NAME

       B::Utils - Helper functions for op tree manipulation

SYNOPSIS

         use B::Utils;

DESCRIPTION

       These functions make it easier to manipulate the op tree.

FUNCTIONS

       "all_starts"
       "all_roots"
          Returns a hash of all of the starting ops or root ops of optrees, keyed to subroutine name; the optree
          for main program is simply keyed to "__MAIN__".

          Note:  Certain  "dangerous"  stashes  are not scanned for subroutines: the list of such stashes can be
          found in @B::Utils::bad_stashes. Feel free to examine and/or modify  this  to  suit  your  needs.  The
          intention  is  that a simple program which uses no modules other than "B" and "B::Utils" would show no
          addition symbols.

          This does not return the details of ops  in  anonymous  subroutines  compiled  at  compile  time.  For
          instance, given

              $a = sub { ... };

          the  subroutine  will  not appear in the hash. This is just as well, since they're anonymous... If you
          want to get at them, use...

       "anon_subs()"
          This returns an array of hash references. Each element has the keys "start" and "root". These are  the
          starting and root ops of all of the anonymous subroutines in the program.

       "$op->oldname"
          Returns  the name of the op, even if it is currently optimized to null.  This helps you understand the
          stucture of the op tree.

       "$op->kids"
          Returns an array of all this op's non-null children, in order.

       "$op->first"
       "$op->last"
       "$op->other"
          Normally if you call first, last or other on anything which is not an UNOP, BINOP or LOGOP respectivly
          it will die.  This leads to lots of code like:

              $op->first if $op->can('first');

          B::Utils provides every op with first, last and other methods which will simply return nothing  if  it
          isn't relevent.

       "$op->parent"
          Returns  the  parent  node  in  the  op tree, if possible. Currently "possible" means "if the tree has
          already been optimized"; that is, if we're during a "CHECK" block. (and hence, if we have valid "next"
          pointers.)

          In the future, it may be possible to search for the parent before  we  have  the  "next"  pointers  in
          place, but it'll take me a while to figure out how to do that.

       "$op->previous"
          Like "$op->next", but not quite.

       walkoptree_simple($op, \&callback, [$data])
          The  "B"  module  provides  various functions to walk the op tree, but they're all rather difficult to
          use, requiring you to inject methods into the "B::OP" class. This is a very simple op tree walker with
          more expected semantics.

          The &callback is called at each op with the op  itself  passed  in  as  the  first  argument  and  any
          additional $data as the second.

          All the "walk" functions set $B::Utils::file and $B::Utils::line to the appropriate values of file and
          line  number  in  the  program  being  examined.   Since  only COPs contain this information it may be
          unavailable in the first few callback calls.

       walkoptree_filtered($op, \&filter, \&callback, [$data])
          This is much the same as "walkoptree_simple", but will only call the callback if the "filter"  returns
          true. The "filter" is passed the op in question as a parameter; the "opgrep" function is fantastic for
          building your own filters.

       walkallops_simple(\&callback, [$data])
          This combines "walkoptree_simple" with "all_roots" and "anon_subs" to examine every op in the program.
          $B::Utils::sub  is  set  to the subroutine name if you're in a subroutine, "__MAIN__" if you're in the
          main program and "__ANON__" if you're in an anonymous subroutine.

       walkallops_filtered(\&filter, \&callback, [$data])
          Same as above, but filtered.

       carp(@args)
       croak(@args)
          Warn and die, respectively, from the perspective of the position of the  op  in  the  program.  Sounds
          complicated, but it's exactly the kind of error reporting you expect when you're grovelling through an
          op tree.

       opgrep(\%conditions, @ops)
          Returns the ops which meet the given conditions. The conditions should be specified like this:

              @barewords = opgrep(
                                  { name => "const", private => OPpCONST_BARE },
                                  @ops
                                 );

          You can specify alternation by giving an arrayref of values:

              @svs = opgrep ( { name => ["padsv", "gvsv"] }, @ops)

          And you can specify inversion by making the first element of the arrayref a "!". (Hint: if you want to
          say "anything", say "not nothing": "["!"]")

          You may also specify the conditions to be matched in nearby ops.

              walkallops_filtered(
                  sub { opgrep( {name => "exec",
                                 next => {
                                           name    => "nextstate",
                                           sibling => { name => [qw(! exit warn die)] }
                                         }
                                }, @_)},
                  sub {
                        carp("Statement unlikely to be reached");
                        carp("\t(Maybe you meant system() when you said exec()?)\n");
                  }
              )

          Get that?

          Here are the things that can be tested:

                  name targ type seq flags private pmflags pmpermflags
                  first other last sibling next pmreplroot pmreplstart pmnext

   EXPORT
       None by default.

AUTHOR

       Simon Cozens, "simon@cpan.org"

TODO

       I need to add more Fun Things, and possibly clean up some parts where the (previous/parent) algorithm has
       catastrophic cases, but it's more important to get this out right now than get it right.

SEE ALSO

       B, B::Generate.

perl v5.18.1                                       2013-10-22                                     B::BUtils(3pm)