1/* Type definitions for the finite state machine for Bison.
2
3 Copyright (C) 1984, 1989, 2000-2004, 2007, 2009-2015, 2018-2019 Free
4 Software Foundation, Inc.
5
6 This file is part of Bison, the GNU Compiler Compiler.
7
8 This program is free software: you can redistribute it and/or modify
9 it under the terms of the GNU General Public License as published by
10 the Free Software Foundation, either version 3 of the License, or
11 (at your option) any later version.
12
13 This program is distributed in the hope that it will be useful,
14 but WITHOUT ANY WARRANTY; without even the implied warranty of
15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 GNU General Public License for more details.
17
18 You should have received a copy of the GNU General Public License
19 along with this program. If not, see <http://www.gnu.org/licenses/>. */
20
21
22/* These type definitions are used to represent a nondeterministic
23 finite state machine that parses the specified grammar. This
24 information is generated by the function generate_states in the
25 file LR0.
26
27 Each state of the machine is described by a set of items --
28 particular positions in particular rules -- that are the possible
29 places where parsing could continue when the machine is in this
30 state. These symbols at these items are the allowable inputs that
31 can follow now.
32
33 A core represents one state. States are numbered in the NUMBER
34 field. When generate_states is finished, the starting state is
35 state 0 and NSTATES is the number of states. (FIXME: This sentence
36 is no longer true: A transition to a state whose state number is
37 NSTATES indicates termination.) All the cores are chained together
38 and FIRST_STATE points to the first one (state 0).
39
40 For each state there is a particular symbol which must have been
41 the last thing accepted to reach that state. It is the
42 ACCESSING_SYMBOL of the core.
43
44 Each core contains a vector of NITEMS items which are the indices
45 in the RITEM vector of the items that are selected in this state.
46
47 The two types of actions are shifts/gotos (push the lookahead token
48 and read another/goto to the state designated by a nterm) and
49 reductions (combine the last n things on the stack via a rule,
50 replace them with the symbol that the rule derives, and leave the
51 lookahead token alone). When the states are generated, these
52 actions are represented in two other lists.
53
54 Each transition structure describes the possible transitions out of
55 one state (there are NUM of them). Each contains a vector of
56 numbers of the states that transitions can go to. The
57 accessing_symbol fields of those states' cores say what kind of
58 input leads to them.
59
60 A transition to state zero should be ignored: conflict resolution
61 deletes transitions by having them point to zero.
62
63 Each reductions structure describes the possible reductions at the
64 state whose number is in the number field. rules is an array of
65 num rules. lookahead_tokens is an array of bitsets, one per rule.
66
67 Conflict resolution can decide that certain tokens in certain
68 states should explicitly be errors (for implementing %nonassoc).
69 For each state, the tokens that are errors for this reason are
70 recorded in an errs structure, which holds the token numbers.
71
72 There is at least one goto transition present in state zero. It
73 leads to a next-to-final state whose accessing_symbol is the
74 grammar's start symbol. The next-to-final state has one shift to
75 the final state, whose accessing_symbol is zero (end of input).
76 The final state has one shift, which goes to the termination state.
77 The reason for the extra state at the end is to placate the
78 parser's strategy of making all decisions one token ahead of its
79 actions. */
80
81#ifndef STATE_H_
82# define STATE_H_
83
84# include <stdbool.h>
85
86# include <bitset.h>
87
88# include "gram.h"
89# include "symtab.h"
90
91
92/*-------------------.
93| Numbering states. |
94`-------------------*/
95
96typedef int state_number;
97# define STATE_NUMBER_MAXIMUM INT_MAX
98
99/* Be ready to map a state_number to an int. */
100static inline int
101state_number_as_int (state_number s)
102{
103 return s;
104}
105
106
107typedef struct state state;
108
109/*--------------.
110| Transitions. |
111`--------------*/
112
113typedef struct
114{
115 int num; /** Size of destination STATES. */
116 state *states[1];
117} transitions;
118
119
120/* What is the symbol labelling the transition to
121 TRANSITIONS->states[Num]? Can be a token (amongst which the error
122 token), or nonterminals in case of gotos. */
123
124# define TRANSITION_SYMBOL(Transitions, Num) \
125 (Transitions->states[Num]->accessing_symbol)
126
127/* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos). */
128
129# define TRANSITION_IS_SHIFT(Transitions, Num) \
130 (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
131
132/* Is the TRANSITIONS->states[Num] a goto?. */
133
134# define TRANSITION_IS_GOTO(Transitions, Num) \
135 (!TRANSITION_IS_SHIFT (Transitions, Num))
136
137/* Is the TRANSITIONS->states[Num] labelled by the error token? */
138
139# define TRANSITION_IS_ERROR(Transitions, Num) \
140 (TRANSITION_SYMBOL (Transitions, Num) == errtoken->content->number)
141
142/* When resolving a SR conflicts, if the reduction wins, the shift is
143 disabled. */
144
145# define TRANSITION_DISABLE(Transitions, Num) \
146 (Transitions->states[Num] = NULL)
147
148# define TRANSITION_IS_DISABLED(Transitions, Num) \
149 (Transitions->states[Num] == NULL)
150
151
152/* Iterate over each transition over a token (shifts). */
153# define FOR_EACH_SHIFT(Transitions, Iter) \
154 for (Iter = 0; \
155 Iter < Transitions->num \
156 && (TRANSITION_IS_DISABLED (Transitions, Iter) \
157 || TRANSITION_IS_SHIFT (Transitions, Iter)); \
158 ++Iter) \
159 if (!TRANSITION_IS_DISABLED (Transitions, Iter))
160
161
162/* The destination of the transition (shift/goto) from state S on
163 label SYM (term or nterm). Abort if none found. */
164struct state *transitions_to (state *s, symbol_number sym);
165
166
167/*-------.
168| Errs. |
169`-------*/
170
171typedef struct
172{
173 int num;
174 symbol *symbols[1];
175} errs;
176
177errs *errs_new (int num, symbol **tokens);
178
179
180/*-------------.
181| Reductions. |
182`-------------*/
183
184typedef struct
185{
186 int num;
187 bitset *lookahead_tokens;
188 /* Sorted ascendingly on rule number. */
189 rule *rules[1];
190} reductions;
191
192
193
194/*---------.
195| states. |
196`---------*/
197
198struct state_list;
199
200struct state
201{
202 state_number number;
203 symbol_number accessing_symbol;
204 transitions *transitions;
205 reductions *reductions;
206 errs *errs;
207
208 /* When an includer (such as ielr.c) needs to store states in a list, the
209 includer can define struct state_list as the list node structure and can
210 store in this member a reference to the node containing each state. */
211 struct state_list *state_list;
212
213 /* Whether no lookahead sets on reduce actions are needed to decide
214 what to do in state S. */
215 bool consistent;
216
217 /* If some conflicts were solved thanks to precedence/associativity,
218 a human readable description of the resolution. */
219 const char *solved_conflicts;
220 const char *solved_conflicts_xml;
221
222 /* Its items. Must be last, since ITEMS can be arbitrarily large. Sorted
223 ascendingly on item index in RITEM, which is sorted on rule number. */
224 size_t nitems;
225 item_number items[1];
226};
227
228extern state_number nstates;
229extern state *final_state;
230
231/* Create a new state with ACCESSING_SYMBOL for those items. */
232state *state_new (symbol_number accessing_symbol,
233 size_t core_size, item_number *core);
234state *state_new_isocore (state const *s);
235
236/* Record that from S we can reach all the DST states (NUM of them). */
237void state_transitions_set (state *s, int num, state **dst);
238
239/* Print the transitions of state s for debug. */
240void state_transitions_print (const state *s, FILE *out);
241
242/* Set the reductions of STATE. */
243void state_reductions_set (state *s, int num, rule **reds);
244
245/* The index of the reduction of state S that corresponds to rule R.
246 Aborts if there is no reduction of R in S. */
247int state_reduction_find (state *s, rule const *r);
248
249/* Set the errs of STATE. */
250void state_errs_set (state *s, int num, symbol **errors);
251
252/* Print on OUT all the lookahead tokens such that this STATE wants to
253 reduce R. */
254void state_rule_lookahead_tokens_print (state *s, rule const *r, FILE *out);
255void state_rule_lookahead_tokens_print_xml (state *s, rule const *r,
256 FILE *out, int level);
257
258/* Create/destroy the states hash table. */
259void state_hash_new (void);
260void state_hash_free (void);
261
262/* Find the state associated to the CORE, and return it. If it does
263 not exist yet, return NULL. */
264state *state_hash_lookup (size_t core_size, item_number *core);
265
266/* Insert STATE in the state hash table. */
267void state_hash_insert (state *s);
268
269/* Remove unreachable states, renumber remaining states, update NSTATES, and
270 write to OLD_TO_NEW a mapping of old state numbers to new state numbers such
271 that the old value of NSTATES is written as the new state number for removed
272 states. The size of OLD_TO_NEW must be the old value of NSTATES. */
273void state_remove_unreachable_states (state_number old_to_new[]);
274
275/* All the states, indexed by the state number. */
276extern state **states;
277
278/* Free all the states. */
279void states_free (void);
280
281#endif /* !STATE_H_ */
282