B::Concise(3perl) Perl Programmers Reference Guide B::Concise(3perl)
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, using the default formatting con-
ventions :
% 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 operator. 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.
-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).
-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.
-main
Include the main program in the output, even if subroutines 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 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.
-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 reminiscient 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 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_CON-
CISE_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 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.
#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 parethe-
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 now a sequence
number generated by B::Concise, rather than the real op_seq value
(for which see #seqnum).
#seqnum
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).
#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.
ABBREVIATIONS
OP flags abbreviations
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)
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 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
Using B::Concise outside of the O framework
You can use B::Concise, and call compile() directly, thereby avoiding
the compile-only operation of O. For example, you could use the debug-
ger to step through B::Concise::compile() itself.
When doing so, you can alter Concise output by providing new output
styles, and optionally by adding callback routines which populate new
variables that may be rendered as part of those styles. For all fol-
lowing sections, please review "FORMATTING SPECIFICATIONS".
example: Altering Concise Output
use B::Concise qw(set_style add_callback);
set_style($your_format, $your_gotofmt, $your_treefmt);
add_callback
( sub {
my ($h, $op, $format, $level, $stylename) = @_;
$h->{variable} = some_func($op);
}
);
B::Concise::compile(@options)->();
set_style()
set_style accepts 3 arguments, and updates the three components of an
output style (basic-exec, goto, tree). It has one minor drawback
though: it doesn't register the style under a new name, thus you may
prefer to use add_style() and/or set_style_standard() instead.
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.
set_style_standard($name)
This restores one of the standard styles: "terse", "concise",
"linenoise", "debug", "env", into effect. It also accepts style names
previously defined with add_style().
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.
compile() constructs and returns a coderef, which when invoked, scans
the optree, and prints the results to STDOUT. Once you have the
coderef, you may change the output style; thereafter the coderef ren-
ders 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.
walk_output(\my $buf);
B::Concise::compile('-concise','funcName', \&aSubRef)->();
print "Concise Results: $buf\n";
For each subroutine visited, the opcode info is preceded by a single
line containing either the subroutine name or the stringified coderef.
To switch back to one of the standard styles like "concise" or "terse",
call "set_style_standard", or pass the style name into B::Concise::com-
pile() (as done above).
B::Concise::reset_sequence()
This function (not exported) lets you reset the sequence numbers (note
that they're numbered arbitrarily, their goal being to be human read-
able). Its purpose is mostly to support testing, i.e. to compare the
concise output from two identical anonymous subroutines (but different
instances). Without the reset, B::Concise, seeing that they're sepa-
rate optrees, generates different sequence numbers in the output.
Errors
All detected errors, (invalid arguments, internal errors, etc.) are
resolved with a die($message). Use an eval if you wish to catch these
errors and continue processing.
In particular, compile will die as follows if you've asked for a non-
existent function-name, a non-existent coderef, or a non-CODE refer-
ence.
AUTHOR
Stephen McCamant, <smcc AT CSUA.EDU>.
perl v5.8.4 2001-09-21 B::Concise(3perl)
Huschi als Linux-Admin