MirOS Manual: B::CC(3p)


ext::B::B::CC(3p)Perl Programmers Reference Guidext::B::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 how-
     ever 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 fig-
         ure 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 pack-
         ages (i.e. of the form "A::B") where package "A" does
         not contain any subs.

     -mModulename
         Instead of generating source for a runnable executable,

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         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 debug-
         ging 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

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     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 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. 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 com-
     piled Perl.

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     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 depre-
     cated 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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