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bison/src/bison/2.4.1/bison-2.4.1-src/src/reduce.c

Index: bison/src/bison/2.4.1/bison-2.4.1-src/src/reduce.c
===================================================================
--- bison/src/bison/2.4.1/bison-2.4.1-src/src/reduce.c	(revision 0)
+++ bison/src/bison/2.4.1/bison-2.4.1-src/src/reduce.c	(revision 0)
@@ -0,0 +1,474 @@
+/* Grammar reduction for Bison.
+
+   Copyright (C) 1988, 1989, 2000, 2001, 2002, 2003, 2005, 2006,
+   2007, 2008 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/>.  */
+
+
+/* Reduce the grammar: Find and eliminate unreachable terminals,
+   nonterminals, and productions.  David S. Bakin.  */
+
+/* Don't eliminate unreachable terminals: They may be used by the
+   user's parser.  */
+
+#include <config.h>
+#include "system.h"
+
+#include <bitset.h>
+#include <quotearg.h>
+
+#include "complain.h"
+#include "files.h"
+#include "getargs.h"
+#include "gram.h"
+#include "print-xml.h"
+#include "reader.h"
+#include "reduce.h"
+#include "symtab.h"
+
+/* Set of all nonterminals which are not useless.  */
+static bitset N;
+
+/* Set of all rules which have no useless nonterminals in their RHS.  */
+static bitset P;
+
+/* Set of all accessible symbols.  */
+static bitset V;
+
+/* Set of symbols used to define rule precedence (so they are
+   `useless', but no warning should be issued).  */
+static bitset V1;
+
+static rule_number nuseful_productions;
+rule_number nuseless_productions;
+static int nuseful_nonterminals;
+symbol_number nuseless_nonterminals;
+
+/*-------------------------------------------------------------------.
+| Another way to do this would be with a set for each production and |
+| then do subset tests against N0, but even for the C grammar the    |
+| whole reducing process takes only 2 seconds on my 8Mhz AT.         |
+`-------------------------------------------------------------------*/
+
+static bool
+useful_production (rule_number r, bitset N0)
+{
+  item_number *rhsp;
+
+  /* A production is useful if all of the nonterminals in its appear
+     in the set of useful nonterminals.  */
+
+  for (rhsp = rules[r].rhs; *rhsp >= 0; ++rhsp)
+    if (ISVAR (*rhsp) && !bitset_test (N0, *rhsp - ntokens))
+      return false;
+  return true;
+}
+
+
+/*---------------------------------------------------------.
+| Remember that rules are 1-origin, symbols are 0-origin.  |
+`---------------------------------------------------------*/
+
+static void
+useless_nonterminals (void)
+{
+  bitset Np, Ns;
+  rule_number r;
+
+  /* N is set as built.  Np is set being built this iteration. P is
+     set of all productions which have a RHS all in N.  */
+
+  Np = bitset_create (nvars, BITSET_FIXED);
+
+
+  /* The set being computed is a set of nonterminals which can derive
+     the empty string or strings consisting of all terminals. At each
+     iteration a nonterminal is added to the set if there is a
+     production with that nonterminal as its LHS for which all the
+     nonterminals in its RHS are already in the set.  Iterate until
+     the set being computed remains unchanged.  Any nonterminals not
+     in the set at that point are useless in that they will never be
+     used in deriving a sentence of the language.
+
+     This iteration doesn't use any special traversal over the
+     productions.  A set is kept of all productions for which all the
+     nonterminals in the RHS are in useful.  Only productions not in
+     this set are scanned on each iteration.  At the end, this set is
+     saved to be used when finding useful productions: only
+     productions in this set will appear in the final grammar.  */
+
+  while (1)
+    {
+      bitset_copy (Np, N);
+      for (r = 0; r < nrules; r++)
+	if (!bitset_test (P, r)
+	    && useful_production (r, N))
+	  {
+	    bitset_set (Np, rules[r].lhs->number - ntokens);
+	    bitset_set (P, r);
+	  }
+      if (bitset_equal_p (N, Np))
+	break;
+      Ns = Np;
+      Np = N;
+      N = Ns;
+    }
+  bitset_free (N);
+  N = Np;
+}
+
+
+static void
+inaccessable_symbols (void)
+{
+  bitset Vp, Vs, Pp;
+
+  /* Find out which productions are reachable and which symbols are
+     used.  Starting with an empty set of productions and a set of
+     symbols which only has the start symbol in it, iterate over all
+     productions until the set of productions remains unchanged for an
+     iteration.  For each production which has a LHS in the set of
+     reachable symbols, add the production to the set of reachable
+     productions, and add all of the nonterminals in the RHS of the
+     production to the set of reachable symbols.
+
+     Consider only the (partially) reduced grammar which has only
+     nonterminals in N and productions in P.
+
+     The result is the set P of productions in the reduced grammar,
+     and the set V of symbols in the reduced grammar.
+
+     Although this algorithm also computes the set of terminals which
+     are reachable, no terminal will be deleted from the grammar. Some
+     terminals might not be in the grammar but might be generated by
+     semantic routines, and so the user might want them available with
+     specified numbers.  (Is this true?)  However, the nonreachable
+     terminals are printed (if running in verbose mode) so that the
+     user can know.  */
+
+  Vp = bitset_create (nsyms, BITSET_FIXED);
+  Pp = bitset_create (nrules, BITSET_FIXED);
+
+  /* If the start symbol isn't useful, then nothing will be useful. */
+  if (bitset_test (N, accept->number - ntokens))
+    {
+      bitset_set (V, accept->number);
+
+      while (1)
+	{
+	  rule_number r;
+	  bitset_copy (Vp, V);
+	  for (r = 0; r < nrules; r++)
+	    {
+	      if (!bitset_test (Pp, r)
+		  && bitset_test (P, r)
+		  && bitset_test (V, rules[r].lhs->number))
+		{
+		  item_number *rhsp;
+		  for (rhsp = rules[r].rhs; *rhsp >= 0; rhsp++)
+		    if (ISTOKEN (*rhsp) || bitset_test (N, *rhsp - ntokens))
+		      bitset_set (Vp, *rhsp);
+		  bitset_set (Pp, r);
+		}
+	    }
+	  if (bitset_equal_p (V, Vp))
+	    break;
+	  Vs = Vp;
+	  Vp = V;
+	  V = Vs;
+	}
+    }
+
+  bitset_free (V);
+  V = Vp;
+
+  /* Tokens 0, 1, and 2 are internal to Bison.  Consider them useful. */
+  bitset_set (V, endtoken->number);		/* end-of-input token */
+  bitset_set (V, errtoken->number);		/* error token */
+  bitset_set (V, undeftoken->number);		/* some undefined token */
+
+  bitset_free (P);
+  P = Pp;
+
+  nuseful_productions = bitset_count (P);
+  nuseless_productions = nrules - nuseful_productions;
+
+  nuseful_nonterminals = 0;
+  {
+    symbol_number i;
+    for (i = ntokens; i < nsyms; i++)
+      if (bitset_test (V, i))
+	nuseful_nonterminals++;
+  }
+  nuseless_nonterminals = nvars - nuseful_nonterminals;
+
+  /* A token that was used in %prec should not be warned about.  */
+  {
+    rule_number r;
+    for (r = 0; r < nrules; ++r)
+      if (rules[r].precsym != 0)
+	bitset_set (V1, rules[r].precsym->number);
+  }
+}
+
+
+/*-------------------------------------------------------------------.
+| Put the useless productions at the end of RULES, and adjust NRULES |
+| accordingly.                                                       |
+`-------------------------------------------------------------------*/
+
+static void
+reduce_grammar_tables (void)
+{
+  /* Report and flag useless productions.  */
+  {
+    rule_number r;
+    for (r = 0; r < nrules; r++)
+      rules[r].useful = bitset_test (P, r);
+    grammar_rules_useless_report (_("rule useless in grammar"));
+  }
+
+  /* Map the nonterminals to their new index: useful first, useless
+     afterwards.  Kept for later report.  */
+  {
+    int useful = 0;
+    int useless = nrules - nuseless_productions;
+    rule *rules_sorted = xnmalloc (nrules, sizeof *rules_sorted);
+    rule_number r;
+    for (r = 0; r < nrules; ++r)
+      rules_sorted[rules[r].useful ? useful++ : useless++] = rules[r];
+    free (rules);
+    rules = rules_sorted;
+
+    /* Renumber the rules markers in RITEMS.  */
+    for (r = 0; r < nrules; ++r)
+      {
+	item_number *rhsp = rules[r].rhs;
+	for (/* Nothing. */; *rhsp >= 0; ++rhsp)
+	  /* Nothing. */;
+	*rhsp = rule_number_as_item_number (r);
+	rules[r].number = r;
+      }
+    nrules -= nuseless_productions;
+  }
+
+  /* Adjust NRITEMS.  */
+  {
+    rule_number r;
+    int length;
+    for (r = nrules; r < nrules + nuseless_productions; ++r)
+      {
+	length = rule_rhs_length (&rules[r]);
+	nritems -= length + 1;
+      }
+  }
+}
+
+
+/*------------------------------.
+| Remove useless nonterminals.  |
+`------------------------------*/
+
+static void
+nonterminals_reduce (void)
+{
+  symbol_number i, n;
+
+  /* Map the nonterminals to their new index: useful first, useless
+     afterwards.  Kept for later report.  */
+
+  symbol_number *nontermmap = xnmalloc (nvars, sizeof *nontermmap);
+  n = ntokens;
+  for (i = ntokens; i < nsyms; i++)
+    if (bitset_test (V, i))
+      nontermmap[i - ntokens] = n++;
+  for (i = ntokens; i < nsyms; i++)
+    if (!bitset_test (V, i))
+      {
+	nontermmap[i - ntokens] = n++;
+	warn_at (symbols[i]->location, _("nonterminal useless in grammar: %s"),
+		 symbols[i]->tag);
+      }
+
+
+  /* Shuffle elements of tables indexed by symbol number.  */
+  {
+    symbol **symbols_sorted = xnmalloc (nvars, sizeof *symbols_sorted);
+
+    for (i = ntokens; i < nsyms; i++)
+      symbols[i]->number = nontermmap[i - ntokens];
+    for (i = ntokens; i < nsyms; i++)
+      symbols_sorted[nontermmap[i - ntokens] - ntokens] = symbols[i];
+    for (i = ntokens; i < nsyms; i++)
+      symbols[i] = symbols_sorted[i - ntokens];
+    free (symbols_sorted);
+  }
+
+  {
+    rule_number r;
+    for (r = 0; r < nrules; ++r)
+      {
+	item_number *rhsp;
+	for (rhsp = rules[r].rhs; *rhsp >= 0; ++rhsp)
+	  if (ISVAR (*rhsp))
+	    *rhsp =  symbol_number_as_item_number (nontermmap[*rhsp
+							      - ntokens]);
+      }
+    accept->number = nontermmap[accept->number - ntokens];
+  }
+
+  nsyms -= nuseless_nonterminals;
+  nvars -= nuseless_nonterminals;
+
+  free (nontermmap);
+}
+
+
+/*------------------------------------------------------------------.
+| Output the detailed results of the reductions.  For FILE.output.  |
+`------------------------------------------------------------------*/
+
+void
+reduce_output (FILE *out)
+{
+  if (nuseless_nonterminals > 0)
+    {
+      int i;
+      fprintf (out, "%s\n\n", _("Nonterminals useless in grammar"));
+      for (i = 0; i < nuseless_nonterminals; ++i)
+	fprintf (out, "   %s\n", symbols[nsyms + i]->tag);
+      fputs ("\n\n", out);
+    }
+
+  {
+    bool b = false;
+    int i;
+    for (i = 0; i < ntokens; i++)
+      if (reduce_token_unused_in_grammar (i))
+	{
+	  if (!b)
+	    fprintf (out, "%s\n\n", _("Terminals unused in grammar"));
+	  b = true;
+	  fprintf (out, "   %s\n", symbols[i]->tag);
+	}
+    if (b)
+      fputs ("\n\n", out);
+  }
+
+  if (nuseless_productions > 0)
+    grammar_rules_partial_print (out, _("Rules useless in grammar"),
+				 rule_useless_in_grammar_p);
+}
+
+
+/*-------------------------------.
+| Report the results to STDERR.  |
+`-------------------------------*/
+
+static void
+reduce_print (void)
+{
+  if (nuseless_nonterminals > 0)
+    {
+      fprintf (stderr, "%s: %s: ", grammar_file, _("warning"));
+      fprintf (stderr, ngettext ("%d nonterminal useless in grammar",
+                                 "%d nonterminals useless in grammar",
+                                 nuseless_nonterminals),
+               nuseless_nonterminals);
+      fprintf (stderr, "\n");
+    }
+  if (nuseless_productions > 0)
+    {
+      fprintf (stderr, "%s: %s: ", grammar_file, _("warning"));
+      fprintf (stderr, ngettext ("%d rule useless in grammar",
+                                 "%d rules useless in grammar",
+                                 nuseless_productions),
+               nuseless_productions);
+      fprintf (stderr, "\n");
+    }
+}
+
+void
+reduce_grammar (void)
+{
+  bool reduced;
+
+  /* Allocate the global sets used to compute the reduced grammar */
+
+  N = bitset_create (nvars, BITSET_FIXED);
+  P =  bitset_create (nrules, BITSET_FIXED);
+  V = bitset_create (nsyms, BITSET_FIXED);
+  V1 = bitset_create (nsyms, BITSET_FIXED);
+
+  useless_nonterminals ();
+  inaccessable_symbols ();
+
+  reduced = (nuseless_nonterminals + nuseless_productions > 0);
+  if (!reduced)
+    return;
+
+  reduce_print ();
+
+  if (!bitset_test (N, accept->number - ntokens))
+    fatal_at (startsymbol_location,
+	      _("start symbol %s does not derive any sentence"),
+	      startsymbol->tag);
+
+  /* First reduce the nonterminals, as they renumber themselves in the
+     whole grammar.  If you change the order, nonterms would be
+     renumbered only in the reduced grammar.  */
+  if (nuseless_nonterminals > 0)
+    nonterminals_reduce ();
+  if (nuseless_productions > 0)
+    reduce_grammar_tables ();
+
+  if (trace_flag & trace_grammar)
+    {
+      grammar_dump (stderr, "Reduced Grammar");
+
+      fprintf (stderr, "reduced %s defines %d terminals, %d nonterminals\
+, and %d productions.\n",
+	       grammar_file, ntokens, nvars, nrules);
+    }
+}
+
+bool
+reduce_token_unused_in_grammar (symbol_number i)
+{
+  aver (i < ntokens);
+  return !bitset_test (V, i) && !bitset_test (V1, i);
+}
+
+bool
+reduce_nonterminal_useless_in_grammar (symbol_number i)
+{
+  aver (ntokens <= i && i < nsyms + nuseless_nonterminals);
+  return nsyms <= i;
+}
+
+/*-----------------------------------------------------------.
+| Free the global sets used to compute the reduced grammar.  |
+`-----------------------------------------------------------*/
+
+void
+reduce_free (void)
+{
+  bitset_free (N);
+  bitset_free (V);
+  bitset_free (V1);
+  bitset_free (P);
+}
Property changes on: bison\src\bison\2.4.1\bison-2.4.1-src\src\reduce.c
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Added: svn:eol-style
   + LF