B::Concise
B::Concise(3) Perl Programmers Reference Guide 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 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 displyed 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 is a short example of output (aka 'rendering'), using the
default formatting conventions :
% 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
Each line corresponds to an opcode. Null ops appear as "ex-opname",
where opname is the op that has been optimized 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 exam-
ple, <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, separated 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 OPpREF-
COUNTED.
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 includ-
ing use'd or require'd files) is printed. 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.
-basic
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. 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 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.
-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
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_CON-
CISE_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 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
-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 bigendian.
Other options
These are pairwise exclusive.
-main
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.
-nomain
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.
-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-spec-
ify 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.
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
These symbols represent various flags which alter behavior of the
opcode, sometimes in opcode-specific ways.
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)
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)
FORMATTING SPECIFICATIONS
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.)
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), 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:
#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 "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 parenthe-
ses.
#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
A one- or two-character abbreviation for the OP's name.
#private
The OP's private flags, rendered with abbreviated names if possi-
ble.
#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.
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).
#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 hexidecimal.
#svaddr
The address of the OP's SV, if it has an SV, in hexidecimal.
#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.
Using B::Concise outside of the O framework
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
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 ren-
dering styles, and by optionally adding callback routines which popu-
late 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);
$walker->();
set_style()
set_style accepts 3 arguments, and updates the three format-specs com-
prising a line-style (basic-exec, goto, tree). It has one minor draw-
back though; it doesn't register the style under a new name. This can
become an issue if you render more than once and switch styles. Thus
you may prefer to use add_style() and/or set_style_standard() instead.
set_style_standard($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.
add_callback()
If your newly minted styles refer to any #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<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 (unless you've built with -Uuseperlio) into
a string passed as a ref.
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 call-
ing compile again. Note however that rendering state is still shared
amongst multiple $walker objects, so they must still be used in a coor-
dinated manner.
B::Concise::reset_sequence()
This function (not exported) lets you reset the sequence numbers (note
that they're numbered arbitrarily, their goal being to be human read-
able). Its purpose is mostly to support testing, i.e. to compare the
concise output from two identical anonymous subroutines (but different
instances). Without the reset, B::Concise, seeing that they're sepa-
rate optrees, generates different sequence numbers in the output.
Errors
All detected errors, (invalid arguments, internal errors, etc.) are
resolved with a die($message). Use an eval if you wish to catch these
errors and continue processing.
In particular, compile will die if you've asked for a non-existent
function-name, a non-existent coderef, or a non-CODE reference.
AUTHOR
Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.
perl v5.8.6 2001-09-21 B::Concise(3)
