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