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


           perl -MO=Concise[,OPTIONS]

           use B::Concise qw(set_style add_callback);


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


       Here's two outputs (or 'renderings'), using the -exec and -basic (i.e. default) formatting
       conventions on the same code snippet.

           % perl -MO=Concise,-exec -e '$a = $b + 42'
           1  <0> enter
           2  <;> nextstate(main 1 -e:1) v
           3  <#> gvsv[*b] s
           4  <$> const[IV 42] s
        *  5  <2> add[t3] sK/2
           6  <#> gvsv[*a] s
           7  <2> sassign vKS/2
           8  <@> leave[1 ref] vKP/REFC

       In this -exec rendering, each opcode is executed in the order shown.  The add opcode,
       marked with '*', is discussed in more detail.

       The 1st column is the op's sequence number, starting at 1, and is displayed in base 36 by
       default.  Here they're purely linear; the sequences are very helpful when looking at code
       with loops and branches.

       The symbol between angle brackets indicates the op's type, for example; <2> is a BINOP,
       <@> a LISTOP, and <#> is a PADOP, which is used in threaded perls. (see "OP class

       The opname, as in 'add[t1]', may be followed by op-specific information in parentheses or
       brackets (ex '[t1]').

       The op-flags (ex 'sK/2') are described in ("OP flags abbreviations").

           % perl -MO=Concise -e '$a = $b + 42'
           8  <@> leave[1 ref] vKP/REFC ->(end)
           1     <0> enter ->2
           2     <;> nextstate(main 1 -e:1) v ->3
           7     <2> sassign vKS/2 ->8
        *  5        <2> add[t1] sK/2 ->6
           -           <1> ex-rv2sv sK/1 ->4
           3              <$> gvsv(*b) s ->4
           4           <$> const(IV 42) s ->5
           -        <1> ex-rv2sv sKRM*/1 ->7
           6           <$> gvsv(*a) s ->7

       The default rendering is top-down, so they're not in execution order.  This form reflects
       the way the stack is used to parse and evaluate expressions; the add operates on the two
       terms below it in the tree.

       Nullops appear as "ex-opname", where opname is an op that has been optimized away by perl.
       They're displayed with a sequence-number of '-', because they are not executed (they don't
       appear in previous example), they're printed here because they reflect the parse.

       The arrow points to the sequence number of the next op; they're not displayed in -exec
       mode, for obvious reasons.

       Note that because this rendering was done on a non-threaded perl, the PADOPs in the
       previous examples are now SVOPs, and some (but not all) of the square brackets have been
       replaced by round ones.  This is a subtle feature to provide some visual distinction
       between renderings on threaded and un-threaded perls.


       Arguments that don't start with a hyphen are taken to be the names of subroutines to
       render; if no such functions are specified, the main body of the program (outside any
       subroutines, and not including use'd or require'd files) is rendered.  Passing "BEGIN",
       "UNITCHECK", "CHECK", "INIT", or "END" will cause all of the corresponding special blocks
       to be printed.  Arguments must follow options.

       Options affect how things are rendered (ie printed).  They're presented here by their
       visual effect, 1st being strongest.  They're grouped according to how they interrelate;
       within each group the options are mutually exclusive (unless otherwise stated).

   Options for Opcode Ordering
       These options control the 'vertical display' of opcodes.  The display 'order' is also
       called 'mode' elsewhere in this document.

           Print OPs in the order they appear in the OP tree (a preorder traversal, starting at
           the root). The indentation of each OP shows its level in the tree, and the '->' at the
           end of the line indicates the next opcode in execution order.  This mode is the
           default, so the flag is included simply for completeness.

           Print OPs in the order they would normally execute (for the majority of constructs
           this is a postorder traversal of the tree, ending at the root). In most cases the OP
           that usually follows a given OP will appear directly below it; alternate paths are
           shown by indentation. In cases like loops when control jumps out of a linear path, a
           'goto' line is generated.

           Print OPs in a text approximation of a tree, with the root of the tree at the left and
           'left-to-right' order of children transformed into 'top-to-bottom'. Because this mode
           grows both to the right and down, it isn't suitable for large programs (unless you
           have a very wide terminal).

   Options for Line-Style
       These options select the line-style (or just style) used to render each opcode, and
       dictates what info is actually printed into each line.

           Use the author's favorite set of formatting conventions. This is the default, of

           Use formatting conventions that emulate the output of B::Terse. The basic mode is
           almost indistinguishable from the real B::Terse, and the exec mode looks very similar,
           but is in a more logical order and lacks curly brackets. B::Terse doesn't have a tree
           mode, so the tree mode is only vaguely reminiscent of B::Terse.

           Use formatting conventions in which the name of each OP, rather than being written out
           in full, is represented by a one- or two-character abbreviation.  This is mainly a

           Use formatting conventions reminiscent of B::Debug; these aren't very concise at all.

           Use formatting conventions read from the environment variables "B_CONCISE_FORMAT",

   Options for tree-specific formatting
           Use a tree format in which the minimum amount of space is used for the lines
           connecting nodes (one character in most cases). This squeezes out a few precious
           columns of screen real estate.

           Use a tree format that uses longer edges to separate OP nodes. This format tends to
           look better than the compact one, especially in ASCII, and is the default.

       -vt Use tree connecting characters drawn from the VT100 line-drawing set.  This looks
           better if your terminal supports it.

           Draw the tree with standard ASCII characters like "+" and "|". These don't look as
           clean as the VT100 characters, but they'll work with almost any terminal (or the
           horizontal scrolling mode of less(1)) and are suitable for text documentation or
           email. This is the default.

       These are pairwise exclusive, i.e. compact or loose, vt or ascii.

   Options controlling sequence numbering
           Print OP sequence numbers in base n. If n is greater than 10, the digit for 11 will be
           'a', and so on. If n is greater than 36, the digit for 37 will be 'A', and so on until
           62. Values greater than 62 are not currently supported. The default is 36.

           Print sequence numbers with the most significant digit first. This is the usual
           convention for Arabic numerals, and the default.

           Print seqence numbers with the least significant digit first.  This is obviously
           mutually exclusive with bigendian.

   Other options
           With this option, the rendering of each statement (starting with the nextstate OP)
           will be preceded by the 1st line of source code that generates it.  For example:

               1  <0> enter
               # 1: my $i;
               2  <;> nextstate(main 1 v:{
               3  <0> padsv[$i:1,10] vM/LVINTRO
               # 3: for $i (0..9) {
               4  <;> nextstate(main 3 v:{
               5  <0> pushmark s
               6  <$> const[IV 0] s
               7  <$> const[IV 9] s
               8  <{> enteriter(next->j last->m redo->9)[$i:1,10] lKS
               k  <0> iter s
               l  <|> and(other->9) vK/1
               # 4:     print "line ";
               9      <;> nextstate(main 2 v
               a      <0> pushmark s
               b      <$> const[PV "line "] s
               c      <@> print vK
               # 5:     print "$i\n";

           With this, "somepackage" will be required, then the stash is inspected, and each
           function is rendered.

       The following options are pairwise exclusive.

           Include the main program in the output, even if subroutines were also specified.  This
           rendering is normally suppressed when a subroutine name or reference is given.

           This restores the default behavior after you've changed it with '-main' (it's not
           normally needed).  If no subroutine name/ref is given, main is rendered, regardless of
           this flag.

           Renderings usually include a banner line identifying the function name or stringified
           subref.  This suppresses the printing of the banner.

           TBC: Remove the stringified coderef; while it provides a 'cookie' for each function
           rendered, the cookies used should be 1,2,3.. not a random hex-address.  It also
           complicates string comparison of two different trees.

           restores default banner behavior.

       -banneris => subref
           TBC: a hookpoint (and an option to set it) for a user-supplied function to produce a
           banner appropriate for users needs.  It's not ideal, because the rendering-state
           variables, which are a natural candidate for use in concise.t, are unavailable to the

   Option Stickiness
       If you invoke Concise more than once in a program, you should know that the options are
       'sticky'.  This means that the options you provide in the first call will be remembered
       for the 2nd call, unless you re-specify or change them.


       The concise style uses symbols to convey maximum info with minimal clutter (like hex
       addresses).  With just a little practice, you can start to see the flowers, not just the
       branches, in the trees.

   OP class abbreviations
       These symbols appear before the op-name, and indicate the B:: namespace that represents
       the ops in your Perl code.

           0      OP (aka BASEOP)  An OP with no children
           1      UNOP             An OP with one child
           2      BINOP            An OP with two children
           |      LOGOP            A control branch OP
           @      LISTOP           An OP that could have lots of children
           /      PMOP             An OP with a regular expression
           $      SVOP             An OP with an SV
           "      PVOP             An OP with a string
           {      LOOP             An OP that holds pointers for a loop
           ;      COP              An OP that marks the start of a statement
           #      PADOP            An OP with a GV on the pad

   OP flags abbreviations
       OP flags are either public or private.  The public flags alter the behavior of each opcode
       in consistent ways, and are represented by 0 or more single characters.

           v      OPf_WANT_VOID    Want nothing (void context)
           s      OPf_WANT_SCALAR  Want single value (scalar context)
           l      OPf_WANT_LIST    Want list of any length (list context)
                                   Want is unknown
           K      OPf_KIDS         There is a firstborn child.
           P      OPf_PARENS       This operator was parenthesized.
                                    (Or block needs explicit scope entry.)
           R      OPf_REF          Certified reference.
                                    (Return container, not containee).
           M      OPf_MOD          Will modify (lvalue).
           S      OPf_STACKED      Some arg is arriving on the stack.
           *      OPf_SPECIAL      Do something weird for this op (see op.h)

       Private flags, if any are set for an opcode, are displayed after a '/'

           8  <@> leave[1 ref] vKP/REFC ->(end)
           7     <2> sassign vKS/2 ->8

       They're opcode specific, and occur less often than the public ones, so they're represented
       by short mnemonics instead of single-chars; see op.h for gory details, or try this quick

         $> perl -MB::Concise -de 1
         DB<1> |x \%B::Concise::priv


       For each line-style ('concise', 'terse', 'linenoise', etc.) there are 3 format-specs which
       control how OPs are rendered.

       The first is the 'default' format, which is used in both basic and exec modes to print all
       opcodes.  The 2nd, goto-format, is used in exec mode when branches are encountered.
       They're not real opcodes, and are inserted to look like a closing curly brace.  The tree-
       format is tree specific.

       When a line is rendered, the correct format-spec is copied and scanned for the following
       items; data is substituted in, and other manipulations like basic indenting are done, for
       each opcode rendered.

       There are 3 kinds of items that may be populated; special patterns, #vars, and literal
       text, which is copied verbatim.  (Yes, it's a set of s///g steps.)

   Special Patterns
       These items are the primitives used to perform indenting, and to select text from amongst

           Generates exec_text in exec mode, or basic_text in basic mode.

           Generates one copy of text for each indentation level.

           Generates one fewer copies of text1 than the indentation level, followed by one copy
           of text2 if the indentation level is more than 0.

           If the value of var is true (not empty or zero), generates the value of var surrounded
           by text1 and Text2, otherwise nothing.

       ~   Any number of tildes and surrounding whitespace will be collapsed to a single space.

   # Variables
       These #vars represent opcode properties that you may want as part of your rendering.  The
       '#' is intended as a private sigil; a #var's value is interpolated into the style-line,
       much like "read $this".

       These vars take 3 forms:

           A property named 'var' is assumed to exist for the opcodes, and is interpolated into
           the rendering.

           Generates the value of var, left justified to fill N spaces.  Note that this means
           while you can have properties 'foo' and 'foo2', you cannot render 'foo2', but you
           could with 'foo2a'.  You would be wise not to rely on this behavior going forward ;-)

           This ucfirst form of #var generates a tag-value form of itself for display; it
           converts '#Var' into a 'Var => #var' style, which is then handled as described above.
           (Imp-note: #Vars cannot be used for conditional-fills, because the => #var transform
           is done after the check for #Var's value).

       The following variables are 'defined' by B::Concise; when they are used in a style, their
       respective values are plugged into the rendering of each opcode.

       Only some of these are used by the standard styles, the others are provided for you to
       delve into optree mechanics, should you wish to add a new style (see "add_style" below)
       that uses them.  You can also add new ones using "add_callback".

           The address of the OP, in hexadecimal.

           The OP-specific information of the OP (such as the SV for an SVOP, the non-local exit
           pointers for a LOOP, etc.) enclosed in parentheses.

           The B-determined class of the OP, in all caps.

           A single symbol abbreviating the class of the OP.

           The label of the statement or block the OP is the start of, if any.

           The name of the OP, or 'ex-foo' if the OP is a null that used to be a foo.

           The target of the OP, or nothing for a nulled OP.

           The address of the OP's first child, in hexadecimal.

           The OP's flags, abbreviated as a series of symbols.

           The numeric value of the OP's flags.

           The COP's hint flags, rendered with abbreviated names if possible. An empty string if
           this is not a COP. Here are the symbols used:

               $ strict refs
               & strict subs
               * strict vars
               i integers
               l locale
               b bytes
               [ arybase
               { block scope
               % localise %^H
               < open in
               > open out
               I overload int
               F overload float
               B overload binary
               S overload string
               R overload re
               T taint
               E eval
               X filetest access
               U utf-8

           The numeric value of the COP's hint flags, or an empty string if this is not a COP.

           The sequence number of the OP, or a hyphen if it doesn't have one.

           'NEXT', 'LAST', or 'REDO' if the OP is a target of one of those in exec mode, or empty

           The address of the OP's last child, in hexadecimal.

           The OP's name.

           The OP's name, in all caps.

           The sequence number of the OP's next OP.

           The address of the OP's next OP, in hexadecimal.

           A one- or two-character abbreviation for the OP's name.

           The OP's private flags, rendered with abbreviated names if possible.

           The numeric value of the OP's private flags.

           The sequence number of the OP. Note that this is a sequence number generated by

           5.8.x and earlier only. 5.9 and later do not provide this.

           The real sequence number of the OP, as a regular number and not adjusted to be
           relative to the start of the real program. (This will generally be a fairly large
           number because all of B::Concise is compiled before your program is).

           Whether or not the op has been optimised by the peephole optimiser.

           Only available in 5.9 and later.

           The address of the OP's next youngest sibling, in hexadecimal.

           The address of the OP's SV, if it has an SV, in hexadecimal.

           The class of the OP's SV, if it has one, in all caps (e.g., 'IV').

           The value of the OP's SV, if it has one, in a short human-readable format.

           The numeric value of the OP's targ.

           The name of the variable the OP's targ refers to, if any, otherwise the letter t
           followed by the OP's targ in decimal.

           Same as #targarg, but followed by the COP sequence numbers that delimit the variable's
           lifetime (or 'end' for a variable in an open scope) for a variable.

           The numeric value of the OP's type, in decimal.

One-Liner Command tips

       perl -MO=Concise,bar
           Renders only bar() from  To see main, drop the ',bar'.  To see both, add

       perl -MDigest::MD5=md5 -MO=Concise,md5 -e1
           Identifies md5 as an XS function.  The export is needed so that BC can find it in

       perl -MPOSIX -MO=Concise,_POSIX_ARG_MAX -e1
           Identifies _POSIX_ARG_MAX as a constant sub, optimized to an IV.  Although POSIX isn't
           entirely consistent across platforms, this is likely to be present in virtually all of

       perl -MPOSIX -MO=Concise,a -e 'print _POSIX_SAVED_IDS'
           This renders a print statement, which includes a call to the function.  It's identical
           to rendering a file with a use call and that single statement, except for the filename
           which appears in the nextstate ops.

       perl -MPOSIX -MO=Concise,a -e 'sub a{_POSIX_SAVED_IDS}'
           This is very similar to previous, only the first two ops differ.  This subroutine
           rendering is more representative, insofar as a single main program will have many

       perl -MB::Concise -e 'B::Concise::compile("-exec","-src", \%B::Concise::)->()'
           This renders all functions in the B::Concise package with the source lines.  It
           eschews the O framework so that the stashref can be passed directly to
           B::Concise::compile().  See -stash option for a more convenient way to render a

Using B::Concise outside of the O framework

       The common (and original) usage of B::Concise was for command-line renderings of simple
       code, as given in EXAMPLE.  But you can also use B::Concise from your code, and call
       compile() directly, and repeatedly.  By doing so, you can avoid the compile-time only
       operation of, and even use the debugger to step through B::Concise::compile() itself.

       Once you're doing this, you may alter Concise output by adding new rendering styles, and
       by optionally adding callback routines which populate new variables, if such were
       referenced from those (just added) styles.

   Example: Altering Concise Renderings
           use B::Concise qw(set_style add_callback);
           add_style($yourStyleName => $defaultfmt, $gotofmt, $treefmt);
             ( sub {
                   my ($h, $op, $format, $level, $stylename) = @_;
                   $h->{variable} = some_func($op);
           $walker = B::Concise::compile(@options,@subnames,@subrefs);

       set_style accepts 3 arguments, and updates the three format-specs comprising a line-style
       (basic-exec, goto, tree).  It has one minor drawback though; it doesn't register the style
       under a new name.  This can become an issue if you render more than once and switch
       styles.  Thus you may prefer to use add_style() and/or set_style_standard() instead.

       This restores one of the standard line-styles: "terse", "concise", "linenoise", "debug",
       "env", into effect.  It also accepts style names previously defined with add_style().

   add_style ()
       This subroutine accepts a new style name and three style arguments as above, and creates,
       registers, and selects the newly named style.  It is an error to re-add a style; call
       set_style_standard() to switch between several styles.

   add_callback ()
       If your newly minted styles refer to any new #variables, you'll need to define a callback
       subroutine that will populate (or modify) those variables.  They are then available for
       use in the style you've chosen.

       The callbacks are called for each opcode visited by Concise, in the same order as they are
       added.  Each subroutine is passed five parameters.

         1. A hashref, containing the variable names and values which are
            populated into the report-line for the op
         2. the op, as a B<B::OP> object
         3. a reference to the format string
         4. the formatting (indent) level
         5. the selected stylename

       To define your own variables, simply add them to the hash, or change existing values if
       you need to.  The level and format are passed in as references to scalars, but it is
       unlikely that they will need to be changed or even used.

   Running B::Concise::compile()
       compile accepts options as described above in "OPTIONS", and arguments, which are either
       coderefs, or subroutine names.

       It constructs and returns a $treewalker coderef, which when invoked, traverses, or walks,
       and renders the optrees of the given arguments to STDOUT.  You can reuse this, and can
       change the rendering style used each time; thereafter the coderef renders in the new

       walk_output lets you change the print destination from STDOUT to another open filehandle,
       or into a string passed as a ref (unless you've built perl with -Uuseperlio).

           my $walker = B::Concise::compile('-terse','aFuncName', \&aSubRef);  # 1
           walk_output(\my $buf);
           $walker->();                        # 1 renders -terse
           set_style_standard('concise');      # 2
           $walker->();                        # 2 renders -concise
           $walker->(@new);                    # 3 renders whatever
           print "3 different renderings: terse, concise, and @new: $buf\n";

       When $walker is called, it traverses the subroutines supplied when it was created, and
       renders them using the current style.  You can change the style afterwards in several
       different ways:

         1. call C<compile>, altering style or mode/order
         2. call C<set_style_standard>
         3. call $walker, passing @new options

       Passing new options to the $walker is the easiest way to change amongst any pre-defined
       styles (the ones you add are automatically recognized as options), and is the only way to
       alter rendering order without calling compile again.  Note however that rendering state is
       still shared amongst multiple $walker objects, so they must still be used in a coordinated

       This function (not exported) lets you reset the sequence numbers (note that they're
       numbered arbitrarily, their goal being to be human readable).  Its purpose is mostly to
       support testing, i.e. to compare the concise output from two identical anonymous
       subroutines (but different instances).  Without the reset, B::Concise, seeing that they're
       separate optrees, generates different sequence numbers in the output.

       Errors in rendering (non-existent function-name, non-existent coderef) are written to the
       STDOUT, or wherever you've set it via walk_output().

       Errors using the various *style* calls, and bad args to walk_output(), result in die().
       Use an eval if you wish to catch these errors and continue processing.


       Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.