* doc/bison.texinfo (Stack Overflow): xref to Recursion.
[bison.git] / src / injections.c
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1/* Grammar reduction for Bison.
2 Copyright (C) 2002 Free Software Foundation, Inc.
3
4 This file is part of Bison, the GNU Compiler Compiler.
5
6 Bison is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
10
11 Bison is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with Bison; see the file COPYING. If not, write to
18 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
20
21/* Reduce the grammar: Look for injections. Akim Demaille. */
22
23#include "system.h"
24#include "quotearg.h"
25#include "bitsetv.h"
26#include "bitsetv-print.h"
27#include "complain.h"
28#include "gram.h"
29#include "getargs.h"
30#include "derives.h"
31#include "injections.h"
32
33/* Set of all nonterminals which are not useless. */
34static bitsetv injects;
35
36#define INJECTS(Var) injects[(Var) - ntokens]
37
38/*-----------------------------------------------------------.
39| Free the global sets used to compute the reduced grammar. |
40`-----------------------------------------------------------*/
41
42void
43injections_new (void)
44{
45 if (!injects)
46 injects = bitsetv_create (nvars, nvars, BITSET_FIXED);
47 else
48 bitsetv_zero (injects);
49}
50
51void
52injections_free (void)
53{
54 bitsetv_free (injects);
55 injects = NULL;
56}
57
58
59/*------------------------------.
60| Dump the list of injections. |
61`------------------------------*/
62
63static void
64injections_print (const char *title)
65{
66 int i, j;
67
68 fprintf (stderr, "%s\n", title);
69 for (i = ntokens; i < nsyms; i++)
70 if (bitset_count (INJECTS (i)))
71 {
72 fprintf (stderr, "\t%s injects\n",
73 quotearg_style (escape_quoting_style, symbols[i]->tag));
74 for (j = 0; j < nvars; j++)
75 if (bitset_test (INJECTS (i), j))
76 fprintf (stderr, "\t\t%s\n",
77 quotearg_style (escape_quoting_style,
78 symbols[j + ntokens]->tag));
79 }
80 fprintf (stderr, "\n\n");
81}
82
83
84/*-----------------------------------------------------------------.
85| Set INJECTS[i, j] if the nonterminal j derives the nonterminal j |
86| (typically, `i -> j' is a rule, plus transitive closure). |
87`-----------------------------------------------------------------*/
88
89static void
90injections_compute (void)
91{
92 int i, j;
93
94 injections_new ();
95 for (i = ntokens; i < nsyms; i++)
96 for (j = 0; derives[i][j] >= 0; ++j)
97 {
98 int symbol = rules[derives[i][j]].rhs[0];
99 if (ISVAR (symbol) && rules[derives[i][j]].rhs[1] < 0)
100 bitset_set (INJECTS (i), symbol - ntokens);
101 }
102
103 if (trace_flag & trace_sets)
427c0dda 104 injections_print ("syntactic direct injections");
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105 bitsetv_transitive_closure (injects);
106 if (trace_flag & trace_sets)
427c0dda 107 injections_print ("syntactic injections");
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108}
109
110
111
112/*--------------------------------------------------------------.
113| Look for infinitely ambiguous grammars: they contain cycles. |
114`--------------------------------------------------------------*/
115
116void
117injections_check_cycles (void)
118{
119 int i;
120
121 injections_compute ();
122 for (i = ntokens; i < nsyms; i++)
123 if (bitset_test (INJECTS (i), i - ntokens))
124 complain (_("infinitely ambiguous grammar: %s derives itself"),
125 symbols[i]->tag);
126}