fix: noconfirm auto-selects first AUR match
This commit is contained in:
@@ -0,0 +1,445 @@
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/* Grammar reduction for Bison.
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Copyright (C) 1988-1989, 2000-2003, 2005-2015, 2018-2021 Free
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Software Foundation, Inc.
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This file is part of Bison, the GNU Compiler Compiler.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>. */
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/* Reduce the grammar: Find and eliminate unreachable terminals,
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nonterminals, and productions. David S. Bakin. */
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/* Don't eliminate unreachable terminals: They may be used by the
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user's parser. */
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#include <config.h>
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#include "system.h"
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#include <bitset.h>
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#include "complain.h"
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#include "files.h"
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#include "getargs.h"
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#include "gram.h"
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#include "print-xml.h"
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#include "reader.h"
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#include "reduce.h"
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#include "symtab.h"
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/* Set of nonterminals whose language is not empty. */
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static bitset N;
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/* Set of rules that have no useless nonterminals in their RHS. */
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static bitset P;
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/* Set of accessible symbols. */
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static bitset V;
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/* Set of symbols used to define rule precedence (so they are
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'useless', but no warning should be issued). */
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static bitset V1;
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int nuseless_productions;
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int nuseless_nonterminals;
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#define bitset_swap(Lhs, Rhs) \
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do { \
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bitset lhs__ = Lhs; \
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Lhs = Rhs; \
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Rhs = lhs__; \
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} while (0)
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/*-------------------------------------------------------------------.
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| Another way to do this would be with a set for each production and |
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| then do subset tests against N0, but even for the C grammar the |
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| whole reducing process takes only 2 seconds on my 8Mhz AT. |
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`-------------------------------------------------------------------*/
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static bool
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useful_production (rule_number r, bitset N0)
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{
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/* A production is useful if all of the nonterminals in its appear
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in the set of useful nonterminals. */
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for (item_number *rhsp = rules[r].rhs; 0 <= *rhsp; ++rhsp)
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if (ISVAR (*rhsp) && !bitset_test (N0, *rhsp - ntokens))
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return false;
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return true;
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}
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/*-----------------------------------------------------------------.
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| Compute N, the set of nonterminals whose language is not empty. |
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| |
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| Remember that rules are 1-origin, symbols are 0-origin. |
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`-----------------------------------------------------------------*/
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static void
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useless_nonterminals (void)
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{
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/* N is set as built. Np is set being built this iteration. P is
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set of all productions which have a RHS all in N. */
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bitset Np = bitset_create (nnterms, BITSET_FIXED);
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/* The set being computed is a set of nonterminals which can derive
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the empty string or strings consisting of all terminals. At each
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iteration a nonterminal is added to the set if there is a
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production with that nonterminal as its LHS for which all the
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nonterminals in its RHS are already in the set. Iterate until
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the set being computed remains unchanged. Any nonterminals not
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in the set at that point are useless in that they will never be
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used in deriving a sentence of the language.
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This iteration doesn't use any special traversal over the
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productions. A set is kept of all productions for which all the
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nonterminals in the RHS are in useful. Only productions not in
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this set are scanned on each iteration. At the end, this set is
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saved to be used when finding useful productions: only
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productions in this set will appear in the final grammar. */
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while (1)
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{
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bitset_copy (Np, N);
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for (rule_number r = 0; r < nrules; ++r)
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if (!bitset_test (P, r)
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&& useful_production (r, N))
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{
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bitset_set (Np, rules[r].lhs->number - ntokens);
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bitset_set (P, r);
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}
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if (bitset_equal_p (N, Np))
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break;
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bitset_swap (N, Np);
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}
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bitset_free (N);
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N = Np;
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}
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static void
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inaccessable_symbols (void)
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{
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/* Find out which productions are reachable and which symbols are
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used. Starting with an empty set of productions and a set of
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symbols which only has the start symbol in it, iterate over all
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productions until the set of productions remains unchanged for an
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iteration. For each production which has a LHS in the set of
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reachable symbols, add the production to the set of reachable
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productions, and add all of the nonterminals in the RHS of the
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production to the set of reachable symbols.
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Consider only the (partially) reduced grammar which has only
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nonterminals in N and productions in P.
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The result is the set P of productions in the reduced grammar,
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and the set V of symbols in the reduced grammar.
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Although this algorithm also computes the set of terminals which
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are reachable, no terminal will be deleted from the grammar. Some
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terminals might not be in the grammar but might be generated by
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semantic routines, and so the user might want them available with
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specified numbers. (Is this true?) However, the nonreachable
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terminals are printed (if running in verbose mode) so that the
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user can know. */
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bitset Vp = bitset_create (nsyms, BITSET_FIXED);
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bitset Pp = bitset_create (nrules, BITSET_FIXED);
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/* If the start symbol isn't useful, then nothing will be useful. */
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if (bitset_test (N, acceptsymbol->content->number - ntokens))
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{
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bitset_set (V, acceptsymbol->content->number);
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while (1)
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{
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bitset_copy (Vp, V);
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for (rule_number r = 0; r < nrules; ++r)
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if (!bitset_test (Pp, r)
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&& bitset_test (P, r)
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&& bitset_test (V, rules[r].lhs->number))
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{
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for (item_number *rhsp = rules[r].rhs; 0 <= *rhsp; ++rhsp)
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if (ISTOKEN (*rhsp) || bitset_test (N, *rhsp - ntokens))
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bitset_set (Vp, *rhsp);
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bitset_set (Pp, r);
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}
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if (bitset_equal_p (V, Vp))
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break;
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bitset_swap (V, Vp);
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}
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}
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bitset_free (V);
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V = Vp;
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/* These tokens (numbered 0, 1, and 2) are internal to Bison.
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Consider them useful. */
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bitset_set (V, eoftoken->content->number); /* end-of-input token */
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bitset_set (V, errtoken->content->number); /* error token */
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bitset_set (V, undeftoken->content->number); /* some undefined token */
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bitset_free (P);
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P = Pp;
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int nuseful_productions = bitset_count (P);
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nuseless_productions = nrules - nuseful_productions;
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int nuseful_nonterminals = 0;
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for (symbol_number i = ntokens; i < nsyms; ++i)
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nuseful_nonterminals += bitset_test (V, i);
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nuseless_nonterminals = nnterms - nuseful_nonterminals;
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/* A token that was used in %prec should not be warned about. */
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for (rule_number r = 0; r < nrules; ++r)
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if (rules[r].precsym != 0)
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bitset_set (V1, rules[r].precsym->number);
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}
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/*-------------------------------------------------------------------.
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| Put the useless productions at the end of RULES, and adjust NRULES |
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| accordingly. |
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`-------------------------------------------------------------------*/
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static void
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reduce_grammar_tables (void)
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{
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/* Report and flag useless productions. */
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{
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for (rule_number r = 0; r < nrules; ++r)
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rules[r].useful = bitset_test (P, r);
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grammar_rules_useless_report (_("rule useless in grammar"));
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}
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/* Map the nonterminals to their new index: useful first, useless
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afterwards. Kept for later report. */
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{
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int useful = 0;
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int useless = nrules - nuseless_productions;
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rule *rules_sorted = xnmalloc (nrules, sizeof *rules_sorted);
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for (rule_number r = 0; r < nrules; ++r)
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rules_sorted[rules[r].useful ? useful++ : useless++] = rules[r];
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free (rules);
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rules = rules_sorted;
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/* Renumber the rules markers in RITEMS. */
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for (rule_number r = 0; r < nrules; ++r)
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{
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item_number *rhsp = rules[r].rhs;
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for (/* Nothing. */; 0 <= *rhsp; ++rhsp)
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continue;
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*rhsp = rule_number_as_item_number (r);
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rules[r].number = r;
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}
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nrules -= nuseless_productions;
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}
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/* Adjust NRITEMS. */
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for (rule_number r = nrules; r < nrules + nuseless_productions; ++r)
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nritems -= rule_rhs_length (&rules[r]) + 1;
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}
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/*------------------------------.
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| Remove useless nonterminals. |
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`------------------------------*/
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symbol_number *nterm_map = NULL;
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static void
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nonterminals_reduce (void)
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{
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nterm_map = xnmalloc (nnterms, sizeof *nterm_map);
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/* Map the nonterminals to their new index: useful first, useless
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afterwards. Kept for later report. */
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{
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symbol_number n = ntokens;
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for (symbol_number i = ntokens; i < nsyms; ++i)
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if (bitset_test (V, i))
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nterm_map[i - ntokens] = n++;
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for (symbol_number i = ntokens; i < nsyms; ++i)
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if (!bitset_test (V, i))
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{
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nterm_map[i - ntokens] = n++;
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if (symbols[i]->content->status != used
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&& symbols[i] != acceptsymbol)
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complain (&symbols[i]->location, Wother,
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_("nonterminal useless in grammar: %s"),
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symbols[i]->tag);
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}
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}
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/* Shuffle elements of tables indexed by symbol number. */
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{
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symbol **symbols_sorted = xnmalloc (nnterms, sizeof *symbols_sorted);
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for (symbol_number i = ntokens; i < nsyms; ++i)
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symbols[i]->content->number = nterm_map[i - ntokens];
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for (symbol_number i = ntokens; i < nsyms; ++i)
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symbols_sorted[nterm_map[i - ntokens] - ntokens] = symbols[i];
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for (symbol_number i = ntokens; i < nsyms; ++i)
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symbols[i] = symbols_sorted[i - ntokens];
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free (symbols_sorted);
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}
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/* Update nonterminal numbers in the RHS of the rules. LHS are
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pointers to the symbol structure, they don't need renumbering. */
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{
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for (rule_number r = 0; r < nrules; ++r)
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for (item_number *rhsp = rules[r].rhs; 0 <= *rhsp; ++rhsp)
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if (ISVAR (*rhsp))
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*rhsp = symbol_number_as_item_number (nterm_map[*rhsp - ntokens]);
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acceptsymbol->content->number = nterm_map[acceptsymbol->content->number - ntokens];
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}
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nsyms -= nuseless_nonterminals;
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nnterms -= nuseless_nonterminals;
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}
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/*------------------------------------------------------------------.
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| Output the detailed results of the reductions. For FILE.output. |
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`------------------------------------------------------------------*/
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void
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reduce_output (FILE *out)
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{
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if (nuseless_nonterminals)
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{
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fprintf (out, "%s\n\n", _("Nonterminals useless in grammar"));
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for (int i = 0; i < nuseless_nonterminals; ++i)
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fprintf (out, " %s\n", symbols[nsyms + i]->tag);
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fputs ("\n\n", out);
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}
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{
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bool b = false;
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for (int i = 0; i < ntokens; ++i)
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if (reduce_token_unused_in_grammar (i))
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{
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if (!b)
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fprintf (out, "%s\n\n", _("Terminals unused in grammar"));
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b = true;
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fprintf (out, " %s\n", symbols[i]->tag);
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}
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if (b)
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fputs ("\n\n", out);
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}
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if (nuseless_productions)
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grammar_rules_partial_print (out, _("Rules useless in grammar"),
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rule_useless_in_grammar_p);
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}
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/*-------------------------------.
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| Report the results to STDERR. |
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`-------------------------------*/
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static void
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reduce_print (void)
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{
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if (nuseless_nonterminals)
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complain (NULL, Wother, ngettext ("%d nonterminal useless in grammar",
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"%d nonterminals useless in grammar",
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nuseless_nonterminals),
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nuseless_nonterminals);
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if (nuseless_productions)
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complain (NULL, Wother, ngettext ("%d rule useless in grammar",
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"%d rules useless in grammar",
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nuseless_productions),
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nuseless_productions);
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}
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void
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reduce_grammar (void)
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{
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/* Allocate the global sets used to compute the reduced grammar */
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N = bitset_create (nnterms, BITSET_FIXED);
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P = bitset_create (nrules, BITSET_FIXED);
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V = bitset_create (nsyms, BITSET_FIXED);
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V1 = bitset_create (nsyms, BITSET_FIXED);
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useless_nonterminals ();
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inaccessable_symbols ();
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/* Did we reduce something? */
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if (nuseless_nonterminals || nuseless_productions)
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{
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reduce_print ();
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// Check that start symbols have non-empty languages.
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bool failure = false;
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for (symbol_list *list = start_symbols; list; list = list->next)
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if (!bitset_test (N, list->content.sym->content->number - ntokens))
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{
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failure = true;
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complain (&list->sym_loc, complaint,
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_("start symbol %s does not derive any sentence"),
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list->content.sym->tag);
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}
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if (failure)
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exit (EXIT_FAILURE);
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/* First reduce the nonterminals, as they renumber themselves in the
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whole grammar. If you change the order, nonterms would be
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renumbered only in the reduced grammar. */
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if (nuseless_nonterminals)
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nonterminals_reduce ();
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if (nuseless_productions)
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reduce_grammar_tables ();
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}
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if (trace_flag & trace_grammar)
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{
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grammar_dump (stderr, "Reduced Grammar");
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fprintf (stderr, "reduced %s defines %d terminals, %d nonterminals"
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", and %d productions.\n",
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grammar_file, ntokens, nnterms, nrules);
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}
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}
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bool
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reduce_token_unused_in_grammar (symbol_number i)
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{
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aver (i < ntokens);
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return !bitset_test (V, i) && !bitset_test (V1, i);
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}
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bool
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reduce_nonterminal_useless_in_grammar (const sym_content *sym)
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{
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symbol_number n = sym->number;
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aver (ntokens <= n && n < nsyms + nuseless_nonterminals);
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return nsyms <= n;
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}
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/*-----------------------------------------------------------.
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| Free the global sets used to compute the reduced grammar. |
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`-----------------------------------------------------------*/
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void
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reduce_free (void)
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{
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bitset_free (N);
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bitset_free (V);
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bitset_free (V1);
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bitset_free (P);
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free (nterm_map);
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nterm_map = NULL;
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}
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