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67af719840616ed07ca120b8255a998f4533ce17
bison/src/conflicts.c
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Joel E. Denny 401b73afdf maint: run "make update-copyright"
2009-08-06 19:17:44 -04:00

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/* Find and resolve or report lookahead conflicts for bison,
Copyright (C) 1984, 1989, 1992, 2000, 2001, 2002, 2003, 2004, 2005,
2006, 2007, 2008-2009 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
This program 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 3 of the License, or
(at your option) any later version.
This program 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 this program. If not, see <http://www.gnu.org/licenses/>. */
#include <config.h>
#include "system.h"
#include <bitset.h>
#include "LR0.h"
#include "complain.h"
#include "conflicts.h"
#include "files.h"
#include "getargs.h"
#include "gram.h"
#include "lalr.h"
#include "print-xml.h"
#include "reader.h"
#include "state.h"
#include "symtab.h"
/* -1 stands for not specified. */
int expected_sr_conflicts = -1;
int expected_rr_conflicts = -1;
static char *conflicts;
static struct obstack solved_conflicts_obstack;
static struct obstack solved_conflicts_xml_obstack;
static bitset shift_set;
static bitset lookahead_set;
enum conflict_resolution
{
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 *r, symbol_number token,
enum conflict_resolution 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"),
r->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"),
r->number,
symbols[token]->tag);
break;
case nonassoc_resolution:
obstack_fgrow2 (&solved_conflicts_obstack,
_(" Conflict between rule %d and token %s"
" resolved as an error"),
r->number,
symbols[token]->tag);
break;
}
/* The reason. */
switch (resolution)
{
case shift_resolution:
obstack_fgrow2 (&solved_conflicts_obstack,
" (%s < %s)",
r->prec->tag,
symbols[token]->tag);
break;
case reduce_resolution:
obstack_fgrow2 (&solved_conflicts_obstack,
" (%s < %s)",
symbols[token]->tag,
r->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");
}
/* XML report */
if (xml_flag)
{
/* The description of the resolution. */
switch (resolution)
{
case shift_resolution:
case right_resolution:
obstack_fgrow2 (&solved_conflicts_xml_obstack,
" <resolution rule=\"%d\" symbol=\"%s\""
" type=\"shift\">",
r->number,
xml_escape (symbols[token]->tag));
break;
case reduce_resolution:
case left_resolution:
obstack_fgrow2 (&solved_conflicts_xml_obstack,
" <resolution rule=\"%d\" symbol=\"%s\""
" type=\"reduce\">",
r->number,
xml_escape (symbols[token]->tag));
break;
case nonassoc_resolution:
obstack_fgrow2 (&solved_conflicts_xml_obstack,
" <resolution rule=\"%d\" symbol=\"%s\""
" type=\"error\">",
r->number,
xml_escape (symbols[token]->tag));
break;
}
/* The reason. */
switch (resolution)
{
case shift_resolution:
obstack_fgrow2 (&solved_conflicts_xml_obstack,
"%s &lt; %s",
xml_escape_n (0, r->prec->tag),
xml_escape_n (1, symbols[token]->tag));
break;
case reduce_resolution:
obstack_fgrow2 (&solved_conflicts_xml_obstack,
"%s &lt; %s",
xml_escape_n (0, symbols[token]->tag),
xml_escape_n (1, r->prec->tag));
break;
case left_resolution:
obstack_fgrow1 (&solved_conflicts_xml_obstack,
"%%left %s",
xml_escape (symbols[token]->tag));
break;
case right_resolution:
obstack_fgrow1 (&solved_conflicts_xml_obstack,
"%%right %s",
xml_escape (symbols[token]->tag));
break;
case nonassoc_resolution:
obstack_fgrow1 (&solved_conflicts_xml_obstack,
"%%nonassoc %s",
xml_escape (symbols[token]->tag));
break;
}
obstack_sgrow (&solved_conflicts_xml_obstack, "</resolution>\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 or as an error (%nonassoc). |
`------------------------------------------------------------------*/
static void
flush_shift (state *s, int token)
{
transitions *trans = s->transitions;
int i;
bitset_reset (lookahead_set, token);
for (i = 0; i < trans->num; i++)
if (!TRANSITION_IS_DISABLED (trans, i)
&& TRANSITION_SYMBOL (trans, i) == token)
TRANSITION_DISABLE (trans, i);
}
/*--------------------------------------------------------------------.
| Turn off the reduce recorded for the specified token in the |
| specified lookahead set. Used when we resolve a shift-reduce |
| conflict in favor of the shift or as an error (%nonassoc). |
`--------------------------------------------------------------------*/
static void
flush_reduce (bitset lookahead_tokens, int token)
{
bitset_reset (lookahead_tokens, 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. |
| |
| RULENO is the number of the lookahead bitset to consider. |
| |
| ERRORS and NERRS can be used to store discovered explicit |
| errors. |
`------------------------------------------------------------------*/
static void
resolve_sr_conflict (state *s, int ruleno, symbol **errors, int *nerrs)
{
symbol_number i;
reductions *reds = s->reductions;
/* Find the rule to reduce by to get precedence of reduction. */
rule *redrule = reds->rules[ruleno];
int redprec = redrule->prec->prec;
bitset lookahead_tokens = reds->lookahead_tokens[ruleno];
for (i = 0; i < ntokens; i++)
if (bitset_test (lookahead_tokens, i)
&& bitset_test (lookahead_set, 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 (s, i);
}
else if (symbols[i]->prec > redprec)
{
log_resolution (redrule, i, shift_resolution);
flush_reduce (lookahead_tokens, i);
}
else
/* Matching precedence levels.
For non-defined associativity, keep both: unexpected
associativity conflict.
For left associativity, keep only the reduction.
For right associativity, keep only the shift.
For nonassociativity, keep neither. */
switch (symbols[i]->assoc)
{
case undef_assoc:
abort ();
case precedence_assoc:
break;
case right_assoc:
log_resolution (redrule, i, right_resolution);
flush_reduce (lookahead_tokens, i);
break;
case left_assoc:
log_resolution (redrule, i, left_resolution);
flush_shift (s, i);
break;
case non_assoc:
log_resolution (redrule, i, nonassoc_resolution);
flush_shift (s, i);
flush_reduce (lookahead_tokens, i);
/* Record an explicit error for this token. */
errors[(*nerrs)++] = symbols[i];
break;
}
}
}
/*-------------------------------------------------------------------.
| Solve the S/R conflicts of state S using the |
| precedence/associativity, and flag it inconsistent if it still has |
| conflicts. ERRORS can be used as storage to compute the list of |
| lookahead tokens on which S raises a syntax error (%nonassoc). |
`-------------------------------------------------------------------*/
static void
set_conflicts (state *s, symbol **errors)
{
int i;
transitions *trans = s->transitions;
reductions *reds = s->reductions;
int nerrs = 0;
if (s->consistent)
return;
bitset_zero (lookahead_set);
FOR_EACH_SHIFT (trans, i)
bitset_set (lookahead_set, TRANSITION_SYMBOL (trans, 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->lookahead_tokens[i], lookahead_set))
resolve_sr_conflict (s, i, errors, &nerrs);
if (nerrs)
{
/* Some tokens have been explicitly made errors. Allocate a
permanent errs structure for this state, to record them. */
state_errs_set (s, nerrs, errors);
}
if (obstack_object_size (&solved_conflicts_obstack))
{
obstack_1grow (&solved_conflicts_obstack, '\0');
s->solved_conflicts = obstack_finish (&solved_conflicts_obstack);
}
if (obstack_object_size (&solved_conflicts_xml_obstack))
{
obstack_1grow (&solved_conflicts_xml_obstack, '\0');
s->solved_conflicts_xml = obstack_finish (&solved_conflicts_xml_obstack);
}
/* 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->lookahead_tokens[i], lookahead_set))
conflicts[s->number] = 1;
bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[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 i;
/* List of lookahead tokens on which we explicitly raise a syntax error. */
symbol **errors = xnmalloc (ntokens + 1, sizeof *errors);
conflicts = xcalloc (nstates, sizeof *conflicts);
shift_set = bitset_create (ntokens, BITSET_FIXED);
lookahead_set = bitset_create (ntokens, BITSET_FIXED);
obstack_init (&solved_conflicts_obstack);
obstack_init (&solved_conflicts_xml_obstack);
for (i = 0; i < nstates; i++)
{
set_conflicts (states[i], errors);
/* 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 (errors);
}
void
conflicts_update_state_numbers (state_number old_to_new[],
state_number nstates_old)
{
state_number i;
for (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. |
`---------------------------------------------*/
static int
count_sr_conflicts (state *s)
{
int i;
int src_count = 0;
transitions *trans = s->transitions;
reductions *reds = s->reductions;
if (!trans)
return 0;
bitset_zero (lookahead_set);
bitset_zero (shift_set);
FOR_EACH_SHIFT (trans, i)
bitset_set (shift_set, TRANSITION_SYMBOL (trans, i));
for (i = 0; i < reds->num; ++i)
bitset_or (lookahead_set, lookahead_set, reds->lookahead_tokens[i]);
bitset_and (lookahead_set, lookahead_set, shift_set);
src_count = bitset_count (lookahead_set);
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 *s, bool one_per_token)
{
int i;
reductions *reds = s->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->lookahead_tokens[j], i))
count++;
if (count >= 2)
rrc_count += one_per_token ? 1 : count-1;
}
return rrc_count;
}
/*--------------------------------------------------------.
| Report the number of conflicts, using the Yacc format. |
`--------------------------------------------------------*/
static void
conflict_report (FILE *out, int src_num, int rrc_num)
{
if (src_num && rrc_num)
fprintf (out, _("conflicts: %d shift/reduce, %d reduce/reduce\n"),
src_num, rrc_num);
else if (src_num)
fprintf (out, _("conflicts: %d shift/reduce\n"), src_num);
else if (rrc_num)
fprintf (out, _("conflicts: %d reduce/reduce\n"), rrc_num);
}
/*-----------------------------------------------------------.
| Output the detailed description of states with conflicts. |
`-----------------------------------------------------------*/
void
conflicts_output (FILE *out)
{
bool printed_sth = false;
state_number i;
for (i = 0; i < nstates; i++)
{
state *s = states[i];
if (conflicts[i])
{
fprintf (out, _("State %d "), i);
conflict_report (out, 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 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. */
bool src_ok;
bool rrc_ok;
int src_total = 0;
int rrc_total = 0;
int src_expected;
int rrc_expected;
/* Conflicts by state. */
{
state_number 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);
}
}
if (! glr_parser && rrc_total > 0 && expected_rr_conflicts != -1)
{
warn (_("%%expect-rr applies only to GLR parsers"));
expected_rr_conflicts = -1;
}
src_expected = expected_sr_conflicts == -1 ? 0 : expected_sr_conflicts;
rrc_expected = expected_rr_conflicts == -1 ? 0 : expected_rr_conflicts;
src_ok = src_total == src_expected;
rrc_ok = rrc_total == rrc_expected;
/* If there are as many RR conflicts and SR conflicts as
expected, then there is nothing to report. */
if (rrc_ok & src_ok)
return;
/* Report the total number of conflicts on STDERR. */
if (src_total | rrc_total)
{
if (! yacc_flag)
fprintf (stderr, "%s: ", current_file);
conflict_report (stderr, src_total, rrc_total);
}
if (expected_sr_conflicts != -1 || expected_rr_conflicts != -1)
{
if (! src_ok)
complain (ngettext ("expected %d shift/reduce conflict",
"expected %d shift/reduce conflicts",
src_expected),
src_expected);
if (! rrc_ok)
complain (ngettext ("expected %d reduce/reduce conflict",
"expected %d reduce/reduce conflicts",
rrc_expected),
rrc_expected);
}
}
void
conflicts_free (void)
{
free (conflicts);
bitset_free (shift_set);
bitset_free (lookahead_set);
obstack_free (&solved_conflicts_obstack, NULL);
obstack_free (&solved_conflicts_xml_obstack, NULL);
}
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