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B::CC(3)               Perl Programmers Reference Guide               B::CC(3)



NAME
       B::CC - Perl compiler's optimized C translation backend

SYNOPSIS
               perl -MO=CC[,OPTIONS] foo.pl

DESCRIPTION
       This compiler backend takes Perl source and generates C source code corresponding to the flow of your program.
       In other words, this backend is somewhat a "real" compiler in the sense that many people think about compilers.
       Note however that, currently, it is a very poor compiler in that although it generates (mostly, or at least
       sometimes) correct code, it performs relatively few optimisations.  This will change as the compiler develops.
       The result is that running an executable compiled with this backend may start up more quickly than running the
       original Perl program (a feature shared by the C compiler backend--see B::C) and may also execute slightly
       faster. This is by no means a good optimising compiler--yet.

OPTIONS
       If there are any non-option arguments, they are taken to be names of objects to be saved (probably doesn't work
       properly yet).  Without extra arguments, it saves the main program.

       -ofilename
           Output to filename instead of STDOUT

       -v  Verbose compilation (currently gives a few compilation statistics).

       --  Force end of options

       -uPackname
           Force apparently unused subs from package Packname to be compiled.  This allows programs to use eval
           "foo()" even when sub foo is never seen to be used at compile time. The down side is that any subs which
           really are never used also have code generated. This option is necessary, for example, if you have a signal
           handler foo which you initialise with "$SIG{BAR} = "foo"".  A better fix, though, is just to change it to
           "$SIG{BAR} = \&foo". You can have multiple -u options. The compiler tries to figure out which packages may
           possibly have subs in which need compiling but the current version doesn't do it very well. In particular,
           it is confused by nested packages (i.e.  of the form "A::B") where package "A" does not contain any subs.

       -mModulename
           Instead of generating source for a runnable executable, generate source for an XSUB module. The boot_Modu-
           lename function (which DynaLoader can look for) does the appropriate initialisation and runs the main part
           of the Perl source that is being compiled.

       -D  Debug options (concatenated or separate flags like "perl -D").

       -Dr Writes debugging output to STDERR just as it's about to write to the program's runtime (otherwise writes
           debugging info as comments in its C output).

       -DO Outputs each OP as it's compiled

       -Ds Outputs the contents of the shadow stack at each OP

       -Dp Outputs the contents of the shadow pad of lexicals as it's loaded for each sub or the main program.

       -Dq Outputs the name of each fake PP function in the queue as it's about to process it.

       -Dl Output the filename and line number of each original line of Perl code as it's processed ("pp_nextstate").

       -Dt Outputs timing information of compilation stages.

       -f  Force optimisations on or off one at a time.

       -ffreetmps-each-bblock
           Delays FREETMPS from the end of each statement to the end of the each basic block.

       -ffreetmps-each-loop
           Delays FREETMPS from the end of each statement to the end of the group of basic blocks forming a loop. At
           most one of the freetmps-each-* options can be used.

       -fomit-taint
           Omits generating code for handling perl's tainting mechanism.

       -On Optimisation level (n = 0, 1, 2, ...). -O means -O1.  Currently, -O1 sets -ffreetmps-each-bblock and -O2
           sets -ffreetmps-each-loop.

EXAMPLES
               perl -MO=CC,-O2,-ofoo.c foo.pl
               perl cc_harness -o foo foo.c

       Note that "cc_harness" lives in the "B" subdirectory of your perl library directory. The utility called
       "perlcc" may also be used to help make use of this compiler.

               perl -MO=CC,-mFoo,-oFoo.c Foo.pm
               perl cc_harness -shared -c -o Foo.so Foo.c

BUGS
       Plenty. Current status: experimental.

DIFFERENCES
       These aren't really bugs but they are constructs which are heavily tied to perl's compile-and-go implementation
       and with which this compiler backend cannot cope.

       Loops

       Standard perl calculates the target of "next", "last", and "redo" at run-time. The compiler calculates the tar-
       gets at compile-time.  For example, the program

           sub skip_on_odd { next NUMBER if $_[0] % 2 }
           NUMBER: for ($i = 0; $i < 5; $i++) {
               skip_on_odd($i);
               print $i;
           }

       produces the output

           024

       with standard perl but gives a compile-time error with the compiler.

       Context of ".."

       The context (scalar or array) of the ".." operator determines whether it behaves as a range or a flip/flop.
       Standard perl delays until runtime the decision of which context it is in but the compiler needs to know the
       context at compile-time. For example,

           @a = (4,6,1,0,0,1);
           sub range { (shift @a)..(shift @a) }
           print range();
           while (@a) { print scalar(range()) }

       generates the output

           456123E0

       with standard Perl but gives a compile-time error with compiled Perl.

       Arithmetic

       Compiled Perl programs use native C arithmetic much more frequently than standard perl. Operations on large
       numbers or on boundary cases may produce different behaviour.

       Deprecated features

       Features of standard perl such as $[ which have been deprecated in standard perl since Perl5 was released have
       not been implemented in the compiler.

AUTHOR
       Malcolm Beattie, "mbeattieATsable.uk"



perl v5.8.8                       2001-09-21                          B::CC(3)