--- /dev/null
+/* Grammar reduction for Bison.
+ Copyright (C) 1988, 1989 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
+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.
+
+Bison 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, 675 Mass Ave, Cambridge, MA 02139, USA. */
+
+
+/*
+ * 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 <stdio.h>
+#include "system.h"
+#include "files.h"
+#include "gram.h"
+#include "machine.h"
+#include "new.h"
+
+
+extern char **tags; /* reader.c */
+extern int verboseflag; /* getargs.c */
+static int statisticsflag; /* XXXXXXX */
+
+#ifndef TRUE
+#define TRUE (1)
+#define FALSE (0)
+#endif
+typedef int bool;
+typedef unsigned *BSet;
+typedef short *rule;
+
+
+/*
+ * N is set of all nonterminals which are not useless. P is set of all rules
+ * which have no useless nonterminals in their RHS. V is the set of all
+ * accessible symbols.
+ */
+
+static BSet N, P, V, V1;
+
+static int nuseful_productions, nuseless_productions,
+ nuseful_nonterminals, nuseless_nonterminals;
+
+
+static void useless_nonterminals();
+static void inaccessable_symbols();
+static void reduce_grammar_tables();
+static void print_results();
+static void print_notices();
+void dump_grammar();
+
+extern void fatals ();
+\f
+
+bool
+bits_equal (L, R, n)
+BSet L;
+BSet R;
+int n;
+{
+ int i;
+
+ for (i = n - 1; i >= 0; i--)
+ if (L[i] != R[i])
+ return FALSE;
+ return TRUE;
+}
+
+
+int
+nbits (i)
+unsigned i;
+{
+ int count = 0;
+
+ while (i != 0) {
+ i ^= (i & -i);
+ ++count;
+ }
+ return count;
+}
+
+
+int
+bits_size (S, n)
+BSet S;
+int n;
+{
+ int i, count = 0;
+
+ for (i = n - 1; i >= 0; i--)
+ count += nbits(S[i]);
+ return count;
+}
+\f
+void
+reduce_grammar ()
+{
+ bool reduced;
+
+ /* Allocate the global sets used to compute the reduced grammar */
+
+ N = NEW2(WORDSIZE(nvars), unsigned);
+ P = NEW2(WORDSIZE(nrules + 1), unsigned);
+ V = NEW2(WORDSIZE(nsyms), unsigned);
+ V1 = NEW2(WORDSIZE(nsyms), unsigned);
+
+ useless_nonterminals();
+ inaccessable_symbols();
+
+ reduced = (bool) (nuseless_nonterminals + nuseless_productions > 0);
+
+ if (verboseflag)
+ print_results();
+
+ if (reduced == FALSE)
+ goto done_reducing;
+
+ print_notices();
+
+ if (!BITISSET(N, start_symbol - ntokens))
+ fatals("Start symbol %s does not derive any sentence.",
+ tags[start_symbol]);
+
+ reduce_grammar_tables();
+ /* if (verboseflag) {
+ fprintf(foutput, "REDUCED GRAMMAR\n\n");
+ dump_grammar();
+ }
+ */
+
+ /**/ statisticsflag = FALSE; /* someday getopts should handle this */
+ if (statisticsflag == TRUE)
+ fprintf(stderr,
+ "reduced %s defines %d terminal%s, %d nonterminal%s\
+, and %d production%s.\n", infile,
+ ntokens, (ntokens == 1 ? "" : "s"),
+ nvars, (nvars == 1 ? "" : "s"),
+ nrules, (nrules == 1 ? "" : "s"));
+
+ done_reducing:
+
+ /* Free the global sets used to compute the reduced grammar */
+
+ FREE(N);
+ FREE(V);
+ FREE(P);
+
+}
+\f
+/*
+ * Another way to do this would be with a set for each production and then do
+ * subset tests against N, but even for the C grammar the whole reducing
+ * process takes only 2 seconds on my 8Mhz AT.
+ */
+
+static bool
+useful_production (i, N)
+int i;
+BSet N;
+{
+ rule r;
+ short n;
+
+ /*
+ * A production is useful if all of the nonterminals in its RHS
+ * appear in the set of useful nonterminals.
+ */
+
+ for (r = &ritem[rrhs[i]]; *r > 0; r++)
+ if (ISVAR(n = *r))
+ if (!BITISSET(N, n - ntokens))
+ return FALSE;
+ return TRUE;
+}
+
+
+/* Remember that rules are 1-origin, symbols are 0-origin. */
+
+static void
+useless_nonterminals ()
+{
+ BSet Np, Ns;
+ int i, n;
+
+ /*
+ * 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 = NEW2(WORDSIZE(nvars), unsigned);
+
+ /*
+ * 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.
+ */
+
+ n = 0;
+ while (1)
+ {
+ for (i = WORDSIZE(nvars) - 1; i >= 0; i--)
+ Np[i] = N[i];
+ for (i = 1; i <= nrules; i++)
+ {
+ if (!BITISSET(P, i))
+ {
+ if (useful_production(i, N))
+ {
+ SETBIT(Np, rlhs[i] - ntokens);
+ SETBIT(P, i);
+ }
+ }
+ }
+ if (bits_equal(N, Np, WORDSIZE(nvars)))
+ break;
+ Ns = Np;
+ Np = N;
+ N = Ns;
+ }
+ FREE(N);
+ N = Np;
+}
+\f
+static void
+inaccessable_symbols ()
+{
+ BSet Vp, Vs, Pp;
+ int i, n;
+ short t;
+ rule r;
+
+ /*
+ * 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 = NEW2(WORDSIZE(nsyms), unsigned);
+ Pp = NEW2(WORDSIZE(nrules + 1), unsigned);
+
+ /* If the start symbol isn't useful, then nothing will be useful. */
+ if (!BITISSET(N, start_symbol - ntokens))
+ goto end_iteration;
+
+ SETBIT(V, start_symbol);
+
+ n = 0;
+ while (1)
+ {
+ for (i = WORDSIZE(nsyms) - 1; i >= 0; i--)
+ Vp[i] = V[i];
+ for (i = 1; i <= nrules; i++)
+ {
+ if (!BITISSET(Pp, i) && BITISSET(P, i) &&
+ BITISSET(V, rlhs[i]))
+ {
+ for (r = &ritem[rrhs[i]]; *r >= 0; r++)
+ {
+ if (ISTOKEN(t = *r)
+ || BITISSET(N, t - ntokens))
+ {
+ SETBIT(Vp, t);
+ }
+ }
+ SETBIT(Pp, i);
+ }
+ }
+ if (bits_equal(V, Vp, WORDSIZE(nsyms)))
+ {
+ break;
+ }
+ Vs = Vp;
+ Vp = V;
+ V = Vs;
+ }
+ end_iteration:
+
+ FREE(V);
+ V = Vp;
+
+ /* Tokens 0, 1, and 2 are internal to Bison. Consider them useful. */
+ SETBIT(V, 0); /* end-of-input token */
+ SETBIT(V, 1); /* error token */
+ SETBIT(V, 2); /* some undefined token */
+
+ FREE(P);
+ P = Pp;
+
+ nuseful_productions = bits_size(P, WORDSIZE(nrules + 1));
+ nuseless_productions = nrules - nuseful_productions;
+
+ nuseful_nonterminals = 0;
+ for (i = ntokens; i < nsyms; i++)
+ if (BITISSET(V, i))
+ nuseful_nonterminals++;
+ nuseless_nonterminals = nvars - nuseful_nonterminals;
+
+ /* A token that was used in %prec should not be warned about. */
+ for (i = 1; i < nrules; i++)
+ if (rprecsym[i] != 0)
+ SETBIT(V1, rprecsym[i]);
+}
+\f
+static void
+reduce_grammar_tables ()
+{
+/* This is turned off because we would need to change the numbers
+ in the case statements in the actions file. */
+#if 0
+ /* remove useless productions */
+ if (nuseless_productions > 0)
+ {
+ short np, pn, ni, pi;
+
+ np = 0;
+ ni = 0;
+ for (pn = 1; pn <= nrules; pn++)
+ {
+ if (BITISSET(P, pn))
+ {
+ np++;
+ if (pn != np)
+ {
+ rlhs[np] = rlhs[pn];
+ rline[np] = rline[pn];
+ rprec[np] = rprec[pn];
+ rassoc[np] = rassoc[pn];
+ rrhs[np] = rrhs[pn];
+ if (rrhs[np] != ni)
+ {
+ pi = rrhs[np];
+ rrhs[np] = ni;
+ while (ritem[pi] >= 0)
+ ritem[ni++] = ritem[pi++];
+ ritem[ni++] = -np;
+ }
+ } else {
+ while (ritem[ni++] >= 0);
+ }
+ }
+ }
+ ritem[ni] = 0;
+ nrules -= nuseless_productions;
+ nitems = ni;
+
+ /*
+ * Is it worth it to reduce the amount of memory for the
+ * grammar? Probably not.
+ */
+
+ }
+#endif /* 0 */
+ /* Disable useless productions,
+ since they may contain useless nonterms
+ that would get mapped below to -1 and confuse everyone. */
+ if (nuseless_productions > 0)
+ {
+ int pn;
+
+ for (pn = 1; pn <= nrules; pn++)
+ {
+ if (!BITISSET(P, pn))
+ {
+ rlhs[pn] = -1;
+ }
+ }
+ }
+
+ /* remove useless symbols */
+ if (nuseless_nonterminals > 0)
+ {
+
+ int i, n;
+/* short j; JF unused */
+ short *nontermmap;
+ rule r;
+
+ /*
+ * create a map of nonterminal number to new nonterminal
+ * number. -1 in the map means it was useless and is being
+ * eliminated.
+ */
+
+ nontermmap = NEW2(nvars, short) - ntokens;
+ for (i = ntokens; i < nsyms; i++)
+ nontermmap[i] = -1;
+
+ n = ntokens;
+ for (i = ntokens; i < nsyms; i++)
+ if (BITISSET(V, i))
+ nontermmap[i] = n++;
+
+ /* Shuffle elements of tables indexed by symbol number. */
+
+ for (i = ntokens; i < nsyms; i++)
+ {
+ n = nontermmap[i];
+ if (n >= 0)
+ {
+ sassoc[n] = sassoc[i];
+ sprec[n] = sprec[i];
+ tags[n] = tags[i];
+ } else {
+ free(tags[i]);
+ }
+ }
+
+ /* Replace all symbol numbers in valid data structures. */
+
+ for (i = 1; i <= nrules; i++)
+ {
+ /* Ignore the rules disabled above. */
+ if (rlhs[i] >= 0)
+ rlhs[i] = nontermmap[rlhs[i]];
+ if (ISVAR (rprecsym[i]))
+ /* Can this happen? */
+ rprecsym[i] = nontermmap[rprecsym[i]];
+ }
+
+ for (r = ritem; *r; r++)
+ if (ISVAR(*r))
+ *r = nontermmap[*r];
+
+ start_symbol = nontermmap[start_symbol];
+
+ nsyms -= nuseless_nonterminals;
+ nvars -= nuseless_nonterminals;
+
+ free(&nontermmap[ntokens]);
+ }
+}
+\f
+static void
+print_results ()
+{
+ int i;
+/* short j; JF unused */
+ rule r;
+ bool b;
+
+ if (nuseless_nonterminals > 0)
+ {
+ fprintf(foutput, "Useless nonterminals:\n\n");
+ for (i = ntokens; i < nsyms; i++)
+ if (!BITISSET(V, i))
+ fprintf(foutput, " %s\n", tags[i]);
+ }
+ b = FALSE;
+ for (i = 0; i < ntokens; i++)
+ {
+ if (!BITISSET(V, i) && !BITISSET(V1, i))
+ {
+ if (!b)
+ {
+ fprintf(foutput, "\n\nTerminals which are not used:\n\n");
+ b = TRUE;
+ }
+ fprintf(foutput, " %s\n", tags[i]);
+ }
+ }
+
+ if (nuseless_productions > 0)
+ {
+ fprintf(foutput, "\n\nUseless rules:\n\n");
+ for (i = 1; i <= nrules; i++)
+ {
+ if (!BITISSET(P, i))
+ {
+ fprintf(foutput, "#%-4d ", i);
+ fprintf(foutput, "%s :\t", tags[rlhs[i]]);
+ for (r = &ritem[rrhs[i]]; *r >= 0; r++)
+ {
+ fprintf(foutput, " %s", tags[*r]);
+ }
+ fprintf(foutput, ";\n");
+ }
+ }
+ }
+ if (nuseless_nonterminals > 0 || nuseless_productions > 0 || b)
+ fprintf(foutput, "\n\n");
+}
+\f
+void
+dump_grammar ()
+{
+ int i;
+ rule r;
+
+ fprintf(foutput,
+ "ntokens = %d, nvars = %d, nsyms = %d, nrules = %d, nitems = %d\n\n",
+ ntokens, nvars, nsyms, nrules, nitems);
+ fprintf(foutput, "Variables\n---------\n\n");
+ fprintf(foutput, "Value Sprec Sassoc Tag\n");
+ for (i = ntokens; i < nsyms; i++)
+ fprintf(foutput, "%5d %5d %5d %s\n",
+ i, sprec[i], sassoc[i], tags[i]);
+ fprintf(foutput, "\n\n");
+ fprintf(foutput, "Rules\n-----\n\n");
+ for (i = 1; i <= nrules; i++)
+ {
+ fprintf(foutput, "%-5d(%5d%5d)%5d : (@%-5d)",
+ i, rprec[i], rassoc[i], rlhs[i], rrhs[i]);
+ for (r = &ritem[rrhs[i]]; *r > 0; r++)
+ fprintf(foutput, "%5d", *r);
+ fprintf(foutput, " [%d]\n", -(*r));
+ }
+ fprintf(foutput, "\n\n");
+ fprintf(foutput, "Rules interpreted\n-----------------\n\n");
+ for (i = 1; i <= nrules; i++)
+ {
+ fprintf(foutput, "%-5d %s :", i, tags[rlhs[i]]);
+ for (r = &ritem[rrhs[i]]; *r > 0; r++)
+ fprintf(foutput, " %s", tags[*r]);
+ fprintf(foutput, "\n");
+ }
+ fprintf(foutput, "\n\n");
+}
+
+
+static void
+print_notices ()
+{
+ extern int fixed_outfiles;
+
+ if (fixed_outfiles && nuseless_productions)
+ fprintf(stderr, "%d rules never reduced\n", nuseless_productions);
+
+ fprintf(stderr, "%s contains ", infile);
+
+ if (nuseless_nonterminals > 0)
+ {
+ fprintf(stderr, "%d useless nonterminal%s",
+ nuseless_nonterminals,
+ (nuseless_nonterminals == 1 ? "" : "s"));
+ }
+ if (nuseless_nonterminals > 0 && nuseless_productions > 0)
+ fprintf(stderr, " and ");
+
+ if (nuseless_productions > 0)
+ {
+ fprintf(stderr, "%d useless rule%s",
+ nuseless_productions,
+ (nuseless_productions == 1 ? "" : "s"));
+ }
+ fprintf(stderr, ".\n");
+ fflush(stderr);
+}
projects / bison.git / commitdiff
