-/* Part of the bison parser generator,
- Copyright 1984, 1989, 2000 Free Software Foundation, Inc.
+/* Calculate which nonterminals can expand into the null string for Bison.
+
+ Copyright (C) 1984, 1989, 2000-2006, 2009-2013 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
+ 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 2, or (at your option)
- any later version.
+ the Free Software Foundation, either version 3 of the License, or
+ (at your option) any later version.
- Bison is distributed in the hope that it will be useful,
+ 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 Bison; see the file COPYING. If not, write to
- the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
- Boston, MA 02111-1307, USA. */
+ 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 "types.h"
+
+#include "getargs.h"
#include "gram.h"
-#include "xalloc.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;
-char *nullable = NULL;
+bool *nullable = NULL;
-void
-set_nullable (void)
+static void
+nullable_print (FILE *out)
{
- short *r;
- short *s1;
- short *s2;
- int ruleno;
- int symbol;
- shorts *p;
-
- short *squeue;
- short *rcount;
- shorts **rsets;
- shorts *relts;
- char any_tokens;
- short *r1;
-
-#ifdef TRACE
- fprintf (stderr, _("Entering set_nullable"));
-#endif
-
- nullable = XCALLOC (char, nvars) - ntokens;
-
- squeue = XCALLOC (short, nvars);
- s1 = s2 = squeue;
+ 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);
+}
- rcount = XCALLOC (short, nrules + 1);
- rsets = XCALLOC (shorts *, nvars) - ntokens;
+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 nitems - nrules is enough.
- But why take the risk? */
- relts = XCALLOC (shorts, nitems + nvars + 1);
+ 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;
- r = ritem;
- while (*r)
- {
- if (*r < 0)
- {
- symbol = rlhs[-(*r++)];
- if (symbol >= 0 && !nullable[symbol])
- {
- nullable[symbol] = 1;
- *s2++ = symbol;
- }
- }
- else
- {
- r1 = r;
- any_tokens = 0;
- for (symbol = *r++; symbol > 0; symbol = *r++)
- {
- if (ISTOKEN (symbol))
- any_tokens = 1;
- }
-
- if (!any_tokens)
- {
- ruleno = -symbol;
- r = r1;
- for (symbol = *r++; symbol > 0; symbol = *r++)
- {
- rcount[ruleno]++;
- p->next = rsets[symbol];
- p->value = ruleno;
- rsets[symbol] = p;
- p++;
- }
- }
- }
- }
+ 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)
- {
- p = rsets[*s1++];
- while (p)
- {
- ruleno = p->value;
- p = p->next;
- if (--rcount[ruleno] == 0)
- {
- symbol = rlhs[ruleno];
- if (symbol >= 0 && !nullable[symbol])
- {
- nullable[symbol] = 1;
- *s2++ = symbol;
- }
- }
- }
- }
-
- XFREE (squeue);
- XFREE (rcount);
- XFREE (rsets + ntokens);
- XFREE (relts);
+ 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
-free_nullable (void)
+nullable_free (void)
{
- XFREE (nullable + ntokens);
+ free (nullable);
}
projects / bison.git / blobdiff