cex: add support for state-item pair graph generation

* src/lssi.h, src/lssi.c, src/state-item.h, src/state-item.c: New.

src/state-item.h

@@ -0,0 +1,100 @@
+/* Counterexample Generation Search Nodes
+
+   Copyright (C) 2020 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/>.  */
+
+#ifndef STATE_ITEM_H
+# define STATE_ITEM_H
+
+# include <bitsetv.h>
+# include <gl_list.h>
+# include <hash.h>
+
+# include "gram.h"
+# include "state.h"
+
+/* Initializes a graph connecting (state, production item) pairs to
+   pairs they can make a transition or production step to. This graph
+   is used to search for paths that represent counterexamples of some
+   conflict.
+
+   state_items is an array of state state-item pairs ordered by state.
+   state_item_map maps state numbers to the first item which
+   corresponds to it in the array. A state's portion in state_items
+   begins with its items in the same order as it was in the
+   state. This is then followed by productions from the closure of the
+   state in order by rule.
+
+   There are two type of edges in this graph transitions and
+   productions.  Transitions are the same as transitions from the
+   parser except edges are only between items from the same
+   rule. These are stored as an array "si_trans" (as most items will
+   have transitions) which are indexed the same way as state_items.
+
+   Productions are edges from items with a nonterminal after the dot to
+   the production of that nonterminal in the same state. These edges are
+   stored as a hash map "si_prods" from a state_item to a set of what productions
+   it goes from/to
+
+   The inverses of these edges are stored in an array of bitsets,
+   "si_revs."  A state-item that begins with a dot will have reverse
+   production edges, and all others will have reverse transition
+   edges. */
+
+# define SI_DISABLED(sin) (si_trans[sin] == -2)
+# define SI_PRODUCTION(si) ((si) == state_items || *((si)->item - 1) < 0)
+# define SI_TRANSITION(si) ((si) != state_items && *((si)->item - 1) >= 0)
+
+typedef int state_item_number;
+
+typedef struct
+{
+  state *state;
+  item_number *item;
+  bitset lookahead;
+} state_item;
+
+extern bitsetv firsts;
+# define FIRSTS(sym) firsts[(sym) - ntokens]
+
+extern size_t nstate_items;
+extern state_item_number *state_item_map;
+
+/** Array mapping state_item_numbers to state_items */
+extern state_item *state_items;
+
+/** state-item graph edges */
+extern state_item_number *si_trans;
+extern bitsetv si_revs;
+
+state_item *state_item_lookup (state_number s, state_item_number off);
+
+static inline state_item_number
+state_item_index_lookup (state_number s, state_item_number off)
+{
+  return state_item_map[s] + off;
+}
+
+bitset si_prods_lookup (state_item_number si);
+
+void state_items_init (void);
+void print_state_item (const state_item *si, FILE *out);
+void state_items_free (void);
+
+bool production_allowed (const state_item *si, const state_item *next);
+
+#endif /* STATE_ITEM_H */