b::concise(3)

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 struc
ture, and the format of the information displyed is cus
tomizable. 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 is a short example of output, using the default
formatting conventions :

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

Each line corresponds to an operator. Null ops appear as
"ex-opname", where opname is the op that has been opti
mized away by perl.

The number on the first row indicates the op's sequence
number. It's given in base 36 by default.

The symbol between angle brackets indicates the op's type
: for example, <2> is a BINOP, <@> a LISTOP, etc. (see "OP
class abbreviations").

The opname may be followed by op-specific information in
parentheses (e.g. "gvsv(*b)"), and by targ information in
brackets (e.g. "leave[t1]").

Next come the op flags. The common flags are listed below
("OP flags abbreviations"). The private flags follow, sep
arated by a slash. For example, "vKP/REFC" means that the
leave op has public flags OPf_WANT_VOID, OPf_KIDS, and
OPf_PARENS, and the private flag OPpREFCOUNTED.

Finally an arrow points to the sequence number of the next
op.

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
functions are specified, the main body of the program
(outside any subroutines, and not including use'd or
require'd files) is printed.

-basic

Print OPs in the order they appear in the OP tree (a
preorder traversal, starting at the root). The inden
tation of each OP shows its level in the tree. 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).

-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 char
acters, 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.

-main

Include the main program in the output, even if sub
routines were also specified.

-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 cur
rently supported. The default is 36.

-bigendian

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

-littleendian

Print seqence numbers with the least significant digit
first.

-concise

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

-terse

Use formatting conventions that emulate the ouput 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 reminiscient of
B::Terse.

-linenoise

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

-debug

Use formatting conventions reminiscient 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".

FORMATTING SPECIFICATIONS

For each general style ('concise', 'terse', 'linenoise',
etc.) there are three specifications: one of how OPs
should appear in the basic or exec modes, one of how
'goto' lines should appear (these occur in the exec mode
only), and one of how nodes should appear in tree mode.
Each has the same format, described below. Any text that
doesn't match a special pattern is copied verbatim.

(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 indenta
tion 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.

#var

Generates the value of the variable var.

#varN

Generates the value of var, left jutified to fill N
spaces.

~ Any number of tildes and surrounding whitespace will

be collapsed to a single space.

The following variables are recognized:

#addr

The address of the OP, in hexidecimal.

#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 paretheses.

#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

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

#firstaddr

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

#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 hexidecimal.

#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 hexidecimal.

#noise

The 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.

#seqnum

The real sequence number of the OP, as a regular num
ber 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).

#sibaddr

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

#svaddr

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

#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.

ABBREVIATIONS

OP flags abbreviations

v OPf_WANT_VOID Want nothing (void context)
s OPf_WANT_SCALAR Want single value (scalar con

text)
l OPf_WANT_LIST Want list of any length (list

context)
K OPf_KIDS There is a firstborn child.
P OPf_PARENS This operator was parenthe

sized.

(Or block needs explicit

scope entry.)

R OPf_REF Certified reference.

(Return container, not con

tainee).

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)

OP class abbreviations

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 expres

sion
$ 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

Using B::Concise outside of the O framework

It is possible to extend B::Concise by using it outside of the O framework and providing new styles and new vari
ables.

use B::Concise qw(set_style add_callback);
set_style($format, $gotofmt, $treefmt);
add_callback
(

sub
{

my ($h, $op, $level, $format) = @_;
$h->{variable} = some_func($op);

}

);
B::Concise::compile(@options)->();

You can specify a style by calling the set_style subrou tine. If you have a new variable in your style, or you
want to change the value of an existing variable, you will
need to add a callback to specify the value for that vari
able.

This is done by calling add_callback passing references to any callback subroutines. The subroutines are called in
the same order as they are added. Each subroutine is
passed four parameters. These are a reference to a hash,
the keys of which are the names of the variables and the
values of which are their values, the op, the level and
the format.

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.

To see the output, call the subroutine returned by compile in the same way that O does.

AUTHOR

Stephen McCamant, "smcc@CSUA.Berkeley.EDU"

perl v5.8.0 2002-06-01 B::Concise(3)