mirror of
https://git.savannah.gnu.org/git/bison.git
synced 2026-03-09 20:33:03 +00:00
143 lines
4.0 KiB
C
143 lines
4.0 KiB
C
/* Calculate which nonterminals can expand into the null string for Bison.
|
|
|
|
Copyright (C) 1984, 1989, 2000-2006, 2009-2015, 2018-2019 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/>. */
|
|
|
|
|
|
/* Set up NULLABLE, a vector saying which nonterminals can expand into
|
|
the null string. NULLABLE[I - NTOKENS] is nonzero if symbol I can
|
|
do so. */
|
|
|
|
#include <config.h>
|
|
#include "system.h"
|
|
|
|
#include "getargs.h"
|
|
#include "gram.h"
|
|
#include "nullable.h"
|
|
#include "reduce.h"
|
|
#include "symtab.h"
|
|
|
|
/* Linked list of rules. */
|
|
typedef struct rule_list
|
|
{
|
|
struct rule_list *next;
|
|
rule *value;
|
|
} rule_list;
|
|
|
|
bool *nullable = NULL;
|
|
|
|
static void
|
|
nullable_print (FILE *out)
|
|
{
|
|
int i;
|
|
fputs ("NULLABLE\n", out);
|
|
for (i = ntokens; i < nsyms; i++)
|
|
fprintf (out, " %s: %s\n", symbols[i]->tag,
|
|
nullable[i - ntokens] ? "yes" : "no");
|
|
fputs ("\n\n", out);
|
|
}
|
|
|
|
void
|
|
nullable_compute (void)
|
|
{
|
|
rule_number ruleno;
|
|
symbol_number *s1;
|
|
symbol_number *s2;
|
|
rule_list *p;
|
|
|
|
symbol_number *squeue = xnmalloc (nvars, sizeof *squeue);
|
|
size_t *rcount = xcalloc (nrules, sizeof *rcount);
|
|
/* RITEM contains all the rules, including useless productions.
|
|
Hence we must allocate room for useless nonterminals too. */
|
|
rule_list **rsets = xcalloc (nvars, sizeof *rsets);
|
|
/* This is said to be more elements than we actually use.
|
|
Supposedly NRITEMS - NRULES is enough. But why take the risk? */
|
|
rule_list *relts = xnmalloc (nritems + nvars + 1, sizeof *relts);
|
|
|
|
nullable = xcalloc (nvars, sizeof *nullable);
|
|
|
|
s1 = s2 = squeue;
|
|
p = relts;
|
|
|
|
for (ruleno = 0; ruleno < nrules; ++ruleno)
|
|
if (rules[ruleno].useful)
|
|
{
|
|
rule *rules_ruleno = &rules[ruleno];
|
|
if (rules_ruleno->rhs[0] >= 0)
|
|
{
|
|
/* This rule has a non empty RHS. */
|
|
item_number *rp = NULL;
|
|
bool any_tokens = false;
|
|
for (rp = rules_ruleno->rhs; *rp >= 0; ++rp)
|
|
if (ISTOKEN (*rp))
|
|
any_tokens = true;
|
|
|
|
/* This rule has only nonterminals: schedule it for the second
|
|
pass. */
|
|
if (!any_tokens)
|
|
for (rp = rules_ruleno->rhs; *rp >= 0; ++rp)
|
|
{
|
|
rcount[ruleno]++;
|
|
p->next = rsets[*rp - ntokens];
|
|
p->value = rules_ruleno;
|
|
rsets[*rp - ntokens] = p;
|
|
p++;
|
|
}
|
|
}
|
|
else
|
|
{
|
|
/* This rule has an empty RHS. */
|
|
aver (item_number_as_rule_number (rules_ruleno->rhs[0])
|
|
== ruleno);
|
|
if (rules_ruleno->useful
|
|
&& ! nullable[rules_ruleno->lhs->number - ntokens])
|
|
{
|
|
nullable[rules_ruleno->lhs->number - ntokens] = true;
|
|
*s2++ = rules_ruleno->lhs->number;
|
|
}
|
|
}
|
|
}
|
|
|
|
while (s1 < s2)
|
|
for (p = rsets[*s1++ - ntokens]; p; p = p->next)
|
|
{
|
|
rule *r = p->value;
|
|
if (--rcount[r->number] == 0)
|
|
if (r->useful && ! nullable[r->lhs->number - ntokens])
|
|
{
|
|
nullable[r->lhs->number - ntokens] = true;
|
|
*s2++ = r->lhs->number;
|
|
}
|
|
}
|
|
|
|
free (squeue);
|
|
free (rcount);
|
|
free (rsets);
|
|
free (relts);
|
|
|
|
if (trace_flag & trace_sets)
|
|
nullable_print (stderr);
|
|
}
|
|
|
|
|
|
void
|
|
nullable_free (void)
|
|
{
|
|
free (nullable);
|
|
}
|