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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 with unrolled ops and optimised stack handling and lexicals variable types. 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.


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


Verbose compilation (prints a few compilation stages).


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 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.


Instead of generating source for a runnable 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.


Debug options (concatenated or separate flags like perl -D). Verbose debugging options are crucial, because we have no interactive debugger at the early CHECK step, where the compilation happens.


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).


Outputs each OP as it's compiled


Outputs the contents of the shadow stack at each OP


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


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


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


Outputs timing information of compilation stages.


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.


Do not inline calls to certain small pp ops.

Most of the inlinable ops were already inlined. Turns off inlining for some new ops.


pp_null pp_stub pp_unstack pp_and pp_or pp_cond_expr pp_padsv pp_const pp_nextstate pp_dbstate pp_rv2gv pp_sort pp_gv pp_gvsv pp_aelemfast pp_ncmp pp_add pp_subtract pp_multiply pp_divide pp_modulo pp_left_shift pp_right_shift pp_i_add pp_i_subtract pp_i_multiply pp_i_divide pp_i_modulo pp_eq pp_ne pp_lt pp_gt pp_le pp_ge pp_i_eq pp_i_ne pp_i_lt pp_i_gt pp_i_le pp_i_ge pp_scmp pp_slt pp_sgt pp_sle pp_sge pp_seq pp_sne pp_sassign pp_preinc pp_pushmark pp_list pp_entersub pp_formline pp_goto pp_enterwrite pp_leavesub pp_leavewrite pp_entergiven pp_leavegiven pp_entereval pp_dofile pp_require pp_entertry pp_leavetry pp_grepstart pp_mapstart pp_grepwhile pp_mapwhile pp_return pp_range pp_flip pp_flop pp_enterloop pp_enteriter pp_leaveloop pp_next pp_redo pp_last pp_subst pp_substcont

DONE with -finline-ops:

pp_enter pp_reset pp_regcreset pp_stringify

TODO with -finline-ops:

pp_anoncode pp_wantarray pp_srefgen pp_refgen pp_ref pp_trans pp_schop pp_chop pp_schomp pp_chomp pp_not pp_sprintf pp_anonlist pp_shift pp_once pp_lock pp_rcatline pp_close pp_time pp_alarm pp_av2arylen: no lvalue, pp_length: no magic


Omits generating code for handling perl's tainting mechanism.


Add PERL_ASYNC_CHECK after every op as in the Perl runloop or B::C.

perl "Safe signals" check the state of incoming signals after every op. See http://perldoc.perl.org/perlipc.html#Deferred-Signals-(Safe-Signals) We trade safety for more speed and delay the execution of non-IO signals (IO signals are already handled in PerlIO) from after every single Perl op to after every Basic Block.

Only with -fslow-signals we get the old slow and safe behaviour.


Optimisation level (n = 0, 1, 2). -O means -O1.

-O1 sets -ffreetmps-each-bblock.

-O2 adds -ffreetmps-each-loop.

-fomit-taint must be set explicitly.


        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


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 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


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


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.


Malcolm Beattie, mbeattie@sable.ox.ac.uk Reini Urban, rurban@cpan.org