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* src/lalr.c (state_lookahead_tokens_count): For code readability,

Browse Source 
move the check for disabled transitions to an aver since conflict
resolution hasn't happened yet.

* src/lalr.c (state_lookahead_tokens_count): Remove the check that
labels a state as inconsistent just because it has error transitions.
The original form of this check appeared in revision 1.1 of lalr.c,
which was committed on 1991-12-21.  Now (at least), changing the
consistency label on such a state appears to have no useful effect in
any of the places it is examined, which I enumerate below.  The key
point to understanding each item in this enumeration is that a state
with an error transition is labelled consistent in the first place only
if it has no rules, so the check cannot matter for states that have
rules.  (1) Labelling a state as inconsistent will cause set_conflicts
to try to identify its conflicts, and a state must have *rules* to have
conflicts.  (2) Labelling a state as inconsistent will affect how
action_row sets the default *rule* for the state.  (3) Labelling a
state as inconsistent will cause build_relations to add lookback edges
to *rules* in that state.
* src/state.h (struct state): Word the comment for member consistent
more carefully.
This commit is contained in:
Joel E. Denny
2007-05-28 04:14:18 +00:00
parent 14462c2b1b
commit 2a6b783def
3 changed files with 32 additions and 12 deletions
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24
ChangeLog
View File

@@ -1,3 +1,27 @@
2007-05-28 Joel E. Denny <jdenny@ces.clemson.edu>
* src/lalr.c (state_lookahead_tokens_count): For code readability,
move the check for disabled transitions to an aver since conflict
resolution hasn't happened yet.
* src/lalr.c (state_lookahead_tokens_count): Remove the check that
labels a state as inconsistent just because it has error transitions.
The original form of this check appeared in revision 1.1 of lalr.c,
which was committed on 1991-12-21. Now (at least), changing the
consistency label on such a state appears to have no useful effect in
any of the places it is examined, which I enumerate below. The key
point to understanding each item in this enumeration is that a state
with an error transition is labelled consistent in the first place only
if it has no rules, so the check cannot matter for states that have
rules. (1) Labelling a state as inconsistent will cause set_conflicts
to try to identify its conflicts, and a state must have *rules* to have
conflicts. (2) Labelling a state as inconsistent will affect how
action_row sets the default *rule* for the state. (3) Labelling a
state as inconsistent will cause build_relations to add lookback edges
to *rules* in that state.
* src/state.h (struct state): Word the comment for member consistent
more carefully.
2007-05-27 Joel E. Denny <jdenny@ces.clemson.edu>
Don't depend on C99 features.

17
src/lalr.c
View File

@@ -340,7 +340,6 @@ compute_lookahead_tokens (void)
static int
state_lookahead_tokens_count (state *s)
{
int k;
int n_lookahead_tokens = 0;
reductions *rp = s->reductions;
transitions *sp = s->transitions;
@@ -348,21 +347,17 @@ state_lookahead_tokens_count (state *s)
/* We need a lookahead either to distinguish different
reductions (i.e., there are two or more), or to distinguish a
reduction from a shift. Otherwise, it is straightforward,
and the state is `consistent'. */
and the state is `consistent'. There is no need to check that
transition 0 hasn't been disabled before checking if it is a
shift since transitions are only disabled during conflict
resolution, and that hasn't happened yet. */
aver (sp->num == 0 || !TRANSITION_IS_DISABLED (sp, 0));
if (rp->num > 1
|| (rp->num == 1 && sp->num &&
!TRANSITION_IS_DISABLED (sp, 0) && TRANSITION_IS_SHIFT (sp, 0)))
|| (rp->num == 1 && sp->num && TRANSITION_IS_SHIFT (sp, 0)))
n_lookahead_tokens += rp->num;
else
s->consistent = 1;
for (k = 0; k < sp->num; k++)
if (!TRANSITION_IS_DISABLED (sp, k) && TRANSITION_IS_ERROR (sp, k))
{
s->consistent = 0;
break;
}
return n_lookahead_tokens;
}

3
src/state.h
View File

@@ -202,7 +202,8 @@ struct state
reductions *reductions;
errs *errs;
/* Nonzero if no lookahead is needed to decide what to do in state S. */
/* If non-zero, then no lookahead sets on reduce actions are needed to
decide what to do in state S. */
char consistent;
/* If some conflicts were solved thanks to precedence/associativity,