1B::Concise(3pm)        Perl Programmers Reference Guide        B::Concise(3pm)
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NAME

6       B::Concise - Walk Perl syntax tree, printing concise info about ops
7

SYNOPSIS

9           perl -MO=Concise[,OPTIONS] foo.pl
10
11           use B::Concise qw(set_style add_callback);
12

DESCRIPTION

14       This compiler backend prints the internal OPs of a Perl program's
15       syntax tree in one of several space-efficient text formats suitable for
16       debugging the inner workings of perl or other compiler backends. It can
17       print OPs in the order they appear in the OP tree, in the order they
18       will execute, or in a text approximation to their tree structure, and
19       the format of the information displayed is customizable. Its function
20       is similar to that of perl's -Dx debugging flag or the B::Terse module,
21       but it is more sophisticated and flexible.
22

EXAMPLE

24       Here's two outputs (or 'renderings'), using the -exec and -basic (i.e.
25       default) formatting conventions on the same code snippet.
26
27           % perl -MO=Concise,-exec -e '$a = $b + 42'
28           1  <0> enter
29           2  <;> nextstate(main 1 -e:1) v
30           3  <#> gvsv[*b] s
31           4  <$> const[IV 42] s
32        *  5  <2> add[t3] sK/2
33           6  <#> gvsv[*a] s
34           7  <2> sassign vKS/2
35           8  <@> leave[1 ref] vKP/REFC
36
37       In this -exec rendering, each opcode is executed in the order shown.
38       The add opcode, marked with '*', is discussed in more detail.
39
40       The 1st column is the op's sequence number, starting at 1, and is
41       displayed in base 36 by default.  Here they're purely linear; the
42       sequences are very helpful when looking at code with loops and
43       branches.
44
45       The symbol between angle brackets indicates the op's type, for example;
46       <2> is a BINOP, <@> a LISTOP, and <#> is a PADOP, which is used in
47       threaded perls. (see "OP class abbreviations").
48
49       The opname, as in 'add[t1]', may be followed by op-specific information
50       in parentheses or brackets (ex '[t1]').
51
52       The op-flags (ex 'sK/2') are described in ("OP flags abbreviations").
53
54           % perl -MO=Concise -e '$a = $b + 42'
55           8  <@> leave[1 ref] vKP/REFC ->(end)
56           1     <0> enter ->2
57           2     <;> nextstate(main 1 -e:1) v ->3
58           7     <2> sassign vKS/2 ->8
59        *  5        <2> add[t1] sK/2 ->6
60           -           <1> ex-rv2sv sK/1 ->4
61           3              <$> gvsv(*b) s ->4
62           4           <$> const(IV 42) s ->5
63           -        <1> ex-rv2sv sKRM*/1 ->7
64           6           <$> gvsv(*a) s ->7
65
66       The default rendering is top-down, so they're not in execution order.
67       This form reflects the way the stack is used to parse and evaluate
68       expressions; the add operates on the two terms below it in the tree.
69
70       Nullops appear as "ex-opname", where opname is an op that has been
71       optimized away by perl.  They're displayed with a sequence-number of
72       '-', because they are not executed (they don't appear in previous
73       example), they're printed here because they reflect the parse.
74
75       The arrow points to the sequence number of the next op; they're not
76       displayed in -exec mode, for obvious reasons.
77
78       Note that because this rendering was done on a non-threaded perl, the
79       PADOPs in the previous examples are now SVOPs, and some (but not all)
80       of the square brackets have been replaced by round ones.  This is a
81       subtle feature to provide some visual distinction between renderings on
82       threaded and un-threaded perls.
83

OPTIONS

85       Arguments that don't start with a hyphen are taken to be the names of
86       subroutines or formats to render; if no such functions are specified,
87       the main body of the program (outside any subroutines, and not
88       including use'd or require'd files) is rendered.  Passing "BEGIN",
89       "UNITCHECK", "CHECK", "INIT", or "END" will cause all of the
90       corresponding special blocks to be printed.  Arguments must follow
91       options.
92
93       Options affect how things are rendered (ie printed).  They're presented
94       here by their visual effect, 1st being strongest.  They're grouped
95       according to how they interrelate; within each group the options are
96       mutually exclusive (unless otherwise stated).
97
98   Options for Opcode Ordering
99       These options control the 'vertical display' of opcodes.  The display
100       'order' is also called 'mode' elsewhere in this document.
101
102       -basic
103           Print OPs in the order they appear in the OP tree (a preorder
104           traversal, starting at the root). The indentation of each OP shows
105           its level in the tree, and the '->' at the end of the line
106           indicates the next opcode in execution order.  This mode is the
107           default, so the flag is included simply for completeness.
108
109       -exec
110           Print OPs in the order they would normally execute (for the
111           majority of constructs this is a postorder traversal of the tree,
112           ending at the root). In most cases the OP that usually follows a
113           given OP will appear directly below it; alternate paths are shown
114           by indentation. In cases like loops when control jumps out of a
115           linear path, a 'goto' line is generated.
116
117       -tree
118           Print OPs in a text approximation of a tree, with the root of the
119           tree at the left and 'left-to-right' order of children transformed
120           into 'top-to-bottom'. Because this mode grows both to the right and
121           down, it isn't suitable for large programs (unless you have a very
122           wide terminal).
123
124   Options for Line-Style
125       These options select the line-style (or just style) used to render each
126       opcode, and dictates what info is actually printed into each line.
127
128       -concise
129           Use the author's favorite set of formatting conventions. This is
130           the default, of course.
131
132       -terse
133           Use formatting conventions that emulate the output of B::Terse. The
134           basic mode is almost indistinguishable from the real B::Terse, and
135           the exec mode looks very similar, but is in a more logical order
136           and lacks curly brackets. B::Terse doesn't have a tree mode, so the
137           tree mode is only vaguely reminiscent of B::Terse.
138
139       -linenoise
140           Use formatting conventions in which the name of each OP, rather
141           than being written out in full, is represented by a one- or two-
142           character abbreviation.  This is mainly a joke.
143
144       -debug
145           Use formatting conventions reminiscent of CPAN module B::Debug;
146           these aren't very concise at all.
147
148       -env
149           Use formatting conventions read from the environment variables
150           "B_CONCISE_FORMAT", "B_CONCISE_GOTO_FORMAT", and
151           "B_CONCISE_TREE_FORMAT".
152
153   Options for tree-specific formatting
154       -compact
155           Use a tree format in which the minimum amount of space is used for
156           the lines connecting nodes (one character in most cases). This
157           squeezes out a few precious columns of screen real estate.
158
159       -loose
160           Use a tree format that uses longer edges to separate OP nodes. This
161           format tends to look better than the compact one, especially in
162           ASCII, and is the default.
163
164       -vt Use tree connecting characters drawn from the VT100 line-drawing
165           set.  This looks better if your terminal supports it.
166
167       -ascii
168           Draw the tree with standard ASCII characters like "+" and "|".
169           These don't look as clean as the VT100 characters, but they'll work
170           with almost any terminal (or the horizontal scrolling mode of
171           less(1)) and are suitable for text documentation or email. This is
172           the default.
173
174       These are pairwise exclusive, i.e. compact or loose, vt or ascii.
175
176   Options controlling sequence numbering
177       -basen
178           Print OP sequence numbers in base n. If n is greater than 10, the
179           digit for 11 will be 'a', and so on. If n is greater than 36, the
180           digit for 37 will be 'A', and so on until 62. Values greater than
181           62 are not currently supported. The default is 36.
182
183       -bigendian
184           Print sequence numbers with the most significant digit first. This
185           is the usual convention for Arabic numerals, and the default.
186
187       -littleendian
188           Print sequence numbers with the least significant digit first.
189           This is obviously mutually exclusive with bigendian.
190
191   Other options
192       -src
193           With this option, the rendering of each statement (starting with
194           the nextstate OP) will be preceded by the 1st line of source code
195           that generates it.  For example:
196
197               1  <0> enter
198               # 1: my $i;
199               2  <;> nextstate(main 1 junk.pl:1) v:{
200               3  <0> padsv[$i:1,10] vM/LVINTRO
201               # 3: for $i (0..9) {
202               4  <;> nextstate(main 3 junk.pl:3) v:{
203               5  <0> pushmark s
204               6  <$> const[IV 0] s
205               7  <$> const[IV 9] s
206               8  <{> enteriter(next->j last->m redo->9)[$i:1,10] lKS
207               k  <0> iter s
208               l  <|> and(other->9) vK/1
209               # 4:     print "line ";
210               9      <;> nextstate(main 2 junk.pl:4) v
211               a      <0> pushmark s
212               b      <$> const[PV "line "] s
213               c      <@> print vK
214               # 5:     print "$i\n";
215               ...
216
217       -stash="somepackage"
218           With this, "somepackage" will be required, then the stash is
219           inspected, and each function is rendered.
220
221       The following options are pairwise exclusive.
222
223       -main
224           Include the main program in the output, even if subroutines were
225           also specified.  This rendering is normally suppressed when a
226           subroutine name or reference is given.
227
228       -nomain
229           This restores the default behavior after you've changed it with
230           '-main' (it's not normally needed).  If no subroutine name/ref is
231           given, main is rendered, regardless of this flag.
232
233       -nobanner
234           Renderings usually include a banner line identifying the function
235           name or stringified subref.  This suppresses the printing of the
236           banner.
237
238           TBC: Remove the stringified coderef; while it provides a 'cookie'
239           for each function rendered, the cookies used should be 1,2,3.. not
240           a random hex-address.  It also complicates string comparison of two
241           different trees.
242
243       -banner
244           restores default banner behavior.
245
246       -banneris => subref
247           TBC: a hookpoint (and an option to set it) for a user-supplied
248           function to produce a banner appropriate for users needs.  It's not
249           ideal, because the rendering-state variables, which are a natural
250           candidate for use in concise.t, are unavailable to the user.
251
252   Option Stickiness
253       If you invoke Concise more than once in a program, you should know that
254       the options are 'sticky'.  This means that the options you provide in
255       the first call will be remembered for the 2nd call, unless you re-
256       specify or change them.
257

ABBREVIATIONS

259       The concise style uses symbols to convey maximum info with minimal
260       clutter (like hex addresses).  With just a little practice, you can
261       start to see the flowers, not just the branches, in the trees.
262
263   OP class abbreviations
264       These symbols appear before the op-name, and indicate the B:: namespace
265       that represents the ops in your Perl code.
266
267           0      OP (aka BASEOP)  An OP with no children
268           1      UNOP             An OP with one child
269           +      UNOP_AUX         A UNOP with auxillary fields
270           2      BINOP            An OP with two children
271           |      LOGOP            A control branch OP
272           @      LISTOP           An OP that could have lots of children
273           /      PMOP             An OP with a regular expression
274           $      SVOP             An OP with an SV
275           "      PVOP             An OP with a string
276           {      LOOP             An OP that holds pointers for a loop
277           ;      COP              An OP that marks the start of a statement
278           #      PADOP            An OP with a GV on the pad
279           .      METHOP           An OP with method call info
280
281   OP flags abbreviations
282       OP flags are either public or private.  The public flags alter the
283       behavior of each opcode in consistent ways, and are represented by 0 or
284       more single characters.
285
286           v      OPf_WANT_VOID    Want nothing (void context)
287           s      OPf_WANT_SCALAR  Want single value (scalar context)
288           l      OPf_WANT_LIST    Want list of any length (list context)
289                                   Want is unknown
290           K      OPf_KIDS         There is a firstborn child.
291           P      OPf_PARENS       This operator was parenthesized.
292                                    (Or block needs explicit scope entry.)
293           R      OPf_REF          Certified reference.
294                                    (Return container, not containee).
295           M      OPf_MOD          Will modify (lvalue).
296           S      OPf_STACKED      Some arg is arriving on the stack.
297           *      OPf_SPECIAL      Do something weird for this op (see op.h)
298
299       Private flags, if any are set for an opcode, are displayed after a '/'
300
301           8  <@> leave[1 ref] vKP/REFC ->(end)
302           7     <2> sassign vKS/2 ->8
303
304       They're opcode specific, and occur less often than the public ones, so
305       they're represented by short mnemonics instead of single-chars; see
306       B::Op_private and regen/op_private for more details.
307

FORMATTING SPECIFICATIONS

309       For each line-style ('concise', 'terse', 'linenoise', etc.) there are 3
310       format-specs which control how OPs are rendered.
311
312       The first is the 'default' format, which is used in both basic and exec
313       modes to print all opcodes.  The 2nd, goto-format, is used in exec mode
314       when branches are encountered.  They're not real opcodes, and are
315       inserted to look like a closing curly brace.  The tree-format is tree
316       specific.
317
318       When a line is rendered, the correct format-spec is copied and scanned
319       for the following items; data is substituted in, and other
320       manipulations like basic indenting are done, for each opcode rendered.
321
322       There are 3 kinds of items that may be populated; special patterns,
323       #vars, and literal text, which is copied verbatim.  (Yes, it's a set of
324       s///g steps.)
325
326   Special Patterns
327       These items are the primitives used to perform indenting, and to select
328       text from amongst alternatives.
329
330       (x(exec_text;basic_text)x)
331           Generates exec_text in exec mode, or basic_text in basic mode.
332
333       (*(text)*)
334           Generates one copy of text for each indentation level.
335
336       (*(text1;text2)*)
337           Generates one fewer copies of text1 than the indentation level,
338           followed by one copy of text2 if the indentation level is more than
339           0.
340
341       (?(text1#varText2)?)
342           If the value of var is true (not empty or zero), generates the
343           value of var surrounded by text1 and Text2, otherwise nothing.
344
345       ~   Any number of tildes and surrounding whitespace will be collapsed
346           to a single space.
347
348   # Variables
349       These #vars represent opcode properties that you may want as part of
350       your rendering.  The '#' is intended as a private sigil; a #var's value
351       is interpolated into the style-line, much like "read $this".
352
353       These vars take 3 forms:
354
355       #var
356           A property named 'var' is assumed to exist for the opcodes, and is
357           interpolated into the rendering.
358
359       #varN
360           Generates the value of var, left justified to fill N spaces.  Note
361           that this means while you can have properties 'foo' and 'foo2', you
362           cannot render 'foo2', but you could with 'foo2a'.  You would be
363           wise not to rely on this behavior going forward ;-)
364
365       #Var
366           This ucfirst form of #var generates a tag-value form of itself for
367           display; it converts '#Var' into a 'Var => #var' style, which is
368           then handled as described above.  (Imp-note: #Vars cannot be used
369           for conditional-fills, because the => #var transform is done after
370           the check for #Var's value).
371
372       The following variables are 'defined' by B::Concise; when they are used
373       in a style, their respective values are plugged into the rendering of
374       each opcode.
375
376       Only some of these are used by the standard styles, the others are
377       provided for you to delve into optree mechanics, should you wish to add
378       a new style (see "add_style" below) that uses them.  You can also add
379       new ones using "add_callback".
380
381       #addr
382           The address of the OP, in hexadecimal.
383
384       #arg
385           The OP-specific information of the OP (such as the SV for an SVOP,
386           the non-local exit pointers for a LOOP, etc.) enclosed in
387           parentheses.
388
389       #class
390           The B-determined class of the OP, in all caps.
391
392       #classsym
393           A single symbol abbreviating the class of the OP.
394
395       #coplabel
396           The label of the statement or block the OP is the start of, if any.
397
398       #exname
399           The name of the OP, or 'ex-foo' if the OP is a null that used to be
400           a foo.
401
402       #extarg
403           The target of the OP, or nothing for a nulled OP.
404
405       #firstaddr
406           The address of the OP's first child, in hexadecimal.
407
408       #flags
409           The OP's flags, abbreviated as a series of symbols.
410
411       #flagval
412           The numeric value of the OP's flags.
413
414       #hints
415           The COP's hint flags, rendered with abbreviated names if possible.
416           An empty string if this is not a COP. Here are the symbols used:
417
418               $ strict refs
419               & strict subs
420               * strict vars
421              x$ explicit use/no strict refs
422              x& explicit use/no strict subs
423              x* explicit use/no strict vars
424               i integers
425               l locale
426               b bytes
427               { block scope
428               % localise %^H
429               < open in
430               > open out
431               I overload int
432               F overload float
433               B overload binary
434               S overload string
435               R overload re
436               T taint
437               E eval
438               X filetest access
439               U utf-8
440
441               us      use feature 'unicode_strings'
442               fea=NNN feature bundle number
443
444       #hintsval
445           The numeric value of the COP's hint flags, or an empty string if
446           this is not a COP.
447
448       #hyphseq
449           The sequence number of the OP, or a hyphen if it doesn't have one.
450
451       #label
452           'NEXT', 'LAST', or 'REDO' if the OP is a target of one of those in
453           exec mode, or empty otherwise.
454
455       #lastaddr
456           The address of the OP's last child, in hexadecimal.
457
458       #name
459           The OP's name.
460
461       #NAME
462           The OP's name, in all caps.
463
464       #next
465           The sequence number of the OP's next OP.
466
467       #nextaddr
468           The address of the OP's next OP, in hexadecimal.
469
470       #noise
471           A one- or two-character abbreviation for the OP's name.
472
473       #private
474           The OP's private flags, rendered with abbreviated names if
475           possible.
476
477       #privval
478           The numeric value of the OP's private flags.
479
480       #seq
481           The sequence number of the OP. Note that this is a sequence number
482           generated by B::Concise.
483
484       #opt
485           Whether or not the op has been optimized by the peephole optimizer.
486
487       #sibaddr
488           The address of the OP's next youngest sibling, in hexadecimal.
489
490       #svaddr
491           The address of the OP's SV, if it has an SV, in hexadecimal.
492
493       #svclass
494           The class of the OP's SV, if it has one, in all caps (e.g., 'IV').
495
496       #svval
497           The value of the OP's SV, if it has one, in a short human-readable
498           format.
499
500       #targ
501           The numeric value of the OP's targ.
502
503       #targarg
504           The name of the variable the OP's targ refers to, if any, otherwise
505           the letter t followed by the OP's targ in decimal.
506
507       #targarglife
508           Same as #targarg, but followed by the COP sequence numbers that
509           delimit the variable's lifetime (or 'end' for a variable in an open
510           scope) for a variable.
511
512       #typenum
513           The numeric value of the OP's type, in decimal.
514

One-Liner Command tips

516       perl -MO=Concise,bar foo.pl
517           Renders only bar() from foo.pl.  To see main, drop the ',bar'.  To
518           see both, add ',-main'
519
520       perl -MDigest::MD5=md5 -MO=Concise,md5 -e1
521           Identifies md5 as an XS function.  The export is needed so that BC
522           can find it in main.
523
524       perl -MPOSIX -MO=Concise,_POSIX_ARG_MAX -e1
525           Identifies _POSIX_ARG_MAX as a constant sub, optimized to an IV.
526           Although POSIX isn't entirely consistent across platforms, this is
527           likely to be present in virtually all of them.
528
529       perl -MPOSIX -MO=Concise,a -e 'print _POSIX_SAVED_IDS'
530           This renders a print statement, which includes a call to the
531           function.  It's identical to rendering a file with a use call and
532           that single statement, except for the filename which appears in the
533           nextstate ops.
534
535       perl -MPOSIX -MO=Concise,a -e 'sub a{_POSIX_SAVED_IDS}'
536           This is very similar to previous, only the first two ops differ.
537           This subroutine rendering is more representative, insofar as a
538           single main program will have many subs.
539
540       perl -MB::Concise -e 'B::Concise::compile("-exec","-src",
541       \%B::Concise::)->()'
542           This renders all functions in the B::Concise package with the
543           source lines.  It eschews the O framework so that the stashref can
544           be passed directly to B::Concise::compile().  See -stash option for
545           a more convenient way to render a package.
546

Using B::Concise outside of the O framework

548       The common (and original) usage of B::Concise was for command-line
549       renderings of simple code, as given in EXAMPLE.  But you can also use
550       B::Concise from your code, and call compile() directly, and repeatedly.
551       By doing so, you can avoid the compile-time only operation of O.pm, and
552       even use the debugger to step through B::Concise::compile() itself.
553
554       Once you're doing this, you may alter Concise output by adding new
555       rendering styles, and by optionally adding callback routines which
556       populate new variables, if such were referenced from those (just added)
557       styles.
558
559   Example: Altering Concise Renderings
560           use B::Concise qw(set_style add_callback);
561           add_style($yourStyleName => $defaultfmt, $gotofmt, $treefmt);
562           add_callback
563             ( sub {
564                   my ($h, $op, $format, $level, $stylename) = @_;
565                   $h->{variable} = some_func($op);
566               });
567           $walker = B::Concise::compile(@options,@subnames,@subrefs);
568           $walker->();
569
570   set_style()
571       set_style accepts 3 arguments, and updates the three format-specs
572       comprising a line-style (basic-exec, goto, tree).  It has one minor
573       drawback though; it doesn't register the style under a new name.  This
574       can become an issue if you render more than once and switch styles.
575       Thus you may prefer to use add_style() and/or set_style_standard()
576       instead.
577
578   set_style_standard($name)
579       This restores one of the standard line-styles: "terse", "concise",
580       "linenoise", "debug", "env", into effect.  It also accepts style names
581       previously defined with add_style().
582
583   add_style ()
584       This subroutine accepts a new style name and three style arguments as
585       above, and creates, registers, and selects the newly named style.  It
586       is an error to re-add a style; call set_style_standard() to switch
587       between several styles.
588
589   add_callback ()
590       If your newly minted styles refer to any new #variables, you'll need to
591       define a callback subroutine that will populate (or modify) those
592       variables.  They are then available for use in the style you've chosen.
593
594       The callbacks are called for each opcode visited by Concise, in the
595       same order as they are added.  Each subroutine is passed five
596       parameters.
597
598         1. A hashref, containing the variable names and values which are
599            populated into the report-line for the op
600         2. the op, as a B<B::OP> object
601         3. a reference to the format string
602         4. the formatting (indent) level
603         5. the selected stylename
604
605       To define your own variables, simply add them to the hash, or change
606       existing values if you need to.  The level and format are passed in as
607       references to scalars, but it is unlikely that they will need to be
608       changed or even used.
609
610   Running B::Concise::compile()
611       compile accepts options as described above in "OPTIONS", and arguments,
612       which are either coderefs, or subroutine names.
613
614       It constructs and returns a $treewalker coderef, which when invoked,
615       traverses, or walks, and renders the optrees of the given arguments to
616       STDOUT.  You can reuse this, and can change the rendering style used
617       each time; thereafter the coderef renders in the new style.
618
619       walk_output lets you change the print destination from STDOUT to
620       another open filehandle, or into a string passed as a ref (unless
621       you've built perl with -Uuseperlio).
622
623         my $walker = B::Concise::compile('-terse','aFuncName', \&aSubRef); # 1
624         walk_output(\my $buf);
625         $walker->();                          # 1 renders -terse
626         set_style_standard('concise');        # 2
627         $walker->();                          # 2 renders -concise
628         $walker->(@new);                      # 3 renders whatever
629         print "3 different renderings: terse, concise, and @new: $buf\n";
630
631       When $walker is called, it traverses the subroutines supplied when it
632       was created, and renders them using the current style.  You can change
633       the style afterwards in several different ways:
634
635         1. call C<compile>, altering style or mode/order
636         2. call C<set_style_standard>
637         3. call $walker, passing @new options
638
639       Passing new options to the $walker is the easiest way to change amongst
640       any pre-defined styles (the ones you add are automatically recognized
641       as options), and is the only way to alter rendering order without
642       calling compile again.  Note however that rendering state is still
643       shared amongst multiple $walker objects, so they must still be used in
644       a coordinated manner.
645
646   B::Concise::reset_sequence()
647       This function (not exported) lets you reset the sequence numbers (note
648       that they're numbered arbitrarily, their goal being to be human
649       readable).  Its purpose is mostly to support testing, i.e. to compare
650       the concise output from two identical anonymous subroutines (but
651       different instances).  Without the reset, B::Concise, seeing that
652       they're separate optrees, generates different sequence numbers in the
653       output.
654
655   Errors
656       Errors in rendering (non-existent function-name, non-existent coderef)
657       are written to the STDOUT, or wherever you've set it via walk_output().
658
659       Errors using the various *style* calls, and bad args to walk_output(),
660       result in die().  Use an eval if you wish to catch these errors and
661       continue processing.
662

AUTHOR

664       Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.
665
666
667
668perl v5.34.0                      2021-10-18                   B::Concise(3pm)
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