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B::Utils(3)	      User Contributed Perl Documentation	   B::Utils(3)

NAME
       B::Utils - Helper functions for op tree manipulation

VERSION
       0.19

INSTALLATION
       To install this module, run the following commands:

	   perl Makefile.PL
	   make
	   make test
	   make install

SYNOPSIS
	 use B::Utils;

OP METHODS
       "$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->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->ancestors"
	   Returns all parents of this node, recursively. The list is ordered
	   from younger/closer parents to older/farther parents.

       "$op->descendants"
	   Returns all children of this node, recursively. The list is
	   unordered.

       "$op->siblings"
	   Returns all younger siblings of this node. The list is ordered from
	   younger/closer siblings to older/farther siblings.

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

       "$op->stringify"
	   Returns a nice stringification of an opcode.

       "$op->as_opgrep_pattern(%options)"
	   From the op tree it is called on, "as_opgrep_pattern()" generates a
	   data structure suitable for use as a condition pattern for the
	   "opgrep()" function described below in detail.  Beware: When using
	   such generated patterns, there may be false positives: The pattern
	   will most likely not match only the op tree it was generated from
	   since by default, not all properties of the op are reproduced.

	   You can control which properties of the op to include in the
	   pattern by passing named arguments. The default behaviour is as if
	   you passed in the following options:

	     my $pattern = $op->as_opgrep_pattern(
	       attributes	   => [qw(name flags)],
	       max_recursion_depth => undef,
	     );

	   So obviously, you can set "max_recursion_depth" to a number to
	   limit the maximum depth of recursion into the op tree. Setting it
	   to 0 will limit the dump to the current op.

	   "attributes" is a list of attributes to include in the produced
	   pattern. The attributes that can be checked against in this way are

	     name targ type seq flags private pmflags pmpermflags.

EXPORTABLE 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.

       "recalc_sub_cache"
	   If PL_sub_generation has changed or you have some other reason to
	   want to force the re-examination of the optrees, everywhere, call
	   this function.

       "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.

	   All the "walk" functions set $B::Utils::file, $B::Utils::line, and
	   $B::Utils::sub to the appropriate values of file, line number, and
	   sub name in the program being examined.

       "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.

       "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
				  );

	   where the first argument to "opgrep()" is the condition to be
	   matched against the op structure. We'll henceforth refer to it as
	   an op-pattern.

	   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 as
	   nested patterns.

	       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 in this way:

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

	   Additionally, you can use the "kids" keyword with an array
	   reference to match the result of a call to "$op->kids()". An
	   example use is given in the documentation for "op_or" below.

	   For debugging, you can have many properties of an op that is
	   currently being matched against a given condition dumped to STDERR
	   by specifying "dump =" 1> in the condition's hash reference.

	   If you match a complex condition against an op tree, you may want
	   to extract a specific piece of information from the tree if the
	   condition matches.  This normally entails manually walking the tree
	   a second time down to the op you wish to extract, investigate or
	   modify. Since this is tedious duplication of code and information,
	   you can specify a special property in the pattern of the op you
	   wish to extract to capture the sub-op of interest. Example:

	     my ($result) = opgrep(
	       { name => "exec",
		 next => { name	   => "nextstate",
			   sibling => { name => [qw(! exit warn die)]
					capture => "notreached",
				      },
			 }
	       },
	       $root_op
	     );

	     if ($result) {
	       my $name = $result->{notreached}->name; # result is *not* the root op
	       carp("Statement unlikely to be reached (op name: $name)");
	       carp("\t(Maybe you meant system() when you said exec()?)\n");
	     }

	   While the above is a terribly contrived example, consider the win
	   for a deeply nested pattern or worse yet, a pattern with many
	   disjunctions.  If a "capture" property is found anywhere in the op
	   pattern, "opgrep()" returns an unblessed hash reference on success
	   instead of the tested op. You can tell them apart using
	   Scalar::Util's "blessed()". That hash reference contains all
	   captured ops plus the tested root up as the hash entry
	   "$result->{op}". Note that you cannot use this feature with
	   "walkoptree_filtered" since that function was specifically
	   documented to pass the tested op itself to the callback.

	   You cannot capture disjunctions, but that doesn't really make sense
	   anyway.

       "opgrep( \@conditions, @ops )"
	   Same as above, except that you don't have to chain the conditions
	   yourself.  If you pass an array-ref, opgrep will chain the
	   conditions for you using "next".  The conditions can either be
	   strings (taken as op-names), or hash-refs, with the same testable
	   conditions as given above.

       "op_or( @conditions )"
	   Unlike the chaining of conditions done by "opgrep" itself if there
	   are multiple conditions, this function creates a disjunction
	   ("$cond1 || $cond2 || ...") of the conditions and returns a
	   structure (hash reference) that can be passed to opgrep as a single
	   condition.

	   Example:

	     my $sub_structure = {
	       name => 'helem',
	       first => { name => 'rv2hv', },
	       'last' => { name => 'const', },
	     };

	     my @ops = opgrep( {
		 name => 'leavesub',
		 first => {
		   name => 'lineseq',
		   kids => [,
		     { name => 'nextstate', },
		     op_or(
		       {
			 name => 'return',
			 first => { name => 'pushmark' },
			 last => $sub_structure,
		       },
		       $sub_structure,
		     ),
		   ],
		 },
	     }, $op_obj );

	   This example matches the code in a typical simplest-possible
	   accessor method (albeit not down to the last bit):

	     sub get_foo { $_[0]->{foo} }

	   But by adding an alternation we can also match optional op layers.
	   In this case, we optionally match a return statement, so the
	   following implementation is also recognized:

	     sub get_foo { return $_[0]->{foo} }

	   Essentially, this is syntactic sugar for the following structure
	   recognized by "opgrep()":

	     { disjunction => [@conditions] }

       "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.

   EXPORT
       None by default.

   XS EXPORT
       This modules uses ExtUtils::Depends to export some useful functions for
       XS modules to use.  To use those, include in your Makefile.PL:

	 my $pkg = ExtUtils::Depends->new("Your::XSModule", "B::Utils");
	 WriteMakefile(
	   ... # your normal makefile flags
	   $pkg->get_makefile_vars,
	 );

       Your XS module can now include BUtils.h and BUtils_op.h.	 To see
       document for the functions provided, use:

	 perldoc -m B::Utils::Install::BUtils.h
	 perldoc -m B::Utils::Install::BUtils_op.h

AUTHOR
       Originally written by Simon Cozens, "simon@cpan.org" Maintained by
       Joshua ben Jore, "jjore@cpan.org"

       Contributions from Mattia Barbon, Jim Cromie, Steffen Mueller, and
       Chia-liang Kao, Alexandr Ciornii.

LICENSE
       This module is free software; you can redistribute it and/or modify it
       under the same terms as Perl itself.

SEE ALSO
       B, B::Generate.

perl v5.14.2			  2012-03-12			   B::Utils(3)
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