MirOS Manual: B::CC(3p)

ext::B::B::CC(3p)Perl Programmers Reference Guidext::B::B::CC(3p)


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


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


     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.


     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.

         Output to filename instead of STDOUT

     -v  Verbose compilation (currently gives a few compilation

     --  Force end of options

         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.

         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

     -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.

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

         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.

         Omits generating code for handling perl's tainting

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


             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


     Plenty. Current status: experimental.


     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.


     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++) {
             print $i;

     produces the output


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

     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


     with standard Perl but gives a compile-time error with com-
     piled Perl.

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     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.


     Malcolm Beattie, "mbeattie@sable.ox.ac.uk"

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