


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


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 pro-
       gram (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 com-
           piler tries to figure out which packages may possibly
           have subs in which need compiling but the current ver-
           sion 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



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


           executable, generate source for an XSUB module. The
           boot_Modulename 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.




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


               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 targets 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 deter-
       mines whether it behaves as a range or a flip/flop. Stan-
       dard perl delays until runtime the decision of which con-
       text 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.







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


       Arithmetic

       Compiled Perl programs use native C arithemtic 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, "mbeattie@sable.ox.ac.uk"











































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