1B::Utils(3) User Contributed Perl Documentation B::Utils(3)
2
6 B::Utils - Helper functions for op tree manipulation
7
9 version 0.27
10
12 To install this module, run the following commands:
13 perl Makefile.PL
15 make
16 make test
17 make install
18
20 use B::Utils;
21
23 "$op->oldname"
24 Returns the name of the op, even if it is currently optimized to
25 null. This helps you understand the structure of the op tree.
26 "$op->kids"
28 Returns an array of all this op's non-null children, in order.
29 "$op->parent"
31 Returns the parent node in the op tree, if possible. Currently
32 "possible" means "if the tree has already been optimized"; that is,
33 if we're during a "CHECK" block. (and hence, if we have valid
34 "next" pointers.)
35 In the future, it may be possible to search for the parent before
37 we have the "next" pointers in place, but it'll take me a while to
38 figure out how to do that.
39 Warning: Since 5.21.2 B comes with its own version of B::OP::parent
41 which returns either B::NULL or the real parent when ccflags
42 contains -DPERL_OP_PARENT. In this case rather use $op->_parent.
43 "$op->ancestors"
45 Returns all parents of this node, recursively. The list is ordered
46 from younger/closer parents to older/farther parents.
47 "$op->descendants"
49 Returns all children of this node, recursively. The list is
50 unordered.
51 "$op->siblings"
53 Returns all younger siblings of this node. The list is ordered from
54 younger/closer siblings to older/farther siblings.
55 "$op->previous"
57 Like " $op->next ", but not quite.
58 "$op->stringify"
60 Returns a nice stringification of an opcode.
61 "$op->as_opgrep_pattern(%options)"
63 From the op tree it is called on, "as_opgrep_pattern()" generates a
64 data structure suitable for use as a condition pattern for the
65 "opgrep()" function described below in detail. Beware: When using
66 such generated patterns, there may be false positives: The pattern
67 will most likely not match only the op tree it was generated from
68 since by default, not all properties of the op are reproduced.
69 You can control which properties of the op to include in the
71 pattern by passing named arguments. The default behaviour is as if
72 you passed in the following options:
73 my $pattern = $op->as_opgrep_pattern(
75 attributes => [qw(name flags)],
76 max_recursion_depth => undef,
77 );
78 So obviously, you can set "max_recursion_depth" to a number to
80 limit the maximum depth of recursion into the op tree. Setting it
81 to 0 will limit the dump to the current op.
82 "attributes" is a list of attributes to include in the produced
84 pattern. The attributes that can be checked against in this way
85 are:
86 name targ type seq flags private pmflags pmpermflags.
88
90 "all_starts"
91 "all_roots"
92 Returns a hash of all of the starting ops or root ops of optrees,
93 keyed to subroutine name; the optree for main program is simply
94 keyed to "__MAIN__".
95 Note: Certain "dangerous" stashes are not scanned for subroutines:
97 the list of such stashes can be found in @B::Utils::bad_stashes.
98 Feel free to examine and/or modify this to suit your needs. The
99 intention is that a simple program which uses no modules other than
100 "B" and "B::Utils" would show no addition symbols.
101 This does not return the details of ops in anonymous subroutines
103 compiled at compile time. For instance, given
104 $a = sub { ... };
106 the subroutine will not appear in the hash. This is just as well,
108 since they're anonymous... If you want to get at them, use...
109 "anon_subs"
111 This returns an array of hash references. Each element has the keys
112 "start" and "root". These are the starting and root ops of all of
113 the anonymous subroutines in the program.
114 "recalc_sub_cache"
116 If PL_sub_generation has changed or you have some other reason to
117 want to force the re-examination of the optrees, everywhere, call
118 this function.
119 "walkoptree_simple($op, \&callback, [$data])"
121 The "B" module provides various functions to walk the op tree, but
122 they're all rather difficult to use, requiring you to inject
123 methods into the "B::OP" class. This is a very simple op tree
124 walker with more expected semantics.
125 All the "walk" functions set $B::Utils::file, $B::Utils::line, and
127 $B::Utils::sub to the appropriate values of file, line number, and
128 sub name in the program being examined.
129 "walkoptree_filtered($op, \&filter, \&callback, [$data])"
131 This is much the same as "walkoptree_simple", but will only call
132 the callback if the "filter" returns true. The "filter" is passed
133 the op in question as a parameter; the "opgrep" function is
134 fantastic for building your own filters.
135 "walkallops_simple(\&callback, [$data])"
137 This combines "walkoptree_simple" with "all_roots" and "anon_subs"
138 to examine every op in the program. $B::Utils::sub is set to the
139 subroutine name if you're in a subroutine, "__MAIN__" if you're in
140 the main program and "__ANON__" if you're in an anonymous
141 subroutine.
142 "walkallops_filtered(\&filter, \&callback, [$data])"
144 Same as above, but filtered.
145 "opgrep(\%conditions, @ops)"
147 Returns the ops which meet the given conditions. The conditions
148 should be specified like this:
149 @barewords = opgrep(
151 { name => "const", private => OPpCONST_BARE },
152 @ops
153 );
154 where the first argument to "opgrep()" is the condition to be
156 matched against the op structure. We'll henceforth refer to it as
157 an op-pattern.
158 You can specify alternation by giving an arrayref of values:
160 @svs = opgrep ( { name => ["padsv", "gvsv"] }, @ops)
162 And you can specify inversion by making the first element of the
164 arrayref a "!". (Hint: if you want to say "anything", say "not
165 nothing": "["!"]")
166 You may also specify the conditions to be matched in nearby ops as
168 nested patterns.
169 walkallops_filtered(
171 sub { opgrep( {name => "exec",
172 next => {
173 name => "nextstate",
174 sibling => { name => [qw(! exit warn die)] }
175 }
176 }, @_)},
177 sub {
178 carp("Statement unlikely to be reached");
179 carp("\t(Maybe you meant system() when you said exec()?)\n");
180 }
181 )
182 Get that?
184 Here are the things that can be tested in this way:
186 name targ type seq flags private pmflags pmpermflags
188 first other last sibling next pmreplroot pmreplstart pmnext
189 Additionally, you can use the "kids" keyword with an array
191 reference to match the result of a call to "$op->kids()". An
192 example use is given in the documentation for "op_or" below.
193 For debugging, you can have many properties of an op that is
195 currently being matched against a given condition dumped to STDERR
196 by specifying "dump =" 1> in the condition's hash reference.
197 If you match a complex condition against an op tree, you may want
199 to extract a specific piece of information from the tree if the
200 condition matches. This normally entails manually walking the tree
201 a second time down to the op you wish to extract, investigate or
202 modify. Since this is tedious duplication of code and information,
203 you can specify a special property in the pattern of the op you
204 wish to extract to capture the sub-op of interest. Example:
205 my ($result) = opgrep(
207 { name => "exec",
208 next => { name => "nextstate",
209 sibling => { name => [qw(! exit warn die)]
210 capture => "notreached",
211 },
212 }
213 },
214 $root_op
215 );
216 if ($result) {
218 my $name = $result->{notreached}->name; # result is *not* the root op
219 carp("Statement unlikely to be reached (op name: $name)");
220 carp("\t(Maybe you meant system() when you said exec()?)\n");
221 }
222 While the above is a terribly contrived example, consider the win
224 for a deeply nested pattern or worse yet, a pattern with many
225 disjunctions. If a "capture" property is found anywhere in the op
226 pattern, "opgrep()" returns an unblessed hash reference on success
227 instead of the tested op. You can tell them apart using
228 Scalar::Util's "blessed()". That hash reference contains all
229 captured ops plus the tested root up as the hash entry
230 "$result->{op}". Note that you cannot use this feature with
231 "walkoptree_filtered" since that function was specifically
232 documented to pass the tested op itself to the callback.
233 You cannot capture disjunctions, but that doesn't really make sense
235 anyway.
236 "opgrep( \@conditions, @ops )"
238 Same as above, except that you don't have to chain the conditions
239 yourself. If you pass an array-ref, opgrep will chain the
240 conditions for you using "next". The conditions can either be
241 strings (taken as op-names), or hash-refs, with the same testable
242 conditions as given above.
243 "op_or( @conditions )"
245 Unlike the chaining of conditions done by "opgrep" itself if there
246 are multiple conditions, this function creates a disjunction
247 ("$cond1 || $cond2 || ...") of the conditions and returns a
248 structure (hash reference) that can be passed to opgrep as a single
249 condition.
250 Example:
252 my $sub_structure = {
254 name => 'helem',
255 first => { name => 'rv2hv', },
256 'last' => { name => 'const', },
257 };
258 my @ops = opgrep( {
260 name => 'leavesub',
261 first => {
262 name => 'lineseq',
263 kids => [,
264 { name => 'nextstate', },
265 op_or(
266 {
267 name => 'return',
268 first => { name => 'pushmark' },
269 last => $sub_structure,
270 },
271 $sub_structure,
272 ),
273 ],
274 },
275 }, $op_obj );
276 This example matches the code in a typical simplest-possible
278 accessor method (albeit not down to the last bit):
279 sub get_foo { $_[0]->{foo} }
281 But by adding an alternation we can also match optional op layers.
283 In this case, we optionally match a return statement, so the
284 following implementation is also recognized:
285 sub get_foo { return $_[0]->{foo} }
287 Essentially, this is syntactic sugar for the following structure
289 recognized by "opgrep()":
290 { disjunction => [@conditions] }
292 "carp(@args)"
294 "croak(@args)"
295 Warn and die, respectively, from the perspective of the position of
296 the op in the program. Sounds complicated, but it's exactly the
297 kind of error reporting you expect when you're grovelling through
298 an op tree.
299 EXPORT
301 None by default.
302 XS EXPORT
304 This modules uses ExtUtils::Depends to export some useful functions for
305 XS modules to use. To use those, include in your Makefile.PL:
306 my $pkg = ExtUtils::Depends->new("Your::XSModule", "B::Utils");
308 WriteMakefile(
309 ... # your normal makefile flags
310 $pkg->get_makefile_vars,
311 );
312 Your XS module can now include BUtils.h and BUtils_op.h. To see
314 document for the functions provided, use:
315 perldoc -m B::Utils::Install::BUtils.h
317 perldoc -m B::Utils::Install::BUtils_op.h
318
320 Originally written by Simon Cozens, "simon@cpan.org" Maintained by
321 Joshua ben Jore, "jjore@cpan.org"
322 Contributions from Mattia Barbon, Jim Cromie, Steffen Mueller, and
324 Chia-liang Kao, Alexandr Ciornii, Reini Urban.
325
327 This module is free software; you can redistribute it and/or modify it
328 under the same terms as Perl itself.
329
331 B, B::Generate.
332perl v5.36.0 2022-07-22 B::Utils(3)