/* Find and resolve or report look-ahead conflicts for bison, Copyright (C) 1984, 1989, 1992, 2000, 2001, 2002 Free Software Foundation, Inc. This file is part of Bison, the GNU Compiler Compiler. Bison is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. Bison is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with Bison; see the file COPYING. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ #include "system.h" #include "bitset.h" #include "complain.h" #include "getargs.h" #include "symtab.h" #include "files.h" #include "gram.h" #include "state.h" #include "lalr.h" #include "conflicts.h" #include "reader.h" #include "LR0.h" /* -1 stands for not specified. */ int expected_conflicts = -1; static char *conflicts = NULL; struct obstack solved_conflicts_obstack; static bitset shiftset; static bitset lookaheadset; enum conflict_resolution_e { shift_resolution, reduce_resolution, left_resolution, right_resolution, nonassoc_resolution }; /*----------------------------------------------------------------. | Explain how an SR conflict between TOKEN and RULE was resolved: | | RESOLUTION. | `----------------------------------------------------------------*/ static inline void log_resolution (rule_t *rule, symbol_number_t token, enum conflict_resolution_e resolution) { if (report_flag & report_solved_conflicts) { /* The description of the resolution. */ switch (resolution) { case shift_resolution: case right_resolution: obstack_fgrow2 (&solved_conflicts_obstack, _("\ Conflict between rule %d and token %s resolved as shift"), rule->number, symbols[token]->tag); break; case reduce_resolution: case left_resolution: obstack_fgrow2 (&solved_conflicts_obstack, _("\ Conflict between rule %d and token %s resolved as reduce"), rule->number, symbols[token]->tag); break; case nonassoc_resolution: obstack_fgrow2 (&solved_conflicts_obstack, _("\ Conflict between rule %d and token %s resolved as an error"), rule->number, symbols[token]->tag); break; } /* The reason. */ switch (resolution) { case shift_resolution: obstack_fgrow2 (&solved_conflicts_obstack, " (%s < %s)", rule->prec->tag, symbols[token]->tag); break; case reduce_resolution: obstack_fgrow2 (&solved_conflicts_obstack, " (%s < %s)", symbols[token]->tag, rule->prec->tag); break; case left_resolution: obstack_fgrow1 (&solved_conflicts_obstack, " (%%left %s)", symbols[token]->tag); break; case right_resolution: obstack_fgrow1 (&solved_conflicts_obstack, " (%%right %s)", symbols[token]->tag); break; case nonassoc_resolution: obstack_fgrow1 (&solved_conflicts_obstack, " (%%nonassoc %s)", symbols[token]->tag); break; } obstack_sgrow (&solved_conflicts_obstack, ".\n"); } } /*------------------------------------------------------------------. | Turn off the shift recorded for the specified token in the | | specified state. Used when we resolve a shift-reduce conflict in | | favor of the reduction. | `------------------------------------------------------------------*/ static void flush_shift (state_t *state, int token) { transitions_t *transitions = state->transitions; int i; bitset_reset (lookaheadset, token); for (i = 0; i < transitions->num; i++) if (!TRANSITION_IS_DISABLED (transitions, i) && TRANSITION_SYMBOL (transitions, i) == token) TRANSITION_DISABLE (transitions, i); } /*-------------------------------------------------------------------. | Turn off the reduce recorded for the specified token for the | | specified lookahead. Used when we resolve a shift-reduce conflict | | in favor of the shift. | `-------------------------------------------------------------------*/ static void flush_reduce (bitset lookaheads, int token) { bitset_reset (lookaheads, token); } /*------------------------------------------------------------------. | Attempt to resolve shift-reduce conflict for one rule by means of | | precedence declarations. It has already been checked that the | | rule has a precedence. A conflict is resolved by modifying the | | shift or reduce tables so that there is no longer a conflict. | | | | LOOKAHEAD is the number of the lookahead bitset to consider. | | | | ERRS can be used to store discovered explicit errors. | `------------------------------------------------------------------*/ static void resolve_sr_conflict (state_t *state, int ruleno, symbol_t **errs) { symbol_number_t i; reductions_t *reds = state->reductions; /* Find the rule to reduce by to get precedence of reduction. */ rule_t *redrule = reds->rules[ruleno]; int redprec = redrule->prec->prec; bitset lookaheads = reds->lookaheads[ruleno]; int nerrs = 0; for (i = 0; i < ntokens; i++) if (bitset_test (lookaheads, i) && bitset_test (lookaheadset, i) && symbols[i]->prec) { /* Shift-reduce conflict occurs for token number i and it has a precedence. The precedence of shifting is that of token i. */ if (symbols[i]->prec < redprec) { log_resolution (redrule, i, reduce_resolution); flush_shift (state, i); } else if (symbols[i]->prec > redprec) { log_resolution (redrule, i, shift_resolution); flush_reduce (lookaheads, i); } else /* Matching precedence levels. For left association, keep only the reduction. For right association, keep only the shift. For nonassociation, keep neither. */ switch (symbols[i]->assoc) { case right_assoc: log_resolution (redrule, i, right_resolution); flush_reduce (lookaheads, i); break; case left_assoc: log_resolution (redrule, i, left_resolution); flush_shift (state, i); break; case non_assoc: log_resolution (redrule, i, nonassoc_resolution); flush_shift (state, i); flush_reduce (lookaheads, i); /* Record an explicit error for this token. */ errs[nerrs++] = symbols[i]; break; case undef_assoc: abort (); } } /* Some tokens have been explicitly made errors. Allocate a permanent errs structure for this state, to record them. */ state_errs_set (state, nerrs, errs); if (obstack_object_size (&solved_conflicts_obstack)) { obstack_1grow (&solved_conflicts_obstack, '\0'); state->solved_conflicts = obstack_finish (&solved_conflicts_obstack); } } /*-------------------------------------------------------------------. | Solve the S/R conflicts of STATE using the | | precedence/associativity, and flag it inconsistent if it still has | | conflicts. ERRS can be used as storage to compute the list of | | lookaheads on which this STATE raises a syntax error (%nonassoc). | `-------------------------------------------------------------------*/ static void set_conflicts (state_t *state, symbol_t **errs) { int i; transitions_t *transitions = state->transitions; reductions_t *reds = state->reductions; if (state->consistent) return; bitset_zero (lookaheadset); FOR_EACH_SHIFT (transitions, i) bitset_set (lookaheadset, TRANSITION_SYMBOL (transitions, i)); /* Loop over all rules which require lookahead in this state. First check for shift-reduce conflict, and try to resolve using precedence. */ for (i = 0; i < reds->num; ++i) if (reds->rules[i]->prec && reds->rules[i]->prec->prec && !bitset_disjoint_p (reds->lookaheads[i], lookaheadset)) { resolve_sr_conflict (state, i, errs); break; } /* Loop over all rules which require lookahead in this state. Check for conflicts not resolved above. */ for (i = 0; i < reds->num; ++i) { if (!bitset_disjoint_p (reds->lookaheads[i], lookaheadset)) conflicts[state->number] = 1; bitset_or (lookaheadset, lookaheadset, reds->lookaheads[i]); } } /*----------------------------------------------------------------. | Solve all the S/R conflicts using the precedence/associativity, | | and flag as inconsistent the states that still have conflicts. | `----------------------------------------------------------------*/ void conflicts_solve (void) { state_number_t i; /* List of lookaheads on which we explicitly raise a syntax error. */ symbol_t **errs = XMALLOC (symbol_t *, ntokens + 1); conflicts = XCALLOC (char, nstates); shiftset = bitset_create (ntokens, BITSET_FIXED); lookaheadset = bitset_create (ntokens, BITSET_FIXED); obstack_init (&solved_conflicts_obstack); for (i = 0; i < nstates; i++) { set_conflicts (states[i], errs); /* For uniformity of the code, make sure all the states have a valid `errs' member. */ if (!states[i]->errs) states[i]->errs = errs_new (0, 0); } free (errs); } /*---------------------------------------------. | Count the number of shift/reduce conflicts. | `---------------------------------------------*/ static int count_sr_conflicts (state_t *state) { int i; int src_count = 0; transitions_t *transitions = state->transitions; reductions_t *reds = state->reductions; if (!transitions) return 0; bitset_zero (lookaheadset); bitset_zero (shiftset); FOR_EACH_SHIFT (transitions, i) bitset_set (shiftset, TRANSITION_SYMBOL (transitions, i)); for (i = 0; i < reds->num; ++i) bitset_or (lookaheadset, lookaheadset, reds->lookaheads[i]); bitset_and (lookaheadset, lookaheadset, shiftset); src_count = bitset_count (lookaheadset); return src_count; } /*----------------------------------------------------------------. | Count the number of reduce/reduce conflicts. If ONE_PER_TOKEN, | | count one conflict for each token that has any reduce/reduce | | conflicts. Otherwise, count one conflict for each pair of | | conflicting reductions. | +`----------------------------------------------------------------*/ static int count_rr_conflicts (state_t *state, int one_per_token) { int i; reductions_t *reds = state->reductions; int rrc_count = 0; for (i = 0; i < ntokens; i++) { int count = 0; int j; for (j = 0; j < reds->num; ++j) if (bitset_test (reds->lookaheads[j], i)) count++; if (count >= 2) rrc_count += one_per_token ? 1 : count-1; } return rrc_count; } /*--------------------------------------------------------------. | Return a human readable string which reports shift/reduce and | | reduce/reduce conflict numbers (SRC_NUM, RRC_NUM). | `--------------------------------------------------------------*/ static const char * conflict_report (int src_num, int rrc_num) { static char res[4096]; char *cp = res; if (src_num >= 1) { sprintf (cp, ngettext ("%d shift/reduce conflict", "%d shift/reduce conflicts", src_num), src_num); cp += strlen (cp); } if (src_num > 0 && rrc_num > 0) { sprintf (cp, " %s ", _("and")); cp += strlen (cp); } if (rrc_num >= 1) { sprintf (cp, ngettext ("%d reduce/reduce conflict", "%d reduce/reduce conflicts", rrc_num), rrc_num); cp += strlen (cp); } *cp++ = '\0'; return res; } /*----------------------------------------------------------------. | Same as above, but report the number of conflicts a` la POSIX. | `----------------------------------------------------------------*/ static void conflict_report_yacc (int src_num, int rrc_num) { /* If invoked with `--yacc', use the output format specified by POSIX. */ fprintf (stderr, _("conflicts: ")); if (src_num > 0) fprintf (stderr, _(" %d shift/reduce"), src_num); if (src_num > 0 && rrc_num > 0) fprintf (stderr, ","); if (rrc_num > 0) fprintf (stderr, _(" %d reduce/reduce"), rrc_num); putc ('\n', stderr); } /*-----------------------------------------------------------. | Output the detailed description of states with conflicts. | `-----------------------------------------------------------*/ void conflicts_output (FILE *out) { bool printed_sth = false; state_number_t i; for (i = 0; i < nstates; i++) { state_t *s = states[i]; if (conflicts[i]) { fprintf (out, _("State %d contains "), i); fprintf (out, "%s.\n", conflict_report (count_sr_conflicts (s), count_rr_conflicts (s, true))); printed_sth = true; } } if (printed_sth) fputs ("\n\n", out); } /*--------------------------------------------------------. | Total the number of S/R and R/R conflicts. Unlike the | | code in conflicts_output, however, count EACH pair of | | reductions for the same state and lookahead as one | | conflict. | `--------------------------------------------------------*/ int conflicts_total_count (void) { state_number_t i; int count; /* Conflicts by state. */ count = 0; for (i = 0; i < nstates; i++) if (conflicts[i]) { count += count_sr_conflicts (states[i]); count += count_rr_conflicts (states[i], false); } return count; } /*------------------------------------------. | Reporting the total number of conflicts. | `------------------------------------------*/ void conflicts_print (void) { /* Is the number of SR conflicts OK? Either EXPECTED_CONFLICTS is not set, and then we want 0 SR, or else it is specified, in which case we want equality. */ int src_ok = 0; int src_total = 0; int rrc_total = 0; /* Conflicts by state. */ { state_number_t i; for (i = 0; i < nstates; i++) if (conflicts[i]) { src_total += count_sr_conflicts (states[i]); rrc_total += count_rr_conflicts (states[i], true); } } src_ok = src_total == (expected_conflicts == -1 ? 0 : expected_conflicts); /* If there are no RR conflicts, and as many SR conflicts as expected, then there is nothing to report. */ if (!rrc_total && src_ok) return; /* Report the total number of conflicts on STDERR. */ if (yacc_flag) conflict_report_yacc (src_total, rrc_total); else warn ("%s", conflict_report (src_total, rrc_total)); if (expected_conflicts != -1 && !src_ok) complain (ngettext ("expected %d shift/reduce conflict", "expected %d shift/reduce conflicts", expected_conflicts), expected_conflicts); } void conflicts_free (void) { XFREE (conflicts); bitset_free (shiftset); bitset_free (lookaheadset); obstack_free (&solved_conflicts_obstack, NULL); }