B::CC
B::CC(3) Perl Programmers Reference Guide B::CC(3)
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 back-
end is somewhat a "real" compiler in the sense that many people think
about compilers. Note however that, currently, it is a very poor com-
piler 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 exe-
cutable compiled with this backend may start up more quickly than run-
ning 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 statis-
tics).
-- 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 figure out which pack-
ages may possibly have subs in which need compiling but the cur-
rent version doesn’t do it very well. In particular, it is con-
fused 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 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.
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 com-
piler 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 determines whether
it behaves as a range or a flip/flop. Standard perl delays until run-
time 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 compiled Perl.
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 deprecated in
standard perl since Perl5 was released have not been implemented in
the compiler.
AUTHOR
Malcolm Beattie, "mbeattie@sable.ox.ac.uk"
perl v5.8.8 2001-09-21 B::CC(3)
