src/lalr.c

   1 /* Compute look-ahead criteria for bison,
   2    Copyright (C) 1984, 1986, 1989, 2000, 2001, 2002
   3    Free Software Foundation, Inc.
   4
   5    This file is part of Bison, the GNU Compiler Compiler.
   6
   7    Bison is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2, or (at your option)
  10    any later version.
  11
  12    Bison is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with Bison; see the file COPYING.  If not, write to
  19    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22
  23 /* Compute how to make the finite state machine deterministic; find
  24    which rules need lookahead in each state, and which lookahead
  25    tokens they accept.  */
  26
  27 #include "system.h"
  28 #include "bitset.h"
  29 #include "bitsetv.h"
  30 #include "relation.h"
  31 #include "quotearg.h"
  32 #include "symtab.h"
  33 #include "gram.h"
  34 #include "reader.h"
  35 #include "LR0.h"
  36 #include "complain.h"
  37 #include "lalr.h"
  38 #include "nullable.h"
  39 #include "derives.h"
  40 #include "getargs.h"
  41
  42 goto_number_t *goto_map = NULL;
  43 static goto_number_t ngotos = 0;
  44 state_number_t *from_state = NULL;
  45 state_number_t *to_state = NULL;
  46
  47 /* Linked list of goto numbers.  */
  48 typedef struct goto_list_s
  49 {
  50   struct goto_list_s *next;
  51   goto_number_t value;
  52 } goto_list_t;
  53
  54
  55 /* LA is a LR by NTOKENS matrix of bits.  LA[l, i] is 1 if the rule
  56    LArule[l] is applicable in the appropriate state when the next
  57    token is symbol i.  If LA[l, i] and LA[l, j] are both 1 for i != j,
  58    it is a conflict.  */
  59
  60 static bitsetv LA = NULL;
  61 size_t nLA;
  62
  63
  64 /* And for the famous F variable, which name is so descriptive that a
  65    comment is hardly needed.  <grin>.  */
  66 static bitsetv F = NULL;
  67
  68 static goto_number_t **includes;
  69 static goto_list_t **lookback;
  70
  71
  72
  73
  74 static void
  75 set_goto_map (void)
  76 {
  77   state_number_t state;
  78   goto_number_t *temp_map;
  79
  80   goto_map = XCALLOC (goto_number_t, nvars + 1) - ntokens;
  81   temp_map = XCALLOC (goto_number_t, nvars + 1) - ntokens;
  82
  83   ngotos = 0;
  84   for (state = 0; state < nstates; ++state)
  85     {
  86       transitions_t *sp = states[state]->transitions;
  87       int i;
  88       for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
  89         {
  90           if (ngotos >= GOTO_NUMBER_MAX)
  91             abort ();
  92           ngotos++;
  93           goto_map[TRANSITION_SYMBOL (sp, i)]++;
  94         }
  95     }
  96
  97   {
  98     int k = 0;
  99     int i;
 100     for (i = ntokens; i < nsyms; i++)
 101       {
 102         temp_map[i] = k;
 103         k += goto_map[i];
 104       }
 105
 106     for (i = ntokens; i < nsyms; i++)
 107       goto_map[i] = temp_map[i];
 108
 109     goto_map[nsyms] = ngotos;
 110     temp_map[nsyms] = ngotos;
 111   }
 112
 113   from_state = XCALLOC (state_number_t, ngotos);
 114   to_state = XCALLOC (state_number_t, ngotos);
 115
 116   for (state = 0; state < nstates; ++state)
 117     {
 118       transitions_t *sp = states[state]->transitions;
 119       int i;
 120       for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
 121         {
 122           int k = temp_map[TRANSITION_SYMBOL (sp, i)]++;
 123           from_state[k] = state;
 124           to_state[k] = sp->states[i]->number;
 125         }
 126     }
 127
 128   XFREE (temp_map + ntokens);
 129 }
 130
 131
 132
 133 /*----------------------------------------------------------.
 134 | Map a state/symbol pair into its numeric representation.  |
 135 `----------------------------------------------------------*/
 136
 137 static int
 138 map_goto (state_number_t state, symbol_number_t symbol)
 139 {
 140   int high;
 141   int low;
 142   int middle;
 143   state_number_t s;
 144
 145   low = goto_map[symbol];
 146   high = goto_map[symbol + 1] - 1;
 147
 148   for (;;)
 149     {
 150       if (high < low)
 151         abort ();
 152       middle = (low + high) / 2;
 153       s = from_state[middle];
 154       if (s == state)
 155         return middle;
 156       else if (s < state)
 157         low = middle + 1;
 158       else
 159         high = middle - 1;
 160     }
 161 }
 162
 163
 164 static void
 165 initialize_F (void)
 166 {
 167   goto_number_t **reads = XCALLOC (goto_number_t *, ngotos);
 168   goto_number_t *edge = XCALLOC (goto_number_t, ngotos + 1);
 169   int nedges = 0;
 170
 171   int i;
 172
 173   F = bitsetv_create (ngotos, ntokens, BITSET_FIXED);
 174
 175   for (i = 0; i < ngotos; i++)
 176     {
 177       state_number_t stateno = to_state[i];
 178       transitions_t *sp = states[stateno]->transitions;
 179
 180       int j;
 181       FOR_EACH_SHIFT (sp, j)
 182         bitset_set (F[i], TRANSITION_SYMBOL (sp, j));
 183
 184       for (; j < sp->num; j++)
 185         {
 186           symbol_number_t symbol = TRANSITION_SYMBOL (sp, j);
 187           if (nullable[symbol])
 188             edge[nedges++] = map_goto (stateno, symbol);
 189         }
 190
 191       if (nedges)
 192         {
 193           reads[i] = XCALLOC (goto_number_t, nedges + 1);
 194           memcpy (reads[i], edge, nedges * sizeof (edge[0]));
 195           reads[i][nedges] = -1;
 196           nedges = 0;
 197         }
 198     }
 199
 200   relation_digraph (reads, ngotos, &F);
 201
 202   for (i = 0; i < ngotos; i++)
 203     XFREE (reads[i]);
 204
 205   XFREE (reads);
 206   XFREE (edge);
 207 }
 208
 209
 210 static void
 211 add_lookback_edge (state_t *state, rule_t *rule, int gotono)
 212 {
 213   int r = state_reduction_find (state, rule);
 214   goto_list_t *sp = XCALLOC (goto_list_t, 1);
 215   sp->next = lookback[(state->reductions->lookaheads - LA) + r];
 216   sp->value = gotono;
 217   lookback[(state->reductions->lookaheads - LA) + r] = sp;
 218 }
 219
 220
 221
 222 static void
 223 build_relations (void)
 224 {
 225   goto_number_t *edge = XCALLOC (goto_number_t, ngotos + 1);
 226   state_number_t *states1 = XCALLOC (state_number_t, ritem_longest_rhs () + 1);
 227   int i;
 228
 229   includes = XCALLOC (goto_number_t *, ngotos);
 230
 231   for (i = 0; i < ngotos; i++)
 232     {
 233       int nedges = 0;
 234       symbol_number_t symbol1 = states[to_state[i]]->accessing_symbol;
 235       rule_t **rulep;
 236
 237       for (rulep = derives[symbol1]; *rulep; rulep++)
 238         {
 239           int done;
 240           int length = 1;
 241           item_number_t *rp;
 242           state_t *state = states[from_state[i]];
 243           states1[0] = state->number;
 244
 245           for (rp = (*rulep)->rhs; *rp >= 0; rp++)
 246             {
 247               state = transitions_to (state->transitions,
 248                                       item_number_as_symbol_number (*rp));
 249               states1[length++] = state->number;
 250             }
 251
 252           if (!state->consistent)
 253             add_lookback_edge (state, *rulep, i);
 254
 255           length--;
 256           done = 0;
 257           while (!done)
 258             {
 259               done = 1;
 260               rp--;
 261               /* JF added rp>=ritem &&   I hope to god its right! */
 262               if (rp >= ritem && ISVAR (*rp))
 263                 {
 264                   /* Downcasting from item_number_t to symbol_number_t. */
 265                   edge[nedges++] = map_goto (states1[--length],
 266                                              item_number_as_symbol_number (*rp));
 267                   if (nullable[*rp])
 268                     done = 0;
 269                 }
 270             }
 271         }
 272
 273       if (nedges)
 274         {
 275           int j;
 276           includes[i] = XCALLOC (goto_number_t, nedges + 1);
 277           for (j = 0; j < nedges; j++)
 278             includes[i][j] = edge[j];
 279           includes[i][nedges] = -1;
 280         }
 281     }
 282
 283   XFREE (edge);
 284   XFREE (states1);
 285
 286   relation_transpose (&includes, ngotos);
 287 }
 288
 289
 290
 291 static void
 292 compute_FOLLOWS (void)
 293 {
 294   int i;
 295
 296   relation_digraph (includes, ngotos, &F);
 297
 298   for (i = 0; i < ngotos; i++)
 299     XFREE (includes[i]);
 300
 301   XFREE (includes);
 302 }
 303
 304
 305 static void
 306 compute_lookaheads (void)
 307 {
 308   size_t i;
 309   goto_list_t *sp;
 310
 311   for (i = 0; i < nLA; i++)
 312     for (sp = lookback[i]; sp; sp = sp->next)
 313       bitset_or (LA[i], LA[i], F[sp->value]);
 314
 315   /* Free LOOKBACK. */
 316   for (i = 0; i < nLA; i++)
 317     LIST_FREE (goto_list_t, lookback[i]);
 318
 319   XFREE (lookback);
 320   bitsetv_free (F);
 321 }
 322
 323
 324 /*---------------------------------------------------------------.
 325 | Count the number of lookaheads required for STATE (NLOOKAHEADS |
 326 | member).                                                       |
 327 `---------------------------------------------------------------*/
 328
 329 static int
 330 state_lookaheads_count (state_t *state)
 331 {
 332   int k;
 333   int nlookaheads = 0;
 334   reductions_t *rp = state->reductions;
 335   transitions_t *sp = state->transitions;
 336
 337   /* We need a lookahead either to distinguish different
 338      reductions (i.e., there are two or more), or to distinguish a
 339      reduction from a shift.  Otherwise, it is straightforward,
 340      and the state is `consistent'.  */
 341   if (rp->num > 1
 342       || (rp->num == 1 && sp->num &&
 343           !TRANSITION_IS_DISABLED (sp, 0) && TRANSITION_IS_SHIFT (sp, 0)))
 344     nlookaheads += rp->num;
 345   else
 346     state->consistent = 1;
 347
 348   for (k = 0; k < sp->num; k++)
 349     if (!TRANSITION_IS_DISABLED (sp, k) && TRANSITION_IS_ERROR (sp, k))
 350       {
 351         state->consistent = 0;
 352         break;
 353       }
 354
 355   return nlookaheads;
 356 }
 357
 358
 359 /*----------------------------------------------.
 360 | Compute LA, NLA, and the lookaheads members.  |
 361 `----------------------------------------------*/
 362
 363 static void
 364 initialize_LA (void)
 365 {
 366   state_number_t i;
 367   bitsetv pLA;
 368
 369   /* Compute the total number of reductions requiring a lookahead.  */
 370   nLA = 0;
 371   for (i = 0; i < nstates; i++)
 372     nLA += state_lookaheads_count (states[i]);
 373   /* Avoid having to special case 0.  */
 374   if (!nLA)
 375     nLA = 1;
 376
 377   pLA = LA = bitsetv_create (nLA, ntokens, BITSET_FIXED);
 378   lookback = XCALLOC (goto_list_t *, nLA);
 379
 380   /* Initialize the members LOOKAHEADS for each state which reductions
 381      require lookaheads.  */
 382   for (i = 0; i < nstates; i++)
 383     {
 384       int count = state_lookaheads_count (states[i]);
 385       if (count)
 386         {
 387           states[i]->reductions->lookaheads = pLA;
 388           pLA += count;
 389         }
 390     }
 391 }
 392
 393
 394 /*---------------------------------------.
 395 | Output the lookaheads for each state.  |
 396 `---------------------------------------*/
 397
 398 static void
 399 lookaheads_print (FILE *out)
 400 {
 401   state_number_t i;
 402   int j, k;
 403   fprintf (out, "Lookaheads: BEGIN\n");
 404   for (i = 0; i < nstates; ++i)
 405     {
 406       reductions_t *reds = states[i]->reductions;
 407       bitset_iterator iter;
 408       int nlookaheads = 0;
 409
 410       if (reds->lookaheads)
 411         for (k = 0; k < reds->num; ++k)
 412           if (reds->lookaheads[k])
 413             ++nlookaheads;
 414
 415       fprintf (out, "State %d: %d lookaheads\n",
 416                i, nlookaheads);
 417
 418       if (reds->lookaheads)
 419         for (j = 0; j < reds->num; ++j)
 420           BITSET_FOR_EACH (iter, reds->lookaheads[j], k, 0)
 421           {
 422             fprintf (out, "   on %d (%s) -> rule %d\n",
 423                      k, symbols[k]->tag,
 424                      reds->rules[j]->number);
 425           };
 426     }
 427   fprintf (out, "Lookaheads: END\n");
 428 }
 429
 430 void
 431 lalr (void)
 432 {
 433   initialize_LA ();
 434   set_goto_map ();
 435   initialize_F ();
 436   build_relations ();
 437   compute_FOLLOWS ();
 438   compute_lookaheads ();
 439
 440   if (trace_flag & trace_sets)
 441     lookaheads_print (stderr);
 442 }
 443
 444
 445 void
 446 lalr_free (void)
 447 {
 448   state_number_t s;
 449   for (s = 0; s < nstates; ++s)
 450     states[s]->reductions->lookaheads = NULL;
 451   bitsetv_free (LA);
 452 }