MirOS Manual: B::Concise(3p)


ext::B::B::ConcisPerl)Programmers Referenceext::B::B::Concise(3p)

NAME

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

SYNOPSIS

         perl -MO=Concise[,OPTIONS] foo.pl

         use B::Concise qw(set_style add_callback);

DESCRIPTION

     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 flexible.

EXAMPLE

     Here's an example of 2 outputs (aka '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

     Each line corresponds to an opcode. The opcode marked with
     '*' is used in a few examples below.

     The 1st column is the op's sequence number, starting at 1,
     and is displayed in base 36 by default.  This rendering is
     in -exec (i.e. execution) order.

     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
     abbreviations").

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

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

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         % 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 execu-
     tion 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.

OPTIONS

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

     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 interre-
     late; 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

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     document.

     -basic
         Print OPs in the order they appear in the OP tree (a
         preorder traversal, starting at the root). The indenta-
         tion 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.

     -exec
         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.

     -tree
         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.

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

     -terse
         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.

     -linenoise
         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
         joke.

     -debug

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

     -env
         Use formatting conventions read from the environment
         variables "B_CONCISE_FORMAT", "B_CONCISE_GOTO_FORMAT",
         and "B_CONCISE_TREE_FORMAT".

     Options for tree-specific formatting

     -compact
         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.

     -loose
         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.

     -ascii
         Draw the tree with standard ASCII characters like "+"
         and "|". These don't look as clean as the VT100 charac-
         ters, 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

     -basen
         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.

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

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

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         bigendian.

     Other options

     These are pairwise exclusive.

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

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

     -nobanner
         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.

     -banner
         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 user.

     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.

ABBREVIATIONS

     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.

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     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 pub-
     lic ones, so they're represented by short mnemonics instead
     of single-chars; see op.h for gory details, or try this
     quick 2-liner:

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

FORMATTING SPECIFICATIONS

     For each line-style ('concise', 'terse', 'linenoise', etc.)

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     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 encoun-
     tered.  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 alternatives.

     (x(exec_text;basic_text)x)
         Generates exec_text in exec mode, or basic_text in basic
         mode.

     (*(text)*)
         Generates one copy of text for each indentation level.

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

     (?(text1#varText2)?)
         If the value of var is true (not empty or zero), gen-
         erates 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:

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

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

     #Var
         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 oth-
     ers 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".

     #addr
         The address of the OP, in hexadecimal.

     #arg
         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.

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

     #classsym
         A single symbol abbreviating the class of the OP.

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

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

     #extarg

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

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

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

     #flagval
         The numeric value of the OP's flags.

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

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

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

     #name
         The OP's name.

     #NAME
         The OP's name, in all caps.

     #next
         The sequence number of the OP's next OP.

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

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

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

     #privval
         The numeric value of the OP's private flags.

     #seq
         The sequence number of the OP. Note that this is a
         sequence number generated by B::Concise.

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

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         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 pro-
         gram is).

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

         Only available in 5.9 and later.

     #static
         Whether or not the op is statically defined.  This flag
         is used by the B::C compiler backend and indicates that
         the op should not be freed.

         Only available in 5.9 and later.

     #sibaddr
         The address of the OP's next youngest sibling, in hexa-
         decimal.

     #svaddr
         The address of the OP's SV, if it has an SV, in hexade-
         cimal.

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

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

     #targ
         The numeric value of the OP's targ.

     #targarg
         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.

     #targarglife
         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.

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

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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 O.pm, 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 call-
     back 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, $treefmt);
         add_callback
           ( sub {
                 my ($h, $op, $format, $level, $stylename) = @_;
                 $h->{variable} = some_func($op);
             });
         $walker = B::Concise::compile(@options,@subnames,@subrefs);
         $walker->();

     set_style()

     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 regis-
     ter 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.

     set_style_standard($name)

     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.

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     add_callback()

     If your newly minted styles refer to any new #variables,
     you'll need to define a callback subroutine that will popu-
     late (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 style.

     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 sup-
     plied when it was created, and renders them using the
     current style.  You can change the style afterwards in
     several different ways:

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       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 multi-
     ple $walker objects, so they must still be used in a coordi-
     nated manner.

     B::Concise::reset_sequence()

     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 sup-
     port 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

     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.

AUTHOR

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

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