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

NAME

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

SYNOPSIS

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

use B::Concise qw(setstyle addcallback);

DESCRIPTION

This compiler backend prints the internal OPs of a Perl program's syn-

tax 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 -DDxx debugging flag or the BB::::TTeerrssee module,

but it is more sophisticated and flexible. EEXXAAMMPPLLEE

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 dis-

played in base 36 by default. This rendering is in -exec (i.e. execu-

tion) 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 ''aadddd[[tt11]]'', which may be followed by op-specific

information in parentheses or brackets (ex ''[[tt11]]'').

The op-flags (ex ''ssKK//22'') follow, and are described in ("OP flags abbre-

viations").

% 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 exam-

ple), 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.

OOPPTTIIOONNSS Arguments that don't start with a hyphen are taken to be the names of subroutines to print the OPs of; if no such functions are specified,

the main body of the program (outside any subroutines, and not includ-

ing 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 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.

-bbaassiicc

Print OPs in the order they appear in the OP tree (a preorder tra-

versal, 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.

-eexxeecc

Print OPs in the order they would normally execute (for the major-

ity 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 inden-

tation. In cases like loops when control jumps out of a linear path, a 'goto' line is generated.

-ttrreeee

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 LineStyle

These options select the line-style (or just style) used to render each

opcode, and dictates what info is actually printed into each line.

-ccoonncciissee

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

-tteerrssee

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

-lliinneennooiissee

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.

-ddeebbuugg

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

-eennvv

Use formatting conventions read from the environment variables

"BCONCISEFORMAT", "BCONCISEGOTOFORMAT", and "BCON-

CISETREEFORMAT". Options for treespecific formatting

-ccoommppaacctt

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.

-lloooossee

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.

-vvtt Use tree connecting characters drawn from the VT100 line-drawing

set. This looks better if your terminal supports it.

-aasscciiii

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

-bbaasseen

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.

-bbiiggeennddiiaann

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

-lliittttlleeeennddiiaann

Print seqence numbers with the least significant digit first. This is obviously mutually exclusive with bigendian. OOtthheerr ooppttiioonnss These are pairwise exclusive.

-mmaaiinn

Include the main program in the output, even if subroutines were

also specified. This rendering is normally suppressed when a sub-

routine name or reference is given.

-nnoommaaiinn

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.

-nnoobbaannnneerr

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.

-bbaannnneerr

restores default banner behavior.

-bbaannnneerriiss => 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-spec-

ify or change them. AABBBBRREEVVIIAATTIIOONNSS 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. OOPP ccllaassss aabbbbrreevviiaattiioonnss

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

OOPP ffllaaggss aabbbbrreevviiaattiioonnss 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 OPfWANTVOID Want nothing (void context) s OPfWANTSCALAR Want single value (scalar context) l OPfWANTLIST Want list of any length (list context) Want is unknown K OPfKIDS There is a firstborn child. P OPfPARENS This operator was parenthesized. (Or block needs explicit scope entry.) R OPfREF Certified reference. (Return container, not containee). M OPfMOD Will modify (lvalue). S OPfSTACKED Some arg is arriving on the stack. * OPfSPECIAL 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 2-liner:

$> perl -MB::Concise -de 1

DB<1> |x \%B::Concise::priv

FFOORRMMAATTTTIINNGG SSPPEECCIIFFIICCAATTIIOONNSS

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 manipula-

tions 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.) SSppeecciiaall PPaatttteerrnnss These items are the primitives used to perform indenting, and to select text from amongst alternatives. ((xx((exectext;;basictext))xx)) Generates exectext in exec mode, or basictext 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), 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.

## VVaarriiaabblleess

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:

##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 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 ;-)

##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 others are pro-

vided for you to delve into optree mechanics, should you wish to add a new style (see "addstyle" below) that uses them. You can also add new ones using "addcallback".

##aaddddrr

The address of the OP, in hexadecimal.

##aarrgg

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 parenthe-

ses.

##ccllaassss

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

##ccllaassssssyymm

A single symbol abbreviating the class of the OP.

##ccooppllaabbeell

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

##eexxnnaammee

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

a foo.

##eexxttaarrgg

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

##ffiirrssttaaddddrr

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

##ffllaaggss

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

##ffllaaggvvaall

The numeric value of the OP's flags.

##hhyypphhsseeqq

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

##llaabbeell

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

##llaassttaaddddrr

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

##nnaammee

The OP's name.

#NAME

The OP's name, in all caps.

##nneexxtt

The sequence number of the OP's next OP.

##nneexxttaaddddrr

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

##nnooiissee

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

##pprriivvaattee

The OP's private flags, rendered with abbreviated names if possi-

ble.

##pprriivvvvaall

The numeric value of the OP's private flags.

##sseeqq

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

generated by B::Concise.

##sseeqqnnuumm

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 BB::::CCoonncciissee is compiled before your program is).

##oopptt

Whether or not the op has been optimised by the peephole optimiser. Only available in 5.9 and later.

##ssttaattiicc

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.

##ssiibbaaddddrr

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

##ssvvaaddddrr

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

##ssvvccllaassss

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

##ssvvvvaall

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

format.

##ttaarrgg

The numeric value of the OP's targ.

##ttaarrggaarrgg

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.

##ttaarrggaarrgglliiffee

Same as ##ttaarrggaarrgg, 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.

##ttyyppeennuumm

The numeric value of the OP's type, in decimal. UUssiinngg BB::::CCoonncciissee oouuttssiiddee ooff tthhee OO ffrraammeewwoorrkk

The common (and original) usage of B::Concise was for command-line ren-

derings of simple code, as given in EXAMPLE. But you can also use

BB::::CCoonncciissee 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 ren-

dering styles, and by optionally adding callback routines which popu-

late new variables, if such were referenced from those (just added) styles. EExxaammppllee:: AAlltteerriinngg CCoonncciissee RReennddeerriinnggss

use B::Concise qw(setstyle addcallback);

addstyle($yourStyleName => $defaultfmt, $gotofmt, $treefmt);

addcallback ( sub {

my ($h, $op, $format, $level, $stylename) = @;

$h->{variable} = somefunc($op);

});

$walker = B::Concise::compile(@options,@subnames,@subrefs);

$walker->();

setstyle()

sseettssttyyllee accepts 3 arguments, and updates the three format-specs com-

prising a line-style (basic-exec, goto, tree). It has one minor draw-

back 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 addstyle() and/or setstylestandard() instead.

sseettssttyylleessttaannddaarrdd(($$nnaammee))

This restores one of the standard line-styles: "terse", "concise",

"linenoise", "debug", "env", into effect. It also accepts style names previously defined with addstyle(). addstyle() 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 setstylestandard() to switch

between several styles. addcallback()

If your newly minted styles refer to any new #variables, you'll need to

define a callback subroutine that will populate (or modify) those vari-

ables. 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 parame-

ters. 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 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.

RRuunnnniinngg B::Concise::compile()

ccoommppiillee 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. wwaallkkoouuttppuutt 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

walkoutput(\my $buf);

$walker->(); # 1 renders -terse

setstylestandard('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, altering style or mode/order 2. call C

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 call-

ing compile again. Note however that rendering state is still shared

amongst multiple $walker objects, so they must still be used in a coor-

dinated manner.

B::Concise::resetsequence()

This function (not exported) lets you reset the sequence numbers (note

that they're numbered arbitrarily, their goal being to be human read-

able). 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 sepa-

rate optrees, generates different sequence numbers in the output. EErrrroorrss

Errors in rendering (non-existent function-name, non-existent coderef)

are written to the STDOUT, or wherever you've set it via walkoutput(). Errors using the various *style* calls, and bad args to walkoutput(), result in die(). Use an eval if you wish to catch these errors and continue processing. AUTHOR Stephen McCamant, .