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             fatal (_("too many gotos (max %d)"), GOTO_NUMBER_MAX);
  92
  93           ngotos++;
  94           goto_map[TRANSITION_SYMBOL (sp, i)]++;
  95         }
  96     }
  97
  98   {
  99     int k = 0;
 100     int i;
 101     for (i = ntokens; i < nsyms; i++)
 102       {
 103         temp_map[i] = k;
 104         k += goto_map[i];
 105       }
 106
 107     for (i = ntokens; i < nsyms; i++)
 108       goto_map[i] = temp_map[i];
 109
 110     goto_map[nsyms] = ngotos;
 111     temp_map[nsyms] = ngotos;
 112   }
 113
 114   from_state = XCALLOC (state_number_t, ngotos);
 115   to_state = XCALLOC (state_number_t, ngotos);
 116
 117   for (state = 0; state < nstates; ++state)
 118     {
 119       transitions_t *sp = states[state]->transitions;
 120       int i;
 121       for (i = sp->num - 1; i >= 0 && TRANSITION_IS_GOTO (sp, i); --i)
 122         {
 123           int k = temp_map[TRANSITION_SYMBOL (sp, i)]++;
 124           from_state[k] = state;
 125           to_state[k] = sp->states[i]->number;
 126         }
 127     }
 128
 129   XFREE (temp_map + ntokens);
 130 }
 131
 132
 133
 134 /*----------------------------------------------------------.
 135 | Map a state/symbol pair into its numeric representation.  |
 136 `----------------------------------------------------------*/
 137
 138 static int
 139 map_goto (state_number_t state, symbol_number_t symbol)
 140 {
 141   int high;
 142   int low;
 143   int middle;
 144   state_number_t s;
 145
 146   low = goto_map[symbol];
 147   high = goto_map[symbol + 1] - 1;
 148
 149   while (low <= high)
 150     {
 151       middle = (low + high) / 2;
 152       s = from_state[middle];
 153       if (s == state)
 154         return middle;
 155       else if (s < state)
 156         low = middle + 1;
 157       else
 158         high = middle - 1;
 159     }
 160
 161   assert (0);
 162   /* NOTREACHED */
 163   return 0;
 164 }
 165
 166
 167 static void
 168 initialize_F (void)
 169 {
 170   goto_number_t **reads = XCALLOC (goto_number_t *, ngotos);
 171   goto_number_t *edge = XCALLOC (goto_number_t, ngotos + 1);
 172   int nedges = 0;
 173
 174   int i;
 175
 176   F = bitsetv_create (ngotos, ntokens, BITSET_FIXED);
 177
 178   for (i = 0; i < ngotos; i++)
 179     {
 180       state_number_t stateno = to_state[i];
 181       transitions_t *sp = states[stateno]->transitions;
 182
 183       int j;
 184       FOR_EACH_SHIFT (sp, j)
 185         bitset_set (F[i], TRANSITION_SYMBOL (sp, j));
 186
 187       for (; j < sp->num; j++)
 188         {
 189           symbol_number_t symbol = TRANSITION_SYMBOL (sp, j);
 190           if (nullable[symbol])
 191             edge[nedges++] = map_goto (stateno, symbol);
 192         }
 193
 194       if (nedges)
 195         {
 196           reads[i] = XCALLOC (goto_number_t, nedges + 1);
 197           memcpy (reads[i], edge, nedges * sizeof (edge[0]));
 198           reads[i][nedges] = -1;
 199           nedges = 0;
 200         }
 201     }
 202
 203   relation_digraph (reads, ngotos, &F);
 204
 205   for (i = 0; i < ngotos; i++)
 206     XFREE (reads[i]);
 207
 208   XFREE (reads);
 209   XFREE (edge);
 210 }
 211
 212
 213 static void
 214 add_lookback_edge (state_t *state, rule_t *rule, int gotono)
 215 {
 216   int r = state_reduction_find (state, rule);
 217   goto_list_t *sp = XCALLOC (goto_list_t, 1);
 218   sp->next = lookback[(state->reductions->lookaheads - LA) + r];
 219   sp->value = gotono;
 220   lookback[(state->reductions->lookaheads - LA) + r] = sp;
 221 }
 222
 223
 224
 225 static void
 226 build_relations (void)
 227 {
 228   goto_number_t *edge = XCALLOC (goto_number_t, ngotos + 1);
 229   state_number_t *states1 = XCALLOC (state_number_t, ritem_longest_rhs () + 1);
 230   int i;
 231
 232   includes = XCALLOC (goto_number_t *, ngotos);
 233
 234   for (i = 0; i < ngotos; i++)
 235     {
 236       int nedges = 0;
 237       symbol_number_t symbol1 = states[to_state[i]]->accessing_symbol;
 238       rule_t **rulep;
 239
 240       for (rulep = derives[symbol1]; *rulep; rulep++)
 241         {
 242           int done;
 243           int length = 1;
 244           item_number_t *rp;
 245           state_t *state = states[from_state[i]];
 246           states1[0] = state->number;
 247
 248           for (rp = (*rulep)->rhs; *rp >= 0; rp++)
 249             {
 250               state = transitions_to (state->transitions,
 251                                       item_number_as_symbol_number (*rp));
 252               states1[length++] = state->number;
 253             }
 254
 255           if (!state->consistent)
 256             add_lookback_edge (state, *rulep, i);
 257
 258           length--;
 259           done = 0;
 260           while (!done)
 261             {
 262               done = 1;
 263               rp--;
 264               /* JF added rp>=ritem &&   I hope to god its right! */
 265               if (rp >= ritem && ISVAR (*rp))
 266                 {
 267                   /* Downcasting from item_number_t to symbol_number_t. */
 268                   edge[nedges++] = map_goto (states1[--length],
 269                                              item_number_as_symbol_number (*rp));
 270                   if (nullable[*rp])
 271                     done = 0;
 272                 }
 273             }
 274         }
 275
 276       if (nedges)
 277         {
 278           int j;
 279           includes[i] = XCALLOC (goto_number_t, nedges + 1);
 280           for (j = 0; j < nedges; j++)
 281             includes[i][j] = edge[j];
 282           includes[i][nedges] = -1;
 283         }
 284     }
 285
 286   XFREE (edge);
 287   XFREE (states1);
 288
 289   relation_transpose (&includes, ngotos);
 290 }
 291
 292
 293
 294 static void
 295 compute_FOLLOWS (void)
 296 {
 297   int i;
 298
 299   relation_digraph (includes, ngotos, &F);
 300
 301   for (i = 0; i < ngotos; i++)
 302     XFREE (includes[i]);
 303
 304   XFREE (includes);
 305 }
 306
 307
 308 static void
 309 compute_lookaheads (void)
 310 {
 311   size_t i;
 312   goto_list_t *sp;
 313
 314   for (i = 0; i < nLA; i++)
 315     for (sp = lookback[i]; sp; sp = sp->next)
 316       bitset_or (LA[i], LA[i], F[sp->value]);
 317
 318   /* Free LOOKBACK. */
 319   for (i = 0; i < nLA; i++)
 320     LIST_FREE (goto_list_t, lookback[i]);
 321
 322   XFREE (lookback);
 323   bitsetv_free (F);
 324 }
 325
 326
 327 /*---------------------------------------------------------------.
 328 | Count the number of lookaheads required for STATE (NLOOKAHEADS |
 329 | member).                                                       |
 330 `---------------------------------------------------------------*/
 331
 332 static int
 333 state_lookaheads_count (state_t *state)
 334 {
 335   int k;
 336   int nlookaheads = 0;
 337   reductions_t *rp = state->reductions;
 338   transitions_t *sp = state->transitions;
 339
 340   /* We need a lookahead either to distinguish different
 341      reductions (i.e., there are two or more), or to distinguish a
 342      reduction from a shift.  Otherwise, it is straightforward,
 343      and the state is `consistent'.  */
 344   if (rp->num > 1
 345       || (rp->num == 1 && sp->num &&
 346           !TRANSITION_IS_DISABLED (sp, 0) && TRANSITION_IS_SHIFT (sp, 0)))
 347     nlookaheads += rp->num;
 348   else
 349     state->consistent = 1;
 350
 351   for (k = 0; k < sp->num; k++)
 352     if (!TRANSITION_IS_DISABLED (sp, k) && TRANSITION_IS_ERROR (sp, k))
 353       {
 354         state->consistent = 0;
 355         break;
 356       }
 357
 358   return nlookaheads;
 359 }
 360
 361
 362 /*----------------------------------------------.
 363 | Compute LA, NLA, and the lookaheads members.  |
 364 `----------------------------------------------*/
 365
 366 static void
 367 initialize_LA (void)
 368 {
 369   state_number_t i;
 370   bitsetv pLA;
 371
 372   /* Compute the total number of reductions requiring a lookahead.  */
 373   nLA = 0;
 374   for (i = 0; i < nstates; i++)
 375     nLA += state_lookaheads_count (states[i]);
 376   /* Avoid having to special case 0.  */
 377   if (!nLA)
 378     nLA = 1;
 379
 380   pLA = LA = bitsetv_create (nLA, ntokens, BITSET_FIXED);
 381   lookback = XCALLOC (goto_list_t *, nLA);
 382
 383   /* Initialize the members LOOKAHEADS for each state which reductions
 384      require lookaheads.  */
 385   for (i = 0; i < nstates; i++)
 386     {
 387       int count = state_lookaheads_count (states[i]);
 388       if (count)
 389         {
 390           states[i]->reductions->lookaheads = pLA;
 391           pLA += count;
 392         }
 393     }
 394 }
 395
 396
 397 /*---------------------------------------.
 398 | Output the lookaheads for each state.  |
 399 `---------------------------------------*/
 400
 401 static void
 402 lookaheads_print (FILE *out)
 403 {
 404   state_number_t i;
 405   int j, k;
 406   fprintf (out, "Lookaheads: BEGIN\n");
 407   for (i = 0; i < nstates; ++i)
 408     {
 409       reductions_t *reds = states[i]->reductions;
 410       bitset_iterator iter;
 411       int nlookaheads = 0;
 412
 413       if (reds->lookaheads)
 414         for (k = 0; k < reds->num; ++k)
 415           if (reds->lookaheads[k])
 416             ++nlookaheads;
 417
 418       fprintf (out, "State %d: %d lookaheads\n",
 419                i, nlookaheads);
 420
 421       if (reds->lookaheads)
 422         for (j = 0; j < reds->num; ++j)
 423           BITSET_FOR_EACH (iter, reds->lookaheads[j], k, 0)
 424           {
 425             fprintf (out, "   on %d (%s) -> rule %d\n",
 426                      k, symbols[k]->tag,
 427                      reds->rules[j]->number);
 428           };
 429     }
 430   fprintf (out, "Lookaheads: END\n");
 431 }
 432
 433 void
 434 lalr (void)
 435 {
 436   initialize_LA ();
 437   set_goto_map ();
 438   initialize_F ();
 439   build_relations ();
 440   compute_FOLLOWS ();
 441   compute_lookaheads ();
 442
 443   if (trace_flag & trace_sets)
 444     lookaheads_print (stderr);
 445 }
 446
 447
 448 void
 449 lalr_free (void)
 450 {
 451   state_number_t s;
 452   for (s = 0; s < nstates; ++s)
 453     states[s]->reductions->lookaheads = NULL;
 454   bitsetv_free (LA);
 455 }