Bblock.pm

# Maintained now in B::C by Reini Urban <rurban@x-ray.at>
package B::Bblock;

our $VERSION = '1.03_02';

use Exporter ();
@ISA       = "Exporter";
@EXPORT_OK = qw(find_leaders);
my $have_B_Concise;

use B qw(peekop walkoptree walkoptree_exec
  main_root main_start svref_2object
  OPf_SPECIAL OPf_STACKED );

BEGIN {
  eval { require B::Concise; 1 } and $have_B_Concise = 1;
  B::Concise->import(qw(concise_cv concise_main set_style_standard))
    if $have_B_Concise;
}

use strict;

my $bblock;
my @bblock_ends;

sub mark_leader {
  my $op = shift;
  if ($$op) {
    $bblock->{$$op} = $op;
  }
}

sub remove_sortblock {
  foreach ( keys %$bblock ) {
    my $leader = $$bblock{$_};
    delete $$bblock{$_} if ( $leader == 0 );
  }
}

sub find_leaders {
  my ( $root, $start ) = @_;
  $bblock = {};
  mark_leader($start) if ( ref $start ne "B::NULL" );
  walkoptree( $root, "mark_if_leader" ) if ( ( ref $root ) ne "B::NULL" );
  remove_sortblock();
  return $bblock;
}

# Debugging
sub walk_bblocks {
  my ( $root, $start ) = @_;
  my ( $op, $lastop, $leader, $bb );
  $bblock = {};
  mark_leader($start);
  walkoptree( $root, "mark_if_leader" );
  my @leaders = values %$bblock;
  while ( $leader = shift @leaders ) {
    $lastop = $leader;
    $op     = $leader->next;
    while ( $$op && !exists( $bblock->{$$op} ) ) {
      $bblock->{$$op} = $leader;
      $lastop         = $op;
      $op             = $op->next;
    }
    push( @bblock_ends, [ $leader, $lastop ] );
  }
  foreach $bb (@bblock_ends) {
    ( $leader, $lastop ) = @$bb;
    printf "%s .. %s\n", peekop($leader), peekop($lastop);
    for ( $op = $leader ; $$op != $$lastop ; $op = $op->next ) {
      printf "    %s\n", peekop($op);
    }
    printf "    %s\n", peekop($lastop);
  }
}

sub walk_bblocks_obj {
  my $cvref = shift;
  my $cv    = svref_2object($cvref);
  walk_bblocks( $cv->ROOT, $cv->START );
}

sub B::OP::mark_if_leader { }

sub B::COP::mark_if_leader {
  my $op = shift;
  if ( $op->label ) {
    mark_leader($op);
  }
}

sub B::LOOP::mark_if_leader {
  my $op = shift;
  mark_leader( $op->next );
  mark_leader( $op->nextop );
  mark_leader( $op->redoop );
  mark_leader( $op->lastop->next );
}

sub B::LOGOP::mark_if_leader {
  my $op     = shift;
  my $opname = $op->name;
  mark_leader( $op->next );
  if ( $opname eq "entertry" ) {
    mark_leader( $op->other->next );
  }
  else {
    mark_leader( $op->other );
  }
}

sub B::LISTOP::mark_if_leader {
  my $op    = shift;
  my $first = $op->first;
  $first = $first->next while ( $first->name eq "null" );
  mark_leader( $op->first ) unless ( exists( $bblock->{$$first} ) );
  mark_leader( $op->next );
  if (  $op->name eq "sort"
    and $op->flags & OPf_SPECIAL
    and $op->flags & OPf_STACKED )
  {
    my $root   = $op->first->sibling->first;
    my $leader = $root->first;
    $bblock->{$$leader} = 0;
  }
}

sub B::PMOP::mark_if_leader {
  my $op = shift;
  if ( $op->name ne "pushre" ) {
    my $replroot = $op->pmreplroot;
    if ($$replroot) {
      mark_leader( $replroot );
      mark_leader( $op->next );
      mark_leader( $op->pmreplstart );
    }
  }
}

# PMOP stuff omitted

sub compile {
  my @options = @_;
  B::clearsym();
  if ( @options and $have_B_Concise ) {
    return sub {
      my $objname;
      foreach $objname (@options) {
        $objname = "main::$objname" unless $objname =~ /::/;
        print "walk_bblocks $objname\n";
        eval "walk_bblocks_obj(\\&$objname)";
        die "walk_bblocks_obj(\\&$objname) failed: $@" if $@;
        print "-------\n";
        set_style_standard("terse");
        eval "concise_cv('exec', \\&$objname)";
        die "concise_cv('exec', \\&$objname) failed: $@" if $@;
      }
      }
  }
  else {
    return sub {
      walk_bblocks( main_root, main_start );
      print "-------\n";
      if ($have_B_Concise) {
        set_style_standard("terse");
        concise_main("exec");
      }
    };
  }
}

1;

__END__

=head1 NAME

B::Bblock - Walk basic blocks

=head1 SYNOPSIS

  # External interface
  perl -MO=Bblock[,OPTIONS] foo.pl

    perl -MO=Bblock foo.pl     prints the basic block for main_root
    perl -MO=Bblock,foo::mysub foo.pm prints the basic block for &pkg::mysub
    perl -MO=Bblock,mysub foo.pm prints the basic block for &main::mysub

  # Programmatic API
  use B::Bblock qw(find_leaders);
  my $leaders = find_leaders($root_op, $start_op);

=head1 DESCRIPTION

This module is used by the L<B::CC> backend.  It walks "basic blocks".
A basic block is a series of operations which is known to execute from
start to finish, with no possibility of branching or halting.

The block is the list of ops from the every leader up to the next.
The leaders are the separator of each basic block.

The module can be used either stand alone or from inside another program.
Standalone it just prints the basic blocks ops in L<B::Concise>.
terse format to STDOUT.
Without options it starts at the main_root.

Basic block leaders are:

     Any COP (pp_nextstate) with a non-NULL label.
       [The op after a pp_enter] Omit
       [The op after a pp_entersub. Don't count this one.]
     The ops pointed at by nextop, redoop and lastop->op_next of a LOOP.
     The ops pointed at by op_next and op_other of a LOGOP, except
       for pp_entertry which has op_next and op_other->op_next
     The op pointed at by op_pmreplstart of a PMOP.
     The op pointed at by op_other->op_pmreplstart of pp_substcont?
       [The op after a pp_return] Omit

=head1 OPTIONS

A comma-separated list of sub names to walk.

=head2 Functions

=over 4

=item B<find_leaders>

  my $leaders = find_leaders($root_op, $start_op);

Given the root of the op tree and an op from which to start
processing, it will return a hash ref representing all the ops which
start a block.

The values of %$leaders are the op objects themselves.  Keys are $$op
addresses.

=back

=head1 AUTHOR

Malcolm Beattie C<MICB at cpan.org> I<(retired)>,
Reini Urban C<perl-compiler@googlegroups.com>

=cut

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