1 /* Type definitions for the finite state machine for Bison.
2
3 Copyright (C) 1984, 1989, 2000-2004, 2007, 2009-2015, 2018-2021 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 <https://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. lookaheads 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. The generated parser does not
71 depend on this errs structure, it is used only in the reports
72 (*.output, etc.) to describe conflicted actions that have been
73 discarded.
74
75 There is at least one goto transition present in state zero. It
76 leads to a next-to-final state whose accessing_symbol is the
77 grammar's start symbol. The next-to-final state has one shift to
78 the final state, whose accessing_symbol is zero (end of input).
79 The final state has one shift, which goes to the termination state.
80 The reason for the extra state at the end is to placate the
81 parser's strategy of making all decisions one token ahead of its
82 actions. */
83
84 #ifndef STATE_H_
85 # define STATE_H_
86
87 # include <stdbool.h>
88
89 # include <bitset.h>
90
91 # include "gram.h"
92 # include "symtab.h"
93
94
95 /*-------------------.
96 | Numbering states. |
97 `-------------------*/
98
99 typedef int state_number;
100 # define STATE_NUMBER_MAXIMUM INT_MAX
101
102 /* Be ready to map a state_number to an int. */
103 static inline int
104 state_number_as_int (state_number s)
105 {
106 return s;
107 }
108
109
110 typedef struct state state;
111
112 /*--------------.
113 | Transitions. |
114 `--------------*/
115
116 typedef struct
117 {
118 int num; /** Size of destination STATES. */
119 state *states[1];
120 } transitions;
121
122
123 /* What is the symbol labelling the transition to
124 TRANSITIONS->states[Num]? Can be a token (amongst which the error
125 token), or nonterminals in case of gotos. */
126
127 # define TRANSITION_SYMBOL(Transitions, Num) \
128 (Transitions->states[Num]->accessing_symbol)
129
130 /* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos). */
131
132 # define TRANSITION_IS_SHIFT(Transitions, Num) \
133 (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
134
135 /* Is the TRANSITIONS->states[Num] a goto?. */
136
137 # define TRANSITION_IS_GOTO(Transitions, Num) \
138 (!TRANSITION_IS_SHIFT (Transitions, Num))
139
140 /* Is the TRANSITIONS->states[Num] labelled by the error token? */
141
142 # define TRANSITION_IS_ERROR(Transitions, Num) \
143 (TRANSITION_SYMBOL (Transitions, Num) == errtoken->content->number)
144
145 /* When resolving a SR conflicts, if the reduction wins, the shift is
146 disabled. */
147
148 # define TRANSITION_DISABLE(Transitions, Num) \
149 (Transitions->states[Num] = NULL)
150
151 # define TRANSITION_IS_DISABLED(Transitions, Num) \
152 (Transitions->states[Num] == NULL)
153
154
155 /* Iterate over each transition over a token (shifts). */
156 # define FOR_EACH_SHIFT(Transitions, Iter) \
157 for (Iter = 0; \
158 Iter < Transitions->num \
159 && (TRANSITION_IS_DISABLED (Transitions, Iter) \
160 || TRANSITION_IS_SHIFT (Transitions, Iter)); \
161 ++Iter) \
162 if (!TRANSITION_IS_DISABLED (Transitions, Iter))
163
164
165 /* The destination of the transition (shift/goto) from state S on
166 label SYM (term or nterm). Abort if none found. */
167 struct state *transitions_to (state *s, symbol_number sym);
168
169
170 /*-------.
171 | Errs. |
172 `-------*/
173
174 typedef struct
175 {
176 int num;
177 symbol *symbols[1];
178 } errs;
179
180 errs *errs_new (int num, symbol **tokens);
181
182
183 /*-------------.
184 | Reductions. |
185 `-------------*/
186
187 typedef struct
188 {
189 int num;
190 bitset *lookaheads;
191 /* Sorted ascendingly on rule number. */
192 rule *rules[1];
193 } reductions;
194
195
196
197 /*---------.
198 | states. |
199 `---------*/
200
201 struct state_list;
202
203 struct state
204 {
205 state_number number;
206 symbol_number accessing_symbol;
207 transitions *transitions;
208 reductions *reductions;
209 errs *errs;
210
211 /* When an includer (such as ielr.c) needs to store states in a list, the
212 includer can define struct state_list as the list node structure and can
213 store in this member a reference to the node containing each state. */
214 struct state_list *state_list;
215
216 /* Whether no lookahead sets on reduce actions are needed to decide
217 what to do in state S. */
218 bool consistent;
219
220 /* If some conflicts were solved thanks to precedence/associativity,
221 a human readable description of the resolution. */
222 const char *solved_conflicts;
223 const char *solved_conflicts_xml;
224
225 /* Its items. Must be last, since ITEMS can be arbitrarily large. Sorted
226 ascendingly on item index in RITEM, which is sorted on rule number. */
227 size_t nitems;
228 item_index items[1];
229 };
230
231 extern state_number nstates;
232 extern state *final_state;
233
234 /* Create a new state with ACCESSING_SYMBOL for those items. */
235 state *state_new (symbol_number accessing_symbol,
236 size_t core_size, item_index *core);
237 /* Create a new state with the same kernel as S (same accessing
238 symbol, transitions, reductions, consistency and items). */
239 state *state_new_isocore (state const *s);
240
241 /* Record that from S we can reach all the DST states (NUM of them). */
242 void state_transitions_set (state *s, int num, state **dst);
243
244 /* Print the transitions of state s for debug. */
245 void state_transitions_print (const state *s, FILE *out);
246
247 /* Set the reductions of STATE. */
248 void state_reductions_set (state *s, int num, rule **reds);
249
250 /* The index of the reduction of state S that corresponds to rule R.
251 Aborts if there is no reduction of R in S. */
252 int state_reduction_find (state const *s, rule const *r);
253
254 /* Set the errs of STATE. */
255 void state_errs_set (state *s, int num, symbol **errors);
256
257 /* Print on OUT all the lookahead tokens such that this STATE wants to
258 reduce R. */
259 void state_rule_lookaheads_print (state const *s, rule const *r, FILE *out);
260 void state_rule_lookaheads_print_xml (state const *s, rule const *r,
261 FILE *out, int level);
262
263 /* Create/destroy the states hash table. */
264 void state_hash_new (void);
265 void state_hash_free (void);
266
267 /* Find the state associated to the CORE, and return it. If it does
268 not exist yet, return NULL. */
269 state *state_hash_lookup (size_t core_size, const item_index *core);
270
271 /* Insert STATE in the state hash table. */
272 void state_hash_insert (state *s);
273
274 /* Remove unreachable states, renumber remaining states, update NSTATES, and
275 write to OLD_TO_NEW a mapping of old state numbers to new state numbers such
276 that the old value of NSTATES is written as the new state number for removed
277 states. The size of OLD_TO_NEW must be the old value of NSTATES. */
278 void state_remove_unreachable_states (state_number old_to_new[]);
279
280 /* All the states, indexed by the state number. */
281 extern state **states;
282
283 /* Free all the states. */
284 void states_free (void);
285
286 #endif /* !STATE_H_ */