In some rare conditions, the generated parser can be wrong when there
are useless tokens.
Reported by Balázs Scheidler.
https://github.com/akimd/bison/issues/72
Balázs managed to prove that the bug was introduced in
commit af1c6f973a
Author: Theophile Ranquet <ranquet@lrde.epita.fr>
Date: Tue Nov 13 10:38:49 2012 +0000
tables: use bitsets for a performance boost
Suggested by Yuri at
<http://lists.gnu.org/archive/html/bison-patches/2012-01/msg00000.html>.
The improvement is marginal for most grammars, but notable for large
grammars (e.g., PosgreSQL's postgre.y), and very large for the
sample.y grammar submitted by Yuri in
http://lists.gnu.org/archive/html/bison-patches/2012-01/msg00012.html.
Measured with --trace=time -fsyntax-only.
parser action tables postgre.y sample.y
Before 0,129 (44%) 37,095 (99%)
After 0,117 (42%) 5,046 (93%)
* src/tables.c (pos): Replace this set of integer coded as an unsorted
array of integers with...
(pos_set): this bitset.
which was implemented long ago, but that I installed only recently
(March 2019), first published in v3.3.90.
That patch introduces a bitset to represent a set of integers. It
managed negative integers by using a (fixed) base (the smallest
integer to represent). It avoided negative accesses into the bitset
by ignoring integers smaller than the base, under the asumption that
these cases correspond to useless tokens that are ignored anyway.
While it turns out to be true for all the test cases in the test suite
(!), Balázs' use case demonstrates that it is not always the case.
So we need to be able to accept negative integers that are smaller
than the current base.
"Amusingly" enough, the aforementioned patch was visibly unsure about
itself:
/* Store PLACE into POS_SET. PLACE might not belong to the set
of possible values for instance with useless tokens. It
would be more satisfying to eliminate the need for this
'if'. */
This commit needs several improvements in the future:
- support from bitset for bit assignment and shifts
- amortized resizing of pos_set
- test cases
* src/tables.c (pos_set_base, pos_set_dump, pos_set_set, pos_set_test):
New.
Use them instead of using bitset_set and bitset_test directly.
There were several bugs in pruning that would leave the state-item
graph in an inconsistent state which could cause crashes later on:
- Pruning now happens in one pass instead of two.
- Disabled state-items no longer prune the state-items they transition
to if that state-item has other states that transition to it.
- State-items that transition to disabled state-items are always
pruned even if they have productions.
Reported by Michal Bartkowiak <michal.bartkowiak@nokia.com>
https://lists.gnu.org/r/bug-bison/2021-01/msg00000.html
and Zartaj Majeed
https://github.com/akimd/bison/issues/71
* src/state-item.c (prune_forward, prune_backward): Fuse into...
(prune_state_item): this.
Adjust callers.
Currently each time we meet %merge we record this location as the
defining location (and symbol). Instead, record the first definition.
In the generated code we go from
yy0->A = merge (*yy0, *yy1);
to
yy0->S = merge (*yy0, *yy1);
where S was indeed the first symbol, and in the diagnostics we go from
glr-regr18.y:30.18-24: error: result type clash on merge function 'merge': <type2> != <type1>
30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
glr-regr18.y:29.18-24: note: previous declaration
29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
glr-regr18.y:31.13-19: error: result type clash on merge function 'merge': <type3> != <type2>
31 | sym3: %merge<merge> { $$ = 0; } ;
| ^~~~~~~
glr-regr18.y:30.18-24: note: previous declaration
30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
to
glr-regr18.y:30.18-24: error: result type clash on merge function 'merge': <type2> != <type1>
30 | sym2: sym3 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
glr-regr18.y:29.18-24: note: previous declaration
29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
glr-regr18.y:31.13-19: error: result type clash on merge function 'merge': <type3> != <type1>
31 | sym3: %merge<merge> { $$ = 0; } ;
| ^~~~~~~
glr-regr18.y:29.18-24: note: previous declaration
29 | sym1: sym2 %merge<merge> { $$ = $1; } ;
| ^~~~~~~
where both duplicates are reported against definition 1, rather than
using definition 1 as a reference when diagnosing about definition 2,
and then 2 as a reference for 3.
* src/reader.c (record_merge_function_type): Keep the first definition.
* tests/glr-regression.at: Adjust.
Reported by Jot Dot.
https://lists.gnu.org/r/help-bison/2020-12/msg00014.html
* data/skeletons/glr.c, data/skeletons/glr2.cc (b4_call_merger): Use
the symbol's slot, not its type.
* examples/c/glr/c++-types.y: Use explicit per-symbol typing together
with api.value.type=union.
(yylex): Use yytoken_kind_t.
Don't generate C code from bison, leave that to the skeletons.
* src/output.c (merger_output): Emit invocations to b4_call_merger.
* data/skeletons/glr.c (b4_call_merger): New.
Symbols are richer than types, and in M4 it is my simpler (and more
common) to deal with symbols rather than types. So let's associate
mergers to a symbol rather than a type name.
* src/reader.h (merger_list): Replace the 'type' member by a symbol
member.
* src/reader.c (record_merge_function_type): Take a symbol as
argument, rather than a type name.
* src/output.c (merger_output): Adjust.
This macro is not exposed to users, make start it with 'YY_'.
* data/skeletons/bison.m4, data/skeletons/c.m4, data/skeletons/glr.c,
* data/skeletons/glr.cc, data/skeletons/lalr1.cc,
* src/parse-gram.c, tests/actions.at, tests/c++.at, tests/headers.at,
* tests/local.at (YYUSE): Rename as...
(YY_USE): this.
When comparing traces from different machines, the mixture of
stdout/stderr in the output are making things uselessly difficult.
* src/lssi.c, src/state-item.c: Output debug traces on stderr.
When using glr.cc, the C function yyparse is an internal detail that
should not be exposed. Users might call it by accident (I did).
* data/skeletons/glr.c (yyparse): When used for glr.cc, rename as yy_parse_impl.
* data/skeletons/glr.cc: Adjust.
The yydefgoto table uses -1 as an invalid for an impossible case (we
never use yydefgoto[0], since it corresponds to the reduction to
$accept, which never happens). Since yydefgoto is a table of state
numbers, this -1 forces a signed type uselessly, which (1) might
trigger compiler warnings when storing a value from yydefgoto into a
state number (nonnegative), and (2) wastes bits which might result in
using a int16 where a uint8 suffices.
Reported by Jot Dot <jotdot@shaw.ca>.
https://lists.gnu.org/r/bug-bison/2020-11/msg00027.html
* src/tables.c (default_goto): Use 0 rather than -1 as invalid value.
* tests/regression.at: Adjust.
* data/skeletons/lalr1.d (YYLocation.step): New.
* examples/d/calc/calc.y (Lexer): Reduce scopes to avoid uninitialized
varibles.
Factor the handling of locations.
We don't need lenChars.
Suggested by Joe Nelson <joe@begriffs.com>.
https://lists.gnu.org/r/help-bison/2020-12/msg00020.html
* data/skeletons/glr.c, data/skeletons/yacc.c (YYNOMEM): New.
Use it.
(yyexhaustedlab): Rename as...
(yynomemlab): this.
* tests/calc.at: Check it.
* doc/bison.texi: Document it.
Fix incorrect statements about non-existing constants for YYERROR etc.
There are some tests that cover them, but nothing for all the
skeletons. Let's do that in the calculator tests.
* tests/calc.at: Check YYACCEPT and YYABORT.
I am not aware of people subclassing the parser class, and I fail to
see how this could be useful. Rather than leaving a badly baked
feature (as in glr.cc currently), let's not support it at all, until
someone comes and explains why and how it would be useful.
* data/skeletons/glr2.cc (parser): We need no virtual function members.
