perl-compiler/README

	The B::C, B::CC, B::Bytecode Perl Compiler Kit

	Copyright (c) 1996, 1997, Malcolm Beattie
	Copyright (c) 2008, 2009, 2010, 2011 Reini Urban

Homepage: http://www.perl-compiler.org/
Releases: http://search.cpan.org/dist/B-C/
Code: http://code.google.com/p/perl-compiler/
  git clone https://code.google.com/p/perl-compiler/
was previously:
  svn checkout http://perl-compiler.googlecode.com/svn/trunk/ perl-compiler

INSTALL

cpan B::C

On strawberry I needed
  perl Makefile.PL FIXIN="perl -S pl2bat.bat"

On Windows and AIX for 5.12 and 5.14 you need to patch and rebuild CORE perl:
  ramblings/Export-store_cop_label-for-the-perl-compiler.patch

For 5.14 and 5.15 I recommend also the following patches:
  ramblings/revert-B-load-BEGIN.patch (The 5.14.1 version)
  ramblings/Carp-wo-B.patch

USAGE

The Bytecode, C and CC backends are now all functional
enough to compile almost the whole of the main perl test
suite and 97-100% of the top100 modules.

In the case of the CC backend, any failures are all
due to differences and/or known bugs documented below. See
the file TESTS.

(1) To compile perl program foo.pl with the C backend, do

    perl -MO=C,-ofoo.c foo.pl

Then use the cc_harness perl program to compile the
resulting C source:

    perl cc_harness -O2 -o foo foo.c

If you are using a non-ANSI pre-Standard C compiler that
can't handle pre-declaring static arrays, then add
-DBROKEN_STATIC_REDECL to the options you use:

    perl cc_harness -O2 -o foo -DBROKEN_STATIC_REDECL foo.c

If you are using a non-ANSI pre-Standard C compiler that
can't handle static initialisation of structures with union
members then add -DBROKEN_UNION_INIT to the options you
use. If you want command line arguments passed to your
executable to be interpreted by perl (e.g. -Dx) then compile
foo.c with -DALLOW_PERL_OPTIONS. Otherwise, all command line
arguments passed to foo will appear directly in @ARGV.  The
resulting executable foo is the compiled version of
foo.pl. See the file NOTES for extra options you can pass to
-MO=C.

There are some constraints on the contents on foo.pl if you
want to be able to compile it successfully. Some problems
can be fixed fairly easily by altering foo.pl; some problems
with the compiler are known to be straightforward to solve
and I'll do so soon. The file Todo lists a number of known
problems. See the XSUB section lower down for information
about compiling programs which use XSUBs.

(2) To compile foo.pl with the CC backend (which generates
actual optimised C code for the execution path of your perl
program), use

    perl -MO=CC,-ofoo.c foo.pl

and proceed just as with the C backend. You should almost
certainly use an option such as -O2 with the subsequent
cc_harness invocation so that your C compiler uses
optimisation. The C code generated by the Perl compiler's CC
backend looks ugly to humans but is easily optimised by C
compilers.

To make the most of this optimizing compiler backend, you need to tell
the compiler when you're using int or double variables so that it can
optimise appropriately. The old deprecated way do that was by naming
lexical variables ending in "_i" for ints, "_d" for doubles, "_ir" for
int "register" variables or "_dr" for double "register"
variables. Here "register" is a promise that you won't pass a
reference to the variable into a sub which then modifies the variable.
The new way is to declare those lexicals with "my int" and "my
double". The compiler ought to catch attempts to use "\$i" just as C
compilers catch attempts to do "&i" for a register int i, but it
doesn't at the moment. Bugs in the CC backend may make your program
fail in mysterious ways and give wrong answers rather than just crash
in boring ways. CC is still on the experimental level. Please use your 
test suite.

If your program uses classes which define methods (or other subs which
are not exported and not apparently used until runtime) then you'll
need to use -u compile-time options (see the NOTES file) to force the
subs to be compiled. Future releases will probably default the other
way, do more auto-detection and provide more fine-grained control.

Since compiled executables need linking with libperl, you
may want to turn libperl.a into a shared library if your
platform supports it, -Duseshrplib.
You'll probably also want to link your main perl executable
against libperl.so; it's nice having an 11K perl executable.

(3) To compile foo.pl into bytecode do

    perl -MO=Bytecode,-ofoo.plc foo.pl

To run the resulting bytecode file foo.plc, you use the
ByteLoader module which should have been built along with
the extensions.

    perl -MByteLoader foo.plc

Previous Perl releases had ByteLoader in CORE, so you can omit 
-MByteLoader there.
You can also do -H to automatically use ByteLoader

    perl -MO=Bytecode,-H,-ofoo.plc foo.pl
    perl foo.plc

Any extra arguments are passed in as @ARGV; they are not interpreted
as perl options.
See the NOTES file for details of these and other options (including
optimisation options and ways of getting at the intermediate "assembler"
code that the Bytecode backend uses).

(3) There are little Bourne shell scripts and perl programs to aid with
some common operations:

  perlcc, assemble, disassemble, cc_harness

XSUBS

The C and CC backends can successfully compile some perl programs which
make use of XSUB extensions. [I'll add more detail to this section in a
later release.] As a prerequisite, such extensions must not need to do
anything in their BOOT: section which needs to be done at runtime rather
than compile time. Normally, the only code in the boot_Foo() function is
a list of newXS() calls which xsubpp puts there and the compiler handles
saving those XS subs itself. For each XSUB used, the C and CC compiler
will generate an initialiser in their C output which refers to the name
of the relevant C function (XS_Foo_somesub). What is not yet automated
is the necessary commands and cc command-line options (e.g. via
"perl cc_harness") which link against the extension libraries. For now,
you need the XSUB extension to have installed files in the right format
for using as C libraries (e.g. Foo.a or Foo.so). As the Foo.so files (or
your platform's version) aren't suitable for linking against, you will
have to reget the extension source and rebuild it as a static extension
to force the generation of a suitable Foo.a file. Then you need to make
a symlink (or copy or rename) of that file into a libFoo.a suitable for
cc linking. Then add the appropriate -L and -l options to your
"perl cc_harness" command line to find and link against those libraries.
You may also need to fix up some platform-dependent environment variable
to ensure that linked-against .so files are found at runtime too.

DIFFERENCES

The result of running a CC compiled Perl program can sometimes be different
from running the same program with standard perl. Think of the compiler
as having a slightly different implementation of the language Perl.

Unfortunately, since Perl has had a single implementation until now,
there are no formal standards or documents defining what behaviour is
guaranteed of Perl the language and what just "happens to work".
Some of the differences below are almost impossible to change because of
the way the compiler works. Others can be changed to produce "standard"
perl behaviour if it's deemed proper and the resulting performance hit
is accepted. I'll use "standard perl" to mean the result of running a
Perl program using the perl executable from the perl distribution.
I'll use "compiled Perl program" to mean running an executable produced
by this compiler kit ("the compiler") with the CC backend.

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.
    See test 21.

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
        456123E0
    with standard Perl but gives a compile-time error with compiled Perl.
    See test 30.

Arithmetic

    Optimized compiled Perl programs use native C arithmetic
    much more frequently than standard perl. So 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 version 5 was released have not been
    implemented in the compiler.

STATUS

C and Bytecode works fine, best with non-threaded perls. 3-4% fails on the top100 modules.
CC fails on some tests. See Todo.
The Bytecode compiler is disabled for 5.6.2, use the default instead.

See STATUS for details.

BUGS

Here are some things which may cause the compiler problems.

The following render the compiler useless (without serious hacking):

* Use of the DATA filehandle (via __END__ or __DATA__ tokens) on earlier 
  Perl versions withotu IO::Scalar. See test 15.
* Operator overloading with %OVERLOAD
* The (deprecated) magic array-offset variable $[ does not work
* For -O1 and -O2 copy-on-grow of static pvs and heks since 5.10 is disabled. 
  Fixes of the destruction failures there is work in progress.
* The following operators are not yet implemented for CC
    goto
    continue/next/last to a outer LABEL
* You can't use "last" to exit from a non-loop block.

The following may give significant problems:

* BEGIN blocks containing complex initialisation code, 
  esp. sideeffects. All the BEGIN code is evaluated once at compile-time,
  and NOT executed at run-time.
* Code which is only ever referred to at runtime (e.g. via eval "..." or
  via method calls): see the -u option for the C and CC backends.
* Run-time lookups of lexical variables in "outside" closures

The following may cause problems (not thoroughly tested):

* Dependencies on whether values of some "magic" Perl variables are
  determined at compile-time or runtime.
* For the C and CC backends: compile-time strings which are longer than
  your C compiler can cope with in a single line or definition.
* Reliance on intimate details of global destruction
* Any "-w" option in the first line of your perl program is seen and
  acted on by perl itself before the compiler starts. The compiler
  itself then runs with warnings turned on. This may cause perl to
  print out warnings about the compiler itself since I haven't tested
  it thoroughly with warnings turned on.

There is a terser but more complete list in the Todo file.

LICENSE

    This program is free software; you can redistribute it and/or modify
    it under the terms of either:

	a) the GNU General Public License as published by the Free
	Software Foundation; either version 1, or (at your option) any
	later version, or

	b) the "Artistic License" which comes with this kit.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See either
    the GNU General Public License or the Artistic License for more details.

    You should have received a copy of the Artistic License with this kit,
    in the file named "Artistic".  If not, you can get one from the Perl
    distribution. You should also have received a copy of the GNU General
    Public License, in the file named "Copying". If not, you can get one
    from the Perl distribution or else write to the Free Software Foundation,
    Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.

Reini Urban
2011-04-21

Malcolm Beattie
2 September 1996