B::Concise(3p) Perl Programmers Reference Guide B::Concise(3p) #
B::Concise(3p) Perl Programmers Reference Guide B::Concise(3p)
NNAAMMEE #
B::Concise - Walk Perl syntax tree, printing concise info about ops
SSYYNNOOPPSSIISS #
perl -MO=Concise[,OPTIONS] foo.pl
use B::Concise qw(set_style add_callback);
DDEESSCCRRIIPPTTIIOONN #
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 --DDxx debugging flag or the BB::::TTeerrssee module, but
it is more sophisticated and flexible.
EEXXAAMMPPLLEE #
Here's two outputs (or '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
In this -exec rendering, each opcode is executed in the order shown. The
add opcode, marked with '*', is discussed in more detail.
The 1st column is the op's sequence number, starting at 1, and is
displayed in base 36 by default. Here they're purely linear; the
sequences are very helpful when looking at code with loops and branches.
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]]'', may be followed by op-specific information
in parentheses or brackets (ex ''[[tt11]]'').
The op-flags (ex ''ssKK//22'') are described in ("OP flags abbreviations").
% 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 _o_p_n_a_m_e 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.
OOPPTTIIOONNSS #
Arguments that don't start with a hyphen are taken to be the names of
subroutines or formats to render; 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 rendered. Passing "BEGIN", "UNITCHECK",
"CHECK", "INIT", or "END" will cause all of the corresponding special
blocks to be printed. Arguments must follow options.
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).
OOppttiioonnss ffoorr OOppccooddee OOrrddeerriinngg 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
traversal, 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 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.
--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).
OOppttiioonnss ffoorr LLiinnee--SSttyyllee 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 CPAN module BB::::DDeebbuugg; these
aren't very concise at all.
--eennvv
Use formatting conventions read from the environment variables
"B_CONCISE_FORMAT", "B_CONCISE_GOTO_FORMAT", and
“B_CONCISE_TREE_FORMAT”. #
OOppttiioonnss ffoorr ttrreeee--ssppeecciiffiicc ffoorrmmaattttiinngg --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 lleessss(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.
OOppttiioonnss ccoonnttrroolllliinngg sseeqquueennccee nnuummbbeerriinngg --bbaassee_n 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 sequence numbers with the least significant digit first. This
is obviously mutually exclusive with bigendian.
OOtthheerr ooppttiioonnss --ssrrcc With this option, the rendering of each statement (starting with the nextstate OP) will be preceded by the 1st line of source code that generates it. For example:
1 <0> enter
# 1: my $i;
2 <;> nextstate(main 1 junk.pl:1) v:{
3 <0> padsv[$i:1,10] vM/LVINTRO
# 3: for $i (0..9) {
4 <;> nextstate(main 3 junk.pl:3) v:{
5 <0> pushmark s
6 <$> const[IV 0] s
7 <$> const[IV 9] s
8 <{> enteriter(next->j last->m redo->9)[$i:1,10] lKS
k <0> iter s
l <|> and(other->9) vK/1
# 4: print "line ";
9 <;> nextstate(main 2 junk.pl:4) v
a <0> pushmark s
b <$> const[PV "line "] s
c <@> print vK
# 5: print "$i\n";
...
--ssttaasshh==""ssoommeeppaacckkaaggee""
With this, "somepackage" will be required, then the stash is
inspected, and each function is rendered.
The following options are pairwise exclusive.
--mmaaiinn
Include the main program in the output, even if subroutines were also
specified. This rendering is normally suppressed when a subroutine
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.
OOppttiioonn SSttiicckkiinneessss 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.
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
+ UNOP_AUX A UNOP with auxillary fields
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
. METHOP An OP with method call info
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 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 public ones, so
they're represented by short mnemonics instead of single-chars; see
B::Op_private and _r_e_g_e_n_/_o_p___p_r_i_v_a_t_e for more details.
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 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.)
SSppeecciiaall PPaatttteerrnnss These items are the primitives used to perform indenting, and to select text from amongst alternatives.
((xx((_e_x_e_c___t_e_x_t;;_b_a_s_i_c___t_e_x_t))xx))
Generates _e_x_e_c___t_e_x_t in exec mode, or _b_a_s_i_c___t_e_x_t in basic mode.
((**((_t_e_x_t))**))
Generates one copy of _t_e_x_t for each indentation level.
((**((_t_e_x_t_1;;_t_e_x_t_2))**))
Generates one fewer copies of _t_e_x_t_1 than the indentation level,
followed by one copy of _t_e_x_t_2 if the indentation level is more than
0.
((??((_t_e_x_t_1##_v_a_r_T_e_x_t_2))??))
If the value of _v_a_r is true (not empty or zero), generates the value
of _v_a_r surrounded by _t_e_x_t_1 and _T_e_x_t_2, 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:
##_v_a_r
A property named 'var' is assumed to exist for the opcodes, and is
interpolated into the rendering.
##_v_a_r_N
Generates the value of _v_a_r, 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 ;-)
##_V_a_r
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
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".
##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
parentheses.
##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.
##hhiinnttss
The COP's hint flags, rendered with abbreviated names if possible. An
empty string if this is not a COP. Here are the symbols used:
$ strict refs
& strict subs
* strict vars
x$ explicit use/no strict refs
x& explicit use/no strict subs
x* explicit use/no strict vars
i integers
l locale
b bytes
{ block scope
% localise %^H
< open in
> open out
I overload int
F overload float
B overload binary
S overload string
R overload re
T taint
E eval
X filetest access
U utf-8
us use feature 'unicode_strings'
fea=NNN feature bundle number
##hhiinnttssvvaall
The numeric value of the COP's hint flags, or an empty string if this
is not a COP.
##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.
##NNAAMMEE #
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 possible.
##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.
##oopptt
Whether or not the op has been optimized by the peephole optimizer.
##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.
OOnnee--LLiinneerr CCoommmmaanndd ttiippss perl -MO=Concise,bar foo.pl Renders only bbaarr(()) from foo.pl. To see main, drop the ‘,bar’. To see both, add ‘,-main’
perl -MDigest::MD5=md5 -MO=Concise,md5 -e1
Identifies md5 as an XS function. The export is needed so that BC
can find it in main.
perl -MPOSIX -MO=Concise,_POSIX_ARG_MAX -e1
Identifies _POSIX_ARG_MAX as a constant sub, optimized to an IV.
Although POSIX isn't entirely consistent across platforms, this is
likely to be present in virtually all of them.
perl -MPOSIX -MO=Concise,a -e 'print _POSIX_SAVED_IDS'
This renders a print statement, which includes a call to the
function. It's identical to rendering a file with a use call and
that single statement, except for the filename which appears in the
nextstate ops.
perl -MPOSIX -MO=Concise,a -e 'sub a{_POSIX_SAVED_IDS}'
This is vveerryy similar to previous, only the first two ops differ.
This subroutine rendering is more representative, insofar as a single
main program will have many subs.
perl -MB::Concise -e 'B::Concise::compile("-exec","-src",
\%B::Concise::)->()'
This renders all functions in the B::Concise package with the source
lines. It eschews the O framework so that the stashref can be passed
directly to BB::::CCoonncciissee::::ccoommppiillee(()). See -stash option for a more
convenient way to render a package.
UUssiinngg BB::::CCoonncciissee oouuttssiiddee ooff tthhee OO ffrraammeewwoorrkk 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 BB::::CCoonncciissee from your code, and call ccoommppiillee(()) 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 BB::::CCoonncciissee::::ccoommppiillee(()) itself.
Once you're doing this, you may alter Concise output by adding new
rendering styles, and by optionally adding callback routines which
populate new variables, if such were referenced from those (just added)
styles.
EExxaammppllee:: AAlltteerriinngg CCoonncciissee RReennddeerriinnggss 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->();
sseett__ssttyyllee(()) sseett__ssttyyllee 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 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 aadddd__ssttyyllee(()) and/or sseett__ssttyyllee__ssttaannddaarrdd(()) instead.
sseett__ssttyyllee__ssttaannddaarrdd(($$nnaammee)) This restores one of the standard line-styles: “terse”, “concise”, “linenoise”, “debug”, “env”, into effect. It also accepts style names previously defined with aadddd__ssttyyllee(()).
aadddd__ssttyyllee (()) 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 sseett__ssttyyllee__ssttaannddaarrdd(()) to switch between several styles.
aadddd__ccaallllbbaacckk (()) If your newly minted styles refer to any new #variables, you’ll need to define a callback subroutine that will populate (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.
RRuunnnniinngg BB::::CCoonncciissee::::ccoommppiillee(()) 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.
wwaallkk__oouuttppuutt 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 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 calling
compile again. Note however that rendering state is still shared amongst
multiple $walker objects, so they must still be used in a coordinated
manner.
BB::::CCoonncciissee::::rreesseett__sseeqquueennccee(()) 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 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 separate 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 wwaallkk__oouuttppuutt(()).
Errors using the various *style* calls, and bad args to wwaallkk__oouuttppuutt(()),
result in ddiiee(()). Use an eval if you wish to catch these errors and
continue processing.
AAUUTTHHOORR #
Stephen McCamant, <smcc@CSUA.Berkeley.EDU>.
perl v5.36.3 2023-02-15 B::Concise(3p)