src/state.h

   1 /* Type definitions for the finite state machine for Bison.
   2
   3    Copyright (C) 1984, 1989, 2000-2004, 2007, 2009-2013 Free Software
   4    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
  55    of one state, the state whose number is in the number field.  Each
  56    contains a vector of numbers of the states that transitions can go
  57    to.  The accessing_symbol fields of those states' cores say what
  58    kind of 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 <bitset.h>
  85
  86 # include "gram.h"
  87 # include "symtab.h"
  88
  89
  90 /*-------------------.
  91 | Numbering states.  |
  92 `-------------------*/
  93
  94 typedef int state_number;
  95 # define STATE_NUMBER_MAXIMUM INT_MAX
  96
  97 /* Be ready to map a state_number to an int.  */
  98 static inline int
  99 state_number_as_int (state_number s)
 100 {
 101   return s;
 102 }
 103
 104
 105 typedef struct state state;
 106
 107 /*--------------.
 108 | Transitions.  |
 109 `--------------*/
 110
 111 typedef struct
 112 {
 113   int num;
 114   state *states[1];
 115 } transitions;
 116
 117
 118 /* What is the symbol labelling the transition to
 119    TRANSITIONS->states[Num]?  Can be a token (amongst which the error
 120    token), or non terminals in case of gotos.  */
 121
 122 #define TRANSITION_SYMBOL(Transitions, Num) \
 123   (Transitions->states[Num]->accessing_symbol)
 124
 125 /* Is the TRANSITIONS->states[Num] a shift? (as opposed to gotos).  */
 126
 127 #define TRANSITION_IS_SHIFT(Transitions, Num) \
 128   (ISTOKEN (TRANSITION_SYMBOL (Transitions, Num)))
 129
 130 /* Is the TRANSITIONS->states[Num] a goto?. */
 131
 132 #define TRANSITION_IS_GOTO(Transitions, Num) \
 133   (!TRANSITION_IS_SHIFT (Transitions, Num))
 134
 135 /* Is the TRANSITIONS->states[Num] labelled by the error token?  */
 136
 137 #define TRANSITION_IS_ERROR(Transitions, Num) \
 138   (TRANSITION_SYMBOL (Transitions, Num) == errtoken->number)
 139
 140 /* When resolving a SR conflicts, if the reduction wins, the shift is
 141    disabled.  */
 142
 143 #define TRANSITION_DISABLE(Transitions, Num) \
 144   (Transitions->states[Num] = NULL)
 145
 146 #define TRANSITION_IS_DISABLED(Transitions, Num) \
 147   (Transitions->states[Num] == NULL)
 148
 149
 150 /* Iterate over each transition over a token (shifts).  */
 151 #define FOR_EACH_SHIFT(Transitions, Iter)                       \
 152   for (Iter = 0;                                                \
 153        Iter < Transitions->num                                  \
 154          && (TRANSITION_IS_DISABLED (Transitions, Iter)         \
 155              || TRANSITION_IS_SHIFT (Transitions, Iter));       \
 156        ++Iter)                                                  \
 157     if (!TRANSITION_IS_DISABLED (Transitions, Iter))
 158
 159
 160 /* Return the state such SHIFTS contain a shift/goto to it on SYM.
 161    Abort if none found.  */
 162 struct state *transitions_to (transitions *shifts, symbol_number sym);
 163
 164
 165 /*-------.
 166 | Errs.  |
 167 `-------*/
 168
 169 typedef struct
 170 {
 171   int num;
 172   symbol *symbols[1];
 173 } errs;
 174
 175 errs *errs_new (int num, symbol **tokens);
 176
 177
 178 /*-------------.
 179 | Reductions.  |
 180 `-------------*/
 181
 182 typedef struct
 183 {
 184   int num;
 185   bitset *lookahead_tokens;
 186   /* Sorted ascendingly on rule number.  */
 187   rule *rules[1];
 188 } reductions;
 189
 190
 191
 192 /*---------.
 193 | states.  |
 194 `---------*/
 195
 196 struct state_list;
 197
 198 struct state
 199 {
 200   state_number number;
 201   symbol_number accessing_symbol;
 202   transitions *transitions;
 203   reductions *reductions;
 204   errs *errs;
 205
 206   /* When an includer (such as ielr.c) needs to store states in a list, the
 207      includer can define struct state_list as the list node structure and can
 208      store in this member a reference to the node containing each state.  */
 209   struct state_list *state_list;
 210
 211   /* If non-zero, then no lookahead sets on reduce actions are needed to
 212      decide what to do in state S.  */
 213   char consistent;
 214
 215   /* If some conflicts were solved thanks to precedence/associativity,
 216      a human readable description of the resolution.  */
 217   const char *solved_conflicts;
 218   const char *solved_conflicts_xml;
 219
 220   /* Its items.  Must be last, since ITEMS can be arbitrarily large.  Sorted
 221      ascendingly on item index in RITEM, which is sorted on rule number.  */
 222   size_t nitems;
 223   item_number items[1];
 224 };
 225
 226 extern state_number nstates;
 227 extern state *final_state;
 228
 229 /* Create a new state with ACCESSING_SYMBOL for those items.  */
 230 state *state_new (symbol_number accessing_symbol,
 231                   size_t core_size, item_number *core);
 232 state *state_new_isocore (state const *s);
 233
 234 /* Set the transitions of STATE.  */
 235 void state_transitions_set (state *s, int num, state **trans);
 236
 237 /* Set the reductions of STATE.  */
 238 void state_reductions_set (state *s, int num, rule **reds);
 239
 240 int state_reduction_find (state *s, rule *r);
 241
 242 /* Set the errs of STATE.  */
 243 void state_errs_set (state *s, int num, symbol **errors);
 244
 245 /* Print on OUT all the lookahead tokens such that this STATE wants to
 246    reduce R.  */
 247 void state_rule_lookahead_tokens_print (state *s, rule *r, FILE *out);
 248 void state_rule_lookahead_tokens_print_xml (state *s, rule *r,
 249                                             FILE *out, int level);
 250
 251 /* Create/destroy the states hash table.  */
 252 void state_hash_new (void);
 253 void state_hash_free (void);
 254
 255 /* Find the state associated to the CORE, and return it.  If it does
 256    not exist yet, return NULL.  */
 257 state *state_hash_lookup (size_t core_size, item_number *core);
 258
 259 /* Insert STATE in the state hash table.  */
 260 void state_hash_insert (state *s);
 261
 262 /* Remove unreachable states, renumber remaining states, update NSTATES, and
 263    write to OLD_TO_NEW a mapping of old state numbers to new state numbers such
 264    that the old value of NSTATES is written as the new state number for removed
 265    states.  The size of OLD_TO_NEW must be the old value of NSTATES.  */
 266 void state_remove_unreachable_states (state_number old_to_new[]);
 267
 268 /* All the states, indexed by the state number.  */
 269 extern state **states;
 270
 271 /* Free all the states.  */
 272 void states_free (void);
 273
 274 #endif /* !STATE_H_ */