance, the declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull (1, 2)));

     causes the compiler to check that, in calls to `my_memcpy',
     arguments DEST and SRC are non-null.  If the compiler determines
     that a null pointer is passed in an argument slot marked as
     non-null, and the `-Wnonnull' option is enabled, a warning is
     issued.  The compiler may also choose to make optimizations based
     on the knowledge that certain function arguments will not be null.

     If no argument index list is given to the `nonnull' attribute, all
     pointer arguments are marked as non-null.  To illustrate, the
     following declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
                  __attribute__((nonnull));

`noreturn'
     A few standard library functions, such as `abort' and `exit',
     cannot return.  GCC knows this automatically.  Some programs define
     their own functions that never return.  You can declare them
     `noreturn' to tell the compiler this fact.  For example,

          void fatal () __attribute__ ((noreturn));

          void
          fatal (/* ... */)
          {
            /* ... */ /* Print error message. */ /* ... */
            exit (1);
          }

     The `noreturn' keyword tells the compiler to assume that `fatal'
     cannot return.  It can then optimize without regard to what would
     happen if `fatal' ever did return.  This makes slightly better
     code.  More importantly, it helps avoid spurious warnings of
     uninitialized variables.

     The `noreturn' keyword does not affect the exceptional path when
     that applies: a `noreturn'-marked function may still return to the
     caller by throwing an exception or calling `longjmp'.

     Do not assume that registers saved by the calling function are
     restored before calling the `noreturn' function.

     It does not make sense for a `noreturn' function to have a return
     type other than `void'.

     The attribute `noreturn' is not implemented in GCC versions
     earlier than 2.5.  An alternative way to declare that a function
     does not return, which works in the current version and in some
     older versions, is as follows:

          typedef void voidfn ();

          volatile voidfn fatal;

     This approach does not work in GNU C++.

`nothrow'
     The `nothrow' attribute is used to inform the compiler that a
     function cannot throw an exception.  For example, most functions in
     the standard C library can be guaranteed not to throw an exception
     with the notable exceptions of `qsort' and `bsearch' that take
     function pointer arguments.  The `nothrow' attribute is not
     implemented in GCC versions earlier than 3.3.

`optimize'
     The `optimize' attribute is used to specify that a function is to
     be compiled with different optimization options than specified on
     the command line.  Arguments can either be numbers or strings.
     Numbers are assumed to be an optimization level.  Strings that
     begin with `O' are assumed to be an optimization option, while
     other options are assumed to be used with a `-f' prefix.  You can
     also use the `#pragma GCC optimize' pragma to set the optimization
     options that affect more than one function.  *Note Function
     Specific Option Pragmas::, for details about the `#pragma GCC
     optimize' pragma.

     This can be used for instance to have frequently executed functions
     compiled with more aggressive optimization options that produce
     faster and larger code, while other functions can be called with
     less aggressive options.

`pure'
     Many functions have no effects except the return value and their
     return value depends only on the parameters and/or global
     variables.  Such a function can be subject to common subexpression
     elimination and loop optimization just as an arithmetic operator
     would be.  These functions should be declared with the attribute
     `pure'.  For example,

          int square (int) __attribute__ ((pure));

     says that the hypothetical function `square' is safe to call fewer
     times than the program says.

     Some of common examples of pure functions are `strlen' or `memcmp'.
     Interesting non-pure functions are functions with infinite loops
     or those depending on volatile memory or other system resource,
     that may change between two consecutive calls (such as `feof' in a
     multithreading environment).

     The attribute `pure' is not implemented in GCC versions earlier
     than 2.96.

`hot'
     The `hot' attribute is used to inform the compiler that a function
     is a hot spot of the compiled program.  The function is optimized
     more aggressively and on many target it is placed into special
     subsection of the text section so all hot functions appears close
     together improving locality.

     When profile feedback is available, via `-fprofile-use', hot
     functions are automatically detected and this attribute is ignored.

     The `hot' attribute is not implemented in GCC versions earlier
     than 4.3.

`cold'
     The `cold' attribute is used to inform the compiler that a
     function is unlikely executed.  The function is optimized for size
     rather than speed and on many targets it is placed into special
     subsection of the text section so all cold functions appears close
     together improving code locality of non-cold parts of program.
     The paths leading to call of cold functions within code are marked
     as unlikely by the branch prediction mechanism. It is thus useful
     to mark functions used to handle unlikely conditions, such as
     `perror', as cold to improve optimization of hot functions that do
     call marked functions in rare occasions.

     When profile feedback is available, via `-fprofile-use', hot
     functions are automatically detected and this attribute is ignored.

     The `cold' attribute is not implemented in GCC versions earlier
     than 4.3.

`regparm (NUMBER)'
     On the Intel 386, the `regparm' attribute causes the compiler to
     pass arguments number one to NUMBER if they are of integral type
     in registers EAX, EDX, and ECX instead of on the stack.  Functions
     that take a variable number of arguments will continue to be
     passed all of their arguments on the stack.

     Beware that on some ELF systems this attribute is unsuitable for
     global functions in shared libraries with lazy binding (which is
     the default).  Lazy binding will send the first call via resolving
     code in the loader, which might assume EAX, EDX and ECX can be
     clobbered, as per the standard calling conventions.  Solaris 8 is
     affected by this.  GNU systems with GLIBC 2.1 or higher, and
     FreeBSD, are believed to be safe since the loaders there save EAX,
     EDX and ECX.  (Lazy binding can be disabled with the linker or the
     loader if desired, to avoid the problem.)

`sseregparm'
     On the Intel 386 with SSE support, the `sseregparm' attribute
     causes the compiler to pass up to 3 floating point arguments in
     SSE registers instead of on the stack.  Functions that take a
     variable number of arguments will continue to pass all of their
     floating point arguments on the stack.

`force_align_arg_pointer'
     On the Intel x86, the `force_align_arg_pointer' attribute may be
     applied to individual function definitions, generating an alternate
     prologue and epilogue that realigns the runtime stack if necessary.
     This supports mixing legacy codes that run with a 4-byte aligned
     stack with modern codes that keep a 16-byte stack for SSE
     compatibility.

`resbank'
     On the SH2A target, this attribute enables the high-speed register
     saving and restoration using a register bank for
     `interrupt_handler' routines.  Saving to the bank is performed
     automatically after the CPU accepts an interrupt that uses a
     register bank.

     The nineteen 32-bit registers comprising general register R0 to
     R14, control register GBR, and system registers MACH, MACL, and PR
     and the vector table address offset are saved into a register
     bank.  Register banks are stacked in first-in last-out (FILO)
     sequence.  Restoration from the bank is executed by issuing a
     RESBANK instruction.

`returns_twice'
     The `returns_twice' attribute tells the compiler that a function
     may return more than one time.  The compiler will ensure that all
     registers are dead before calling such a function and will emit a
     warning about the variables that may be clobbered after the second
     return from the function.  Examples of such functions are `setjmp'
     and `vfork'.  The `longjmp'-like counterpart of such function, if
     any, might need to be marked with the `noreturn' attribute.

`saveall'
     Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to
     indicate that all registers except the stack pointer should be
     saved in the prologue regardless of whether they are used or not.

`section ("SECTION-NAME")'
     Normally, the compiler places the code it generates in the `text'
     section.  Sometimes, however, you need additional sections, or you
     need certain particular functions to appear in special sections.
     The `section' attribute specifies that a function lives in a
     particular section.  For example, the declaration:

          extern void foobar (void) __attribute__ ((section ("bar")));

     puts the function `foobar' in the `bar' section.

     Some file formats do not support arbitrary sections so the
     `section' attribute is not available on all platforms.  If you
     need to map the entire contents of a module to a particular
     section, consider using the facilities of the linker instead.

`sentinel'
     This function attribute ensures that a parameter in a function
     call is an explicit `NULL'.  The attribute is only valid on
     variadic functions.  By default, the sentinel is located at
     position zero, the last parameter of the function call.  If an
     optional integer position argument P is supplied to the attribute,
     the sentinel must be located at position P counting backwards from
     the end of the argument list.

          __attribute__ ((sentinel))
          is equivalent to
          __attribute__ ((sentinel(0)))

     The attribute is automatically set with a position of 0 for the
     built-in functions `execl' and `execlp'.  The built-in function
     `execle' has the attribute set with a position of 1.

     A valid `NULL' in this context is defined as zero with any pointer
     type.  If your system defines the `NULL' macro with an integer type
     then you need to add an explicit cast.  GCC replaces `stddef.h'
     with a copy that redefines NULL appropriately.

     The warnings for missing or incorrect sentinels are enabled with
     `-Wformat'.

`short_call'
     See long_call/short_call.

`shortcall'
     See longcall/shortcall.

`signal'
     Use this attribute on the AVR to indicate that the specified
     function is a signal handler.  The compiler will generate function
     entry and exit sequences suitable for use in a signal handler when
     this attribute is present.  Interrupts will be disabled inside the
     function.

`sp_switch'
     Use this attribute on the SH to indicate an `interrupt_handler'
     function should switch to an alternate stack.  It expects a string
     argument that names a global variable holding the address of the
     alternate stack.

          void *alt_stack;
          void f () __attribute__ ((interrupt_handler,
                                    sp_switch ("alt_stack")));

`stdcall'
     On the Intel 386, the `stdcall' attribute causes the compiler to
     assume that the called function will pop off the stack space used
     to pass arguments, unless it takes a variable number of arguments.

`syscall_linkage'
     This attribute is used to modify the IA64 calling convention by
     marking all input registers as live at all function exits.  This
     makes it possible to restart a system call after an interrupt
     without having to save/restore the input registers.  This also
     prevents kernel data from leaking into application code.

`target'
     The `target' attribute is used to specify that a function is to be
     compiled with different target options than specified on the
     command line.  This can be used for instance to have functions
     compiled with a different ISA (instruction set architecture) than
     the default.  You can also use the `#pragma GCC target' pragma to
     set more than one function to be compiled with specific target
     options.  *Note Function Specific Option Pragmas::, for details
     about the `#pragma GCC target' pragma.

     For instance on a 386, you could compile one function with
     `target("sse4.1,arch=core2")' and another with
     `target("sse4a,arch=amdfam10")' that would be equivalent to
     compiling the first function with `-msse4.1' and `-march=core2'
     options, and the second function with `-msse4a' and
     `-march=amdfam10' options.  It is up to the user to make sure that
     a function is only invoked on a machine that supports the
     particular ISA it was compiled for (for example by using `cpuid'
     on 386 to determine what feature bits and architecture family are
     used).

          int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
          int sse3_func (void) __attribute__ ((__target__ ("sse3")));

     On the 386, the following options are allowed:

    `abm'
    `no-abm'
          Enable/disable the generation of the advanced bit
          instructions.

    `aes'
    `no-aes'
          Enable/disable the generation of the AES instructions.

    `mmx'
    `no-mmx'
          Enable/disable the generation of the MMX instructions.

    `pclmul'
    `no-pclmul'
          Enable/disable the generation of the PCLMUL instructions.

    `popcnt'
    `no-popcnt'
          Enable/disable the generation of the POPCNT instruction.

    `sse'
    `no-sse'
          Enable/disable the generation of the SSE instructions.

    `sse2'
    `no-sse2'
          Enable/disable the generation of the SSE2 instructions.

    `sse3'
    `no-sse3'
          Enable/disable the generation of the SSE3 instructions.

    `sse4'
    `no-sse4'
          Enable/disable the generation of the SSE4 instructions (both
          SSE4.1 and SSE4.2).

    `sse4.1'
    `no-sse4.1'
          Enable/disable the generation of the sse4.1 instructions.

    `sse4.2'
    `no-sse4.2'
          Enable/disable the generation of the sse4.2 instructions.

    `sse4a'
    `no-sse4a'
          Enable/disable the generation of the SSE4A instructions.

    `fma4'
    `no-fma4'
          Enable/disable the generation of the FMA4 instructions.

    `xop'
    `no-xop'
          Enable/disable the generation of the XOP instructions.

    `lwp'
    `no-lwp'
          Enable/disable the generation of the LWP instructions.

    `ssse3'
    `no-ssse3'
          Enable/disable the generation of the SSSE3 instructions.

    `cld'
    `no-cld'
          Enable/disable the generation of the CLD before string moves.

    `fancy-math-387'
    `no-fancy-math-387'
          Enable/disable the generation of the `sin', `cos', and `sqrt'
          instructions on the 387 floating point unit.

    `fused-madd'
    `no-fused-madd'
          Enable/disable the generation of the fused multiply/add
          instructions.

    `ieee-fp'
    `no-ieee-fp'
          Enable/disable the generation of floating point that depends
          on IEEE arithmetic.

    `inline-all-stringops'
    `no-inline-all-stringops'
          Enable/disable inlining of string operations.

    `inline-stringops-dynamically'
    `no-inline-stringops-dynamically'
          Enable/disable the generation of the inline code to do small
          string operations and calling the library routines for large
          operations.

    `align-stringops'
    `no-align-stringops'
          Do/do not align destination of inlined string operations.

    `recip'
    `no-recip'
          Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and
          RSQRTPS instructions followed an additional Newton-Raphson
          step instead of doing a floating point division.

    `arch=ARCH'
          Specify the architecture to generate code for in compiling
          the function.

    `tune=TUNE'
          Specify the architecture to tune for in compiling the
          function.

    `fpmath=FPMATH'
          Specify which floating point unit to use.  The
          `target("fpmath=sse,387")' option must be specified as
          `target("fpmath=sse+387")' because the comma would separate
          different options.

     On the 386, you can use either multiple strings to specify multiple
     options, or you can separate the option with a comma (`,').

     On the 386, the inliner will not inline a function that has
     different target options than the caller, unless the callee has a
     subset of the target options of the caller.  For example a
     function declared with `target("sse3")' can inline a function with
     `target("sse2")', since `-msse3' implies `-msse2'.

     The `target' attribute is not implemented in GCC versions earlier
     than 4.4, and at present only the 386 uses it.

`tiny_data'
     Use this attribute on the H8/300H and H8S to indicate that the
     specified variable should be placed into the tiny data section.
     The compiler will generate more efficient code for loads and stores
     on data in the tiny data section.  Note the tiny data area is
     limited to slightly under 32kbytes of data.

`trap_exit'
     Use this attribute on the SH for an `interrupt_handler' to return
     using `trapa' instead of `rte'.  This attribute expects an integer
     argument specifying the trap number to be used.

`unused'
     This attribute, attached to a function, means that the function is
     meant to be possibly unused.  GCC will not produce a warning for
     this function.

`used'
     This attribute, attached to a function, means that code must be
     emitted for the function even if it appears that the function is
     not referenced.  This is useful, for example, when the function is
     referenced only in inline assembly.

     When applied to a member function of a C++ class template, the
     attribute also means that the function will be instantiated if the
     class itself is instantiated.

`version_id'
     This IA64 HP-UX attribute, attached to a global variable or
     function, renames a symbol to contain a version string, thus
     allowing for function level versioning.  HP-UX system header files
     may use version level functioning for some system calls.

          extern int foo () __attribute__((version_id ("20040821")));

     Calls to FOO will be mapped to calls to FOO{20040821}.

`visibility ("VISIBILITY_TYPE")'
     This attribute affects the linkage of the declaration to which it
     is attached.  There are four supported VISIBILITY_TYPE values:
     default, hidden, protected or internal visibility.

          void __attribute__ ((visibility ("protected")))
          f () { /* Do something. */; }
          int i __attribute__ ((visibility ("hidden")));

     The possible values of VISIBILITY_TYPE correspond to the
     visibility settings in the ELF gABI.

    "default"
          Default visibility is the normal case for the object file
          format.  This value is available for the visibility attribute
          to override other options that may change the assumed
          visibility of entities.

          On ELF, default visibility means that the declaration is
          visible to other modules and, in shared libraries, means that
          the declared entity may be overridden.

          On Darwin, default visibility means that the declaration is
          visible to other modules.

          Default visibility corresponds to "external linkage" in the
          language.

    "hidden"
          Hidden visibility indicates that the entity declared will
          have a new form of linkage, which we'll call "hidden
          linkage".  Two declarations of an object with hidden linkage
          refer to the same object if they are in the same shared
          object.

    "internal"
          Internal visibility is like hidden visibility, but with
          additional processor specific semantics.  Unless otherwise
          specified by the psABI, GCC defines internal visibility to
          mean that a function is _never_ called from another module.
          Compare this with hidden functions which, while they cannot
          be referenced directly by other modules, can be referenced
          indirectly via function pointers.  By indicating that a
          function cannot be called from outside the module, GCC may
          for instance omit the load of a PIC register since it is known
          that the calling function loaded the correct value.

    "protected"
          Protected visibility is like default visibility except that it
          indicates that references within the defining module will
          bind to the definition in that module.  That is, the declared
          entity cannot be overridden by another module.


     All visibilities are supported on many, but not all, ELF targets
     (supported when the assembler supports the `.visibility'
     pseudo-op).  Default visibility is supported everywhere.  Hidden
     visibility is supported on Darwin targets.

     The visibility attribute should be applied only to declarations
     which would otherwise have external linkage.  The attribute should
     be applied consistently, so that the same entity should not be
     declared with different settings of the attribute.

     In C++, the visibility attribute applies to types as well as
     functions and objects, because in C++ types have linkage.  A class
     must not have greater visibility than its non-static data member
     types and bases, and class members default to the visibility of
     their class.  Also, a declaration without explicit visibility is
     limited to the visibility of its type.

     In C++, you can mark member functions and static member variables
     of a class with the visibility attribute.  This is useful if you
     know a particular method or static member variable should only be
     used from one shared object; then you can mark it hidden while the
     rest of the class has default visibility.  Care must be taken to
     avoid breaking the One Definition Rule; for example, it is usually
     not useful to mark an inline method as hidden without marking the
     whole class as hidden.

     A C++ namespace declaration can also have the visibility attribute.
     This attribute applies only to the particular namespace body, not
     to other definitions of the same namespace; it is equivalent to
     using `#pragma GCC visibility' before and after the namespace
     definition (*note Visibility Pragmas::).

     In C++, if a template argument has limited visibility, this
     restriction is implicitly propagated to the template instantiation.
     Otherwise, template instantiations and specializations default to
     the visibility of their template.

     If both the template and enclosing class have explicit visibility,
     the visibility from the template is used.

`warn_unused_result'
     The `warn_unused_result' attribute causes a warning to be emitted
     if a caller of the function with this attribute does not use its
     return value.  This is useful for functions where not checking the
     result is either a security problem or always a bug, such as
     `realloc'.

          int fn () __attribute__ ((warn_unused_result));
          int foo ()
          {
            if (fn () < 0) return -1;
            fn ();
            return 0;
          }

     results in warning on line 5.

`weak'
     The `weak' attribute causes the declaration to be emitted as a weak
     symbol rather than a global.  This is primarily useful in defining
     library functions which can be overridden in user code, though it
     can also be used with non-function declarations.  Weak symbols are
     supported for ELF targets, and also for a.out targets when using
     the GNU assembler and linker.

`weakref'
`weakref ("TARGET")'
     The `weakref' attribute marks a declaration as a weak reference.
     Without arguments, it should be accompanied by an `alias' attribute
     naming the target symbol.  Optionally, the TARGET may be given as
     an argument to `weakref' itself.  In either case, `weakref'
     implicitly marks the declaration as `weak'.  Without a TARGET,
     given as an argument to `weakref' or to `alias', `weakref' is
     equivalent to `weak'.

          static int x() __attribute__ ((weakref ("y")));
          /* is equivalent to... */
          static int x() __attribute__ ((weak, weakref, alias ("y")));
          /* and to... */
          static int x() __attribute__ ((weakref));
          static int x() __attribute__ ((alias ("y")));

     A weak reference is an alias that does not by itself require a
     definition to be given for the target symbol.  If the target
     symbol is only referenced through weak references, then the
     becomes a `weak' undefined symbol.  If it is directly referenced,
     however, then such strong references prevail, and a definition
     will be required for the symbol, not necessarily in the same
     translation unit.

     The effect is equivalent to moving all references to the alias to a
     separate translation unit, renaming the alias to the aliased
     symbol, declaring it as weak, compiling the two separate
     translation units and performing a reloadable link on them.

     At present, a declaration to which `weakref' is attached can only
     be `static'.


 You can specify multiple attributes in a declaration by separating them
by commas within the double parentheses or by immediately following an
attribute declaration with another attribute declaration.

 Some people object to the `__attribute__' feature, suggesting that ISO
C's `#pragma' should be used instead.  At the time `__attribute__' was
designed, there were two reasons for not doing this.

  1. It is impossible to generate `#pragma' commands from a macro.

  2. There is no telling what the same `#pragma' might mean in another
     compiler.

 These two reasons applied to almost any application that might have
been proposed for `#pragma'.  It was basically a mistake to use
`#pragma' for _anything_.

 The ISO C99 standard includes `_Pragma', which now allows pragmas to
be generated from macros.  In addition, a `#pragma GCC' namespace is
now in use for GCC-specific pragmas.  However, it has been found
convenient to use `__attribute__' to achieve a natural attachment of
attributes to their corresponding declarations, whereas `#pragma GCC'
is of use for constructs that do not naturally form part of the
grammar.  *Note Miscellaneous Preprocessing Directives: (cpp)Other
Directives.

File: gcc.info,  Node: Attribute Syntax,  Next: Function Prototypes,  Prev: Function Attributes,  Up: C Extensions

5.28 Attribute Syntax
=====================

This section describes the syntax with which `__attribute__' may be
used, and the constructs to which attribute specifiers bind, for the C
language.  Some details may vary for C++ and Objective-C.  Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.

 There are some problems with the semantics of attributes in C++.  For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading.  Similarly, `typeid' does
not distinguish between types with different attributes.  Support for
attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.

 *Note Function Attributes::, for details of the semantics of attributes
applying to functions.  *Note Variable Attributes::, for details of the
semantics of attributes applying to variables.  *Note Type Attributes::,
for details of the semantics of attributes applying to structure, union
and enumerated types.

 An "attribute specifier" is of the form `__attribute__
((ATTRIBUTE-LIST))'.  An "attribute list" is a possibly empty
comma-separated sequence of "attributes", where each attribute is one
of the following:

   * Empty.  Empty attributes are ignored.

   * A word (which may be an identifier such as `unused', or a reserved
     word such as `const').

   * A word, followed by, in parentheses, parameters for the attribute.
     These parameters take one of the following forms:

        * An identifier.  For example, `mode' attributes use this form.

        * An identifier followed by a comma and a non-empty
          comma-separated list of expressions.  For example, `format'
          attributes use this form.

        * A possibly empty comma-separated list of expressions.  For
          example, `format_arg' attributes use this form with the list
          being a single integer constant expression, and `alias'
          attributes use this form with the list being a single string
          constant.

 An "attribute specifier list" is a sequence of one or more attribute
specifiers, not separated by any other tokens.

 In GNU C, an attribute specifier list may appear after the colon
following a label, other than a `case' or `default' label.  The only
attribute it makes sense to use after a label is `unused'.  This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with `-Wall'.  It would not
normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an `#ifdef' conditional.  GNU C++ does not permit such
placement of attribute lists, as it is permissible for a declaration,
which could begin with an attribute list, to be labelled in C++.
Declarations cannot be labelled in C90 or C99, so the ambiguity does
not arise there.

 An attribute specifier list may appear as part of a `struct', `union'
or `enum' specifier.  It may go either immediately after the `struct',
`union' or `enum' keyword, or after the closing brace.  The former
syntax is preferred.  Where attribute specifiers follow the closing
brace, they are considered to relate to the structure, union or
enumerated type defined, not to any enclosing declaration the type
specifier appears in, and the type defined is not complete until after
the attribute specifiers.

 Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular
declarator within a declaration.  Where an attribute specifier is
applied to a parameter declared as a function or an array, it should
apply to the function or array rather than the pointer to which the
parameter is implicitly converted, but this is not yet correctly
implemented.

 Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers.  (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
`section'.)  There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case).  In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler.  All attribute specifiers in this place relate to the
declaration as a whole.  In the obsolescent usage where a type of `int'
is implied by the absence of type specifiers, such a list of specifiers
and qualifiers may be an attribute specifier list with no other
specifiers or qualifiers.

 At present, the first parameter in a function prototype must have some
type specifier which is not an attribute specifier; this resolves an
ambiguity in the interpretation of `void f(int (__attribute__((foo))
x))', but is subject to change.  At present, if the parentheses of a
function declarator contain only attributes then those attributes are
ignored, rather than yielding an error or warning or implying a single
parameter of type int, but this is subject to change.

 An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers.  Such attribute specifiers apply only to the
identifier before whose declarator they appear.  For example, in

     __attribute__((noreturn)) void d0 (void),
         __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
          d2 (void)

the `noreturn' attribute applies to all the functions declared; the
`format' attribute only applies to `d1'.

 An attribute specifier list may appear immediately before the comma,
`=' or semicolon terminating the declaration of an identifier other
than a function definition.  Such attribute specifiers apply to the
declared object or function.  Where an assembler name for an object or
function is specified (*note Asm Labels::), the attribute must follow
the `asm' specification.

 An attribute specifier list may, in future, be permitted to appear
after the declarator in a function definition (before any old-style
parameter declarations or the function body).

 Attribute specifiers may be mixed with type qualifiers appearing inside
the `[]' of a parameter array declarator, in the C99 construct by which
such qualifiers are applied to the pointer to which the array is
implicitly converted.  Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.

 An attribute specifier list may appear at the start of a nested
declarator.  At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.  When
attribute specifiers follow the `*' of a pointer declarator, they may
be mixed with any type qualifiers present.  The following describes the
formal semantics of this syntax.  It will make the most sense if you
are familiar with the formal specification of declarators in the ISO C
standard.

 Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration `T D1',
where `T' contains declaration specifiers that specify a type TYPE
(such as `int') and `D1' is a declarator that contains an identifier
IDENT.  The type specified for IDENT for derived declarators whose type
does not include an attribute specifier is as in the ISO C standard.

 If `D1' has the form `( ATTRIBUTE-SPECIFIER-LIST D )', and the
declaration `T D' specifies the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE" for IDENT, then `T D1' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.

 If `D1' has the form `* TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST
D', and the declaration `T D' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST TYPE" for IDENT, then `T D1' specifies
the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.

 For example,

     void (__attribute__((noreturn)) ****f) (void);

specifies the type "pointer to pointer to pointer to pointer to
non-returning function returning `void'".  As another example,

     char *__attribute__((aligned(8))) *f;

specifies the type "pointer to 8-byte-aligned pointer to `char'".  Note
again that this does not work with most attributes; for example, the
usage of `aligned' and `noreturn' attributes given above is not yet
supported.

 For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes.  If an attribute that only applies
to types is applied to a declaration, it will be treated as applying to
the type of that declaration.  If an attribute that only applies to
declarations is applied to the type of a declaration, it will be treated
as applying to that declaration; and, for compatibility with code
placing the attributes immediately before the identifier declared, such
an attribute applied to a function return type will be treated as
applying to the function type, and such an attribute applied to an array
element type will be treated as applying to the array type.  If an
attribute that only applies to function types is applied to a
pointer-to-function type, it will be treated as applying to the pointer
target type; if such an attribute is applied to a function return type
that is not a pointer-to-function type, it will be treated as applying
to the function type.

File: gcc.info,  Node: Function Prototypes,  Next: C++ Comments,  Prev: Attribute Syntax,  Up: C Extensions

5.29 Prototypes and Old-Style Function Definitions
==================================================

GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition.  Consider the following example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #ifdef __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

 Suppose the type `uid_t' happens to be `short'.  ISO C does not allow
this example, because subword arguments in old-style non-prototype
definitions are promoted.  Therefore in this example the function
definition's argument is really an `int', which does not match the
prototype argument type of `short'.

 This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the `uid_t' type is `short', `int', or `long'.  Therefore, in
cases like these GNU C allows a prototype to override a later old-style
definition.  More precisely, in GNU C, a function prototype argument
type overrides the argument type specified by a later old-style
definition if the former type is the same as the latter type before
promotion.  Thus in GNU C the above example is equivalent to the
following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }

GNU C++ does not support old-style function definitions, so this
extension is irrelevant.

File: gcc.info,  Node: C++ Comments,  Next: Dollar Signs,  Prev: Function Prototypes,  Up: C Extensions

5.30 C++ Style Comments
=======================

In GNU C, you may use C++ style comments, which start with `//' and
continue until the end of the line.  Many other C implementations allow
such comments, and they are included in the 1999 C standard.  However,
C++ style comments are not recognized if you specify an `-std' option
specifying a version of ISO C before C99, or `-ansi' (equivalent to
`-std=c89').

File: gcc.info,  Node: Dollar Signs,  Next: Character Escapes,  Prev: C++ Comments,  Up: C Extensions

5.31 Dollar Signs in Identifier Names
=====================================

In GNU C, you may normally use dollar signs in identifier names.  This
is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.

File: gcc.info,  Node: Character Escapes,  Next: Variable Attributes,  Prev: Dollar Signs,  Up: C Extensions

5.32 The Character <ESC> in Constants
=====================================

You can use the sequence `\e' in a string or character constant to
stand for the ASCII character <ESC>.

File: gcc.info,  Node: Variable Attributes,  Next: Type Attributes,  Prev: Character Escapes,  Up: C Extensions

5.33 Specifying Attributes of Variables
=======================================

The keyword `__attribute__' allows you to specify special attributes of
variables or structure fields.  This keyword is followed by an
attribute specification inside double parentheses.  Some attributes are
currently defined generically for variables.  Other attributes are
defined for variables on particular target systems.  Other attributes
are available for functions (*note Function Attributes::) and for types
(*note Type Attributes::).  Other front ends might define more
attributes (*note Extensions to the C++ Language: C++ Extensions.).

 You may also specify attributes with `__' preceding and following each
keyword.  This allows you to use them in header files without being
concerned about a possible macro of the same name.  For example, you
may use `__aligned__' instead of `aligned'.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment for the variable or
     structure field, measured in bytes.  For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable `x' on a
     16-byte boundary.  On a 68040, this could be used in conjunction
     with an `asm' expression to access the `move16' instruction which
     requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For
     example, to create a double-word aligned `int' pair, you could
     write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a `double' member
     that forces the union to be double-word aligned.

     As in the preceding examples, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     variable or structure field.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a variable or
     field to the default alignment for the target architecture you are
     compiling for.  The default alignment is sufficient for all scalar
     types, but may not be enough for all vector types on a target
     which supports vector operations.  The default alignment is fixed
     for a particular target ABI.

     Gcc also provides a target specific macro `__BIGGEST_ALIGNMENT__',
     which is the largest alignment ever used for any data type on the
     target machine you are compiling for.  For example, you could
     write:

          short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));

     The compiler automatically sets the alignment for the declared
     variable or field to `__BIGGEST_ALIGNMENT__'.  Doing this can
     often make copy operations more efficient, because the compiler can
     use whatever instructions copy the biggest chunks of memory when
     performing copies to or from the variables or fields that you have
     aligned this way.  Note that the value of `__BIGGEST_ALIGNMENT__'
     may change depending on command line options.

     When used on a struct, or struct member, the `aligned' attribute
     can only increase the alignment; in order to decrease it, the
     `packed' attribute must be specified as well.  When used as part
     of a typedef, the `aligned' attribute can both increase and
     decrease alignment, and specifying the `packed' attribute will
     generate a warning.

     Note that the effectiveness of `aligned' attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for variables to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  If your linker is
     only able to align variables up to a maximum of 8 byte alignment,
     then specifying `aligned(16)' in an `__attribute__' will still
     only provide you with 8 byte alignment.  See your linker
     documentation for further information.

     The `aligned' attribute can also be used for functions (*note
     Function Attributes::.)

`cleanup (CLEANUP_FUNCTION)'
     The `cleanup' attribute runs a function when the variable goes out
     of scope.  This attribute can only be applied to auto function
     scope variables; it may not be applied to parameters or variables
     with static storage duration.  The function must take one
     parameter, a pointer to a type compatible with the variable.  The
     return value of the function (if any) is ignored.

     If `-fexceptions' is enabled, then CLEANUP_FUNCTION will be run
     during the stack unwinding that happens during the processing of
     the exception.  Note that the `cleanup' attribute does not allow
     the exception to be caught, only to perform an action.  It is
     undefined what happens if CLEANUP_FUNCTION does not return
     normally.

`common'
`nocommon'
     The `common' attribute requests GCC to place a variable in
     "common" storage.  The `nocommon' attribute requests the
     opposite--to allocate space for it directly.

     These attributes override the default chosen by the `-fno-common'
     and `-fcommon' flags respectively.

`deprecated'
     The `deprecated' attribute results in a warning if the variable is
     used anywhere in the source file.  This is useful when identifying
     variables that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated variable, to enable users to easily find further
     information about why the variable is deprecated, or what they
     should do instead.  Note that the warning only occurs for uses:

          extern int old_var __attribute__ ((deprecated));
          extern int old_var;
          int new_fn () { return old_var; }

     results in a warning on line 3 but not line 2.

     The `deprecated' attribute can also be used for functions and
     types (*note Function Attributes::, *note Type Attributes::.)

`mode (MODE)'
     This attribute specifies the data type for the
     declaration--whichever type corresponds to the mode MODE.  This in
     effect lets you request an integer or floating point type
     according to its width.

     You may also specify a mode of `byte' or `__byte__' to indicate
     the mode corresponding to a one-byte integer, `word' or `__word__'
     for the mode of a one-word integer, and `pointer' or `__pointer__'
     for the mode used to represent pointers.

`packed'
     The `packed' attribute specifies that a variable or structure field
     should have the smallest possible alignment--one byte for a
     variable, and one bit for a field, unless you specify a larger
     value with the `aligned' attribute.

     Here is a structure in which the field `x' is packed, so that it
     immediately follows `a':

          struct foo
          {
            char a;
            int x[2] __attribute__ ((packed));
          };

     _Note:_ The 4.1, 4.2 and 4.3 series of GCC ignore the `packed'
     attribute on bit-fields of type `char'.  This has been fixed in
     GCC 4.4 but the change can lead to differences in the structure
     layout.  See the documentation of `-Wpacked-bitfield-compat' for
     more information.

`section ("SECTION-NAME")'
     Normally, the compiler places the objects it generates in sections
     like `data' and `bss'.  Sometimes, however, you need additional
     sections, or you need certain particular variables to appear in
     special sections, for example to map to special hardware.  The
     `section' attribute specifies that a variable (or function) lives
     in a particular section.  For example, this small program uses
     several specific section names:

          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
          int init_data __attribute__ ((section ("INITDATA")));

          main()
          {
            /* Initialize stack pointer */
            init_sp (stack + sizeof (stack));

            /* Initialize initialized data */
            memcpy (&init_data, &data, &edata - &data);

            /* Turn on the serial ports */
            init_duart (&a);
            init_duart (&b);
          }

     Use the `section' attribute with _global_ variables and not
     _local_ variables, as shown in the example.

     You may use the `section' attribute with initialized or
     uninitialized global variables but the linker requires each object
     be defined once, with the exception that uninitialized variables
     tentatively go in the `common' (or `bss') section and can be
     multiply "defined".  Using the `section' attribute will change
     what section the variable goes into and may cause the linker to
     issue an error if an uninitialized variable has multiple
     definitions.  You can force a variable to be initialized with the
     `-fno-common' flag or the `nocommon' attribute.

     Some file formats do not support arbitrary sections so the
     `section' attribute is not available on all platforms.  If you
     need to map the entire contents of a module to a particular
     section, consider using the facilities of the linker instead.

`shared'
     On Microsoft Windows, in addition to putting variable definitions
     in a named section, the section can also be shared among all
     running copies of an executable or DLL.  For example, this small
     program defines shared data by putting it in a named section
     `shared' and marking the section shareable:

          int foo __attribute__((section ("shared"), shared)) = 0;

          int
          main()
          {
            /* Read and write foo.  All running
               copies see the same value.  */
            return 0;
          }

     You may only use the `shared' attribute along with `section'
     attribute with a fully initialized global definition because of
     the way linkers work.  See `section' attribute for more
     information.

     The `shared' attribute is only available on Microsoft Windows.

`tls_model ("TLS_MODEL")'
     The `tls_model' attribute sets thread-local storage model (*note
     Thread-Local::) of a particular `__thread' variable, overriding
     `-ftls-model=' command line switch on a per-variable basis.  The
     TLS_MODEL argument should be one of `global-dynamic',
     `local-dynamic', `initial-exec' or `local-exec'.

     Not all targets support this attribute.

`unused'
     This attribute, attached to a variable, means that the variable is
     meant to be possibly unused.  GCC will not produce a warning for
     this variable.

`used'
     This attribute, attached to a variable, means that the variable
     must be emitted even if it appears that the variable is not
     referenced.

     When applied to a static data member of a C++ class template, the
     attribute also means that the member will be instantiated if the
     class itself is instantiated.

`vector_size (BYTES)'
     This attribute specifies the vector size for the variable,
     measured in bytes.  For example, the declaration:

          int foo __attribute__ ((vector_size (16)));

     causes the compiler to set the mode for `foo', to be 16 bytes,
     divided into `int' sized units.  Assuming a 32-bit int (a vector of
     4 units of 4 bytes), the corresponding mode of `foo' will be V4SI.

     This attribute is only applicable to integral and float scalars,
     although arrays, pointers, and function return values are allowed
     in conjunction with this construct.

     Aggregates with this attribute are invalid, even if they are of
     the same size as a corresponding scalar.  For example, the
     declaration:

          struct S { int a; };
          struct S  __attribute__ ((vector_size (16))) foo;

     is invalid even if the size of the structure is the same as the
     size of the `int'.

`selectany'
     The `selectany' attribute causes an initialized global variable to
     have link-once semantics.  When multiple definitions of the
     variable are encountered by the linker, the first is selected and
     the remainder are discarded.  Following usage by the Microsoft
     compiler, the linker is told _not_ to warn about size or content
     differences of the multiple definitions.

     Although the primary usage of this attribute is for POD types, the
     attribute can also be applied to global C++ objects that are
     initialized by a constructor.  In this case, the static
     initialization and destruction code for the object is emitted in
     each translation defining the object, but the calls to the
     constructor and destructor are protected by a link-once guard
     variable.

     The `selectany' attribute is only available on Microsoft Windows
     targets.  You can use `__declspec (selectany)' as a synonym for
     `__attribute__ ((selectany))' for compatibility with other
     compilers.

`weak'
     The `weak' attribute is described in *note Function Attributes::.

`dllimport'
     The `dllimport' attribute is described in *note Function
     Attributes::.

`dllexport'
     The `dllexport' attribute is described in *note Function
     Attributes::.


5.33.1 Blackfin Variable Attributes
-----------------------------------

Three attributes are currently defined for the Blackfin.

`l1_data'

`l1_data_A'

`l1_data_B'
     Use these attributes on the Blackfin to place the variable into L1
     Data SRAM.  Variables with `l1_data' attribute will be put into
     the specific section named `.l1.data'. Those with `l1_data_A'
     attribute will be put into the specific section named
     `.l1.data.A'. Those with `l1_data_B' attribute will be put into
     the specific section named `.l1.data.B'.

5.33.2 M32R/D Variable Attributes
---------------------------------

One attribute is currently defined for the M32R/D.

`model (MODEL-NAME)'
     Use this attribute on the M32R/D to set the addressability of an
     object.  The identifier MODEL-NAME is one of `small', `medium', or
     `large', representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction).

     Medium and large model objects may live anywhere in the 32-bit
     address space (the compiler will generate `seth/add3' instructions
     to load their addresses).

5.33.3 i386 Variable Attributes
-------------------------------

Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'

`ms_struct'
`gcc_struct'
     If `packed' is used on a structure, or if bit-fields are used it
     may be that the Microsoft ABI packs them differently than GCC
     would normally pack them.  Particularly when moving packed data
     between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may
     be necessary to access either format.

     Currently `-m[no-]ms-bitfields' is provided for the Microsoft
     Windows X86 compilers to match the native Microsoft compiler.

     The Microsoft structure layout algorithm is fairly simple with the
     exception of the bitfield packing:

     The padding and alignment of members of structures and whether a
     bit field can straddle a storage-unit boundary

       1. Structure members are stored sequentially in the order in
          which they are declared: the first member has the lowest
          memory address and the last member the highest.

       2. Every data object has an alignment-requirement. The
          alignment-requirement for all data except structures, unions,
          and arrays is either the size of the object or the current
          packing size (specified with either the aligned attribute or
          the pack pragma), whichever is less. For structures,  unions,
          and arrays, the alignment-requirement is the largest
          alignment-requirement of its members.  Every object is
          allocated an offset so that:

          offset %  alignment-requirement == 0

       3. Adjacent bit fields are packed into the same 1-, 2-, or
          4-byte allocation unit if the integral types are the same
          size and if the next bit field fits into the current
          allocation unit without crossing the boundary imposed by the
          common alignment requirements of the bit fields.

     Handling of zero-length bitfields:

     MSVC interprets zero-length bitfields in the following ways:

       1. If a zero-length bitfield is inserted between two bitfields
          that would normally be coalesced, the bitfields will not be
          coalesced.

          For example:

               struct
                {
                  unsigned long bf_1 : 12;
                  unsigned long : 0;
                  unsigned long bf_2 : 12;
                } t1;

          The size of `t1' would be 8 bytes with the zero-length
          bitfield.  If the zero-length bitfield were removed, `t1''s
          size would be 4 bytes.

       2. If a zero-length bitfield is inserted after a bitfield,
          `foo', and the alignment of the zero-length bitfield is
          greater than the member that follows it, `bar', `bar' will be
          aligned as the type of the zero-length bitfield.

          For example:

               struct
                {
                  char foo : 4;
                  short : 0;
                  char bar;
                } t2;

               struct
                {
                  char foo : 4;
                  short : 0;
                  double bar;
                } t3;

          For `t2', `bar' will be placed at offset 2, rather than
          offset 1.  Accordingly, the size of `t2' will be 4.  For
          `t3', the zero-length bitfield will not affect the alignment
          of `bar' or, as a result, the size of the structure.

          Taking this into account, it is important to note the
          following:

            1. If a zero-length bitfield follows a normal bitfield, the
               type of the zero-length bitfield may affect the
               alignment of the structure as whole. For example, `t2'
               has a size of 4 bytes, since the zero-length bitfield
               follows a normal bitfield, and is of type short.

            2. Even if a zero-length bitfield is not followed by a
               normal bitfield, it may still affect the alignment of
               the structure:

                    struct
                     {
                       char foo : 6;
                       long : 0;
                     } t4;

               Here, `t4' will take up 4 bytes.

       3. Zero-length bitfields following non-bitfield members are
          ignored:

               struct
                {
                  char foo;
                  long : 0;
                  char bar;
                } t5;

          Here, `t5' will take up 2 bytes.

5.33.4 PowerPC Variable Attributes
----------------------------------

Three attributes currently are defined for PowerPC configurations:
`altivec', `ms_struct' and `gcc_struct'.

 For full documentation of the struct attributes please see the
documentation in *note i386 Variable Attributes::.

 For documentation of `altivec' attribute please see the documentation
in *note PowerPC Type Attributes::.

5.33.5 SPU Variable Attributes
------------------------------

The SPU supports the `spu_vector' attribute for variables.  For
documentation of this attribute please see the documentation in *note
SPU Type Attributes::.

5.33.6 Xstormy16 Variable Attributes
------------------------------------

One attribute is currently defined for xstormy16 configurations:
`below100'.

`below100'
     If a variable has the `below100' attribute (`BELOW100' is allowed
     also), GCC will place the variable in the first 0x100 bytes of
     memory and use special opcodes to access it.  Such variables will
     be placed in either the `.bss_below100' section or the
     `.data_below100' section.


5.33.7 AVR Variable Attributes
------------------------------

`progmem'
     The `progmem' attribute is used on the AVR to place data in the
     Program Memory address space. The AVR is a Harvard Architecture
     processor and data normally resides in the Data Memory address
     space.

File: gcc.info,  Node: Type Attributes,  Next: Alignment,  Prev: Variable Attributes,  Up: C Extensions

5.34 Specifying Attributes of Types
===================================

The keyword `__attribute__' allows you to specify special attributes of
`struct' and `union' types when you define such types.  This keyword is
followed by an attribute specification inside double parentheses.
Seven attributes are currently defined for types: `aligned', `packed',
`transparent_union', `unused', `deprecated', `visibility', and
`may_alias'.  Other attributes are defined for functions (*note
Function Attributes::) and for variables (*note Variable Attributes::).

 You may also specify any one of these attributes with `__' preceding
and following its keyword.  This allows you to use these attributes in
header files without being concerned about a possible macro of the same
name.  For example, you may use `__aligned__' instead of `aligned'.

 You may specify type attributes in an enum, struct or union type
declaration or definition, or for other types in a `typedef'
declaration.

 For an enum, struct or union type, you may specify attributes either
between the enum, struct or union tag and the name of the type, or just
past the closing curly brace of the _definition_.  The former syntax is
preferred.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment (in bytes) for
     variables of the specified type.  For example, the declarations:

          struct S { short f[3]; } __attribute__ ((aligned (8)));
          typedef int more_aligned_int __attribute__ ((aligned (8)));

     force the compiler to insure (as far as it can) that each variable
     whose type is `struct S' or `more_aligned_int' will be allocated
     and aligned _at least_ on a 8-byte boundary.  On a SPARC, having
     all variables of type `struct S' aligned to 8-byte boundaries
     allows the compiler to use the `ldd' and `std' (doubleword load and
     store) instructions when copying one variable of type `struct S' to
     another, thus improving run-time efficiency.

     Note that the alignment of any given `struct' or `union' type is
     required by the ISO C standard to be at least a perfect multiple of
     the lowest common multiple of the alignments of all of the members
     of the `struct' or `union' in question.  This means that you _can_
     effectively adjust the alignment of a `struct' or `union' type by
     attaching an `aligned' attribute to any one of the members of such
     a type, but the notation illustrated in the example above is a
     more obvious, intuitive, and readable way to request the compiler
     to adjust the alignment of an entire `struct' or `union' type.

     As in the preceding example, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     `struct' or `union' type.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a type to the
     maximum useful alignment for the target machine you are compiling
     for.  For example, you could write:

          struct S { short f[3]; } __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an `aligned'
     attribute specification, the compiler automatically sets the
     alignment for the type to the largest alignment which is ever used
     for any data type on the target machine you are compiling for.
     Doing this can often make copy operations more efficient, because
     the compiler can use whatever instructions copy the biggest chunks
     of memory when performing copies to or from the variables which
     have types that you have aligned this way.

     In the example above, if the size of each `short' is 2 bytes, then
     the size of the entire `struct S' type is 6 bytes.  The smallest
     power of two which is greater than or equal to that is 8, so the
     compiler sets the alignment for the entire `struct S' type to 8
     bytes.

     Note that although you can ask the compiler to select a
     time-efficient alignment for a given type and then declare only
     individual stand-alone objects of that type, the compiler's
     ability to select a time-efficient alignment is primarily useful
     only when you plan to create arrays of variables having the
     relevant (efficiently aligned) type.  If you declare or use arrays
     of variables of an efficiently-aligned type, then it is likely
     that your program will also be doing pointer arithmetic (or
     subscripting, which amounts to the same thing) on pointers to the
     relevant type, and the code that the compiler generates for these
     pointer arithmetic operations will often be more efficient for
     efficiently-aligned types than for other types.

     The `aligned' attribute can only increase the alignment; but you
     can decrease it by specifying `packed' as well.  See below.

     Note that the effectiveness of `aligned' attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for variables to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  If your linker is
     only able to align variables up to a maximum of 8 byte alignment,
     then specifying `aligned(16)' in an `__attribute__' will still
     only provide you with 8 byte alignment.  See your linker
     documentation for further information.

`packed'
     This attribute, attached to `struct' or `union' type definition,
     specifies that each member (other than zero-width bitfields) of
     the structure or union is placed to minimize the memory required.
     When attached to an `enum' definition, it indicates that the
     smallest integral type should be used.

     Specifying this attribute for `struct' and `union' types is
     equivalent to specifying the `packed' attribute on each of the
     structure or union members.  Specifying the `-fshort-enums' flag
     on the line is equivalent to specifying the `packed' attribute on
     all `enum' definitions.

     In the following example `struct my_packed_struct''s members are
     packed closely together, but the internal layout of its `s' member
     is not packed--to do that, `struct my_unpacked_struct' would need
     to be packed too.

          struct my_unpacked_struct
           {
              char c;
              int i;
           };

          struct __attribute__ ((__packed__)) my_packed_struct
            {
               char c;
               int  i;
               struct my_unpacked_struct s;
            };

     You may only specify this attribute on the definition of a `enum',
     `struct' or `union', not on a `typedef' which does not also define
     the enumerated type, structure or union.

`transparent_union'
     This attribute, attached to a `union' type definition, indicates
     that any function parameter having that union type causes calls to
     that function to be treated in a special way.

     First, the argument corresponding to a transparent union type can
     be of any type in the union; no cast is required.  Also, if the
     union contains a pointer type, the corresponding argument can be a
     null pointer constant or a void pointer expression; and if the
     union contains a void pointer type, the corresponding argument can
     be any pointer expression.  If the union member type is a pointer,
     qualifiers like `const' on the referenced type must be respected,
     just as with normal pointer conversions.

     Second, the argument is passed to the function using the calling
     conventions of the first member of the transparent union, not the
     calling conventions of the union itself.  All members of the union
     must have the same machine representation; this is necessary for
     this argument passing to work properly.

     Transparent unions are designed for library functions that have
     multiple interfaces for compatibility reasons.  For example,
     suppose the `wait' function must accept either a value of type
     `int *' to comply with Posix, or a value of type `union wait *' to
     comply with the 4.1BSD interface.  If `wait''s parameter were
     `void *', `wait' would accept both kinds of arguments, but it
     would also accept any other pointer type and this would make
     argument type checking less useful.  Instead, `<sys/wait.h>' might
     define the interface as follows:

          typedef union __attribute__ ((__transparent_union__))
            {
              int *__ip;
              union wait *__up;
            } wait_status_ptr_t;

          pid_t wait (wait_status_ptr_t);

     This interface allows either `int *' or `union wait *' arguments
     to be passed, using the `int *' calling convention.  The program
     can call `wait' with arguments of either type:

          int w1 () { int w; return wait (&w); }
          int w2 () { union wait w; return wait (&w); }

     With this interface, `wait''s implementation might look like this:

          pid_t wait (wait_status_ptr_t p)
          {
            return waitpid (-1, p.__ip, 0);
          }

`unused'
     When attached to a type (including a `union' or a `struct'), this
     attribute means that variables of that type are meant to appear
     possibly unused.  GCC will not produce a warning for any variables
     of that type, even if the variable appears to do nothing.  This is
     often the case with lock or thread classes, which are usually
     defined and then not referenced, but contain constructors and
     destructors that have nontrivial bookkeeping functions.

`deprecated'
     The `deprecated' attribute results in a warning if the type is
     used anywhere in the source file.  This is useful when identifying
     types that are expected to be removed in a future version of a
     program.  If possible, the warning also includes the location of
     the declaration of the deprecated type, to enable users to easily
     find further information about why the type is deprecated, or what
     they should do instead.  Note that the warnings only occur for
     uses and then only if the type is being applied to an identifier
     that itself is not being declared as deprecated.

          typedef int T1 __attribute__ ((deprecated));
          T1 x;
          typedef T1 T2;
          T2 y;
          typedef T1 T3 __attribute__ ((deprecated));
          T3 z __attribute__ ((deprecated));

     results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No
     warning is issued for line 4 because T2 is not explicitly
     deprecated.  Line 5 has no warning because T3 is explicitly
     deprecated.  Similarly for line 6.

     The `deprecated' attribute can also be used for functions and
     variables (*note Function Attributes::, *note Variable
     Attributes::.)

`may_alias'
     Accesses through pointers to types with this attribute are not
     subject to type-based alias analysis, but are instead assumed to
     be able to alias any other type of objects.  In the context of
     6.5/7 an lvalue expression dereferencing such a pointer is treated
     like having a character type.  See `-fstrict-aliasing' for more
     information on aliasing issues.  This extension exists to support
     some vector APIs, in which pointers to one vector type are
     permitted to alias pointers to a different vector type.

     Note that an object of a type with this attribute does not have any
     special semantics.

     Example of use:

          typedef short __attribute__((__may_alias__)) short_a;

          int
          main (void)
          {
            int a = 0x12345678;
            short_a *b = (short_a *) &a;

            b[1] = 0;

            if (a == 0x12345678)
              abort();

            exit(0);
          }

     If you replaced `short_a' with `short' in the variable
     declaration, the above program would abort when compiled with
     `-fstrict-aliasing', which is on by default at `-O2' or above in
     recent GCC versions.

`visibility'
     In C++, attribute visibility (*note Function Attributes::) can
     also be applied to class, struct, union and enum types.  Unlike
     other type attributes, the attribute must appear between the
     initial keyword and the name of the type; it cannot appear after
     the body of the type.

     Note that the type visibility is applied to vague linkage entities
     associated with the class (vtable, typeinfo node, etc.).  In
     particular, if a class is thrown as an exception in one shared
     object and caught in another, the class must have default
     visibility.  Otherwise the two shared objects will be unable to
     use the same typeinfo node and exception handling will break.


5.34.1 ARM Type Attributes
--------------------------

On those ARM targets that support `dllimport' (such as Symbian OS), you
can use the `notshared' attribute to indicate that the virtual table
and other similar data for a class should not be exported from a DLL.
For example:

     class __declspec(notshared) C {
     public:
       __declspec(dllimport) C();
       virtual void f();
     }

     __declspec(dllexport)
     C::C() {}

 In this code, `C::C' is exported from the current DLL, but the virtual
table for `C' is not exported.  (You can use `__attribute__' instead of
`__declspec' if you prefer, but most Symbian OS code uses `__declspec'.)

5.34.2 i386 Type Attributes
---------------------------

Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'.

`ms_struct'
`gcc_struct'
     If `packed' is used on a structure, or if bit-fields are used it
     may be that the Microsoft ABI packs them differently than GCC
     would normally pack them.  Particularly when moving packed data
     between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may
     be necessary to access either format.

     Currently `-m[no-]ms-bitfields' is provided for the Microsoft
     Windows X86 compilers to match the native Microsoft compiler.

 To specify multiple attributes, separate them by commas within the
double parentheses: for example, `__attribute__ ((aligned (16),
packed))'.

5.34.3 PowerPC Type Attributes
------------------------------

Three attributes currently are defined for PowerPC configurations:
`altivec', `ms_struct' and `gcc_struct'.

 For full documentation of the `ms_struct' and `gcc_struct' attributes
please see the documentation in *note i386 Type Attributes::.

 The `altivec' attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual.  The
attribute requires an argument to specify one of three vector types:
`vector__', `pixel__' (always followed by unsigned short), and `bool__'
(always followed by unsigned).

     __attribute__((altivec(vector__)))
     __attribute__((altivec(pixel__))) unsigned short
     __attribute__((altivec(bool__))) unsigned

 These attributes mainly are intended to support the `__vector',
`__pixel', and `__bool' AltiVec keywords.

5.34.4 SPU Type Attributes
--------------------------

The SPU supports the `spu_vector' attribute for types.  This attribute
allows one to declare vector data types supported by the
Sony/Toshiba/IBM SPU Language Extensions Specification.  It is intended
to support the `__vector' keyword.

File: gcc.info,  Node: Alignment,  Next: Inline,  Prev: Type Attributes,  Up: C Extensions

5.35 Inquiring on Alignment of Types or Variables
=================================================

The keyword `__alignof__' allows you to inquire about how an object is
aligned, or the minimum alignment usually required by a type.  Its
syntax is just like `sizeof'.

 For example, if the target machine requires a `double' value to be
aligned on an 8-byte boundary, then `__alignof__ (double)' is 8.  This
is true on many RISC machines.  On more traditional machine designs,
`__alignof__ (double)' is 4 or even 2.

 Some machines never actually require alignment; they allow reference
to any data type even at an odd address.  For these machines,
`__alignof__' reports the smallest alignment that GCC will give the
data type, usually as mandated by the target ABI.

 If the operand of `__alignof__' is an lvalue rather than a type, its
value is the required alignment for its type, taking into account any
minimum alignment specified with GCC's `__attribute__' extension (*note
Variable Attributes::).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of `__alignof__ (foo1.y)' is 1, even though its actual
alignment is probably 2 or 4, the same as `__alignof__ (int)'.

 It is an error to ask for the alignment of an incomplete type.

File: gcc.info,  Node: Inline,  Next: Extended Asm,  Prev: Alignment,  Up: C Extensions

5.36 An Inline Function is As Fast As a Macro
=============================================

By declaring a function inline, you can direct GCC to make calls to
that function faster.  One way GCC can achieve this is to integrate
that function's code into the code for its callers.  This makes
execution faster by eliminating the function-call overhead; in
addition, if any of the actual argument values are constant, their
known values may permit simplifications at compile time so that not all
of the inline function's code needs to be included.  The effect on code
size is less predictable; object code may be larger or smaller with
function inlining, depending on the particular case.  You can also
direct GCC to try to integrate all "simple enough" functions into their
callers with the option `-finline-functions'.

 GCC implements three different semantics of declaring a function
inline.  One is available with `-std=gnu89' or `-fgnu89-inline' or when
`gnu_inline' attribute is present on all inline declarations, another
when `-std=c99' or `-std=gnu99' (without `-fgnu89-inline'), and the
third is used when compiling C++.

 To declare a function inline, use the `inline' keyword in its
declaration, like this:

     static inline int
     inc (int *a)
     {
       (*a)++;
     }

 If you are writing a header file to be included in ISO C89 programs,
write `__inline__' instead of `inline'.  *Note Alternate Keywords::.

 The three types of inlining behave similarly in two important cases:
when the `inline' keyword is used on a `static' function, like the
example above, and when a function is first declared without using the
`inline' keyword and then is defined with `inline', like this:

     extern int inc (int *a);
     inline int
     inc (int *a)
     {
       (*a)++;
     }

 In both of these common cases, the program behaves the same as if you
had not used the `inline' keyword, except for its speed.

 When a function is both inline and `static', if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option `-fkeep-inline-functions'.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition).  If there is a
nonintegrated call, then the function is compiled to assembler code as
usual.  The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.

 Note that certain usages in a function definition can make it
unsuitable for inline substitution.  Among these usages are: use of
varargs, use of alloca, use of variable sized data types (*note
Variable Length::), use of computed goto (*note Labels as Values::),
use of nonlocal goto, and nested functions (*note Nested Functions::).
Using `-Winline' will warn when a function marked `inline' could not be
substituted, and will give the reason for the failure.

 As required by ISO C++, GCC considers member functions defined within
the body of a class to be marked inline even if they are not explicitly
declared with the `inline' keyword.  You can override this with
`-fno-default-inline'; *note Options Controlling C++ Dialect: C++
Dialect Options.

 GCC does not inline any functions when not optimizing unless you
specify the `always_inline' attribute for the function, like this:

     /* Prototype.  */
     inline void foo (const char) __attribute__((always_inline));

 The remainder of this section is specific to GNU C89 inlining.

 When an inline function is not `static', then the compiler must assume
that there may be calls from other source files; since a global symbol
can be defined only once in any program, the function must not be
defined in the other source files, so the calls therein cannot be
integrated.  Therefore, a non-`static' inline function is always
compiled on its own in the usual fashion.

 If you specify both `inline' and `extern' in the function definition,
then the definition is used only for inlining.  In no case is the
function compiled on its own, not even if you refer to its address
explicitly.  Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.

 This combination of `inline' and `extern' has almost the effect of a
macro.  The way to use it is to put a function definition in a header
file with these keywords, and put another copy of the definition
(lacking `inline' and `extern') in a library file.  The definition in
the header file will cause most calls to the function to be inlined.
If any uses of the function remain, they will refer to the single copy
in the library.

File: gcc.info,  Node: Extended Asm,  Next: Constraints,  Prev: Inline,  Up: C Extensions

5.37 Assembler Instructions with C Expression Operands
======================================================

In an assembler instruction using `asm', you can specify the operands
of the instruction using C expressions.  This means you need not guess
which registers or memory locations will contain the data you want to
use.

 You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.

 For example, here is how to use the 68881's `fsinx' instruction:

     asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

Here `angle' is the C expression for the input operand while `result'
is that of the output operand.  Each has `"f"' as its operand
constraint, saying that a floating point register is required.  The `='
in `=f' indicates that the operand is an output; all output operands'
constraints must use `='.  The constraints use the same language used
in the machine description (*note Constraints::).

 Each operand is described by an operand-constraint string followed by
the C expression in parentheses.  A colon separates the assembler
template from the first output operand and another separates the last
output operand from the first input, if any.  Commas separate the
operands within each group.  The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
GCC.

 If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
operands would go.

 As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code.  These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using `%[NAME]' instead of a percentage sign followed by
the operand number.  Using named operands the above example could look
like:

     asm ("fsinx %[angle],%[output]"
          : [output] "=f" (result)
          : [angle] "f" (angle));

Note that the symbolic operand names have no relation whatsoever to
other C identifiers.  You may use any name you like, even those of
existing C symbols, but you must ensure that no two operands within the
same assembler construct use the same symbolic name.

 Output operand expressions must be lvalues; the compiler can check
this.  The input operands need not be lvalues.  The compiler cannot
check whether the operands have data types that are reasonable for the
instruction being executed.  It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input.  The extended `asm' feature is most often used for
machine instructions the compiler itself does not know exist.  If the
output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register.  In that case, GCC
will use the register as the output of the `asm', and then store that
register into the output.

 The ordinary output operands must be write-only; GCC will assume that
the values in these operands before the instruction are dead and need
not be generated.  Extended asm supports input-output or read-write
operands.  Use the constraint character `+' to indicate such an operand
and list it with the output operands.  You should only use read-write
operands when the constraints for the operand (or the operand in which
only some of the bits are to be changed) allow a register.

 You may, as an alternative, logically split its function into two
separate operands, one input operand and one write-only output operand.
The connection between them is expressed by constraints which say they
need to be in the same location when the instruction executes.  You can
use the same C expression for both operands, or different expressions.
For example, here we write the (fictitious) `combine' instruction with
`bar' as its read-only source operand and `foo' as its read-write
destination:

     asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));

The constraint `"0"' for operand 1 says that it must occupy the same
location as operand 0.  A number in constraint is allowed only in an
input operand and it must refer to an output operand.

 Only a number in the constraint can guarantee that one operand will be
in the same place as another.  The mere fact that `foo' is the value of
both operands is not enough to guarantee that they will be in the same
place in the generated assembler code.  The following would not work
reliably:

     asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));

 Various optimizations or reloading could cause operands 0 and 1 to be
in different registers; GCC knows no reason not to do so.  For example,
the compiler might find a copy of the value of `foo' in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to `foo''s own address).  Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.

 As of GCC version 3.1, one may write `[NAME]' instead of the operand
number for a matching constraint.  For example:

     asm ("cmoveq %1,%2,%[result]"
          : [result] "=r"(result)
          : "r" (test), "r"(new), "[result]"(old));

 Sometimes you need to make an `asm' operand be a specific register,
but there's no matching constraint letter for that register _by
itself_.  To force the operand into that register, use a local variable
for the operand and specify the register in the variable declaration.
*Note Explicit Reg Vars::.  Then for the `asm' operand, use any
register constraint letter that matches the register:

     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

 In the above example, beware that a register that is call-clobbered by
the target ABI will be overwritten by any function call in the
assignment, including library calls for arithmetic operators.  Also a
register may be clobbered when generating some operations, like
variable shift, memory copy or memory move on x86.  Assuming it is a
call-clobbered register, this may happen to `r0' above by the
assignment to `p2'.  If you have to use such a register, use temporary
variables for expressions between the register assignment and use:

     int t1 = ...;
     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = t1;
     register int *result asm ("r0");
     asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));

 Some instructions clobber specific hard registers.  To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings).  Here is a realistic
example for the VAX:

     asm volatile ("movc3 %0,%1,%2"
                   : /* no outputs */
                   : "g" (from), "g" (to), "g" (count)
                   : "r0", "r1", "r2", "r3", "r4", "r5");

 You may not write a clobber description in a way that overlaps with an
input or output operand.  For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list.  Variables declared to live in specific registers
(*note Explicit Reg Vars::), and used as asm input or output operands
must have no part mentioned in the clobber description.  There is no
way for you to specify that an input operand is modified without also
specifying it as an output operand.  Note that if all the output
operands you specify are for this purpose (and hence unused), you will
then also need to specify `volatile' for the `asm' construct, as
described below, to prevent GCC from deleting the `asm' statement as
unused.

 If you refer to a particular hardware register from the assembler code,
you will probably have to list the register after the third colon to
tell the compiler the register's value is modified.  In some assemblers,
the register names begin with `%'; to produce one `%' in the assembler
code, you must write `%%' in the input.

 If your assembler instruction can alter the condition code register,
add `cc' to the list of clobbered registers.  GCC on some machines
represents the condition codes as a specific hardware register; `cc'
serves to name this register.  On other machines, the condition code is
handled differently, and specifying `cc' has no effect.  But it is
valid no matter what the machine.

 If your assembler instructions access memory in an unpredictable
fashion, add `memory' to the list of clobbered registers.  This will
cause GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You will also want to add the `volatile' keyword if the memory affected
is not listed in the inputs or outputs of the `asm', as the `memory'
clobber does not count as a side-effect of the `asm'.  If you know how
large the accessed memory is, you can add it as input or output but if
this is not known, you should add `memory'.  As an example, if you
access ten bytes of a string, you can use a memory input like:

     {"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.

 Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to `x' away:
     int foo ()
     {
       int x = 42;
       int *y = &x;
       int result;
       asm ("magic stuff accessing an 'int' pointed to by '%1'"
             "=&d" (r) : "a" (y), "m" (*y));
       return result;
     }

 You can put multiple assembler instructions together in a single `asm'
template, separated by the characters normally used in assembly code
for the system.  A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as `\n\t').  Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character.  Note that
some assembler dialects use semicolons to start a comment.  The input
operands are guaranteed not to use any of the clobbered registers, and
neither will the output operands' addresses, so you can read and write
the clobbered registers as many times as you like.  Here is an example
of multiple instructions in a template; it assumes the subroutine
`_foo' accepts arguments in registers 9 and 10:

     asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
          : /* no outputs */
          : "g" (from), "g" (to)
          : "r9", "r10");

 Unless an output operand has the `&' constraint modifier, GCC may
allocate it in the same register as an unrelated input operand, on the
assumption the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction.  In such a case, use `&' for each output
operand that may not overlap an input.  *Note Modifiers::.

 If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the `asm'
construct, as follows:

     asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
          : "g" (result)
          : "g" (input));

This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.

 Speaking of labels, jumps from one `asm' to another are not supported.
The compiler's optimizers do not know about these jumps, and therefore
they cannot take account of them when deciding how to optimize.  *Note
Extended asm with goto::.

 Usually the most convenient way to use these `asm' instructions is to
encapsulate them in macros that look like functions.  For example,

     #define sin(x)       \
     ({ double __value, __arg = (x);   \
        asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
        __value; })

Here the variable `__arg' is used to make sure that the instruction
operates on a proper `double' value, and to accept only those arguments
`x' which can convert automatically to a `double'.

 Another way to make sure the instruction operates on the correct data
type is to use a cast in the `asm'.  This is different from using a
variable `__arg' in that it converts more different types.  For
example, if the desired type were `int', casting the argument to `int'
would accept a pointer with no complaint, while assigning the argument
to an `int' variable named `__arg' would warn about using a pointer
unless the caller explicitly casts it.

 If an `asm' has output operands, GCC assumes for optimization purposes
the instruction has no side effects except to change the output
operands.  This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression.  Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.

 You can prevent an `asm' instruction from being deleted by writing the
keyword `volatile' after the `asm'.  For example:

     #define get_and_set_priority(new)              \
     ({ int __old;                                  \
        asm volatile ("get_and_set_priority %0, %1" \
                      : "=g" (__old) : "g" (new));  \
        __old; })

The `volatile' keyword indicates that the instruction has important
side-effects.  GCC will not delete a volatile `asm' if it is reachable.
(The instruction can still be deleted if GCC can prove that
control-flow will never reach the location of the instruction.)  Note
that even a volatile `asm' instruction can be moved relative to other
code, including across jump instructions.  For example, on many targets
there is a system register which can be set to control the rounding
mode of floating point operations.  You might try setting it with a
volatile `asm', like this PowerPC example:

            asm volatile("mtfsf 255,%0" : : "f" (fpenv));
            sum = x + y;

This will not work reliably, as the compiler may move the addition back
before the volatile `asm'.  To make it work you need to add an
artificial dependency to the `asm' referencing a variable in the code
you don't want moved, for example:

         asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
         sum = x + y;

 Similarly, you can't expect a sequence of volatile `asm' instructions
to remain perfectly consecutive.  If you want consecutive output, use a
single `asm'.  Also, GCC will perform some optimizations across a
volatile `asm' instruction; GCC does not "forget everything" when it
encounters a volatile `asm' instruction the way some other compilers do.

 An `asm' instruction without any output operands will be treated
identically to a volatile `asm' instruction.

 It is a natural idea to look for a way to give access to the condition
code left by the assembler instruction.  However, when we attempted to
implement this, we found no way to make it work reliably.  The problem
is that output operands might need reloading, which would result in
additional following "store" instructions.  On most machines, these
instructions would alter the condition code before there was time to
test it.  This problem doesn't arise for ordinary "test" and "compare"
instructions because they don't have any output operands.

 For reasons similar to those described above, it is not possible to
give an assembler instruction access to the condition code left by
previous instructions.

 As of GCC version 4.5, `asm goto' may be used to have the assembly
jump to one or more C labels.  In this form, a fifth section after the
clobber list contains a list of all C labels to which the assembly may
jump.  Each label operand is implicitly self-named.  The `asm' is also
assumed to fall through to the next statement.

 This form of `asm' is restricted to not have outputs.  This is due to
a internal restriction in the compiler that control transfer
instructions cannot have outputs.  This restriction on `asm goto' may
be lifted in some future version of the compiler.  In the mean time,
`asm goto' may include a memory clobber, and so leave outputs in memory.

     int frob(int x)
     {
       int y;
       asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
                 : : "r"(x), "r"(&y) : "r5", "memory" : error);
       return y;
      error:
       return -1;
     }

 In this (inefficient) example, the `frob' instruction sets the carry
bit to indicate an error.  The `jc' instruction detects this and
branches to the `error' label.  Finally, the output of the `frob'
instruction (`%r5') is stored into the memory for variable `y', which
is later read by the `return' statement.

     void doit(void)
     {
       int i = 0;
       asm goto ("mfsr %%r1, 123; jmp %%r1;"
                 ".pushsection doit_table;"
     	    ".long %l0, %l1, %l2, %l3;"
     	    ".popsection"
     	    : : : "r1" : label1, label2, label3, label4);
       __builtin_unreachable ();

      label1:
       f1();
       return;
      label2:
       f2();
       return;
      label3:
       i = 1;
      label4:
       f3(i);
     }

 In this (also inefficient) example, the `mfsr' instruction reads an
address from some out-of-band machine register, and the following `jmp'
instruction branches to that address.  The address read by the `mfsr'
instruction is assumed to have been previously set via some
application-specific mechanism to be one of the four values stored in
the `doit_table' section.  Finally, the `asm' is followed by a call to
`__builtin_unreachable' to indicate that the `asm' does not in fact
fall through.

     #define TRACE1(NUM)                         \
       do {                                      \
         asm goto ("0: nop;"                     \
                   ".pushsection trace_table;"   \
                   ".long 0b, %l0;"              \
                   ".popsection"                 \
                   : : : : trace#NUM);           \
         if (0) { trace#NUM: trace(); }          \
       } while (0)
     #define TRACE  TRACE1(__COUNTER__)

 In this example (which in fact inspired the `asm goto' feature) we
want on rare occasions to call the `trace' function; on other occasions
we'd like to keep the overhead to the absolute minimum.  The normal
code path consists of a single `nop' instruction.  However, we record
the address of this `nop' together with the address of a label that
calls the `trace' function.  This allows the `nop' instruction to be
patched at runtime to be an unconditional branch to the stored label.
It is assumed that an optimizing compiler will move the labeled block
out of line, to optimize the fall through path from the `asm'.

 If you are writing a header file that should be includable in ISO C
programs, write `__asm__' instead of `asm'.  *Note Alternate Keywords::.

5.37.1 Size of an `asm'
-----------------------

Some targets require that GCC track the size of each instruction used in
order to generate correct code.  Because the final length of an `asm'
is only known by the assembler, GCC must make an estimate as to how big
it will be.  The estimate is formed by counting the number of
statements in the pattern of the `asm' and multiplying that by the
length of the longest instruction on that processor.  Statements in the
`asm' are identified by newline characters and whatever statement
separator characters are supported by the assembler; on most processors
this is the ``;'' character.

 Normally, GCC's estimate is perfectly adequate to ensure that correct
code is generated, but it is possible to confuse the compiler if you use
pseudo instructions or assembler macros that expand into multiple real
instructions or if you use assembler directives that expand to more
space in the object file than would be needed for a single instruction.
If this happens then the assembler will produce a diagnostic saying that
a label is unreachable.

5.37.2 i386 floating point asm operands
---------------------------------------

There are several rules on the usage of stack-like regs in asm_operands
insns.  These rules apply only to the operands that are stack-like regs:

  1. Given a set of input regs that die in an asm_operands, it is
     necessary to know which are implicitly popped by the asm, and
     which must be explicitly popped by gcc.

     An input reg that is implicitly popped by the asm must be
     explicitly clobbered, unless it is constrained to match an output
     operand.

  2. For any input reg that is implicitly popped by an asm, it is
     necessary to know how to adjust the stack to compensate for the
     pop.  If any non-popped input is closer to the top of the
     reg-stack than the implicitly popped reg, it would not be possible
     to know what the stack looked like--it's not clear how the rest of
     the stack "slides up".

     All implicitly popped input regs must be closer to the top of the
     reg-stack than any input that is not implicitly popped.

     It is possible that if an input dies in an insn, reload might use
     the input reg for an output reload.  Consider this example:

          asm ("foo" : "=t" (a) : "f" (b));

     This asm says that input B is not popped by the asm, and that the
     asm pushes a result onto the reg-stack, i.e., the stack is one
     deeper after the asm than it was before.  But, it is possible that
     reload will think that it can use the same reg for both the input
     and the output, if input B dies in this insn.

     If any input operand uses the `f' constraint, all output reg
     constraints must use the `&' earlyclobber.

     The asm above would be written as

          asm ("foo" : "=&t" (a) : "f" (b));

  3. Some operands need to be in particular places on the stack.  All
     output operands fall in this category--there is no other way to
     know which regs the outputs appear in unless the user indicates
     this in the constraints.

     Output operands must specifically indicate which reg an output
     appears in after an asm.  `=f' is not allowed: the operand
     constraints must select a class with a single reg.

  4. Output operands may not be "inserted" between existing stack regs.
     Since no 387 opcode uses a read/write operand, all output operands
     are dead before the asm_operands, and are pushed by the
     asm_operands.  It makes no sense to push anywhere but the top of
     the reg-stack.

     Output operands must start at the top of the reg-stack: output
     operands may not "skip" a reg.

  5. Some asm statements may need extra stack space for internal
     calculations.  This can be guaranteed by clobbering stack registers
     unrelated to the inputs and outputs.


 Here are a couple of reasonable asms to want to write.  This asm takes
one input, which is internally popped, and produces two outputs.

     asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

 This asm takes two inputs, which are popped by the `fyl2xp1' opcode,
and replaces them with one output.  The user must code the `st(1)'
clobber for reg-stack.c to know that `fyl2xp1' pops both inputs.

     asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");

File: gcc.info,  Node: Constraints,  Next: Asm Labels,  Prev: Extended Asm,  Up: C Extensions

5.38 Constraints for `asm' Operands
===================================

Here are specific details on what constraint letters you can use with
`asm' operands.  Constraints can say whether an operand may be in a
register, and which kinds of register; whether the operand can be a
memory reference, and which kinds of address; whether the operand may
be an immediate constant, and which possible values it may have.
Constraints can also require two operands to match.  Side-effects
aren't allowed in operands of inline `asm', unless `<' or `>'
constraints are used, because there is no guarantee that the
side-effects will happen exactly once in an instruction that can update
the addressing register.

* Menu:

* Simple Constraints::  Basic use of constraints.
* Multi-Alternative::   When an insn has two alternative constraint-patterns.
* Modifiers::           More precise control over effects of constraints.
* Machine Constraints:: Special constraints for some particular machines.

File: gcc.info,  Node: Simple Constraints,  Next: Multi-Alternative,  Up: Constraints

5.38.1 Simple Constraints
-------------------------

The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted.  Here are the
letters that are allowed:

whitespace
     Whitespace characters are ignored and can be inserted at any
     position except the first.  This enables each alternative for
     different operands to be visually aligned in the machine
     description even if they have different number of constraints and
     modifiers.

`m'
     A memory operand is allowed, with any kind of address that the
     machine supports in general.  Note that the letter used for the
     general memory constraint can be re-defined by a back end using
     the `TARGET_MEM_CONSTRAINT' macro.

`o'
     A memory operand is allowed, but only if the address is
     "offsettable".  This means that adding a small integer (actually,
     the width in bytes of the operand, as determined by its machine
     mode) may be added to the address and the result is also a valid
     memory address.

     For example, an address which is constant is offsettable; so is an
     address that is the sum of a register and a constant (as long as a
     slightly larger constant is also within the range of
     address-offsets supported by the machine); but an autoincrement or
     autodecrement address is not offsettable.  More complicated
     indirect/indexed addresses may or may not be offsettable depending
     on the other addressing modes that the machine supports.

     Note that in an output operand which can be matched by another
     operand, the constraint letter `o' is valid only when accompanied
     by both `<' (if the target machine has predecrement addressing)
     and `>' (if the target machine has preincrement addressing).

`V'
     A memory operand that is not offsettable.  In other words,
     anything that would fit the `m' constraint but not the `o'
     constraint.

`<'
     A memory operand with autodecrement addressing (either
     predecrement or postdecrement) is allowed.  In inline `asm' this
     constraint is only allowed if the operand is used exactly once in
     an instruction that can handle the side-effects.  Not using an
     operand with `<' in constraint string in the inline `asm' pattern
     at all or using it in multiple instructions isn't valid, because
     the side-effects wouldn't be performed or would be performed more
     than once.  Furthermore, on some targets the operand with `<' in
     constraint string must be accompanied by special instruction
     suffixes like `%U0' instruction suffix on PowerPC or `%P0' on
     IA-64.

`>'
     A memory operand with autoincrement addressing (either
     preincrement or postincrement) is allowed.  In inline `asm' the
     same restrictions as for `<' apply.

`r'
     A register operand is allowed provided that it is in a general
     register.

`i'
     An immediate integer operand (one with constant value) is allowed.
     This includes symbolic constants whose values will be known only at
     assembly time or later.

`n'
     An immediate integer operand with a known numeric value is allowed.
     Many systems cannot support assembly-time constants for operands
     less than a word wide.  Constraints for these operands should use
     `n' rather than `i'.

`I', `J', `K', ... `P'
     Other letters in the range `I' through `P' may be defined in a
     machine-dependent fashion to permit immediate integer operands with
     explicit integer values in specified ranges.  For example, on the
     68000, `I' is defined to stand for the range of values 1 to 8.
     This is the range permitted as a shift count in the shift
     instructions.

`E'
     An immediate floating operand (expression code `const_double') is
     allowed, but only if the target floating point format is the same
     as that of the host machine (on which the compiler is running).

`F'
     An immediate floating operand (expression code `const_double' or
     `const_vector') is allowed.

`G', `H'
     `G' and `H' may be defined in a machine-dependent fashion to
     permit immediate floating operands in particular ranges of values.

`s'
     An immediate integer operand whose value is not an explicit
     integer is allowed.

     This might appear strange; if an insn allows a constant operand
     with a value not known at compile time, it certainly must allow
     any known value.  So why use `s' instead of `i'?  Sometimes it
     allows better code to be generated.

     For example, on the 68000 in a fullword instruction it is possible
     to use an immediate operand; but if the immediate value is between
     -128 and 127, better code results from loading the value into a
     register and using the register.  This is because the load into
     the register can be done with a `moveq' instruction.  We arrange
     for this to happen by defining the letter `K' to mean "any integer
     outside the range -128 to 127", and then specifying `Ks' in the
     operand constraints.

`g'
     Any register, memory or immediate integer operand is allowed,
     except for registers that are not general registers.

`X'
     Any operand whatsoever is allowed.

`0', `1', `2', ... `9'
     An operand that matches the specified operand number is allowed.
     If a digit is used together with letters within the same
     alternative, the digit should come last.

     This number is allowed to be more than a single digit.  If multiple
     digits are encountered consecutively, they are interpreted as a
     single decimal integer.  There is scant chance for ambiguity,
     since to-date it has never been desirable that `10' be interpreted
     as matching either operand 1 _or_ operand 0.  Should this be
     desired, one can use multiple alternatives instead.

     This is called a "matching constraint" and what it really means is
     that the assembler has only a single operand that fills two roles
     which `asm' distinguishes.  For example, an add instruction uses
     two input operands and an output operand, but on most CISC
     machines an add instruction really has only two operands, one of
     them an input-output operand:

          addl #35,r12

     Matching constraints are used in these circumstances.  More
     precisely, the two operands that match must include one input-only
     operand and one output-only operand.  Moreover, the digit must be a
     smaller number than the number of the operand that uses it in the
     constraint.

`p'
     An operand that is a valid memory address is allowed.  This is for
     "load address" and "push address" instructions.

     `p' in the constraint must be accompanied by `address_operand' as
     the predicate in the `match_operand'.  This predicate interprets
     the mode specified in the `match_operand' as the mode of the memory
     reference for which the address would be valid.

OTHER-LETTERS
     Other letters can be defined in machine-dependent fashion to stand
     for particular classes of registers or other arbitrary operand
     types.  `d', `a' and `f' are defined on the 68000/68020 to stand
     for data, address and floating point registers.

File: gcc.info,  Node: Multi-Alternative,  Next: Modifiers,  Prev: Simple Constraints,  Up: Constraints

5.38.2 Multiple Alternative Constraints
---------------------------------------

Sometimes a single instruction has multiple alternative sets of possible
operands.  For example, on the 68000, a logical-or instruction can
combine register or an immediate value into memory, or it can combine
any kind of operand into a register; but it cannot combine one memory
location into another.

 These constraints are represented as multiple alternatives.  An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.

 If all the operands fit any one alternative, the instruction is valid.
Otherwise, for each alternative, the compiler counts how many
instructions must be added to copy the operands so that that
alternative applies.  The alternative requiring the least copying is
chosen.  If two alternatives need the same amount of copying, the one
that comes first is chosen.  These choices can be altered with the `?'
and `!' characters:

`?'
     Disparage slightly the alternative that the `?' appears in, as a
     choice when no alternative applies exactly.  The compiler regards
     this alternative as one unit more costly for each `?' that appears
     in it.

`!'
     Disparage severely the alternative that the `!' appears in.  This
     alternative can still be used if it fits without reloading, but if
     reloading is needed, some other alternative will be used.

File: gcc.info,  Node: Modifiers,  Next: Machine Constraints,  Prev: Multi-Alternative,  Up: Constraints

5.38.3 Constraint Modifier Characters
-------------------------------------

Here are constraint modifier characters.

`='
     Means that this operand is write-only for this instruction: the
     previous value is discarded and replaced by output data.

`+'
     Means that this operand is both read and written by the
     instruction.

     When the compiler fixes up the operands to satisfy the constraints,
     it needs to know which operands are inputs to the instruction and
     which are outputs from it.  `=' identifies an output; `+'
     identifies an operand that is both input and output; all other
     operands are assumed to be input only.

     If you specify `=' or `+' in a constraint, you put it in the first
     character of the constraint string.

`&'
     Means (in a particular alternative) that this operand is an
     "earlyclobber" operand, which is modified before the instruction is
     finished using the input operands.  Therefore, this operand may
     not lie in a register that is used as an input operand or as part
     of any memory address.

     `&' applies only to the alternative in which it is written.  In
     constraints with multiple alternatives, sometimes one alternative
     requires `&' while others do not.  See, for example, the `movdf'
     insn of the 68000.

     An input operand can be tied to an earlyclobber operand if its only
     use as an input occurs before the early result is written.  Adding
     alternatives of this form often allows GCC to produce better code
     when only some of the inputs can be affected by the earlyclobber.
     See, for example, the `mulsi3' insn of the ARM.

     `&' does not obviate the need to write `='.

`%'
     Declares the instruction to be commutative for this operand and the
     following operand.  This means that the compiler may interchange
     the two operands if that is the cheapest way to make all operands
     fit the constraints.  GCC can only handle one commutative pair in
     an asm; if you use more, the compiler may fail.  Note that you
     need not use the modifier if the two alternatives are strictly
     identical; this would only waste time in the reload pass.  The
     modifier is not operational after register allocation, so the
     result of `define_peephole2' and `define_split's performed after
     reload cannot rely on `%' to make the intended insn match.

`#'
     Says that all following characters, up to the next comma, are to be
     ignored as a constraint.  They are significant only for choosing
     register preferences.

`*'
     Says that the following character should be ignored when choosing
     register preferences.  `*' has no effect on the meaning of the
     constraint as a constraint, and no effect on reloading.


File: gcc.info,  Node: Machine Constraints,  Prev: Modifiers,  Up: Constraints

5.38.4 Constraints for Particular Machines
------------------------------------------

Whenever possible, you should use the general-purpose constraint letters
in `asm' arguments, since they will convey meaning more readily to
people reading your code.  Failing that, use the constraint letters
that usually have very similar meanings across architectures.  The most
commonly used constraints are `m' and `r' (for memory and
general-purpose registers respectively; *note Simple Constraints::), and
`I', usually the letter indicating the most common immediate-constant
format.

 Each architecture defines additional constraints.  These constraints
are used by the compiler itself for instruction generation, as well as
for `asm' statements; therefore, some of the constraints are not
particularly useful for `asm'.  Here is a summary of some of the
machine-dependent constraints available on some particular machines; it
includes both constraints that are useful for `asm' and constraints
that aren't.  The compiler source file mentioned in the table heading
for each architecture is the definitive reference for the meanings of
that architecture's constraints.

_ARM family--`config/arm/arm.h'_

    `f'
          Floating-point register

    `w'
          VFP floating-point register

    `F'
          One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0,
          4.0, 5.0 or 10.0

    `G'
          Floating-point constant that would satisfy the constraint `F'
          if it were negated

    `I'
          Integer that is valid as an immediate operand in a data
          processing instruction.  That is, an integer in the range 0
          to 255 rotated by a multiple of 2

    `J'
          Integer in the range -4095 to 4095

    `K'
          Integer that satisfies constraint `I' when inverted (ones
          complement)

    `L'
          Integer that satisfies constraint `I' when negated (twos
          complement)

    `M'
          Integer in the range 0 to 32

    `Q'
          A memory reference where the exact address is in a single
          register (``m'' is preferable for `asm' statements)

    `R'
          An item in the constant pool

    `S'
          A symbol in the text segment of the current file

    `Uv'
          A memory reference suitable for VFP load/store insns
          (reg+constant offset)

    `Uy'
          A memory reference suitable for iWMMXt load/store
          instructions.

    `Uq'
          A memory reference suitable for the ARMv4 ldrsb instruction.

_AVR family--`config/avr/constraints.md'_

    `l'
          Registers from r0 to r15

    `a'
          Registers from r16 to r23

    `d'
          Registers from r16 to r31

    `w'
          Registers from r24 to r31.  These registers can be used in
          `adiw' command

    `e'
          Pointer register (r26-r31)

    `b'
          Base pointer register (r28-r31)

    `q'
          Stack pointer register (SPH:SPL)

    `t'
          Temporary register r0

    `x'
          Register pair X (r27:r26)

    `y'
          Register pair Y (r29:r28)

    `z'
          Register pair Z (r31:r30)

    `I'
          Constant greater than -1, less than 64

    `J'
          Constant greater than -64, less than 1

    `K'
          Constant integer 2

    `L'
          Constant integer 0

    `M'
          Constant that fits in 8 bits

    `N'
          Constant integer -1

    `O'
          Constant integer 8, 16, or 24

    `P'
          Constant integer 1

    `G'
          A floating point constant 0.0

    `R'
          Integer constant in the range -6 ... 5.

    `Q'
          A memory address based on Y or Z pointer with displacement.

_CRX Architecture--`config/crx/crx.h'_

    `b'
          Registers from r0 to r14 (registers without stack pointer)

    `l'
          Register r16 (64-bit accumulator lo register)

    `h'
          Register r17 (64-bit accumulator hi register)

    `k'
          Register pair r16-r17. (64-bit accumulator lo-hi pair)

    `I'
          Constant that fits in 3 bits

    `J'
          Constant that fits in 4 bits

    `K'
          Constant that fits in 5 bits

    `L'
          Constant that is one of -1, 4, -4, 7, 8, 12, 16, 20, 32, 48

    `G'
          Floating point constant that is legal for store immediate

_Hewlett-Packard PA-RISC--`config/pa/pa.h'_

    `a'
          General register 1

    `f'
          Floating point register

    `q'
          Shift amount register

    `x'
          Floating point register (deprecated)

    `y'
          Upper floating point register (32-bit), floating point
          register (64-bit)

    `Z'
          Any register

    `I'
          Signed 11-bit integer constant

    `J'
          Signed 14-bit integer constant

    `K'
          Integer constant that can be deposited with a `zdepi'
          instruction

    `L'
          Signed 5-bit integer constant

    `M'
          Integer constant 0

    `N'
          Integer constant that can be loaded with a `ldil' instruction

    `O'
          Integer constant whose value plus one is a power of 2

    `P'
          Integer constant that can be used for `and' operations in
          `depi' and `extru' instructions

    `S'
          Integer constant 31

    `U'
          Integer constant 63

    `G'
          Floating-point constant 0.0

    `A'
          A `lo_sum' data-linkage-table memory operand

    `Q'
          A memory operand that can be used as the destination operand
          of an integer store instruction

    `R'
          A scaled or unscaled indexed memory operand

    `T'
          A memory operand for floating-point loads and stores

    `W'
          A register indirect memory operand

_picoChip family--`picochip.h'_

    `k'
          Stack register.

    `f'
          Pointer register.  A register which can be used to access
          memory without supplying an offset.  Any other register can
          be used to access memory, but will need a constant offset.
          In the case of the offset being zero, it is more efficient to
          use a pointer register, since this reduces code size.

    `t'
          A twin register.  A register which may be paired with an
          adjacent register to create a 32-bit register.

    `a'
          Any absolute memory address (e.g., symbolic constant, symbolic
          constant + offset).

    `I'
          4-bit signed integer.

    `J'
          4-bit unsigned integer.

    `K'
          8-bit signed integer.

    `M'
          Any constant whose absolute value is no greater than 4-bits.

    `N'
          10-bit signed integer

    `O'
          16-bit signed integer.


_PowerPC and IBM RS6000--`config/rs6000/rs6000.h'_

    `b'
          Address base register

    `f'
          Floating point register

    `v'
          Altivec vector register

    `wd'
          VSX vector register to hold vector double data

    `wf'
          VSX vector register to hold vector float data

    `ws'
          VSX vector register to hold scalar float data

    `wa'
          Any VSX register

    `h'
          `MQ', `CTR', or `LINK' register

    `q'
          `MQ' register

    `c'
          `CTR' register

    `l'
          `LINK' register

    `x'
          `CR' register (condition register) number 0

    `y'
          `CR' register (condition register)

    `z'
          `FPMEM' stack memory for FPR-GPR transfers

    `I'
          Signed 16-bit constant

    `J'
          Unsigned 16-bit constant shifted left 16 bits (use `L'
          instead for `SImode' constants)

    `K'
          Unsigned 16-bit constant

    `L'
          Signed 16-bit constant shifted left 16 bits

    `M'
          Constant larger than 31

    `N'
          Exact power of 2

    `O'
          Zero

    `P'
          Constant whose negation is a signed 16-bit constant

    `G'
          Floating point constant that can be loaded into a register
          with one instruction per word

    `H'
          Integer/Floating point constant that can be loaded into a
          register using three instructions

    `Q'
          Memory operand that is an offset from a register (`m' is
          preferable for `asm' statements)

    `Z'
          Memory operand that is an indexed or indirect from a register
          (`m' is preferable for `asm' statements)

    `R'
          AIX TOC entry

    `a'
          Address operand that is an indexed or indirect from a
          register (`p' is preferable for `asm' statements)

    `S'
          Constant suitable as a 64-bit mask operand

    `T'
          Constant suitable as a 32-bit mask operand

    `U'
          System V Release 4 small data area reference

    `t'
          AND masks that can be performed by two rldic{l, r}
          instructions

    `W'
          Vector constant that does not require memory

    `j'
          Vector constant that is all zeros.


_Intel 386--`config/i386/constraints.md'_

    `R'
          Legacy register--the eight integer registers available on all
          i386 processors (`a', `b', `c', `d', `si', `di', `bp', `sp').

    `q'
          Any register accessible as `Rl'.  In 32-bit mode, `a', `b',
          `c', and `d'; in 64-bit mode, any integer register.

    `Q'
          Any register accessible as `Rh': `a', `b', `c', and `d'.

    `a'
          The `a' register.

    `b'
          The `b' register.

    `c'
          The `c' register.

    `d'
          The `d' register.

    `S'
          The `si' register.

    `D'
          The `di' register.

    `A'
          The `a' and `d' registers, as a pair (for instructions that
          return half the result in one and half in the other).

    `f'
          Any 80387 floating-point (stack) register.

    `t'
          Top of 80387 floating-point stack (`%st(0)').

    `u'
          Second from top of 80387 floating-point stack (`%st(1)').

    `y'
          Any MMX register.

    `x'
          Any SSE register.

    `Yz'
          First SSE register (`%xmm0').

    `I'
          Integer constant in the range 0 ... 31, for 32-bit shifts.

    `J'
          Integer constant in the range 0 ... 63, for 64-bit shifts.

    `K'
          Signed 8-bit integer constant.

    `L'
          `0xFF' or `0xFFFF', for andsi as a zero-extending move.

    `M'
          0, 1, 2, or 3 (shifts for the `lea' instruction).

    `N'
          Unsigned 8-bit integer constant (for `in' and `out'
          instructions).

    `G'
          Standard 80387 floating point constant.

    `C'
          Standard SSE floating point constant.

    `e'
          32-bit signed integer constant, or a symbolic reference known
          to fit that range (for immediate operands in sign-extending
          x86-64 instructions).

    `Z'
          32-bit unsigned integer constant, or a symbolic reference
          known to fit that range (for immediate operands in
          zero-extending x86-64 instructions).


_Intel IA-64--`config/ia64/ia64.h'_

    `a'
          General register `r0' to `r3' for `addl' instruction

    `b'
          Branch register

    `c'
          Predicate register (`c' as in "conditional")

    `d'
          Application register residing in M-unit

    `e'
          Application register residing in I-unit

    `f'
          Floating-point register

    `m'
          Memory operand.  Remember that `m' allows postincrement and
          postdecrement which require printing with `%Pn' on IA-64.
          Use `S' to disallow postincrement and postdecrement.

    `G'
          Floating-point constant 0.0 or 1.0

    `I'
          14-bit signed integer constant

    `J'
          22-bit signed integer constant

    `K'
          8-bit signed integer constant for logical instructions

    `L'
          8-bit adjusted signed integer constant for compare pseudo-ops

    `M'
          6-bit unsigned integer constant for shift counts

    `N'
          9-bit signed integer constant for load and store
          postincrements

    `O'
          The constant zero

    `P'
          0 or -1 for `dep' instruction

    `Q'
          Non-volatile memory for floating-point loads and stores

    `R'
          Integer constant in the range 1 to 4 for `shladd' instruction

    `S'
          Memory operand except postincrement and postdecrement

_FRV--`config/frv/frv.h'_

    `a'
          Register in the class `ACC_REGS' (`acc0' to `acc7').

    `b'
          Register in the class `EVEN_ACC_REGS' (`acc0' to `acc7').

    `c'
          Register in the class `CC_REGS' (`fcc0' to `fcc3' and `icc0'
          to `icc3').

    `d'
          Register in the class `GPR_REGS' (`gr0' to `gr63').

    `e'
          Register in the class `EVEN_REGS' (`gr0' to `gr63').  Odd
          registers are excluded not in the class but through the use
          of a machine mode larger than 4 bytes.

    `f'
          Register in the class `FPR_REGS' (`fr0' to `fr63').

    `h'
          Register in the class `FEVEN_REGS' (`fr0' to `fr63').  Odd
          registers are excluded not in the class but through the use
          of a machine mode larger than 4 bytes.

    `l'
          Register in the class `LR_REG' (the `lr' register).

    `q'
          Register in the class `QUAD_REGS' (`gr2' to `gr63').
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

    `t'
          Register in the class `ICC_REGS' (`icc0' to `icc3').

    `u'
          Register in the class `FCC_REGS' (`fcc0' to `fcc3').

    `v'
          Register in the class `ICR_REGS' (`cc4' to `cc7').

    `w'
          Register in the class `FCR_REGS' (`cc0' to `cc3').

    `x'
          Register in the class `QUAD_FPR_REGS' (`fr0' to `fr63').
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

    `z'
          Register in the class `SPR_REGS' (`lcr' and `lr').

    `A'
          Register in the class `QUAD_ACC_REGS' (`acc0' to `acc7').

    `B'
          Register in the class `ACCG_REGS' (`accg0' to `accg7').

    `C'
          Register in the class `CR_REGS' (`cc0' to `cc7').

    `G'
          Floating point constant zero

    `I'
          6-bit signed integer constant

    `J'
          10-bit signed integer constant

    `L'
          16-bit signed integer constant

    `M'
          16-bit unsigned integer constant

    `N'
          12-bit signed integer constant that is negative--i.e. in the
          range of -2048 to -1

    `O'
          Constant zero

    `P'
          12-bit signed integer constant that is greater than
          zero--i.e. in the range of 1 to 2047.


_Blackfin family--`config/bfin/constraints.md'_

    `a'
          P register

    `d'
          D register

    `z'
          A call clobbered P register.

    `qN'
          A single register.  If N is in the range 0 to 7, the
          corresponding D register.  If it is `A', then the register P0.

    `D'
          Even-numbered D register

    `W'
          Odd-numbered D register

    `e'
          Accumulator register.

    `A'
          Even-numbered accumulator register.

    `B'
          Odd-numbered accumulator register.

    `b'
          I register

    `v'
          B register

    `f'
          M register

    `c'
          Registers used for circular buffering, i.e. I, B, or L
          registers.

    `C'
          The CC register.

    `t'
          LT0 or LT1.

    `k'
          LC0 or LC1.

    `u'
          LB0 or LB1.

    `x'
          Any D, P, B, M, I or L register.

    `y'
          Additional registers typically used only in prologues and
          epilogues: RETS, RETN, RETI, RETX, RETE, ASTAT, SEQSTAT and
          USP.

    `w'
          Any register except accumulators or CC.

    `Ksh'
          Signed 16 bit integer (in the range -32768 to 32767)

    `Kuh'
          Unsigned 16 bit integer (in the range 0 to 65535)

    `Ks7'
          Signed 7 bit integer (in the range -64 to 63)

    `Ku7'
          Unsigned 7 bit integer (in the range 0 to 127)

    `Ku5'
          Unsigned 5 bit integer (in the range 0 to 31)

    `Ks4'
          Signed 4 bit integer (in the range -8 to 7)

    `Ks3'
          Signed 3 bit integer (in the range -3 to 4)

    `Ku3'
          Unsigned 3 bit integer (in the range 0 to 7)

    `PN'
          Constant N, where N is a single-digit constant in the range 0
          to 4.

    `PA'
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use with either accumulator.

    `PB'
          An integer equal to one of the MACFLAG_XXX constants that is
          suitable for use only with accumulator A1.

    `M1'
          Constant 255.

    `M2'
          Constant 65535.

    `J'
          An integer constant with exactly a single bit set.

    `L'
          An integer constant with all bits set except exactly one.

    `H'

    `Q'
          Any SYMBOL_REF.

_M32C--`config/m32c/m32c.c'_

    `Rsp'
    `Rfb'
    `Rsb'
          `$sp', `$fb', `$sb'.

    `Rcr'
          Any control register, when they're 16 bits wide (nothing if
          control registers are 24 bits wide)

    `Rcl'
          Any control register, when they're 24 bits wide.

    `R0w'
    `R1w'
    `R2w'
    `R3w'
          $r0, $r1, $r2, $r3.

    `R02'
          $r0 or $r2, or $r2r0 for 32 bit values.

    `R13'
          $r1 or $r3, or $r3r1 for 32 bit values.

    `Rdi'
          A register that can hold a 64 bit value.

    `Rhl'
          $r0 or $r1 (registers with addressable high/low bytes)

    `R23'
          $r2 or $r3

    `Raa'
          Address registers

    `Raw'
          Address registers when they're 16 bits wide.

    `Ral'
          Address registers when they're 24 bits wide.

    `Rqi'
          Registers that can hold QI values.

    `Rad'
          Registers that can be used with displacements ($a0, $a1, $sb).

    `Rsi'
          Registers that can hold 32 bit values.

    `Rhi'
          Registers that can hold 16 bit values.

    `Rhc'
          Registers chat can hold 16 bit values, including all control
          registers.

    `Rra'
          $r0 through R1, plus $a0 and $a1.

    `Rfl'
          The flags register.

    `Rmm'
          The memory-based pseudo-registers $mem0 through $mem15.

    `Rpi'
          Registers that can hold pointers (16 bit registers for r8c,
          m16c; 24 bit registers for m32cm, m32c).

    `Rpa'
          Matches multiple registers in a PARALLEL to form a larger
          register.  Used to match function return values.

    `Is3'
          -8 ... 7

    `IS1'
          -128 ... 127

    `IS2'
          -32768 ... 32767

    `IU2'
          0 ... 65535

    `In4'
          -8 ... -1 or 1 ... 8

    `In5'
          -16 ... -1 or 1 ... 16

    `In6'
          -32 ... -1 or 1 ... 32

    `IM2'
          -65536 ... -1

    `Ilb'
          An 8 bit value with exactly one bit set.

    `Ilw'
          A 16 bit value with exactly one bit set.

    `Sd'
          The common src/dest memory addressing modes.

    `Sa'
          Memory addressed using $a0 or $a1.

    `Si'
          Memory addressed with immediate addresses.

    `Ss'
          Memory addressed using the stack pointer ($sp).

    `Sf'
          Memory addressed using the frame base register ($fb).

    `Ss'
          Memory addressed using the small base register ($sb).

    `S1'
          $r1h

_MIPS--`config/mips/constraints.md'_

    `d'
          An address register.  This is equivalent to `r' unless
          generating MIPS16 code.

    `f'
          A floating-point register (if available).

    `h'
          Formerly the `hi' register.  This constraint is no longer
          supported.

    `l'
          The `lo' register.  Use this register to store values that are
          no bigger than a word.

    `x'
          The concatenated `hi' and `lo' registers.  Use this register
          to store doubleword values.

    `c'
          A register suitable for use in an indirect jump.  This will
          always be `$25' for `-mabicalls'.

    `v'
          Register `$3'.  Do not use this constraint in new code; it is
          retained only for compatibility with glibc.

    `y'
          Equivalent to `r'; retained for backwards compatibility.

    `z'
          A floating-point condition code register.

    `I'
          A signed 16-bit constant (for arithmetic instructions).

    `J'
          Integer zero.

    `K'
          An unsigned 16-bit constant (for logic instructions).

    `L'
          A signed 32-bit constant in which the lower 16 bits are zero.
          Such constants can be loaded using `lui'.

    `M'
          A constant that cannot be loaded using `lui', `addiu' or
          `ori'.

    `N'
          A constant in the range -65535 to -1 (inclusive).

    `O'
          A signed 15-bit constant.

    `P'
          A constant in the range 1 to 65535 (inclusive).

    `G'
          Floating-point zero.

    `R'
          An address that can be used in a non-macro load or store.

_Motorola 680x0--`config/m68k/constraints.md'_

    `a'
          Address register

    `d'
          Data register

    `f'
          68881 floating-point register, if available

    `I'
          Integer in the range 1 to 8

    `J'
          16-bit signed number

    `K'
          Signed number whose magnitude is greater than 0x80

    `L'
          Integer in the range -8 to -1

    `M'
          Signed number whose magnitude is greater than 0x100

    `N'
          Range 24 to 31, rotatert:SI 8 to 1 expressed as rotate

    `O'
          16 (for rotate using swap)

    `P'
          Range 8 to 15, rotatert:HI 8 to 1 expressed as rotate

    `R'
          Numbers that mov3q can handle

    `G'
          Floating point constant that is not a 68881 constant

    `S'
          Operands that satisfy 'm' when -mpcrel is in effect

    `T'
          Operands that satisfy 's' when -mpcrel is not in effect

    `Q'
          Address register indirect addressing mode

    `U'
          Register offset addressing

    `W'
          const_call_operand

    `Cs'
          symbol_ref or const

    `Ci'
          const_int

    `C0'
          const_int 0

    `Cj'
          Range of signed numbers that don't fit in 16 bits

    `Cmvq'
          Integers valid for mvq

    `Capsw'
          Integers valid for a moveq followed by a swap

    `Cmvz'
          Integers valid for mvz

    `Cmvs'
          Integers valid for mvs

    `Ap'
          push_operand

    `Ac'
          Non-register operands allowed in clr


_Motorola 68HC11 & 68HC12 families--`config/m68hc11/m68hc11.h'_

    `a'
          Register `a'

    `b'
          Register `b'

    `d'
          Register `d'

    `q'
          An 8-bit register

    `t'
          Temporary soft register _.tmp

    `u'
          A soft register _.d1 to _.d31

    `w'
          Stack pointer register

    `x'
          Register `x'

    `y'
          Register `y'

    `z'
          Pseudo register `z' (replaced by `x' or `y' at the end)

    `A'
          An address register: x, y or z

    `B'
          An address register: x or y

    `D'
          Register pair (x:d) to form a 32-bit value

    `L'
          Constants in the range -65536 to 65535

    `M'
          Constants whose 16-bit low part is zero

    `N'
          Constant integer 1 or -1

    `O'
          Constant integer 16

    `P'
          Constants in the range -8 to 2


_SPARC--`config/sparc/sparc.h'_

    `f'
          Floating-point register on the SPARC-V8 architecture and
          lower floating-point register on the SPARC-V9 architecture.

    `e'
          Floating-point register.  It is equivalent to `f' on the
          SPARC-V8 architecture and contains both lower and upper
          floating-point registers on the SPARC-V9 architecture.

    `c'
          Floating-point condition code register.

    `d'
          Lower floating-point register.  It is only valid on the
          SPARC-V9 architecture when the Visual Instruction Set is
          available.

    `b'
          Floating-point register.  It is only valid on the SPARC-V9
          architecture when the Visual Instruction Set is available.

    `h'
          64-bit global or out register for the SPARC-V8+ architecture.

    `D'
          A vector constant

    `I'
          Signed 13-bit constant

    `J'
          Zero

    `K'
          32-bit constant with the low 12 bits clear (a constant that
          can be loaded with the `sethi' instruction)

    `L'
          A constant in the range supported by `movcc' instructions

    `M'
          A constant in the range supported by `movrcc' instructions

    `N'
          Same as `K', except that it verifies that bits that are not
          in the lower 32-bit range are all zero.  Must be used instead
          of `K' for modes wider than `SImode'

    `O'
          The constant 4096

    `G'
          Floating-point zero

    `H'
          Signed 13-bit constant, sign-extended to 32 or 64 bits

    `Q'
          Floating-point constant whose integral representation can be
          moved into an integer register using a single sethi
          instruction

    `R'
          Floating-point constant whose integral representation can be
          moved into an integer register using a single mov instruction

    `S'
          Floating-point constant whose integral representation can be
          moved into an integer register using a high/lo_sum
          instruction sequence

    `T'
          Memory address aligned to an 8-byte boundary

    `U'
          Even register

    `W'
          Memory address for `e' constraint registers

    `Y'
          Vector zero


_SPU--`config/spu/spu.h'_

    `a'
          An immediate which can be loaded with the il/ila/ilh/ilhu
          instructions.  const_int is treated as a 64 bit value.

    `c'
          An immediate for and/xor/or instructions.  const_int is
          treated as a 64 bit value.

    `d'
          An immediate for the `iohl' instruction.  const_int is
          treated as a 64 bit value.

    `f'
          An immediate which can be loaded with `fsmbi'.

    `A'
          An immediate which can be loaded with the il/ila/ilh/ilhu
          instructions.  const_int is treated as a 32 bit value.

    `B'
          An immediate for most arithmetic instructions.  const_int is
          treated as a 32 bit value.

    `C'
          An immediate for and/xor/or instructions.  const_int is
          treated as a 32 bit value.

    `D'
          An immediate for the `iohl' instruction.  const_int is
          treated as a 32 bit value.

    `I'
          A constant in the range [-64, 63] for shift/rotate
          instructions.

    `J'
          An unsigned 7-bit constant for conversion/nop/channel
          instructions.

    `K'
          A signed 10-bit constant for most arithmetic instructions.

    `M'
          A signed 16 bit immediate for `stop'.

    `N'
          An unsigned 16-bit constant for `iohl' and `fsmbi'.

    `O'
          An unsigned 7-bit constant whose 3 least significant bits are
          0.

    `P'
          An unsigned 3-bit constant for 16-byte rotates and shifts

    `R'
          Call operand, reg, for indirect calls

    `S'
          Call operand, symbol, for relative calls.

    `T'
          Call operand, const_int, for absolute calls.

    `U'
          An immediate which can be loaded with the il/ila/ilh/ilhu
          instructions.  const_int is sign extended to 128 bit.

    `W'
          An immediate for shift and rotate instructions.  const_int is
          treated as a 32 bit value.

    `Y'
          An immediate for and/xor/or instructions.  const_int is sign
          extended as a 128 bit.

    `Z'
          An immediate for the `iohl' instruction.  const_int is sign
          extended to 128 bit.


_S/390 and zSeries--`config/s390/s390.h'_

    `a'
          Address register (general purpose register except r0)

    `c'
          Condition code register

    `d'
          Data register (arbitrary general purpose register)

    `f'
          Floating-point register

    `I'
          Unsigned 8-bit constant (0-255)

    `J'
          Unsigned 12-bit constant (0-4095)

    `K'
          Signed 16-bit constant (-32768-32767)

    `L'
          Value appropriate as displacement.
         `(0..4095)'
               for short displacement

         `(-524288..524287)'
               for long displacement

    `M'
          Constant integer with a value of 0x7fffffff.

    `N'
          Multiple letter constraint followed by 4 parameter letters.
         `0..9:'
               number of the part counting from most to least
               significant

         `H,Q:'
               mode of the part

         `D,S,H:'
               mode of the containing operand

         `0,F:'
               value of the other parts (F--all bits set)
          The constraint matches if the specified part of a constant
          has a value different from its other parts.

    `Q'
          Memory reference without index register and with short
          displacement.

    `R'
          Memory reference with index register and short displacement.

    `S'
          Memory reference without index register but with long
          displacement.

    `T'
          Memory reference with index register and long displacement.

    `U'
          Pointer with short displacement.

    `W'
          Pointer with long displacement.

    `Y'
          Shift count operand.


_Score family--`config/score/score.h'_

    `d'
          Registers from r0 to r32.

    `e'
          Registers from r0 to r16.

    `t'
          r8--r11 or r22--r27 registers.

    `h'
          hi register.

    `l'
          lo register.

    `x'
          hi + lo register.

    `q'
          cnt register.

    `y'
          lcb register.

    `z'
          scb register.

    `a'
          cnt + lcb + scb register.

    `c'
          cr0--cr15 register.

    `b'
          cp1 registers.

    `f'
          cp2 registers.

    `i'
          cp3 registers.

    `j'
          cp1 + cp2 + cp3 registers.

    `I'
          High 16-bit constant (32-bit constant with 16 LSBs zero).

    `J'
          Unsigned 5 bit integer (in the range 0 to 31).

    `K'
          Unsigned 16 bit integer (in the range 0 to 65535).

    `L'
          Signed 16 bit integer (in the range -32768 to 32767).

    `M'
          Unsigned 14 bit integer (in the range 0 to 16383).

    `N'
          Signed 14 bit integer (in the range -8192 to 8191).

    `Z'
          Any SYMBOL_REF.

_Xstormy16--`config/stormy16/stormy16.h'_

    `a'
          Register r0.

    `b'
          Register r1.

    `c'
          Register r2.

    `d'
          Register r8.

    `e'
          Registers r0 through r7.

    `t'
          Registers r0 and r1.

    `y'
          The carry register.

    `z'
          Registers r8 and r9.

    `I'
          A constant between 0 and 3 inclusive.

    `J'
          A constant that has exactly one bit set.

    `K'
          A constant that has exactly one bit clear.

    `L'
          A constant between 0 and 255 inclusive.

    `M'
          A constant between -255 and 0 inclusive.

    `N'
          A constant between -3 and 0 inclusive.

    `O'
          A constant between 1 and 4 inclusive.

    `P'
          A constant between -4 and -1 inclusive.

    `Q'
          A memory reference that is a stack push.

    `R'
          A memory reference that is a stack pop.

    `S'
          A memory reference that refers to a constant address of known
          value.

    `T'
          The register indicated by Rx (not implemented yet).

    `U'
          A constant that is not between 2 and 15 inclusive.

    `Z'
          The constant 0.


_Xtensa--`config/xtensa/constraints.md'_

    `a'
          General-purpose 32-bit register

    `b'
          One-bit boolean register

    `A'
          MAC16 40-bit accumulator register

    `I'
          Signed 12-bit integer constant, for use in MOVI instructions

    `J'
          Signed 8-bit integer constant, for use in ADDI instructions

    `K'
          Integer constant valid for BccI instructions

    `L'
          Unsigned constant valid for BccUI instructions



File: gcc.info,  Node: Asm Labels,  Next: Explicit Reg Vars,  Prev: Constraints,  Up: C Extensions

5.39 Controlling Names Used in Assembler Code
=============================================

You can specify the name to be used in the assembler code for a C
function or variable by writing the `asm' (or `__asm__') keyword after
the declarator as follows:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable `foo' in the
assembler code should be `myfoo' rather than the usual `_foo'.

 On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.

 It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see *note Explicit
Reg Vars::.  GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.

 You cannot use `asm' in this way in a function _definition_; but you
can get the same effect by writing a declaration for the function
before its definition and putting `asm' there, like this:

     extern func () asm ("FUNC");

     func (x, y)
          int x, y;
     /* ... */

 It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.
GCC does not as yet have the ability to store static variables in
registers.  Perhaps that will be added.

File: gcc.info,  Node: Explicit Reg Vars,  Next: Alternate Keywords,  Prev: Asm Labels,  Up: C Extensions

5.40 Variables in Specified Registers
=====================================

GNU C allows you to put a few global variables into specified hardware
registers.  You can also specify the register in which an ordinary
register variable should be allocated.

   * Global register variables reserve registers throughout the program.
     This may be useful in programs such as programming language
     interpreters which have a couple of global variables that are
     accessed very often.

   * Local register variables in specific registers do not reserve the
     registers, except at the point where they are used as input or
     output operands in an `asm' statement and the `asm' statement
     itself is not deleted.  The compiler's data flow analysis is
     capable of determining where the specified registers contain live
     values, and where they are available for other uses.  Stores into
     local register variables may be deleted when they appear to be
     dead according to dataflow analysis.  References to local register
     variables may be deleted or moved or simplified.

     These local variables are sometimes convenient for use with the
     extended `asm' feature (*note Extended Asm::), if you want to
     write one output of the assembler instruction directly into a
     particular register.  (This will work provided the register you
     specify fits the constraints specified for that operand in the
     `asm'.)

* Menu:

* Global Reg Vars::
* Local Reg Vars::

File: gcc.info,  Node: Global Reg Vars,  Next: Local Reg Vars,  Up: Explicit Reg Vars

5.40.1 Defining Global Register Variables
-----------------------------------------

You can define a global register variable in GNU C like this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.

 Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type.  The register `a5'
would be a good choice on a 68000 for a variable of pointer type.  On
machines with register windows, be sure to choose a "global" register
that is not affected magically by the function call mechanism.

 In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

 Eventually there may be a way of asking the compiler to choose a
register automatically, but first we need to figure out how it should
choose and how to enable you to guide the choice.  No solution is
evident.

 Defining a global register variable in a certain register reserves that
register entirely for this use, at least within the current compilation.
The register will not be allocated for any other purpose in the
functions in the current compilation.  The register will not be saved
and restored by these functions.  Stores into this register are never
deleted even if they would appear to be dead, but references may be
deleted or moved or simplified.

 It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things
(unless you recompile them specially for the task at hand).

 It is not safe for one function that uses a global register variable to
call another such function `foo' by way of a third function `lose' that
was compiled without knowledge of this variable (i.e. in a different
source file in which the variable wasn't declared).  This is because
`lose' might save the register and put some other value there.  For
example, you can't expect a global register variable to be available in
the comparison-function that you pass to `qsort', since `qsort' might
have put something else in that register.  (If you are prepared to
recompile `qsort' with the same global register variable, you can solve
this problem.)

 If you want to recompile `qsort' or other source files which do not
actually use your global register variable, so that they will not use
that register for any other purpose, then it suffices to specify the
compiler option `-ffixed-REG'.  You need not actually add a global
register declaration to their source code.

 A function which can alter the value of a global register variable
cannot safely be called from a function compiled without this variable,
because it could clobber the value the caller expects to find there on
return.  Therefore, the function which is the entry point into the part
of the program that uses the global register variable must explicitly
save and restore the value which belongs to its caller.

 On most machines, `longjmp' will restore to each global register
variable the value it had at the time of the `setjmp'.  On some
machines, however, `longjmp' will not change the value of global
register variables.  To be portable, the function that called `setjmp'
should make other arrangements to save the values of the global register
variables, and to restore them in a `longjmp'.  This way, the same
thing will happen regardless of what `longjmp' does.

 All global register variable declarations must precede all function
definitions.  If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register
from being used for other purposes in the preceding functions.

 Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.

 On the SPARC, there are reports that g3 ... g7 are suitable registers,
but certain library functions, such as `getwd', as well as the
subroutines for division and remainder, modify g3 and g4.  g1 and g2
are local temporaries.

 On the 68000, a2 ... a5 should be suitable, as should d2 ... d7.  Of
course, it will not do to use more than a few of those.

File: gcc.info,  Node: Local Reg Vars,  Prev: Global Reg Vars,  Up: Explicit Reg Vars

5.40.2 Specifying Registers for Local Variables
-----------------------------------------------

You can define a local register variable with a specified register like
this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Note that
this is the same syntax used for defining global register variables,
but for a local variable it would appear within a function.

 Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (*note Extended Asm::).  Both of these things
generally require that you conditionalize your program according to cpu
type.

 In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

 Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.

 This option does not guarantee that GCC will generate code that has
this variable in the register you specify at all times.  You may not
code an explicit reference to this register in the _assembler
instruction template_ part of an `asm' statement and assume it will
always refer to this variable.  However, using the variable as an `asm'
_operand_ guarantees that the specified register is used for the
operand.

 Stores into local register variables may be deleted when they appear
to be dead according to dataflow analysis.  References to local
register variables may be deleted or moved or simplified.

 As for global register variables, it's recommended that you choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.  A common
pitfall is to initialize multiple call-clobbered registers with
arbitrary expressions, where a function call or library call for an
arithmetic operator will overwrite a register value from a previous
assignment, for example `r0' below:
     register int *p1 asm ("r0") = ...;
     register int *p2 asm ("r1") = ...;
 In those cases, a solution is to use a temporary variable for each
arbitrary expression.   *Note Example of asm with clobbered asm reg::.

File: gcc.info,  Node: Alternate Keywords,  Next: Incomplete Enums,  Prev: Explicit Reg Vars,  Up: C Extensions

5.41 Alternate Keywords
=======================

`-ansi' and the various `-std' options disable certain keywords.  This
causes trouble when you want to use GNU C extensions, or a
general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords `asm', `typeof' and `inline'
are not available in programs compiled with `-ansi' or `-std' (although
`inline' can be used in a program compiled with `-std=c99').  The ISO
C99 keyword `restrict' is only available when `-std=gnu99' (which will
eventually be the default) or `-std=c99' (or the equivalent
`-std=iso9899:1999') is used.

 The way to solve these problems is to put `__' at the beginning and
end of each problematical keyword.  For example, use `__asm__' instead
of `asm', and `__inline__' instead of `inline'.

 Other C compilers won't accept these alternative keywords; if you want
to compile with another compiler, you can define the alternate keywords
as macros to replace them with the customary keywords.  It looks like
this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

 `-pedantic' and other options cause warnings for many GNU C extensions.
You can prevent such warnings within one expression by writing
`__extension__' before the expression.  `__extension__' has no effect
aside from this.

File: gcc.info,  Node: Incomplete Enums,  Next: Function Names,  Prev: Alternate Keywords,  Up: C Extensions

5.42 Incomplete `enum' Types
============================

You can define an `enum' tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
`struct foo' without describing the elements.  A later declaration
which does specify the possible values completes the type.

 You can't allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

 This extension may not be very useful, but it makes the handling of
`enum' more consistent with the way `struct' and `union' are handled.

 This extension is not supported by GNU C++.

File: gcc.info,  Node: Function Names,  Next: Return Address,  Prev: Incomplete Enums,  Up: C Extensions

5.43 Function Names as Strings
==============================

GCC provides three magic variables which hold the name of the current
function, as a string.  The first of these is `__func__', which is part
of the C99 standard:

 The identifier `__func__' is implicitly declared by the translator as
if, immediately following the opening brace of each function
definition, the declaration

     static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing
function.  This name is the unadorned name of the function.

 `__FUNCTION__' is another name for `__func__'.  Older versions of GCC
recognize only this name.  However, it is not standardized.  For
maximum portability, we recommend you use `__func__', but provide a
fallback definition with the preprocessor:

     #if __STDC_VERSION__ < 199901L
     # if __GNUC__ >= 2
     #  define __func__ __FUNCTION__
     # else
     #  define __func__ "<unknown>"
     # endif
     #endif

 In C, `__PRETTY_FUNCTION__' is yet another name for `__func__'.
However, in C++, `__PRETTY_FUNCTION__' contains the type signature of
the function as well as its bare name.  For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }

     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = void a::sub(int)

 These identifiers are not preprocessor macros.  In GCC 3.3 and
earlier, in C only, `__FUNCTION__' and `__PRETTY_FUNCTION__' were
treated as string literals; they could be used to initialize `char'
arrays, and they could be concatenated with other string literals.  GCC
3.4 and later treat them as variables, like `__func__'.  In C++,
`__FUNCTION__' and `__PRETTY_FUNCTION__' have always been variables.

File: gcc.info,  Node: Return Address,  Next: Vector Extensions,  Prev: Function Names,  Up: C Extensions

5.44 Getting the Return or Frame Address of a Function
======================================================

These functions may be used to get information about the callers of a
function.

 -- Built-in Function: void * __builtin_return_address (unsigned int
          LEVEL)
     This function returns the return address of the current function,
     or of one of its callers.  The LEVEL argument is number of frames
     to scan up the call stack.  A value of `0' yields the return
     address of the current function, a value of `1' yields the return
     address of the caller of the current function, and so forth.  When
     inlining the expected behavior is that the function will return
     the address of the function that will be returned to.  To work
     around this behavior use the `noinline' function attribute.

     The LEVEL argument must be a constant integer.

     On some machines it may be impossible to determine the return
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function will
     return `0' or a random value.  In addition,
     `__builtin_frame_address' may be used to determine if the top of
     the stack has been reached.

     This function should only be used with a nonzero argument for
     debugging purposes.

 -- Built-in Function: void * __builtin_frame_address (unsigned int
          LEVEL)
     This function is similar to `__builtin_return_address', but it
     returns the address of the function frame rather than the return
     address of the function.  Calling `__builtin_frame_address' with a
     value of `0' yields the frame address of the current function, a
     value of `1' yields the frame address of the caller of the current
     function, and so forth.

     The frame is the area on the stack which holds local variables and
     saved registers.  The frame address is normally the address of the
     first word pushed on to the stack by the function.  However, the
     exact definition depends upon the processor and the calling
     convention.  If the processor has a dedicated frame pointer
     register, and the function has a frame, then
     `__builtin_frame_address' will return the value of the frame
     pointer register.

     On some machines it may be impossible to determine the frame
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function will
     return `0' if the first frame pointer is properly initialized by
     the startup code.

     This function should only be used with a nonzero argument for
     debugging purposes.

File: gcc.info,  Node: Vector Extensions,  Next: Offsetof,  Prev: Return Address,  Up: C Extensions

5.45 Using vector instructions through built-in functions
=========================================================

On some targets, the instruction set contains SIMD vector instructions
that operate on multiple values contained in one large register at the
same time.  For example, on the i386 the MMX, 3Dnow! and SSE extensions
can be used this way.

 The first step in using these extensions is to provide the necessary
data types.  This should be done using an appropriate `typedef':

     typedef int v4si __attribute__ ((vector_size (16)));

 The `int' type specifies the base type, while the attribute specifies
the vector size for the variable, measured in bytes.  For example, the
declaration above causes the compiler to set the mode for the `v4si'
type to be 16 bytes wide and divided into `int' sized units.  For a
32-bit `int' this means a vector of 4 units of 4 bytes, and the
corresponding mode of `foo' will be V4SI.

 The `vector_size' attribute is only applicable to integral and float
scalars, although arrays, pointers, and function return values are
allowed in conjunction with this construct.

 All the basic integer types can be used as base types, both as signed
and as unsigned: `char', `short', `int', `long', `long long'.  In
addition, `float' and `double' can be used to build floating-point
vector types.

 Specifying a combination that is not valid for the current architecture
will cause GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type `V4SI' and your
architecture does not allow for this specific SIMD type, GCC will
produce code that uses 4 `SIs'.

 The types defined in this manner can be used with a subset of normal C
operations.  Currently, GCC will allow using the following operators on
these types: `+, -, *, /, unary minus, ^, |, &, ~'.

 The operations behave like C++ `valarrays'.  Addition is defined as
the addition of the corresponding elements of the operands.  For
example, in the code below, each of the 4 elements in A will be added
to the corresponding 4 elements in B and the resulting vector will be
stored in C.

     typedef int v4si __attribute__ ((vector_size (16)));

     v4si a, b, c;

     c = a + b;

 Subtraction, multiplication, division, and the logical operations
operate in a similar manner.  Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.

 You can declare variables and use them in function calls and returns,
as well as in assignments and some casts.  You can specify a vector
type as a return type for a function.  Vector types can also be used as
function arguments.  It is possible to cast from one vector type to
another, provided they are of the same size (in fact, you can also cast
vectors to and from other datatypes of the same size).

 You cannot operate between vectors of different lengths or different
signedness without a cast.

 A port that supports hardware vector operations, usually provides a set
of built-in functions that can be used to operate on vectors.  For
example, a function to add two vectors and multiply the result by a
third could look like this:

     v4si f (v4si a, v4si b, v4si c)
     {
       v4si tmp = __builtin_addv4si (a, b);
       return __builtin_mulv4si (tmp, c);
     }

File: gcc.info,  Node: Offsetof,  Next: Atomic Builtins,  Prev: Vector Extensions,  Up: C Extensions

5.46 Offsetof
=============

GCC implements for both C and C++ a syntactic extension to implement
the `offsetof' macro.

     primary:
             "__builtin_offsetof" "(" `typename' "," offsetof_member_designator ")"

     offsetof_member_designator:
               `identifier'
             | offsetof_member_designator "." `identifier'
             | offsetof_member_designator "[" `expr' "]"

 This extension is sufficient such that

     #define offsetof(TYPE, MEMBER)  __builtin_offsetof (TYPE, MEMBER)

 is a suitable definition of the `offsetof' macro.  In C++, TYPE may be
dependent.  In either case, MEMBER may consist of a single identifier,
or a sequence of member accesses and array references.

File: gcc.info,  Node: Atomic Builtins,  Next: Object Size Checking,  Prev: Offsetof,  Up: C Extensions

5.47 Built-in functions for atomic memory access
================================================

The following builtins are intended to be compatible with those
described in the `Intel Itanium Processor-specific Application Binary
Interface', section 7.4.  As such, they depart from the normal GCC
practice of using the "__builtin_" prefix, and further that they are
overloaded such that they work on multiple types.

 The definition given in the Intel documentation allows only for the
use of the types `int', `long', `long long' as well as their unsigned
counterparts.  GCC will allow any integral scalar or pointer type that
is 1, 2, 4 or 8 bytes in length.

 Not all operations are supported by all target processors.  If a
particular operation cannot be implemented on the target processor, a
warning will be generated and a call an external function will be
generated.  The external function will carry the same name as the
builtin, with an additional suffix `_N' where N is the size of the data
type.

 In most cases, these builtins are considered a "full barrier".  That
is, no memory operand will be moved across the operation, either
forward or backward.  Further, instructions will be issued as necessary
to prevent the processor from speculating loads across the operation
and from queuing stores after the operation.

 All of the routines are described in the Intel documentation to take
"an optional list of variables protected by the memory barrier".  It's
not clear what is meant by that; it could mean that _only_ the
following variables are protected, or it could mean that these variables
should in addition be protected.  At present GCC ignores this list and
protects all variables which are globally accessible.  If in the future
we make some use of this list, an empty list will continue to mean all
globally accessible variables.

`TYPE __sync_fetch_and_add (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_sub (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_or (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_and (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_xor (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_fetch_and_nand (TYPE *ptr, TYPE value, ...)'
     These builtins perform the operation suggested by the name, and
     returns the value that had previously been in memory.  That is,

          { tmp = *ptr; *ptr OP= value; return tmp; }
          { tmp = *ptr; *ptr = ~(tmp & value); return tmp; }   // nand

     _Note:_ GCC 4.4 and later implement `__sync_fetch_and_nand'
     builtin as `*ptr = ~(tmp & value)' instead of `*ptr = ~tmp &
     value'.

`TYPE __sync_add_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_sub_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_or_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_and_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_xor_and_fetch (TYPE *ptr, TYPE value, ...)'
`TYPE __sync_nand_and_fetch (TYPE *ptr, TYPE value, ...)'
     These builtins perform the operation suggested by the name, and
     return the new value.  That is,

          { *ptr OP= value; return *ptr; }
          { *ptr = ~(*ptr & value); return *ptr; }   // nand

     _Note:_ GCC 4.4 and later implement `__sync_nand_and_fetch'
     builtin as `*ptr = ~(*ptr & value)' instead of `*ptr = ~*ptr &
     value'.

`bool __sync_bool_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)'
`TYPE __sync_val_compare_and_swap (TYPE *ptr, TYPE oldval TYPE newval, ...)'
     These builtins perform an atomic compare and swap.  That is, if
     the current value of `*PTR' is OLDVAL, then write NEWVAL into
     `*PTR'.

     The "bool" version returns true if the comparison is successful and
     NEWVAL was written.  The "val" version returns the contents of
     `*PTR' before the operation.

`__sync_synchronize (...)'
     This builtin issues a full memory barrier.

`TYPE __sync_lock_test_and_set (TYPE *ptr, TYPE value, ...)'
     This builtin, as described by Intel, is not a traditional
     test-and-set operation, but rather an atomic exchange operation.
     It writes VALUE into `*PTR', and returns the previous contents of
     `*PTR'.

     Many targets have only minimal support for such locks, and do not
     support a full exchange operation.  In this case, a target may
     support reduced functionality here by which the _only_ valid value
     to store is the immediate constant 1.  The exact value actually
     stored in `*PTR' is implementation defined.

     This builtin is not a full barrier, but rather an "acquire
     barrier".  This means that references after the builtin cannot
     move to (or be speculated to) before the builtin, but previous
     memory stores may not be globally visible yet, and previous memory
     loads may not yet be satisfied.

`void __sync_lock_release (TYPE *ptr, ...)'
     This builtin releases the lock acquired by
     `__sync_lock_test_and_set'.  Normally this means writing the
     constant 0 to `*PTR'.

     This builtin is not a full barrier, but rather a "release barrier".
     This means that all previous memory stores are globally visible,
     and all previous memory loads have been satisfied, but following
     memory reads are not prevented from being speculated to before the
     barrier.

File: gcc.info,  Node: Object Size Checking,  Next: Other Builtins,  Prev: Atomic Builtins,  Up: C Extensions

5.48 Object Size Checking Builtins
==================================

GCC implements a limited buffer overflow protection mechanism that can
prevent some buffer overflow attacks.

 -- Built-in Function: size_t __builtin_object_size (void * PTR, int
          TYPE)
     is a built-in construct that returns a constant number of bytes
     from PTR to the end of the object PTR pointer points to (if known
     at compile time).  `__builtin_object_size' never evaluates its
     arguments for side-effects.  If there are any side-effects in
     them, it returns `(size_t) -1' for TYPE 0 or 1 and `(size_t) 0'
     for TYPE 2 or 3.  If there are multiple objects PTR can point to
     and all of them are known at compile time, the returned number is
     the maximum of remaining byte counts in those objects if TYPE & 2
     is 0 and minimum if nonzero.  If it is not possible to determine
     which objects PTR points to at compile time,
     `__builtin_object_size' should return `(size_t) -1' for TYPE 0 or
     1 and `(size_t) 0' for TYPE 2 or 3.

     TYPE is an integer constant from 0 to 3.  If the least significant
     bit is clear, objects are whole variables, if it is set, a closest
     surrounding subobject is considered the object a pointer points to.
     The second bit determines if maximum or minimum of remaining bytes
     is computed.

          struct V { char buf1[10]; int b; char buf2[10]; } var;
          char *p = &var.buf1[1], *q = &var.b;

          /* Here the object p points to is var.  */
          assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
          /* The subobject p points to is var.buf1.  */
          assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
          /* The object q points to is var.  */
          assert (__builtin_object_size (q, 0)
                  == (char *) (&var + 1) - (char *) &var.b);
          /* The subobject q points to is var.b.  */
          assert (__builtin_object_size (q, 1) == sizeof (var.b));

 There are built-in functions added for many common string operation
functions, e.g., for `memcpy' `__builtin___memcpy_chk' built-in is
provided.  This built-in has an additional last argument, which is the
number of bytes remaining in object the DEST argument points to or
`(size_t) -1' if the size is not known.

 The built-in functions are optimized into the normal string functions
like `memcpy' if the last argument is `(size_t) -1' or if it is known
at compile time that the destination object will not be overflown.  If
the compiler can determine at compile time the object will be always
overflown, it issues a warning.

 The intended use can be e.g.

     #undef memcpy
     #define bos0(dest) __builtin_object_size (dest, 0)
     #define memcpy(dest, src, n) \
       __builtin___memcpy_chk (dest, src, n, bos0 (dest))

     char *volatile p;
     char buf[10];
     /* It is unknown what object p points to, so this is optimized
        into plain memcpy - no checking is possible.  */
     memcpy (p, "abcde", n);
     /* Destination is known and length too.  It is known at compile
        time there will be no overflow.  */
     memcpy (&buf[5], "abcde", 5);
     /* Destination is known, but the length is not known at compile time.
        This will result in __memcpy_chk call that can check for overflow
        at runtime.  */
     memcpy (&buf[5], "abcde", n);
     /* Destination is known and it is known at compile time there will
        be overflow.  There will be a warning and __memcpy_chk call that
        will abort the program at runtime.  */
     memcpy (&buf[6], "abcde", 5);

 Such built-in functions are provided for `memcpy', `mempcpy',
`memmove', `memset', `strcpy', `stpcpy', `strncpy', `strcat' and
`strncat'.

 There are also checking built-in functions for formatted output
functions.
     int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
     int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                   const char *fmt, ...);
     int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
                                   va_list ap);
     int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                                    const char *fmt, va_list ap);

 The added FLAG argument is passed unchanged to `__sprintf_chk' etc.
functions and can contain implementation specific flags on what
additional security measures the checking function might take, such as
handling `%n' differently.

 The OS argument is the object size S points to, like in the other
built-in functions.  There is a small difference in the behavior
though, if OS is `(size_t) -1', the built-in functions are optimized
into the non-checking functions only if FLAG is 0, otherwise the
checking function is called with OS argument set to `(size_t) -1'.

 In addition to this, there are checking built-in functions
`__builtin___printf_chk', `__builtin___vprintf_chk',
`__builtin___fprintf_chk' and `__builtin___vfprintf_chk'.  These have
just one additional argument, FLAG, right before format string FMT.  If
the compiler is able to optimize them to `fputc' etc. functions, it
will, otherwise the checking function should be called and the FLAG
argument passed to it.

File: gcc.info,  Node: Other Builtins,  Next: Target Builtins,  Prev: Object Size Checking,  Up: C Extensions

5.49 Other built-in functions provided by GCC
=============================================

GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and will not be
documented here because they may change from time to time; we do not
recommend general use of these functions.

 The remaining functions are provided for optimization purposes.

 GCC includes built-in versions of many of the functions in the standard
C library.  The versions prefixed with `__builtin_' will always be
treated as having the same meaning as the C library function even if you
specify the `-fno-builtin' option.  (*note C Dialect Options::) Many of
these functions are only optimized in certain cases; if they are not
optimized in a particular case, a call to the library function will be
emitted.

 Outside strict ISO C mode (`-ansi', `-std=c89' or `-std=c99'), the
functions `_exit', `alloca', `bcmp', `bzero', `dcgettext', `dgettext',
`dremf', `dreml', `drem', `exp10f', `exp10l', `exp10', `ffsll', `ffsl',
`ffs', `fprintf_unlocked', `fputs_unlocked', `gammaf', `gammal',
`gamma', `gammaf_r', `gammal_r', `gamma_r', `gettext', `index',
`isascii', `j0f', `j0l', `j0', `j1f', `j1l', `j1', `jnf', `jnl', `jn',
`lgammaf_r', `lgammal_r', `lgamma_r', `mempcpy', `pow10f', `pow10l',
`pow10', `printf_unlocked', `rindex', `scalbf', `scalbl', `scalb',
`signbit', `signbitf', `signbitl', `signbitd32', `signbitd64',
`signbitd128', `significandf', `significandl', `significand', `sincosf',
`sincosl', `sincos', `stpcpy', `stpncpy', `strcasecmp', `strdup',
`strfmon', `strncasecmp', `strndup', `toascii', `y0f', `y0l', `y0',
`y1f', `y1l', `y1', `ynf', `ynl' and `yn' may be handled as built-in
functions.  All these functions have corresponding versions prefixed
with `__builtin_', which may be used even in strict C89 mode.

 The ISO C99 functions `_Exit', `acoshf', `acoshl', `acosh', `asinhf',
`asinhl', `asinh', `atanhf', `atanhl', `atanh', `cabsf', `cabsl',
`cabs', `cacosf', `cacoshf', `cacoshl', `cacosh', `cacosl', `cacos',
`cargf', `cargl', `carg', `casinf', `casinhf', `casinhl', `casinh',
`casinl', `casin', `catanf', `catanhf', `catanhl', `catanh', `catanl',
`catan', `cbrtf', `cbrtl', `cbrt', `ccosf', `ccoshf', `ccoshl',
`ccosh', `ccosl', `ccos', `cexpf', `cexpl', `cexp', `cimagf', `cimagl',
`cimag', `clogf', `clogl', `clog', `conjf', `conjl', `conj',
`copysignf', `copysignl', `copysign', `cpowf', `cpowl', `cpow',
`cprojf', `cprojl', `cproj', `crealf', `creall', `creal', `csinf',
`csinhf', `csinhl', `csinh', `csinl', `csin', `csqrtf', `csqrtl',
`csqrt', `ctanf', `ctanhf', `ctanhl', `ctanh', `ctanl', `ctan',
`erfcf', `erfcl', `erfc', `erff', `erfl', `erf', `exp2f', `exp2l',
`exp2', `expm1f', `expm1l', `expm1', `fdimf', `fdiml', `fdim', `fmaf',
`fmal', `fmaxf', `fmaxl', `fmax', `fma', `fminf', `fminl', `fmin',
`hypotf', `hypotl', `hypot', `ilogbf', `ilogbl', `ilogb', `imaxabs',
`isblank', `iswblank', `lgammaf', `lgammal', `lgamma', `llabs',
`llrintf', `llrintl', `llrint', `llroundf', `llroundl', `llround',
`log1pf', `log1pl', `log1p', `log2f', `log2l', `log2', `logbf',
`logbl', `logb', `lrintf', `lrintl', `lrint', `lroundf', `lroundl',
`lround', `nearbyintf', `nearbyintl', `nearbyint', `nextafterf',
`nextafterl', `nextafter', `nexttowardf', `nexttowardl', `nexttoward',
`remainderf', `remainderl', `remainder', `remquof', `remquol',
`remquo', `rintf', `rintl', `rint', `roundf', `roundl', `round',
`scalblnf', `scalblnl', `scalbln', `scalbnf', `scalbnl', `scalbn',
`snprintf', `tgammaf', `tgammal', `tgamma', `truncf', `truncl', `trunc',
`vfscanf', `vscanf', `vsnprintf' and `vsscanf' are handled as built-in
functions except in strict ISO C90 mode (`-ansi' or `-std=c89').

 There are also built-in versions of the ISO C99 functions `acosf',
`acosl', `asinf', `asinl', `atan2f', `atan2l', `atanf', `atanl',
`ceilf', `ceill', `cosf', `coshf', `coshl', `cosl', `expf', `expl',
`fabsf', `fabsl', `floorf', `floorl', `fmodf', `fmodl', `frexpf',
`frexpl', `ldexpf', `ldexpl', `log10f', `log10l', `logf', `logl',
`modfl', `modf', `powf', `powl', `sinf', `sinhf', `sinhl', `sinl',
`sqrtf', `sqrtl', `tanf', `tanhf', `tanhl' and `tanl' that are
recognized in any mode since ISO C90 reserves these names for the
purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with `__builtin_'.

 The ISO C94 functions `iswalnum', `iswalpha', `iswcntrl', `iswdigit',
`iswgraph', `iswlower', `iswprint', `iswpunct', `iswspace', `iswupper',
`iswxdigit', `towlower' and `towupper' are handled as built-in functions
except in strict ISO C90 mode (`-ansi' or `-std=c89').

 The ISO C90 functions `abort', `abs', `acos', `asin', `atan2', `atan',
`calloc', `ceil', `cosh', `cos', `exit', `exp', `fabs', `floor', `fmod',
`fprintf', `fputs', `frexp', `fscanf', `isalnum', `isalpha', `iscntrl',
`isdigit', `isgraph', `islower', `isprint', `ispunct', `isspace',
`isupper', `isxdigit', `tolower', `toupper', `labs', `ldexp', `log10',
`log', `malloc', `memchr', `memcmp', `memcpy', `memset', `modf', `pow',
`printf', `putchar', `puts', `scanf', `sinh', `sin', `snprintf',
`sprintf', `sqrt', `sscanf', `strcat', `strchr', `strcmp', `strcpy',
`strcspn', `strlen', `strncat', `strncmp', `strncpy', `strpbrk',
`strrchr', `strspn', `strstr', `tanh', `tan', `vfprintf', `vprintf' and
`vsprintf' are all recognized as built-in functions unless
`-fno-builtin' is specified (or `-fno-builtin-FUNCTION' is specified
for an individual function).  All of these functions have corresponding
versions prefixed with `__builtin_'.

 GCC provides built-in versions of the ISO C99 floating point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( `isgreater', `isgreaterequal',
`isless', `islessequal', `islessgreater', and `isunordered') , with
`__builtin_' prefixed.  We intend for a library implementor to be able
to simply `#define' each standard macro to its built-in equivalent.  In
the same fashion, GCC provides `fpclassify', `isfinite', `isinf_sign'
and `isnormal' built-ins used with `__builtin_' prefixed.  The `isinf'
and `isnan' builtins appear both with and without the `__builtin_'
prefix.

 -- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)
     You can use the built-in function `__builtin_types_compatible_p' to
     determine whether two types are the same.

     This built-in function returns 1 if the unqualified versions of the
     types TYPE1 and TYPE2 (which are types, not expressions) are
     compatible, 0 otherwise.  The result of this built-in function can
     be used in integer constant expressions.

     This built-in function ignores top level qualifiers (e.g., `const',
     `volatile').  For example, `int' is equivalent to `const int'.

     The type `int[]' and `int[5]' are compatible.  On the other hand,
     `int' and `char *' are not compatible, even if the size of their
     types, on the particular architecture are the same.  Also, the
     amount of pointer indirection is taken into account when
     determining similarity.  Consequently, `short *' is not similar to
     `short **'.  Furthermore, two types that are typedefed are
     considered compatible if their underlying types are compatible.

     An `enum' type is not considered to be compatible with another
     `enum' type even if both are compatible with the same integer
     type; this is what the C standard specifies.  For example, `enum
     {foo, bar}' is not similar to `enum {hot, dog}'.

     You would typically use this function in code whose execution
     varies depending on the arguments' types.  For example:

          #define foo(x)                                                  \
            ({                                                           \
              typeof (x) tmp = (x);                                       \
              if (__builtin_types_compatible_p (typeof (x), long double)) \
                tmp = foo_long_double (tmp);                              \
              else if (__builtin_types_compatible_p (typeof (x), double)) \
                tmp = foo_double (tmp);                                   \
              else if (__builtin_types_compatible_p (typeof (x), float))  \
                tmp = foo_float (tmp);                                    \
              else                                                        \
                abort ();                                                 \
              tmp;                                                        \
            })

     _Note:_ This construct is only available for C.


 -- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1,
          EXP2)
     You can use the built-in function `__builtin_choose_expr' to
     evaluate code depending on the value of a constant expression.
     This built-in function returns EXP1 if CONST_EXP, which is a
     constant expression that must be able to be determined at compile
     time, is nonzero.  Otherwise it returns 0.

     This built-in function is analogous to the `? :' operator in C,
     except that the expression returned has its type unaltered by
     promotion rules.  Also, the built-in function does not evaluate
     the expression that was not chosen.  For example, if CONST_EXP
     evaluates to true, EXP2 is not evaluated even if it has
     side-effects.

     This built-in function can return an lvalue if the chosen argument
     is an lvalue.

     If EXP1 is returned, the return type is the same as EXP1's type.
     Similarly, if EXP2 is returned, its return type is the same as
     EXP2.

     Example:

          #define foo(x)                                                    \
            __builtin_choose_expr (                                         \
              __builtin_types_compatible_p (typeof (x), double),            \
              foo_double (x),                                               \
              __builtin_choose_expr (                                       \
                __builtin_types_compatible_p (typeof (x), float),           \
                foo_float (x),                                              \
                /* The void expression results in a compile-time error  \
                   when assigning the result to something.  */          \
                (void)0))

     _Note:_ This construct is only available for C.  Furthermore, the
     unused expression (EXP1 or EXP2 depending on the value of
     CONST_EXP) may still generate syntax errors.  This may change in
     future revisions.


 -- Built-in Function: int __builtin_constant_p (EXP)
     You can use the built-in function `__builtin_constant_p' to
     determine if a value is known to be constant at compile-time and
     hence that GCC can perform constant-folding on expressions
     involving that value.  The argument of the function is the value
     to test.  The function returns the integer 1 if the argument is
     known to be a compile-time constant and 0 if it is not known to be
     a compile-time constant.  A return of 0 does not indicate that the
     value is _not_ a constant, but merely that GCC cannot prove it is
     a constant with the specified value of the `-O' option.

     You would typically use this function in an embedded application
     where memory was a critical resource.  If you have some complex
     calculation, you may want it to be folded if it involves
     constants, but need to call a function if it does not.  For
     example:

          #define Scale_Value(X)      \
            (__builtin_constant_p (X) \
            ? ((X) * SCALE + OFFSET) : Scale (X))

     You may use this built-in function in either a macro or an inline
     function.  However, if you use it in an inlined function and pass
     an argument of the function as the argument to the built-in, GCC
     will never return 1 when you call the inline function with a
     string constant or compound literal (*note Compound Literals::)
     and will not return 1 when you pass a constant numeric value to
     the inline function unless you specify the `-O' option.

     You may also use `__builtin_constant_p' in initializers for static
     data.  For instance, you can write

          static const int table[] = {
             __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
             /* ... */
          };

     This is an acceptable initializer even if EXPRESSION is not a
     constant expression.  GCC must be more conservative about
     evaluating the built-in in this case, because it has no
     opportunity to perform optimization.

     Previous versions of GCC did not accept this built-in in data
     initializers.  The earliest version where it is completely safe is
     3.0.1.

 -- Built-in Function: long __builtin_expect (long EXP, long C)
     You may use `__builtin_expect' to provide the compiler with branch
     prediction information.  In general, you should prefer to use
     actual profile feedback for this (`-fprofile-arcs'), as
     programmers are notoriously bad at predicting how their programs
     actually perform.  However, there are applications in which this
     data is hard to collect.

     The return value is the value of EXP, which should be an integral
     expression.  The semantics of the built-in are that it is expected
     that EXP == C.  For example:

          if (__builtin_expect (x, 0))
            foo ();

     would indicate that we do not expect to call `foo', since we
     expect `x' to be zero.  Since you are limited to integral
     expressions for EXP, you should use constructions such as

          if (__builtin_expect (ptr != NULL, 1))
            error ();

     when testing pointer or floating-point values.

 -- Built-in Function: void __builtin_trap (void)
     This function causes the program to exit abnormally.  GCC
     implements this function by using a target-dependent mechanism
     (such as intentionally executing an illegal instruction) or by
     calling `abort'.  The mechanism used may vary from release to
     release so you should not rely on any particular implementation.

 -- Built-in Function: void __builtin_unreachable (void)
     If control flow reaches the point of the `__builtin_unreachable',
     the program is undefined.  It is useful in situations where the
     compiler cannot deduce the unreachability of the code.

     One such case is immediately following an `asm' statement that
     will either never terminate, or one that transfers control
     elsewhere and never returns.  In this example, without the
     `__builtin_unreachable', GCC would issue a warning that control
     reaches the end of a non-void function.  It would also generate
     code to return after the `asm'.

          int f (int c, int v)
          {
            if (c)
              {
                return v;
              }
            else
              {
                asm("jmp error_handler");
                __builtin_unreachable ();
              }
          }

     Because the `asm' statement unconditionally transfers control out
     of the function, control will never reach the end of the function
     body.  The `__builtin_unreachable' is in fact unreachable and
     communicates this fact to the compiler.

     Another use for `__builtin_unreachable' is following a call a
     function that never returns but that is not declared
     `__attribute__((noreturn))', as in this example:

          void function_that_never_returns (void);

          int g (int c)
          {
            if (c)
              {
                return 1;
              }
            else
              {
                function_that_never_returns ();
                __builtin_unreachable ();
              }
          }


 -- Built-in Function: void __builtin___clear_cache (char *BEGIN, char
          *END)
     This function is used to flush the processor's instruction cache
     for the region of memory between BEGIN inclusive and END
     exclusive.  Some targets require that the instruction cache be
     flushed, after modifying memory containing code, in order to obtain
     deterministic behavior.

     If the target does not require instruction cache flushes,
     `__builtin___clear_cache' has no effect.  Otherwise either
     instructions are emitted in-line to clear the instruction cache or
     a call to the `__clear_cache' function in libgcc is made.

 -- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
     This function is used to minimize cache-miss latency by moving
     data into a cache before it is accessed.  You can insert calls to
     `__builtin_prefetch' into code for which you know addresses of
     data in memory that is likely to be accessed soon.  If the target
     supports them, data prefetch instructions will be generated.  If
     the prefetch is done early enough before the access then the data
     will be in the cache by the time it is accessed.

     The value of ADDR is the address of the memory to prefetch.  There
     are two optional arguments, RW and LOCALITY.  The value of RW is a
     compile-time constant one or zero; one means that the prefetch is
     preparing for a write to the memory address and zero, the default,
     means that the prefetch is preparing for a read.  The value
     LOCALITY must be a compile-time constant integer between zero and
     three.  A value of zero means that the data has no temporal
     locality, so it need not be left in the cache after the access.  A
     value of three means that the data has a high degree of temporal
     locality and should be left in all levels of cache possible.
     Values of one and two mean, respectively, a low or moderate degree
     of temporal locality.  The default is three.

          for (i = 0; i < n; i++)
            {
              a[i] = a[i] + b[i];
              __builtin_prefetch (&a[i+j], 1, 1);
              __builtin_prefetch (&b[i+j], 0, 1);
              /* ... */
            }

     Data prefetch does not generate faults if ADDR is invalid, but the
     address expression itself must be valid.  For example, a prefetch
     of `p->next' will not fault if `p->next' is not a valid address,
     but evaluation will fault if `p' is not a valid address.

     If the target does not support data prefetch, the address
     expression is evaluated if it includes side effects but no other
     code is generated and GCC does not issue a warning.

 -- Built-in Function: double __builtin_huge_val (void)
     Returns a positive infinity, if supported by the floating-point
     format, else `DBL_MAX'.  This function is suitable for
     implementing the ISO C macro `HUGE_VAL'.

 -- Built-in Function: float __builtin_huge_valf (void)
     Similar to `__builtin_huge_val', except the return type is `float'.

 -- Built-in Function: long double __builtin_huge_vall (void)
     Similar to `__builtin_huge_val', except the return type is `long
     double'.

 -- Built-in Function: int __builtin_fpclassify (int, int, int, int,
          int, ...)
     This built-in implements the C99 fpclassify functionality.  The
     first five int arguments should be the target library's notion of
     the possible FP classes and are used for return values.  They must
     be constant values and they must appear in this order: `FP_NAN',
     `FP_INFINITE', `FP_NORMAL', `FP_SUBNORMAL' and `FP_ZERO'.  The
     ellipsis is for exactly one floating point value to classify.  GCC
     treats the last argument as type-generic, which means it does not
     do default promotion from float to double.

 -- Built-in Function: double __builtin_inf (void)
     Similar to `__builtin_huge_val', except a warning is generated if
     the target floating-point format does not support infinities.

 -- Built-in Function: _Decimal32 __builtin_infd32 (void)
     Similar to `__builtin_inf', except the return type is `_Decimal32'.

 -- Built-in Function: _Decimal64 __builtin_infd64 (void)
     Similar to `__builtin_inf', except the return type is `_Decimal64'.

 -- Built-in Function: _Decimal128 __builtin_infd128 (void)
     Similar to `__builtin_inf', except the return type is
     `_Decimal128'.

 -- Built-in Function: float __builtin_inff (void)
     Similar to `__builtin_inf', except the return type is `float'.
     This function is suitable for implementing the ISO C99 macro
     `INFINITY'.

 -- Built-in Function: long double __builtin_infl (void)
     Similar to `__builtin_inf', except the return type is `long
     double'.

 -- Built-in Function: int __builtin_isinf_sign (...)
     Similar to `isinf', except the return value will be negative for
     an argument of `-Inf'.  Note while the parameter list is an
     ellipsis, this function only accepts exactly one floating point
     argument.  GCC treats this parameter as type-generic, which means
     it does not do default promotion from float to double.

 -- Built-in Function: double __builtin_nan (const char *str)
     This is an implementation of the ISO C99 function `nan'.

     Since ISO C99 defines this function in terms of `strtod', which we
     do not implement, a description of the parsing is in order.  The
     string is parsed as by `strtol'; that is, the base is recognized by
     leading `0' or `0x' prefixes.  The number parsed is placed in the
     significand such that the least significant bit of the number is
     at the least significant bit of the significand.  The number is
     truncated to fit the significand field provided.  The significand
     is forced to be a quiet NaN.

     This function, if given a string literal all of which would have
     been consumed by strtol, is evaluated early enough that it is
     considered a compile-time constant.

 -- Built-in Function: _Decimal32 __builtin_nand32 (const char *str)
     Similar to `__builtin_nan', except the return type is `_Decimal32'.

 -- Built-in Function: _Decimal64 __builtin_nand64 (const char *str)
     Similar to `__builtin_nan', except the return type is `_Decimal64'.

 -- Built-in Function: _Decimal128 __builtin_nand128 (const char *str)
     Similar to `__builtin_nan', except the return type is
     `_Decimal128'.

 -- Built-in Function: float __builtin_nanf (const char *str)
     Similar to `__builtin_nan', except the return type is `float'.

 -- Built-in Function: long double __builtin_nanl (const char *str)
     Similar to `__builtin_nan', except the return type is `long
     double'.

 -- Built-in Function: double __builtin_nans (const char *str)
     Similar to `__builtin_nan', except the significand is forced to be
     a signaling NaN.  The `nans' function is proposed by WG14 N965.

 -- Built-in Function: float __builtin_nansf (const char *str)
     Similar to `__builtin_nans', except the return type is `float'.

 -- Built-in Function: long double __builtin_nansl (const char *str)
     Similar to `__builtin_nans', except the return type is `long
     double'.

 -- Built-in Function: int __builtin_ffs (unsigned int x)
     Returns one plus the index of the least significant 1-bit of X, or
     if X is zero, returns zero.

 -- Built-in Function: int __builtin_clz (unsigned int x)
     Returns the number of leading 0-bits in X, starting at the most
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_ctz (unsigned int x)
     Returns the number of trailing 0-bits in X, starting at the least
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_popcount (unsigned int x)
     Returns the number of 1-bits in X.

 -- Built-in Function: int __builtin_parity (unsigned int x)
     Returns the parity of X, i.e. the number of 1-bits in X modulo 2.

 -- Built-in Function: int __builtin_ffsl (unsigned long)
     Similar to `__builtin_ffs', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_clzl (unsigned long)
     Similar to `__builtin_clz', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_ctzl (unsigned long)
     Similar to `__builtin_ctz', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_popcountl (unsigned long)
     Similar to `__builtin_popcount', except the argument type is
     `unsigned long'.

 -- Built-in Function: int __builtin_parityl (unsigned long)
     Similar to `__builtin_parity', except the argument type is
     `unsigned long'.

 -- Built-in Function: int __builtin_ffsll (unsigned long long)
     Similar to `__builtin_ffs', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_clzll (unsigned long long)
     Similar to `__builtin_clz', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_ctzll (unsigned long long)
     Similar to `__builtin_ctz', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_popcountll (unsigned long long)
     Similar to `__builtin_popcount', except the argument type is
     `unsigned long long'.

 -- Built-in Function: int __builtin_parityll (unsigned long long)
     Similar to `__builtin_parity', except the argument type is
     `unsigned long long'.

 -- Built-in Function: double __builtin_powi (double, int)
     Returns the first argument raised to the power of the second.
     Unlike the `pow' function no guarantees about precision and
     rounding are made.

 -- Built-in Function: float __builtin_powif (float, int)
     Similar to `__builtin_powi', except the argument and return types
     are `float'.

 -- Built-in Function: long double __builtin_powil (long double, int)
     Similar to `__builtin_powi', except the argument and return types
     are `long double'.

 -- Built-in Function: int32_t __builtin_bswap32 (int32_t x)
     Returns X with the order of the bytes reversed; for example,
     `0xaabbccdd' becomes `0xddccbbaa'.  Byte here always means exactly
     8 bits.

 -- Built-in Function: int64_t __builtin_bswap64 (int64_t x)
     Similar to `__builtin_bswap32', except the argument and return
     types are 64-bit.

File: gcc.info,  Node: Target Builtins,  Next: Target Format Checks,  Prev: Other Builtins,  Up: C Extensions

5.50 Built-in Functions Specific to Particular Target Machines
==============================================================

On some target machines, GCC supports many built-in functions specific
to those machines.  Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.

* Menu:

* Alpha Built-in Functions::
* ARM iWMMXt Built-in Functions::
* ARM NEON Intrinsics::
* Blackfin Built-in Functions::
* FR-V Built-in Functions::
* X86 Built-in Functions::
* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* MIPS Loongson Built-in Functions::
* Other MIPS Built-in Functions::
* picoChip Built-in Functions::
* PowerPC AltiVec/VSX Built-in Functions::
* SPARC VIS Built-in Functions::
* SPU Built-in Functions::

File: gcc.info,  Node: Alpha Built-in Functions,  Next: ARM iWMMXt Built-in Functions,  Up: Target Builtins

5.50.1 Alpha Built-in Functions
-------------------------------

These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.

 The following built-in functions are always available.  They all
generate the machine instruction that is part of the name.

     long __builtin_alpha_implver (void)
     long __builtin_alpha_rpcc (void)
     long __builtin_alpha_amask (long)
     long __builtin_alpha_cmpbge (long, long)
     long __builtin_alpha_extbl (long, long)
     long __builtin_alpha_extwl (long, long)
     long __builtin_alpha_extll (long, long)
     long __builtin_alpha_extql (long, long)
     long __builtin_alpha_extwh (long, long)
     long __builtin_alpha_extlh (long, long)
     long __builtin_alpha_extqh (long, long)
     long __builtin_alpha_insbl (long, long)
     long __builtin_alpha_inswl (long, long)
     long __builtin_alpha_insll (long, long)
     long __builtin_alpha_insql (long, long)
     long __builtin_alpha_inswh (long, long)
     long __builtin_alpha_inslh (long, long)
     long __builtin_alpha_insqh (long, long)
     long __builtin_alpha_mskbl (long, long)
     long __builtin_alpha_mskwl (long, long)
     long __builtin_alpha_mskll (long, long)
     long __builtin_alpha_mskql (long, long)
     long __builtin_alpha_mskwh (long, long)
     long __builtin_alpha_msklh (long, long)
     long __builtin_alpha_mskqh (long, long)
     long __builtin_alpha_umulh (long, long)
     long __builtin_alpha_zap (long, long)
     long __builtin_alpha_zapnot (long, long)

 The following built-in functions are always with `-mmax' or
`-mcpu=CPU' where CPU is `pca56' or later.  They all generate the
machine instruction that is part of the name.

     long __builtin_alpha_pklb (long)
     long __builtin_alpha_pkwb (long)
     long __builtin_alpha_unpkbl (long)
     long __builtin_alpha_unpkbw (long)
     long __builtin_alpha_minub8 (long, long)
     long __builtin_alpha_minsb8 (long, long)
     long __builtin_alpha_minuw4 (long, long)
     long __builtin_alpha_minsw4 (long, long)
     long __builtin_alpha_maxub8 (long, long)
     long __builtin_alpha_maxsb8 (long, long)
     long __builtin_alpha_maxuw4 (long, long)
     long __builtin_alpha_maxsw4 (long, long)
     long __builtin_alpha_perr (long, long)

 The following built-in functions are always with `-mcix' or
`-mcpu=CPU' where CPU is `ev67' or later.  They all generate the
machine instruction that is part of the name.

     long __builtin_alpha_cttz (long)
     long __builtin_alpha_ctlz (long)
     long __builtin_alpha_ctpop (long)

 The following builtins are available on systems that use the OSF/1
PALcode.  Normally they invoke the `rduniq' and `wruniq' PAL calls, but
when invoked with `-mtls-kernel', they invoke `rdval' and `wrval'.

     void *__builtin_thread_pointer (void)
     void __builtin_set_thread_pointer (void *)

File: gcc.info,  Node: ARM iWMMXt Built-in Functions,  Next: ARM NEON Intrinsics,  Prev: Alpha Built-in Functions,  Up: Target Builtins

5.50.2 ARM iWMMXt Built-in Functions
------------------------------------

These built-in functions are available for the ARM family of processors
when the `-mcpu=iwmmxt' switch is used:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef char v8qi __attribute__ ((vector_size (8)));

     int __builtin_arm_getwcx (int)
     void __builtin_arm_setwcx (int, int)
     int __builtin_arm_textrmsb (v8qi, int)
     int __builtin_arm_textrmsh (v4hi, int)
     int __builtin_arm_textrmsw (v2si, int)
     int __builtin_arm_textrmub (v8qi, int)
     int __builtin_arm_textrmuh (v4hi, int)
     int __builtin_arm_textrmuw (v2si, int)
     v8qi __builtin_arm_tinsrb (v8qi, int)
     v4hi __builtin_arm_tinsrh (v4hi, int)
     v2si __builtin_arm_tinsrw (v2si, int)
     long long __builtin_arm_tmia (long long, int, int)
     long long __builtin_arm_tmiabb (long long, int, int)
     long long __builtin_arm_tmiabt (long long, int, int)
     long long __builtin_arm_tmiaph (long long, int, int)
     long long __builtin_arm_tmiatb (long long, int, int)
     long long __builtin_arm_tmiatt (long long, int, int)
     int __builtin_arm_tmovmskb (v8qi)
     int __builtin_arm_tmovmskh (v4hi)
     int __builtin_arm_tmovmskw (v2si)
     long long __builtin_arm_waccb (v8qi)
     long long __builtin_arm_wacch (v4hi)
     long long __builtin_arm_waccw (v2si)
     v8qi __builtin_arm_waddb (v8qi, v8qi)
     v8qi __builtin_arm_waddbss (v8qi, v8qi)
     v8qi __builtin_arm_waddbus (v8qi, v8qi)
     v4hi __builtin_arm_waddh (v4hi, v4hi)
     v4hi __builtin_arm_waddhss (v4hi, v4hi)
     v4hi __builtin_arm_waddhus (v4hi, v4hi)
     v2si __builtin_arm_waddw (v2si, v2si)
     v2si __builtin_arm_waddwss (v2si, v2si)
     v2si __builtin_arm_waddwus (v2si, v2si)
     v8qi __builtin_arm_walign (v8qi, v8qi, int)
     long long __builtin_arm_wand(long long, long long)
     long long __builtin_arm_wandn (long long, long long)
     v8qi __builtin_arm_wavg2b (v8qi, v8qi)
     v8qi __builtin_arm_wavg2br (v8qi, v8qi)
     v4hi __builtin_arm_wavg2h (v4hi, v4hi)
     v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
     v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
     v2si __builtin_arm_wcmpeqw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtsw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtuw (v2si, v2si)
     long long __builtin_arm_wmacs (long long, v4hi, v4hi)
     long long __builtin_arm_wmacsz (v4hi, v4hi)
     long long __builtin_arm_wmacu (long long, v4hi, v4hi)
     long long __builtin_arm_wmacuz (v4hi, v4hi)
     v4hi __builtin_arm_wmadds (v4hi, v4hi)
     v4hi __builtin_arm_wmaddu (v4hi, v4hi)
     v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
     v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
     v2si __builtin_arm_wmaxsw (v2si, v2si)
     v8qi __builtin_arm_wmaxub (v8qi, v8qi)
     v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
     v2si __builtin_arm_wmaxuw (v2si, v2si)
     v8qi __builtin_arm_wminsb (v8qi, v8qi)
     v4hi __builtin_arm_wminsh (v4hi, v4hi)
     v2si __builtin_arm_wminsw (v2si, v2si)
     v8qi __builtin_arm_wminub (v8qi, v8qi)
     v4hi __builtin_arm_wminuh (v4hi, v4hi)
     v2si __builtin_arm_wminuw (v2si, v2si)
     v4hi __builtin_arm_wmulsm (v4hi, v4hi)
     v4hi __builtin_arm_wmulul (v4hi, v4hi)
     v4hi __builtin_arm_wmulum (v4hi, v4hi)
     long long __builtin_arm_wor (long long, long long)
     v2si __builtin_arm_wpackdss (long long, long long)
     v2si __builtin_arm_wpackdus (long long, long long)
     v8qi __builtin_arm_wpackhss (v4hi, v4hi)
     v8qi __builtin_arm_wpackhus (v4hi, v4hi)
     v4hi __builtin_arm_wpackwss (v2si, v2si)
     v4hi __builtin_arm_wpackwus (v2si, v2si)
     long long __builtin_arm_wrord (long long, long long)
     long long __builtin_arm_wrordi (long long, int)
     v4hi __builtin_arm_wrorh (v4hi, long long)
     v4hi __builtin_arm_wrorhi (v4hi, int)
     v2si __builtin_arm_wrorw (v2si, long long)
     v2si __builtin_arm_wrorwi (v2si, int)
     v2si __builtin_arm_wsadb (v8qi, v8qi)
     v2si __builtin_arm_wsadbz (v8qi, v8qi)
     v2si __builtin_arm_wsadh (v4hi, v4hi)
     v2si __builtin_arm_wsadhz (v4hi, v4hi)
     v4hi __builtin_arm_wshufh (v4hi, int)
     long long __builtin_arm_wslld (long long, long long)
     long long __builtin_arm_wslldi (long long, int)
     v4hi __builtin_arm_wsllh (v4hi, long long)
     v4hi __builtin_arm_wsllhi (v4hi, int)
     v2si __builtin_arm_wsllw (v2si, long long)
     v2si __builtin_arm_wsllwi (v2si, int)
     long long __builtin_arm_wsrad (long long, long long)
     long long __builtin_arm_wsradi (long long, int)
     v4hi __builtin_arm_wsrah (v4hi, long long)
     v4hi __builtin_arm_wsrahi (v4hi, int)
     v2si __builtin_arm_wsraw (v2si, long long)
     v2si __builtin_arm_wsrawi (v2si, int)
     long long __builtin_arm_wsrld (long long, long long)
     long long __builtin_arm_wsrldi (long long, int)
     v4hi __builtin_arm_wsrlh (v4hi, long long)
     v4hi __builtin_arm_wsrlhi (v4hi, int)
     v2si __builtin_arm_wsrlw (v2si, long long)
     v2si __builtin_arm_wsrlwi (v2si, int)
     v8qi __builtin_arm_wsubb (v8qi, v8qi)
     v8qi __builtin_arm_wsubbss (v8qi, v8qi)
     v8qi __builtin_arm_wsubbus (v8qi, v8qi)
     v4hi __builtin_arm_wsubh (v4hi, v4hi)
     v4hi __builtin_arm_wsubhss (v4hi, v4hi)
     v4hi __builtin_arm_wsubhus (v4hi, v4hi)
     v2si __builtin_arm_wsubw (v2si, v2si)
     v2si __builtin_arm_wsubwss (v2si, v2si)
     v2si __builtin_arm_wsubwus (v2si, v2si)
     v4hi __builtin_arm_wunpckehsb (v8qi)
     v2si __builtin_arm_wunpckehsh (v4hi)
     long long __builtin_arm_wunpckehsw (v2si)
     v4hi __builtin_arm_wunpckehub (v8qi)
     v2si __builtin_arm_wunpckehuh (v4hi)
     long long __builtin_arm_wunpckehuw (v2si)
     v4hi __builtin_arm_wunpckelsb (v8qi)
     v2si __builtin_arm_wunpckelsh (v4hi)
     long long __builtin_arm_wunpckelsw (v2si)
     v4hi __builtin_arm_wunpckelub (v8qi)
     v2si __builtin_arm_wunpckeluh (v4hi)
     long long __builtin_arm_wunpckeluw (v2si)
     v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
     v2si __builtin_arm_wunpckihw (v2si, v2si)
     v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
     v2si __builtin_arm_wunpckilw (v2si, v2si)
     long long __builtin_arm_wxor (long long, long long)
     long long __builtin_arm_wzero ()

File: gcc.info,  Node: ARM NEON Intrinsics,  Next: Blackfin Built-in Functions,  Prev: ARM iWMMXt Built-in Functions,  Up: Target Builtins

5.50.3 ARM NEON Intrinsics
--------------------------

These built-in intrinsics for the ARM Advanced SIMD extension are
available when the `-mfpu=neon' switch is used:

5.50.3.1 Addition
.................

   * uint32x2_t vadd_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vadd.i32 D0, D0, D0'

   * uint16x4_t vadd_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vadd.i16 D0, D0, D0'

   * uint8x8_t vadd_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vadd.i8 D0, D0, D0'

   * int32x2_t vadd_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vadd.i32 D0, D0, D0'

   * int16x4_t vadd_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vadd.i16 D0, D0, D0'

   * int8x8_t vadd_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vadd.i8 D0, D0, D0'

   * uint64x1_t vadd_u64 (uint64x1_t, uint64x1_t)
     _Form of expected instruction(s):_ `vadd.i64 D0, D0, D0'

   * int64x1_t vadd_s64 (int64x1_t, int64x1_t)
     _Form of expected instruction(s):_ `vadd.i64 D0, D0, D0'

   * float32x2_t vadd_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vadd.f32 D0, D0, D0'

   * uint32x4_t vaddq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vadd.i32 Q0, Q0, Q0'

   * uint16x8_t vaddq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vadd.i16 Q0, Q0, Q0'

   * uint8x16_t vaddq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vadd.i8 Q0, Q0, Q0'

   * int32x4_t vaddq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vadd.i32 Q0, Q0, Q0'

   * int16x8_t vaddq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vadd.i16 Q0, Q0, Q0'

   * int8x16_t vaddq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vadd.i8 Q0, Q0, Q0'

   * uint64x2_t vaddq_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vadd.i64 Q0, Q0, Q0'

   * int64x2_t vaddq_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vadd.i64 Q0, Q0, Q0'

   * float32x4_t vaddq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vadd.f32 Q0, Q0, Q0'

   * uint64x2_t vaddl_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vaddl.u32 Q0, D0, D0'

   * uint32x4_t vaddl_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vaddl.u16 Q0, D0, D0'

   * uint16x8_t vaddl_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vaddl.u8 Q0, D0, D0'

   * int64x2_t vaddl_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vaddl.s32 Q0, D0, D0'

   * int32x4_t vaddl_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vaddl.s16 Q0, D0, D0'

   * int16x8_t vaddl_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vaddl.s8 Q0, D0, D0'

   * uint64x2_t vaddw_u32 (uint64x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vaddw.u32 Q0, Q0, D0'

   * uint32x4_t vaddw_u16 (uint32x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vaddw.u16 Q0, Q0, D0'

   * uint16x8_t vaddw_u8 (uint16x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vaddw.u8 Q0, Q0, D0'

   * int64x2_t vaddw_s32 (int64x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vaddw.s32 Q0, Q0, D0'

   * int32x4_t vaddw_s16 (int32x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vaddw.s16 Q0, Q0, D0'

   * int16x8_t vaddw_s8 (int16x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vaddw.s8 Q0, Q0, D0'

   * uint32x2_t vhadd_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vhadd.u32 D0, D0, D0'

   * uint16x4_t vhadd_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vhadd.u16 D0, D0, D0'

   * uint8x8_t vhadd_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vhadd.u8 D0, D0, D0'

   * int32x2_t vhadd_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vhadd.s32 D0, D0, D0'

   * int16x4_t vhadd_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vhadd.s16 D0, D0, D0'

   * int8x8_t vhadd_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vhadd.s8 D0, D0, D0'

   * uint32x4_t vhaddq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vhadd.u32 Q0, Q0, Q0'

   * uint16x8_t vhaddq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vhadd.u16 Q0, Q0, Q0'

   * uint8x16_t vhaddq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vhadd.u8 Q0, Q0, Q0'

   * int32x4_t vhaddq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vhadd.s32 Q0, Q0, Q0'

   * int16x8_t vhaddq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vhadd.s16 Q0, Q0, Q0'

   * int8x16_t vhaddq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vhadd.s8 Q0, Q0, Q0'

   * uint32x2_t vrhadd_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vrhadd.u32 D0, D0, D0'

   * uint16x4_t vrhadd_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vrhadd.u16 D0, D0, D0'

   * uint8x8_t vrhadd_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vrhadd.u8 D0, D0, D0'

   * int32x2_t vrhadd_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vrhadd.s32 D0, D0, D0'

   * int16x4_t vrhadd_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vrhadd.s16 D0, D0, D0'

   * int8x8_t vrhadd_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vrhadd.s8 D0, D0, D0'

   * uint32x4_t vrhaddq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vrhadd.u32 Q0, Q0, Q0'

   * uint16x8_t vrhaddq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vrhadd.u16 Q0, Q0, Q0'

   * uint8x16_t vrhaddq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vrhadd.u8 Q0, Q0, Q0'

   * int32x4_t vrhaddq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vrhadd.s32 Q0, Q0, Q0'

   * int16x8_t vrhaddq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vrhadd.s16 Q0, Q0, Q0'

   * int8x16_t vrhaddq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vrhadd.s8 Q0, Q0, Q0'

   * uint32x2_t vqadd_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vqadd.u32 D0, D0, D0'

   * uint16x4_t vqadd_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vqadd.u16 D0, D0, D0'

   * uint8x8_t vqadd_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vqadd.u8 D0, D0, D0'

   * int32x2_t vqadd_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqadd.s32 D0, D0, D0'

   * int16x4_t vqadd_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqadd.s16 D0, D0, D0'

   * int8x8_t vqadd_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vqadd.s8 D0, D0, D0'

   * uint64x1_t vqadd_u64 (uint64x1_t, uint64x1_t)
     _Form of expected instruction(s):_ `vqadd.u64 D0, D0, D0'

   * int64x1_t vqadd_s64 (int64x1_t, int64x1_t)
     _Form of expected instruction(s):_ `vqadd.s64 D0, D0, D0'

   * uint32x4_t vqaddq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vqadd.u32 Q0, Q0, Q0'

   * uint16x8_t vqaddq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vqadd.u16 Q0, Q0, Q0'

   * uint8x16_t vqaddq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vqadd.u8 Q0, Q0, Q0'

   * int32x4_t vqaddq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vqadd.s32 Q0, Q0, Q0'

   * int16x8_t vqaddq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vqadd.s16 Q0, Q0, Q0'

   * int8x16_t vqaddq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vqadd.s8 Q0, Q0, Q0'

   * uint64x2_t vqaddq_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vqadd.u64 Q0, Q0, Q0'

   * int64x2_t vqaddq_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vqadd.s64 Q0, Q0, Q0'

   * uint32x2_t vaddhn_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vaddhn.i64 D0, Q0, Q0'

   * uint16x4_t vaddhn_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vaddhn.i32 D0, Q0, Q0'

   * uint8x8_t vaddhn_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vaddhn.i16 D0, Q0, Q0'

   * int32x2_t vaddhn_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vaddhn.i64 D0, Q0, Q0'

   * int16x4_t vaddhn_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vaddhn.i32 D0, Q0, Q0'

   * int8x8_t vaddhn_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vaddhn.i16 D0, Q0, Q0'

   * uint32x2_t vraddhn_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vraddhn.i64 D0, Q0, Q0'

   * uint16x4_t vraddhn_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vraddhn.i32 D0, Q0, Q0'

   * uint8x8_t vraddhn_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vraddhn.i16 D0, Q0, Q0'

   * int32x2_t vraddhn_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vraddhn.i64 D0, Q0, Q0'

   * int16x4_t vraddhn_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vraddhn.i32 D0, Q0, Q0'

   * int8x8_t vraddhn_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vraddhn.i16 D0, Q0, Q0'

5.50.3.2 Multiplication
.......................

   * uint32x2_t vmul_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmul.i32 D0, D0, D0'

   * uint16x4_t vmul_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmul.i16 D0, D0, D0'

   * uint8x8_t vmul_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmul.i8 D0, D0, D0'

   * int32x2_t vmul_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmul.i32 D0, D0, D0'

   * int16x4_t vmul_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmul.i16 D0, D0, D0'

   * int8x8_t vmul_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmul.i8 D0, D0, D0'

   * float32x2_t vmul_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vmul.f32 D0, D0, D0'

   * poly8x8_t vmul_p8 (poly8x8_t, poly8x8_t)
     _Form of expected instruction(s):_ `vmul.p8 D0, D0, D0'

   * uint32x4_t vmulq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vmul.i32 Q0, Q0, Q0'

   * uint16x8_t vmulq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vmul.i16 Q0, Q0, Q0'

   * uint8x16_t vmulq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vmul.i8 Q0, Q0, Q0'

   * int32x4_t vmulq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vmul.i32 Q0, Q0, Q0'

   * int16x8_t vmulq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vmul.i16 Q0, Q0, Q0'

   * int8x16_t vmulq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vmul.i8 Q0, Q0, Q0'

   * float32x4_t vmulq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vmul.f32 Q0, Q0, Q0'

   * poly8x16_t vmulq_p8 (poly8x16_t, poly8x16_t)
     _Form of expected instruction(s):_ `vmul.p8 Q0, Q0, Q0'

   * int32x2_t vqdmulh_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqdmulh.s32 D0, D0, D0'

   * int16x4_t vqdmulh_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqdmulh.s16 D0, D0, D0'

   * int32x4_t vqdmulhq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vqdmulh.s32 Q0, Q0, Q0'

   * int16x8_t vqdmulhq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vqdmulh.s16 Q0, Q0, Q0'

   * int32x2_t vqrdmulh_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqrdmulh.s32 D0, D0, D0'

   * int16x4_t vqrdmulh_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqrdmulh.s16 D0, D0, D0'

   * int32x4_t vqrdmulhq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vqrdmulh.s32 Q0, Q0, Q0'

   * int16x8_t vqrdmulhq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vqrdmulh.s16 Q0, Q0, Q0'

   * uint64x2_t vmull_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmull.u32 Q0, D0, D0'

   * uint32x4_t vmull_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmull.u16 Q0, D0, D0'

   * uint16x8_t vmull_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmull.u8 Q0, D0, D0'

   * int64x2_t vmull_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmull.s32 Q0, D0, D0'

   * int32x4_t vmull_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmull.s16 Q0, D0, D0'

   * int16x8_t vmull_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmull.s8 Q0, D0, D0'

   * poly16x8_t vmull_p8 (poly8x8_t, poly8x8_t)
     _Form of expected instruction(s):_ `vmull.p8 Q0, D0, D0'

   * int64x2_t vqdmull_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqdmull.s32 Q0, D0, D0'

   * int32x4_t vqdmull_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqdmull.s16 Q0, D0, D0'

5.50.3.3 Multiply-accumulate
............................

   * uint32x2_t vmla_u32 (uint32x2_t, uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmla.i32 D0, D0, D0'

   * uint16x4_t vmla_u16 (uint16x4_t, uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmla.i16 D0, D0, D0'

   * uint8x8_t vmla_u8 (uint8x8_t, uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmla.i8 D0, D0, D0'

   * int32x2_t vmla_s32 (int32x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmla.i32 D0, D0, D0'

   * int16x4_t vmla_s16 (int16x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmla.i16 D0, D0, D0'

   * int8x8_t vmla_s8 (int8x8_t, int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmla.i8 D0, D0, D0'

   * float32x2_t vmla_f32 (float32x2_t, float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vmla.f32 D0, D0, D0'

   * uint32x4_t vmlaq_u32 (uint32x4_t, uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vmla.i32 Q0, Q0, Q0'

   * uint16x8_t vmlaq_u16 (uint16x8_t, uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vmla.i16 Q0, Q0, Q0'

   * uint8x16_t vmlaq_u8 (uint8x16_t, uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vmla.i8 Q0, Q0, Q0'

   * int32x4_t vmlaq_s32 (int32x4_t, int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vmla.i32 Q0, Q0, Q0'

   * int16x8_t vmlaq_s16 (int16x8_t, int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vmla.i16 Q0, Q0, Q0'

   * int8x16_t vmlaq_s8 (int8x16_t, int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vmla.i8 Q0, Q0, Q0'

   * float32x4_t vmlaq_f32 (float32x4_t, float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vmla.f32 Q0, Q0, Q0'

   * uint64x2_t vmlal_u32 (uint64x2_t, uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmlal.u32 Q0, D0, D0'

   * uint32x4_t vmlal_u16 (uint32x4_t, uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmlal.u16 Q0, D0, D0'

   * uint16x8_t vmlal_u8 (uint16x8_t, uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmlal.u8 Q0, D0, D0'

   * int64x2_t vmlal_s32 (int64x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmlal.s32 Q0, D0, D0'

   * int32x4_t vmlal_s16 (int32x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmlal.s16 Q0, D0, D0'

   * int16x8_t vmlal_s8 (int16x8_t, int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmlal.s8 Q0, D0, D0'

   * int64x2_t vqdmlal_s32 (int64x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqdmlal.s32 Q0, D0, D0'

   * int32x4_t vqdmlal_s16 (int32x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqdmlal.s16 Q0, D0, D0'

5.50.3.4 Multiply-subtract
..........................

   * uint32x2_t vmls_u32 (uint32x2_t, uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmls.i32 D0, D0, D0'

   * uint16x4_t vmls_u16 (uint16x4_t, uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmls.i16 D0, D0, D0'

   * uint8x8_t vmls_u8 (uint8x8_t, uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmls.i8 D0, D0, D0'

   * int32x2_t vmls_s32 (int32x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmls.i32 D0, D0, D0'

   * int16x4_t vmls_s16 (int16x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmls.i16 D0, D0, D0'

   * int8x8_t vmls_s8 (int8x8_t, int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmls.i8 D0, D0, D0'

   * float32x2_t vmls_f32 (float32x2_t, float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vmls.f32 D0, D0, D0'

   * uint32x4_t vmlsq_u32 (uint32x4_t, uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vmls.i32 Q0, Q0, Q0'

   * uint16x8_t vmlsq_u16 (uint16x8_t, uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vmls.i16 Q0, Q0, Q0'

   * uint8x16_t vmlsq_u8 (uint8x16_t, uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vmls.i8 Q0, Q0, Q0'

   * int32x4_t vmlsq_s32 (int32x4_t, int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vmls.i32 Q0, Q0, Q0'

   * int16x8_t vmlsq_s16 (int16x8_t, int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vmls.i16 Q0, Q0, Q0'

   * int8x16_t vmlsq_s8 (int8x16_t, int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vmls.i8 Q0, Q0, Q0'

   * float32x4_t vmlsq_f32 (float32x4_t, float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vmls.f32 Q0, Q0, Q0'

   * uint64x2_t vmlsl_u32 (uint64x2_t, uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vmlsl.u32 Q0, D0, D0'

   * uint32x4_t vmlsl_u16 (uint32x4_t, uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vmlsl.u16 Q0, D0, D0'

   * uint16x8_t vmlsl_u8 (uint16x8_t, uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vmlsl.u8 Q0, D0, D0'

   * int64x2_t vmlsl_s32 (int64x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vmlsl.s32 Q0, D0, D0'

   * int32x4_t vmlsl_s16 (int32x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vmlsl.s16 Q0, D0, D0'

   * int16x8_t vmlsl_s8 (int16x8_t, int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vmlsl.s8 Q0, D0, D0'

   * int64x2_t vqdmlsl_s32 (int64x2_t, int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqdmlsl.s32 Q0, D0, D0'

   * int32x4_t vqdmlsl_s16 (int32x4_t, int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqdmlsl.s16 Q0, D0, D0'

5.50.3.5 Subtraction
....................

   * uint32x2_t vsub_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vsub.i32 D0, D0, D0'

   * uint16x4_t vsub_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vsub.i16 D0, D0, D0'

   * uint8x8_t vsub_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vsub.i8 D0, D0, D0'

   * int32x2_t vsub_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vsub.i32 D0, D0, D0'

   * int16x4_t vsub_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vsub.i16 D0, D0, D0'

   * int8x8_t vsub_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vsub.i8 D0, D0, D0'

   * uint64x1_t vsub_u64 (uint64x1_t, uint64x1_t)
     _Form of expected instruction(s):_ `vsub.i64 D0, D0, D0'

   * int64x1_t vsub_s64 (int64x1_t, int64x1_t)
     _Form of expected instruction(s):_ `vsub.i64 D0, D0, D0'

   * float32x2_t vsub_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vsub.f32 D0, D0, D0'

   * uint32x4_t vsubq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vsub.i32 Q0, Q0, Q0'

   * uint16x8_t vsubq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vsub.i16 Q0, Q0, Q0'

   * uint8x16_t vsubq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vsub.i8 Q0, Q0, Q0'

   * int32x4_t vsubq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vsub.i32 Q0, Q0, Q0'

   * int16x8_t vsubq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vsub.i16 Q0, Q0, Q0'

   * int8x16_t vsubq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vsub.i8 Q0, Q0, Q0'

   * uint64x2_t vsubq_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vsub.i64 Q0, Q0, Q0'

   * int64x2_t vsubq_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vsub.i64 Q0, Q0, Q0'

   * float32x4_t vsubq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vsub.f32 Q0, Q0, Q0'

   * uint64x2_t vsubl_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vsubl.u32 Q0, D0, D0'

   * uint32x4_t vsubl_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vsubl.u16 Q0, D0, D0'

   * uint16x8_t vsubl_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vsubl.u8 Q0, D0, D0'

   * int64x2_t vsubl_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vsubl.s32 Q0, D0, D0'

   * int32x4_t vsubl_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vsubl.s16 Q0, D0, D0'

   * int16x8_t vsubl_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vsubl.s8 Q0, D0, D0'

   * uint64x2_t vsubw_u32 (uint64x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vsubw.u32 Q0, Q0, D0'

   * uint32x4_t vsubw_u16 (uint32x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vsubw.u16 Q0, Q0, D0'

   * uint16x8_t vsubw_u8 (uint16x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vsubw.u8 Q0, Q0, D0'

   * int64x2_t vsubw_s32 (int64x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vsubw.s32 Q0, Q0, D0'

   * int32x4_t vsubw_s16 (int32x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vsubw.s16 Q0, Q0, D0'

   * int16x8_t vsubw_s8 (int16x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vsubw.s8 Q0, Q0, D0'

   * uint32x2_t vhsub_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vhsub.u32 D0, D0, D0'

   * uint16x4_t vhsub_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vhsub.u16 D0, D0, D0'

   * uint8x8_t vhsub_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vhsub.u8 D0, D0, D0'

   * int32x2_t vhsub_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vhsub.s32 D0, D0, D0'

   * int16x4_t vhsub_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vhsub.s16 D0, D0, D0'

   * int8x8_t vhsub_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vhsub.s8 D0, D0, D0'

   * uint32x4_t vhsubq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vhsub.u32 Q0, Q0, Q0'

   * uint16x8_t vhsubq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vhsub.u16 Q0, Q0, Q0'

   * uint8x16_t vhsubq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vhsub.u8 Q0, Q0, Q0'

   * int32x4_t vhsubq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vhsub.s32 Q0, Q0, Q0'

   * int16x8_t vhsubq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vhsub.s16 Q0, Q0, Q0'

   * int8x16_t vhsubq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vhsub.s8 Q0, Q0, Q0'

   * uint32x2_t vqsub_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vqsub.u32 D0, D0, D0'

   * uint16x4_t vqsub_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vqsub.u16 D0, D0, D0'

   * uint8x8_t vqsub_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vqsub.u8 D0, D0, D0'

   * int32x2_t vqsub_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vqsub.s32 D0, D0, D0'

   * int16x4_t vqsub_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vqsub.s16 D0, D0, D0'

   * int8x8_t vqsub_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vqsub.s8 D0, D0, D0'

   * uint64x1_t vqsub_u64 (uint64x1_t, uint64x1_t)
     _Form of expected instruction(s):_ `vqsub.u64 D0, D0, D0'

   * int64x1_t vqsub_s64 (int64x1_t, int64x1_t)
     _Form of expected instruction(s):_ `vqsub.s64 D0, D0, D0'

   * uint32x4_t vqsubq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vqsub.u32 Q0, Q0, Q0'

   * uint16x8_t vqsubq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vqsub.u16 Q0, Q0, Q0'

   * uint8x16_t vqsubq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vqsub.u8 Q0, Q0, Q0'

   * int32x4_t vqsubq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vqsub.s32 Q0, Q0, Q0'

   * int16x8_t vqsubq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vqsub.s16 Q0, Q0, Q0'

   * int8x16_t vqsubq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vqsub.s8 Q0, Q0, Q0'

   * uint64x2_t vqsubq_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vqsub.u64 Q0, Q0, Q0'

   * int64x2_t vqsubq_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vqsub.s64 Q0, Q0, Q0'

   * uint32x2_t vsubhn_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vsubhn.i64 D0, Q0, Q0'

   * uint16x4_t vsubhn_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vsubhn.i32 D0, Q0, Q0'

   * uint8x8_t vsubhn_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vsubhn.i16 D0, Q0, Q0'

   * int32x2_t vsubhn_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vsubhn.i64 D0, Q0, Q0'

   * int16x4_t vsubhn_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vsubhn.i32 D0, Q0, Q0'

   * int8x8_t vsubhn_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vsubhn.i16 D0, Q0, Q0'

   * uint32x2_t vrsubhn_u64 (uint64x2_t, uint64x2_t)
     _Form of expected instruction(s):_ `vrsubhn.i64 D0, Q0, Q0'

   * uint16x4_t vrsubhn_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vrsubhn.i32 D0, Q0, Q0'

   * uint8x8_t vrsubhn_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vrsubhn.i16 D0, Q0, Q0'

   * int32x2_t vrsubhn_s64 (int64x2_t, int64x2_t)
     _Form of expected instruction(s):_ `vrsubhn.i64 D0, Q0, Q0'

   * int16x4_t vrsubhn_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vrsubhn.i32 D0, Q0, Q0'

   * int8x8_t vrsubhn_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vrsubhn.i16 D0, Q0, Q0'

5.50.3.6 Comparison (equal-to)
..............................

   * uint32x2_t vceq_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vceq.i32 D0, D0, D0'

   * uint16x4_t vceq_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vceq.i16 D0, D0, D0'

   * uint8x8_t vceq_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vceq.i8 D0, D0, D0'

   * uint32x2_t vceq_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vceq.i32 D0, D0, D0'

   * uint16x4_t vceq_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vceq.i16 D0, D0, D0'

   * uint8x8_t vceq_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vceq.i8 D0, D0, D0'

   * uint32x2_t vceq_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vceq.f32 D0, D0, D0'

   * uint8x8_t vceq_p8 (poly8x8_t, poly8x8_t)
     _Form of expected instruction(s):_ `vceq.i8 D0, D0, D0'

   * uint32x4_t vceqq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vceq.i32 Q0, Q0, Q0'

   * uint16x8_t vceqq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vceq.i16 Q0, Q0, Q0'

   * uint8x16_t vceqq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vceq.i8 Q0, Q0, Q0'

   * uint32x4_t vceqq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vceq.i32 Q0, Q0, Q0'

   * uint16x8_t vceqq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vceq.i16 Q0, Q0, Q0'

   * uint8x16_t vceqq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vceq.i8 Q0, Q0, Q0'

   * uint32x4_t vceqq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vceq.f32 Q0, Q0, Q0'

   * uint8x16_t vceqq_p8 (poly8x16_t, poly8x16_t)
     _Form of expected instruction(s):_ `vceq.i8 Q0, Q0, Q0'

5.50.3.7 Comparison (greater-than-or-equal-to)
..............................................

   * uint32x2_t vcge_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vcge.u32 D0, D0, D0'

   * uint16x4_t vcge_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vcge.u16 D0, D0, D0'

   * uint8x8_t vcge_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vcge.u8 D0, D0, D0'

   * uint32x2_t vcge_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vcge.s32 D0, D0, D0'

   * uint16x4_t vcge_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vcge.s16 D0, D0, D0'

   * uint8x8_t vcge_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vcge.s8 D0, D0, D0'

   * uint32x2_t vcge_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vcge.f32 D0, D0, D0'

   * uint32x4_t vcgeq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vcge.u32 Q0, Q0, Q0'

   * uint16x8_t vcgeq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vcge.u16 Q0, Q0, Q0'

   * uint8x16_t vcgeq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vcge.u8 Q0, Q0, Q0'

   * uint32x4_t vcgeq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vcge.s32 Q0, Q0, Q0'

   * uint16x8_t vcgeq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vcge.s16 Q0, Q0, Q0'

   * uint8x16_t vcgeq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vcge.s8 Q0, Q0, Q0'

   * uint32x4_t vcgeq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vcge.f32 Q0, Q0, Q0'

5.50.3.8 Comparison (less-than-or-equal-to)
...........................................

   * uint32x2_t vcle_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vcge.u32 D0, D0, D0'

   * uint16x4_t vcle_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vcge.u16 D0, D0, D0'

   * uint8x8_t vcle_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vcge.u8 D0, D0, D0'

   * uint32x2_t vcle_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vcge.s32 D0, D0, D0'

   * uint16x4_t vcle_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vcge.s16 D0, D0, D0'

   * uint8x8_t vcle_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vcge.s8 D0, D0, D0'

   * uint32x2_t vcle_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vcge.f32 D0, D0, D0'

   * uint32x4_t vcleq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vcge.u32 Q0, Q0, Q0'

   * uint16x8_t vcleq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vcge.u16 Q0, Q0, Q0'

   * uint8x16_t vcleq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vcge.u8 Q0, Q0, Q0'

   * uint32x4_t vcleq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vcge.s32 Q0, Q0, Q0'

   * uint16x8_t vcleq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vcge.s16 Q0, Q0, Q0'

   * uint8x16_t vcleq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vcge.s8 Q0, Q0, Q0'

   * uint32x4_t vcleq_f32 (float32x4_t, float32x4_t)
     _Form of expected instruction(s):_ `vcge.f32 Q0, Q0, Q0'

5.50.3.9 Comparison (greater-than)
..................................

   * uint32x2_t vcgt_u32 (uint32x2_t, uint32x2_t)
     _Form of expected instruction(s):_ `vcgt.u32 D0, D0, D0'

   * uint16x4_t vcgt_u16 (uint16x4_t, uint16x4_t)
     _Form of expected instruction(s):_ `vcgt.u16 D0, D0, D0'

   * uint8x8_t vcgt_u8 (uint8x8_t, uint8x8_t)
     _Form of expected instruction(s):_ `vcgt.u8 D0, D0, D0'

   * uint32x2_t vcgt_s32 (int32x2_t, int32x2_t)
     _Form of expected instruction(s):_ `vcgt.s32 D0, D0, D0'

   * uint16x4_t vcgt_s16 (int16x4_t, int16x4_t)
     _Form of expected instruction(s):_ `vcgt.s16 D0, D0, D0'

   * uint8x8_t vcgt_s8 (int8x8_t, int8x8_t)
     _Form of expected instruction(s):_ `vcgt.s8 D0, D0, D0'

   * uint32x2_t vcgt_f32 (float32x2_t, float32x2_t)
     _Form of expected instruction(s):_ `vcgt.f32 D0, D0, D0'

   * uint32x4_t vcgtq_u32 (uint32x4_t, uint32x4_t)
     _Form of expected instruction(s):_ `vcgt.u32 Q0, Q0, Q0'

   * uint16x8_t vcgtq_u16 (uint16x8_t, uint16x8_t)
     _Form of expected instruction(s):_ `vcgt.u16 Q0, Q0, Q0'

   * uint8x16_t vcgtq_u8 (uint8x16_t, uint8x16_t)
     _Form of expected instruction(s):_ `vcgt.u8 Q0, Q0, Q0'

   * uint32x4_t vcgtq_s32 (int32x4_t, int32x4_t)
     _Form of expected instruction(s):_ `vcgt.s32 Q0, Q0, Q0'

   * uint16x8_t vcgtq_s16 (int16x8_t, int16x8_t)
     _Form of expected instruction(s):_ `vcgt.s16 Q0, Q0, Q0'

   * uint8x16_t vcgtq_s8 (int8x16_t, int8x16_t)
     _Form of expected instruction(s):_ `vcgt.s8 Q0, Q0, Q0'

   * uint32x4_t vcgtq_f32