# Copyright (C) 2001-2009, Parrot Foundation.
# $Id: running.pod 39413 2009-06-05 23:19:30Z chromatic $

=head1 NAME

Parrot - Running

=head1 VERSION

$Revision: 39413 $

=head1 OVERVIEW

This document describes Parrot's command line options.

=head1 SYNOPSIS

 parrot [-options] <file> [arguments ...]

=head1 ENVIRONMENT

=over 4

=item PARROT_RUNTIME

If this environment variable is set, parrot will use this path as its runtime
prefix instead of the compiled in path.

=item PARROT_GC_DEBUG

Turn on the I<--gc-debug> flag.

=back

=head1 OPTIONS

=head2 Assembler options

=over 4

=item -a, --pasm

Assume PASM input on stdin.

=item -c, --pbc

Assume PBC file on stdin, run it.

=item -d, --imcc-debug [hexbits]

The B<-d> switch takes an optional argument which is considered to hold a hex
value of debug bits. Without a value, debug is set to 1.

The individual bits can be listed on the command line by use of the
B<--help-debug> switch.

To produce really huge output on F<stderr> run C<"parrot B<-d 0ffff> ...">.
Note: If the argument is separated by whitespace from the B<-d>
switch, it has to start with a number.

=item -h, --help

Print command line option summary.

=item --help-debug

Print debugging and tracing flag bits summary.

=item -o outputfile, --output=outputfile

Act like an assembler. Don't run code, unless B<-r> is given too. If the
outputfile ends with F<.pbc>, a PBC file is written. If it ends with F<.pasm>,
a PASM output is generated, even from PASM input. This can be handy to check
various optimizations, including C<-Op>.

=item --output-pbc

Act like an assembler, but always output bytecode, even if the output file does
not end in F<.pbc>

=item -r, --run-pbc

Only useful after C<-o> or C<--output-pbc>. Run the program from the compiled
in-memory image. If two C<-r> options are given, the F<.pbc> file is read from
disc and run. This is mainly needed for tests.

=item -v, --verbose

One C<-v> shows which files are worked on and prints a summary over register
usage and optimization stats per I<subroutine>.  With two C<-v> switches,
C<parrot> prints a line per individual processing step too.

=item -y, --yydebug

Turn on yydebug in F<yacc>/F<bison>.

=item -V, --version

Print version information and exit.

=item -Ox

Optimize

 -O0 no optimization (default)
 -O1 optimizations without life info (e.g. branches)
 -O  same
 -O2 optimizations with life info
 -Op rewrite I and N PASM registers most used first
 -Ot select fastest runcore (default with -O1 and -O2)
 -Oc turns on the optional/experimental tail call optimizations

See F<docs/dev/optimizer.pod> for more information on the optimizer.  Note that
optimization is currently experimental and these options are likely to change.

=item -E, --pre-process-only

Preprocess source file (expand macros) and print result to stdout:

  $ parrot -E t/op/macro_10.pasm
  $ parrot -E t/op/macro_10.pasm | parrot -- -

=back

=head2 Runcore Options

These options select the runcore, which is useful for performance tuning and
debugging.  See L<About runcores> for details.

=over 4

=item -R, --runcore CORE

Select the runcore. The following cores are available in Parrot, but not all
may be available on your system:

  slow, bounds  bounds checking core (default)
  cgoto         computed goto core
  cgp           computed goto-predereferenced core
  cgp-jit       computed goto-predereferenced core with JIT
  exec          exec core (uses JIT at compile time to generate native code)
  fast          fast core (no bounds checking, profiling, or tracing)
  gcdebug       performs a full GC run before every op dispatch (good for
                debugging GC problems)
  jit           JIT core
  switch        switch core
  switch-jit    switch core with JIT
  trace         bounds checking core w/ trace info (see 'parrot --help-debug')

=item -p, --profile

Run with the slow core and print an execution profile.

=item -t, --trace

Run with the slow core and print trace information to B<stderr>. See C<parrot
--help-debug> for available flag bits.

=back

=head2 VM Options

=over 4

=item -w, --warnings

Turn on warnings. See C<parrot --help-debug> for available flag bits.

=item -D, --parrot-debug

Turn on interpreter debug flag. See C<parrot --help-debug> for available flag
bits.

=item --gc-debug

Turn on GC (Garbage Collection) debugging. This imposes some stress on the GC
subsystem and can slow down execution considerably.

=item -G, --no-gc

This turns off GC. This may be useful to find GC related bugs. Don't use this
option for longer running programs: as memory is no longer recycled, it may
quickly become exhausted.

=item --leak-test, --destroy-at-end

Free all memory of the last interpreter.  This is useful when running leak
checkers.

=item -., --wait

Read a keystroke before starting.  This is useful when you want to attach a
debugger on platforms such as Windows.

=item --runtime-prefix

Print the runtime prefix path and exit.

=back

=head2 <file>

If the file ends in F<.pbc> it will be interpreted immediately.

If the file ends in F<.pasm>, then it is parsed as PASM code. Otherwise, it is
parsed as PIR code. In both cases, it will then be run, unless the C<-o> flag
was given.

If the C<file> is a single dash, input from C<stdin> is read.

=head2 [arguments ...]

Optional arguments passed to the running program as ARGV. The program is
assumed to know what to do with these.

=head1 Generated files

If JIT debugging is enabled (e.g. via C<--parrot-debug 04>), the
following additional output files are generated:

  F<file.stabs.s>     stabsfile for the program
  F<file.o>           object file with debug information
  F<EVAL_n>           source of C<compile> op number I<n>
  F<EVAL_n.stabs.s>   stabsfile for this block
  F<EVAL_n.o>         object file with debug information

See F<docs/jit.pod> for further information.

=head1 About runcores

The runcore (or runloop) tells Parrot how to find the C code that implements
each instruction.  Parrot provides more than one way to do this, partly because
no single runcore will perform optimally on all architectures (or even for all
problems on a given architecture), and partly because some of the runcores have
specific debugging and tracing capabilities.

In the default "slow" runcore, each opcode is a separate C function.
That's pretty easy in pseudocode:

    slow_runcore( op ):
        while ( op ):
            op = op_function( op )
            check_for_events()

The GC debugging runcore is similar:

    gcdebug_runcore( op ):
        while ( op ):
            perform_full_gc_run()
            op = op_function( op )
            check_for_events()

Of course, this is much slower, but is extremely helpful for pinning memory
corruption problems that affect GC down to single-instruction resolution.  See
L<http://www.oreillynet.com/onlamp/blog/2007/10/debugging_gc_problems_in_parro.html>
for more information.

The trace and profile cores are also based on the "slow" core, doing
full bounds checking, and also printing runtime information to stderr.

The switched core eschews these tiny op functions in favor of cases in a large
switch statement:

    switch_runcore( op ):
        while ( op ):
            switch *op:
                case NOP:
                    ...
                case STORE:
                    ...
                ...

Depending on the C compiler implementation, this may be faster than function
calling.  On older systems, it may fail to compile altogether.

The computed-goto ("cgoto") runcore avoids the overhead of function
calls by jumping directly to the address where each opcode's function
starts.  The computed-goto-prederef ("CGP") core takes this one step
further by replacing opcode numbers in the bytecode with those opfunc
addresses.  See "Predereferencing" in F<docs/glossary.pod> for a
fuller explanation.

Finally, the JIT runcore uses the "slow" core, but also creates and
jumps to JIT-compiled native code for supported opcodes.  "cgp-jit"
and "switched-jit" are variations that use the CGP or switched core
but run JIT code when possible.

=head1 Operation table

 Command Line          Action         Output
 ---------------------------------------------
 parrot x.pir          run
 parrot x.pasm         run
 parrot x.pbc          run
 -o x.pasm x.pir       ass            x.pasm
 -o x.pasm y.pasm      ass            x.pasm
 -o x.pbc  x.pir       ass            x.pbc
 -o x.pbc  x.pasm      ass            x.pbc
 -o x.pbc -r x.pasm    ass/run pasm   x.pbc
 -o x.pbc -r -r x.pasm ass/run pbc    x.pbc
 -o x.o    x.pbc       obj

... where the possible actions are:

  run ... yes, run the program
  ass ... assemble sourcefile
  obj ..  produce native (ELF) object file for the EXEC subsystem

=head1 FILES

F<main.c>

=cut