+2007-05-06 Joel E. Denny <jdenny@ces.clemson.edu>
+
+ If conflict resolution makes states unreachable, remove those states,
+ report rules that are then unused, and don't report conflicts in those
+ states.
+ * src/conflicts.c, src/conflicts.h (conflicts_update_state_numbers):
+ New global function.
+ * src/lalr.c, src/lalr.h (lalr_update_state_numbers): New global
+ function.
+ * src/main.c (main): After conflict resolution, remove the unreachable
+ states and update all data structures that reference states by number.
+ * src/state.c (state_new): Initialize each state's reachable member to
+ false.
+ (state_mark_reachable_states): New static function.
+ (state_remove_unreachable_states): New global function.
+ * src/state.h (struct state): Add member bool reachable.
+ (state_remove_unreachable_states): Prototype.
+ * tests/conflicts.at (Unreachable States After Conflict Resolution):
+ New test case.
+ * tests/existing.at (GNU pic Grammar): Update test case output now that
+ an unused rule is discovered.
+
2007-05-06 Joel E. Denny <jdenny@ces.clemson.edu>
Minor code cleanup in parser table construction.
}
+void
+conflicts_update_state_numbers (state_number old_to_new[],
+ state_number nstates_old)
+{
+ for (state_number i = 0; i < nstates_old; ++i)
+ if (old_to_new[i] != nstates_old)
+ conflicts[old_to_new[i]] = conflicts[i];
+}
+
+
/*---------------------------------------------.
| Count the number of shift/reduce conflicts. |
`---------------------------------------------*/
# include "state.h"
void conflicts_solve (void);
+
+/**
+ * Update state numbers recorded in internal arrays such that:
+ * - \c nstates_old is the old number of states.
+ * - Where \c i is the old state number, <tt>old_to_new[i]</tt> is either:
+ * - \c nstates_old if state \c i is removed because it is unreachable.
+ * - The new state number.
+ * - The highest new state number is the number of remaining states - 1.
+ * - The numerical order of the remaining states has not changed.
+ */
+void conflicts_update_state_numbers (state_number old_to_new[],
+ state_number nstates_old);
+
void conflicts_print (void);
int conflicts_total_count (void);
void conflicts_output (FILE *out);
}
+void
+lalr_update_state_numbers (state_number old_to_new[], state_number nstates_old)
+{
+ goto_number ngotos_reachable = 0;
+ symbol_number nonterminal = 0;
+ aver (nsyms == nvars + ntokens);
+ for (goto_number i = 0; i < ngotos; ++i)
+ {
+ while (i == goto_map[nonterminal])
+ goto_map[nonterminal++] = ngotos_reachable;
+ /* If old_to_new[from_state[i]] = nstates_old, remove this goto
+ entry. */
+ if (old_to_new[from_state[i]] != nstates_old)
+ {
+ /* from_state[i] is not removed, so it and thus to_state[i] are
+ reachable, so to_state[i] != nstates_old. */
+ aver (old_to_new[to_state[i]] != nstates_old);
+ from_state[ngotos_reachable] = old_to_new[from_state[i]];
+ to_state[ngotos_reachable] = old_to_new[to_state[i]];
+ ++ngotos_reachable;
+ }
+ }
+ while (nonterminal <= nvars)
+ {
+ aver (ngotos == goto_map[nonterminal]);
+ goto_map[nonterminal++] = ngotos_reachable;
+ }
+ ngotos = ngotos_reachable;
+}
+
+
void
lalr_free (void)
{
*/
void lalr (void);
+/**
+ * Update state numbers recorded in #goto_map, #from_state, and #to_state such
+ * that:
+ * - \c nstates_old is the old number of states.
+ * - Where \c i is the old state number, <tt>old_to_new[i]</tt> is either:
+ * - \c nstates_old if state \c i is removed because it is unreachable.
+ * Thus, remove all goto entries involving this state.
+ * - The new state number.
+ */
+void lalr_update_state_numbers (state_number old_to_new[],
+ state_number nstates_old);
+
/** Release the information related to lookahead tokens.
declarations. */
timevar_push (TV_CONFLICTS);
conflicts_solve ();
+ {
+ state_number old_to_new[nstates];
+ state_number nstates_old = nstates;
+ state_remove_unreachable_states (old_to_new);
+ lalr_update_state_numbers (old_to_new, nstates_old);
+ conflicts_update_state_numbers (old_to_new, nstates_old);
+ }
conflicts_print ();
timevar_pop (TV_CONFLICTS);
res->errs = NULL;
res->consistent = 0;
res->solved_conflicts = NULL;
+ res->reachable = false;
res->nitems = nitems;
memcpy (res->items, core, items_size);
return entry;
}
+
+/*------------------------------------------------------.
+| Mark S and all states reachable from S as reachable. |
+`------------------------------------------------------*/
+
+static void
+state_mark_reachable_states (state *s)
+{
+ if (s->reachable)
+ return;
+ s->reachable = true;
+ for (int i = 0; i < s->transitions->num; ++i)
+ if (!TRANSITION_IS_DISABLED (s->transitions, i))
+ state_mark_reachable_states (s->transitions->states[i]);
+}
+
+void
+state_remove_unreachable_states (state_number old_to_new[])
+{
+ state_number nstates_reachable = 0;
+ state_mark_reachable_states (states[0]);
+ for (state_number i = 0; i < nstates; ++i)
+ {
+ if (states[i]->reachable)
+ {
+ states[nstates_reachable] = states[i];
+ states[nstates_reachable]->number = nstates_reachable;
+ old_to_new[i] = nstates_reachable++;
+ }
+ else
+ {
+ state_free (states[i]);
+ old_to_new[i] = nstates;
+ }
+ }
+ nstates = nstates_reachable;
+}
+
/* All the decorated states, indexed by the state number. */
state **states = NULL;
a human readable description of the resolution. */
const char *solved_conflicts;
+ /* Conflict resolution sometimes makes states unreachable. Initialized to 0
+ in state_new and then used by state_remove_unreachable_states after
+ conflicts_solve. */
+ bool reachable;
+
/* Its items. Must be last, since ITEMS can be arbitrarily large.
*/
size_t nitems;
/* Insert STATE in the state hash table. */
void state_hash_insert (state *s);
+/* Remove unreachable states, renumber remaining states, update NSTATES, and
+ write to OLD_TO_NEW a mapping of old state numbers to new state numbers such
+ that the old value of NSTATES is written as the new state number for removed
+ states. The size of OLD_TO_NEW must be the old value of NSTATES. */
+void state_remove_unreachable_states (state_number old_to_new[]);
+
/* All the states, indexed by the state number. */
extern state **states;
/* Free all the states. */
void states_free (void);
+
#endif /* !STATE_H_ */
AT_CHECK([bison -o input.c input.y])
AT_CLEANUP
+
+
+## ---------------------------------------------- ##
+## Unreachable States After Conflict Resolution. ##
+## ---------------------------------------------- ##
+
+AT_SETUP([[Unreachable States After Conflict Resolution]])
+
+# If conflict resolution makes states unreachable, remove those states, report
+# rules that are then unused, and don't report conflicts in those states. Test
+# what happens when a nonterminal becomes useless as a result of state removal
+# since that causes lalr.o's goto map to be rewritten.
+
+AT_DATA([[input.y]],
+[[%output "input.c"
+%left 'a'
+
+%%
+
+start: resolved_conflict 'a' reported_conflicts 'a' ;
+
+/* S/R conflict resolved as shift, so the state with item
+ * (resolved_conflict: 'a' . unreachable1) and all it transition successors are
+ * unreachable, and the associated production is useless. */
+resolved_conflict:
+ 'a' unreachable1
+ | %prec 'a'
+ ;
+
+/* S/R conflict that need not be reported since it is unreachable because of
+ * the previous conflict resolution. Nonterminal unreachable1 and all its
+ * productions are useless. */
+unreachable1:
+ 'a' unreachable2
+ |
+ ;
+
+/* Likewise for a R/R conflict and nonterminal unreachable2. */
+unreachable2: | ;
+
+/* Make sure remaining S/R and R/R conflicts are still reported correctly even
+ * when their states are renumbered due to state removal. */
+reported_conflicts:
+ 'a'
+ | 'a'
+ |
+ ;
+
+]])
+
+AT_CHECK([[bison --report=all input.y]], 0, [],
+[[input.y: conflicts: 1 shift/reduce, 1 reduce/reduce
+input.y:12.5-20: warning: rule never reduced because of conflicts: resolved_conflict: 'a' unreachable1
+input.y:20.5-20: warning: rule never reduced because of conflicts: unreachable1: 'a' unreachable2
+input.y:21.4: warning: rule never reduced because of conflicts: unreachable1: /* empty */
+input.y:25.13: warning: rule never reduced because of conflicts: unreachable2: /* empty */
+input.y:25.16: warning: rule never reduced because of conflicts: unreachable2: /* empty */
+input.y:31.5-7: warning: rule never reduced because of conflicts: reported_conflicts: 'a'
+input.y:32.4: warning: rule never reduced because of conflicts: reported_conflicts: /* empty */
+]])
+
+AT_CHECK([[cat input.output]], 0,
+[[Rules never reduced
+
+ 2 resolved_conflict: 'a' unreachable1
+
+ 4 unreachable1: 'a' unreachable2
+ 5 | /* empty */
+
+ 6 unreachable2: /* empty */
+ 7 | /* empty */
+
+ 9 reported_conflicts: 'a'
+ 10 | /* empty */
+
+
+State 4 conflicts: 1 shift/reduce
+State 5 conflicts: 1 reduce/reduce
+
+
+Grammar
+
+ 0 $accept: start $end
+
+ 1 start: resolved_conflict 'a' reported_conflicts 'a'
+
+ 2 resolved_conflict: 'a' unreachable1
+ 3 | /* empty */
+
+ 4 unreachable1: 'a' unreachable2
+ 5 | /* empty */
+
+ 6 unreachable2: /* empty */
+ 7 | /* empty */
+
+ 8 reported_conflicts: 'a'
+ 9 | 'a'
+ 10 | /* empty */
+
+
+Terminals, with rules where they appear
+
+$end (0) 0
+'a' (97) 1 2 4 8 9
+error (256)
+
+
+Nonterminals, with rules where they appear
+
+$accept (4)
+ on left: 0
+start (5)
+ on left: 1, on right: 0
+resolved_conflict (6)
+ on left: 2 3, on right: 1
+unreachable1 (7)
+ on left: 4 5, on right: 2
+unreachable2 (8)
+ on left: 6 7, on right: 4
+reported_conflicts (9)
+ on left: 8 9 10, on right: 1
+
+
+state 0
+
+ 0 $accept: . start $end
+ 1 start: . resolved_conflict 'a' reported_conflicts 'a'
+ 2 resolved_conflict: . 'a' unreachable1
+ 3 | . ['a']
+
+ $default reduce using rule 3 (resolved_conflict)
+
+ start go to state 1
+ resolved_conflict go to state 2
+
+ Conflict between rule 3 and token 'a' resolved as reduce (%left 'a').
+
+
+state 1
+
+ 0 $accept: start . $end
+
+ $end shift, and go to state 3
+
+
+state 2
+
+ 1 start: resolved_conflict . 'a' reported_conflicts 'a'
+
+ 'a' shift, and go to state 4
+
+
+state 3
+
+ 0 $accept: start $end .
+
+ $default accept
+
+
+state 4
+
+ 1 start: resolved_conflict 'a' . reported_conflicts 'a'
+ 8 reported_conflicts: . 'a'
+ 9 | . 'a'
+ 10 | . ['a']
+
+ 'a' shift, and go to state 5
+
+ 'a' [reduce using rule 10 (reported_conflicts)]
+
+ reported_conflicts go to state 6
+
+
+state 5
+
+ 8 reported_conflicts: 'a' . ['a']
+ 9 | 'a' . ['a']
+
+ 'a' reduce using rule 8 (reported_conflicts)
+ 'a' [reduce using rule 9 (reported_conflicts)]
+ $default reduce using rule 8 (reported_conflicts)
+
+
+state 6
+
+ 1 start: resolved_conflict 'a' reported_conflicts . 'a'
+
+ 'a' shift, and go to state 7
+
+
+state 7
+
+ 1 start: resolved_conflict 'a' reported_conflicts 'a' .
+
+ $default reduce using rule 1 (start)
+]])
+
+AT_CLEANUP
# Pass plenty of options, to exercise plenty of code, even if we
# don't actually check the output. But SEGV is watching us, and
# so might do dmalloc.
-AT_CHECK([[bison --verbose --defines input.y]], 0, [], [])
+AT_CHECK([[bison --verbose --defines input.y]], 0, [],
+[[input.y:453.11-48: warning: rule never reduced because of conflicts: path: ORDINAL LAST object_type relative_path
+]])
AT_CLEANUP
projects / bison.git / commitdiff
