src/lalr.c

   1 /* Compute look-ahead criteria for bison,
   2    Copyright (C) 1984, 1986, 1989, 2000 Free Software Foundation, Inc.
   3
   4    This file is part of Bison, the GNU Compiler Compiler.
   5
   6    Bison is free software; you can redistribute it and/or modify
   7    it under the terms of the GNU General Public License as published by
   8    the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    Bison is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14    GNU General Public License for more details.
  15
  16    You should have received a copy of the GNU General Public License
  17    along with Bison; see the file COPYING.  If not, write to
  18    the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21
  22 /* Compute how to make the finite state machine deterministic; find
  23    which rules need lookahead in each state, and which lookahead
  24    tokens they accept.  */
  25
  26 #include "system.h"
  27 #include "types.h"
  28 #include "LR0.h"
  29 #include "alloc.h"
  30 #include "gram.h"
  31 #include "complain.h"
  32 #include "lalr.h"
  33 #include "nullable.h"
  34 #include "derives.h"
  35
  36 int tokensetsize;
  37 short *lookaheads;
  38 short *LAruleno;
  39 unsigned *LA;
  40 short *accessing_symbol;
  41 char *consistent;
  42 core **state_table;
  43 shifts **shift_table;
  44 reductions **reduction_table;
  45 short *goto_map;
  46 short *from_state;
  47 short *to_state;
  48
  49 extern void berror PARAMS ((const char *));
  50
  51 static int infinity;
  52 static int maxrhs;
  53 static int ngotos;
  54 static unsigned *F;
  55 static short **includes;
  56 static shorts **lookback;
  57 static short **R;
  58 static short *INDEX;
  59 static short *VERTICES;
  60 static int top;
  61
  62
  63 static void
  64 traverse (int i)
  65 {
  66   unsigned *fp1;
  67   unsigned *fp2;
  68   unsigned *fp3;
  69   int j;
  70   short *rp;
  71
  72   int height;
  73   unsigned *base;
  74
  75   VERTICES[++top] = i;
  76   INDEX[i] = height = top;
  77
  78   base = F + i * tokensetsize;
  79   fp3 = base + tokensetsize;
  80
  81   rp = R[i];
  82   if (rp)
  83     {
  84       while ((j = *rp++) >= 0)
  85         {
  86           if (INDEX[j] == 0)
  87             traverse (j);
  88
  89           if (INDEX[i] > INDEX[j])
  90             INDEX[i] = INDEX[j];
  91
  92           fp1 = base;
  93           fp2 = F + j * tokensetsize;
  94
  95           while (fp1 < fp3)
  96             *fp1++ |= *fp2++;
  97         }
  98     }
  99
 100   if (INDEX[i] == height)
 101     {
 102       for (;;)
 103         {
 104           j = VERTICES[top--];
 105           INDEX[j] = infinity;
 106
 107           if (i == j)
 108             break;
 109
 110           fp1 = base;
 111           fp2 = F + j * tokensetsize;
 112
 113           while (fp1 < fp3)
 114             *fp2++ = *fp1++;
 115         }
 116     }
 117 }
 118
 119
 120 static void
 121 digraph (short **relation)
 122 {
 123   int i;
 124
 125   infinity = ngotos + 2;
 126   INDEX = NEW2 (ngotos + 1, short);
 127   VERTICES = NEW2 (ngotos + 1, short);
 128   top = 0;
 129
 130   R = relation;
 131
 132   for (i = 0; i < ngotos; i++)
 133     INDEX[i] = 0;
 134
 135   for (i = 0; i < ngotos; i++)
 136     {
 137       if (INDEX[i] == 0 && R[i])
 138         traverse (i);
 139     }
 140
 141   FREE (INDEX);
 142   FREE (VERTICES);
 143 }
 144
 145 static void
 146 set_state_table (void)
 147 {
 148   core *sp;
 149
 150   state_table = NEW2 (nstates, core *);
 151
 152   for (sp = first_state; sp; sp = sp->next)
 153     state_table[sp->number] = sp;
 154 }
 155
 156
 157 static void
 158 set_accessing_symbol (void)
 159 {
 160   core *sp;
 161
 162   accessing_symbol = NEW2 (nstates, short);
 163
 164   for (sp = first_state; sp; sp = sp->next)
 165     accessing_symbol[sp->number] = sp->accessing_symbol;
 166 }
 167
 168
 169 static void
 170 set_shift_table (void)
 171 {
 172   shifts *sp;
 173
 174   shift_table = NEW2 (nstates, shifts *);
 175
 176   for (sp = first_shift; sp; sp = sp->next)
 177     shift_table[sp->number] = sp;
 178 }
 179
 180
 181 static void
 182 set_reduction_table (void)
 183 {
 184   reductions *rp;
 185
 186   reduction_table = NEW2 (nstates, reductions *);
 187
 188   for (rp = first_reduction; rp; rp = rp->next)
 189     reduction_table[rp->number] = rp;
 190 }
 191
 192
 193 static void
 194 set_maxrhs (void)
 195 {
 196   short *itemp;
 197   int length;
 198   int max;
 199
 200   length = 0;
 201   max = 0;
 202   for (itemp = ritem; *itemp; itemp++)
 203     {
 204       if (*itemp > 0)
 205         {
 206           length++;
 207         }
 208       else
 209         {
 210           if (length > max)
 211             max = length;
 212           length = 0;
 213         }
 214     }
 215
 216   maxrhs = max;
 217 }
 218
 219
 220 static void
 221 initialize_LA (void)
 222 {
 223   int i;
 224   int j;
 225   int count;
 226   reductions *rp;
 227   shifts *sp;
 228   short *np;
 229
 230   consistent = NEW2 (nstates, char);
 231   lookaheads = NEW2 (nstates + 1, short);
 232
 233   count = 0;
 234   for (i = 0; i < nstates; i++)
 235     {
 236       int k;
 237
 238       lookaheads[i] = count;
 239
 240       rp = reduction_table[i];
 241       sp = shift_table[i];
 242       if (rp && (rp->nreds > 1
 243                  || (sp && !ISVAR (accessing_symbol[sp->shifts[0]]))))
 244         count += rp->nreds;
 245       else
 246         consistent[i] = 1;
 247
 248       if (sp)
 249         for (k = 0; k < sp->nshifts; k++)
 250           {
 251             if (accessing_symbol[sp->shifts[k]] == error_token_number)
 252               {
 253                 consistent[i] = 0;
 254                 break;
 255               }
 256           }
 257     }
 258
 259   lookaheads[nstates] = count;
 260
 261   if (count == 0)
 262     {
 263       LA = NEW2 (1 * tokensetsize, unsigned);
 264       LAruleno = NEW2 (1, short);
 265       lookback = NEW2 (1, shorts *);
 266     }
 267   else
 268     {
 269       LA = NEW2 (count * tokensetsize, unsigned);
 270       LAruleno = NEW2 (count, short);
 271       lookback = NEW2 (count, shorts *);
 272     }
 273
 274   np = LAruleno;
 275   for (i = 0; i < nstates; i++)
 276     {
 277       if (!consistent[i])
 278         {
 279           if ((rp = reduction_table[i]))
 280             for (j = 0; j < rp->nreds; j++)
 281               *np++ = rp->rules[j];
 282         }
 283     }
 284 }
 285
 286
 287 static void
 288 set_goto_map (void)
 289 {
 290   shifts *sp;
 291   int i;
 292   int symbol;
 293   int k;
 294   short *temp_map;
 295   int state2;
 296   int state1;
 297
 298   goto_map = NEW2 (nvars + 1, short) - ntokens;
 299   temp_map = NEW2 (nvars + 1, short) - ntokens;
 300
 301   ngotos = 0;
 302   for (sp = first_shift; sp; sp = sp->next)
 303     {
 304       for (i = sp->nshifts - 1; i >= 0; i--)
 305         {
 306           symbol = accessing_symbol[sp->shifts[i]];
 307
 308           if (ISTOKEN (symbol))
 309             break;
 310
 311           if (ngotos == MAXSHORT)
 312             fatal (_("too many gotos (max %d)"), MAXSHORT);
 313
 314           ngotos++;
 315           goto_map[symbol]++;
 316         }
 317     }
 318
 319   k = 0;
 320   for (i = ntokens; i < nsyms; i++)
 321     {
 322       temp_map[i] = k;
 323       k += goto_map[i];
 324     }
 325
 326   for (i = ntokens; i < nsyms; i++)
 327     goto_map[i] = temp_map[i];
 328
 329   goto_map[nsyms] = ngotos;
 330   temp_map[nsyms] = ngotos;
 331
 332   from_state = NEW2 (ngotos, short);
 333   to_state = NEW2 (ngotos, short);
 334
 335   for (sp = first_shift; sp; sp = sp->next)
 336     {
 337       state1 = sp->number;
 338       for (i = sp->nshifts - 1; i >= 0; i--)
 339         {
 340           state2 = sp->shifts[i];
 341           symbol = accessing_symbol[state2];
 342
 343           if (ISTOKEN (symbol))
 344             break;
 345
 346           k = temp_map[symbol]++;
 347           from_state[k] = state1;
 348           to_state[k] = state2;
 349         }
 350     }
 351
 352   FREE (temp_map + ntokens);
 353 }
 354
 355
 356
 357 /*  Map_goto maps a state/symbol pair into its numeric representation.  */
 358
 359 static int
 360 map_goto (int state, int symbol)
 361 {
 362   int high;
 363   int low;
 364   int middle;
 365   int s;
 366
 367   low = goto_map[symbol];
 368   high = goto_map[symbol + 1] - 1;
 369
 370   while (low <= high)
 371     {
 372       middle = (low + high) / 2;
 373       s = from_state[middle];
 374       if (s == state)
 375         return middle;
 376       else if (s < state)
 377         low = middle + 1;
 378       else
 379         high = middle - 1;
 380     }
 381
 382   berror ("map_goto");
 383 /* NOTREACHED */
 384   return 0;
 385 }
 386
 387
 388 static void
 389 initialize_F (void)
 390 {
 391   int i;
 392   int j;
 393   int k;
 394   shifts *sp;
 395   short *edge;
 396   unsigned *rowp;
 397   short *rp;
 398   short **reads;
 399   int nedges;
 400   int stateno;
 401   int symbol;
 402   int nwords;
 403
 404   nwords = ngotos * tokensetsize;
 405   F = NEW2 (nwords, unsigned);
 406
 407   reads = NEW2 (ngotos, short *);
 408   edge = NEW2 (ngotos + 1, short);
 409   nedges = 0;
 410
 411   rowp = F;
 412   for (i = 0; i < ngotos; i++)
 413     {
 414       stateno = to_state[i];
 415       sp = shift_table[stateno];
 416
 417       if (sp)
 418         {
 419           k = sp->nshifts;
 420
 421           for (j = 0; j < k; j++)
 422             {
 423               symbol = accessing_symbol[sp->shifts[j]];
 424               if (ISVAR (symbol))
 425                 break;
 426               SETBIT (rowp, symbol);
 427             }
 428
 429           for (; j < k; j++)
 430             {
 431               symbol = accessing_symbol[sp->shifts[j]];
 432               if (nullable[symbol])
 433                 edge[nedges++] = map_goto (stateno, symbol);
 434             }
 435
 436           if (nedges)
 437             {
 438               reads[i] = rp = NEW2 (nedges + 1, short);
 439
 440               for (j = 0; j < nedges; j++)
 441                 rp[j] = edge[j];
 442
 443               rp[nedges] = -1;
 444               nedges = 0;
 445             }
 446         }
 447
 448       rowp += tokensetsize;
 449     }
 450
 451   digraph (reads);
 452
 453   for (i = 0; i < ngotos; i++)
 454     {
 455       if (reads[i])
 456         FREE (reads[i]);
 457     }
 458
 459   FREE (reads);
 460   FREE (edge);
 461 }
 462
 463
 464 static void
 465 add_lookback_edge (int stateno, int ruleno, int gotono)
 466 {
 467   int i;
 468   int k;
 469   int found;
 470   shorts *sp;
 471
 472   i = lookaheads[stateno];
 473   k = lookaheads[stateno + 1];
 474   found = 0;
 475   while (!found && i < k)
 476     {
 477       if (LAruleno[i] == ruleno)
 478         found = 1;
 479       else
 480         i++;
 481     }
 482
 483   assert (found);
 484
 485   sp = NEW (shorts);
 486   sp->next = lookback[i];
 487   sp->value = gotono;
 488   lookback[i] = sp;
 489 }
 490
 491
 492 static short **
 493 transpose (short **R_arg, int n)
 494 {
 495   short **new_R;
 496   short **temp_R;
 497   short *nedges;
 498   short *sp;
 499   int i;
 500   int k;
 501
 502   nedges = NEW2 (n, short);
 503
 504   for (i = 0; i < n; i++)
 505     {
 506       sp = R_arg[i];
 507       if (sp)
 508         {
 509           while (*sp >= 0)
 510             nedges[*sp++]++;
 511         }
 512     }
 513
 514   new_R = NEW2 (n, short *);
 515   temp_R = NEW2 (n, short *);
 516
 517   for (i = 0; i < n; i++)
 518     {
 519       k = nedges[i];
 520       if (k > 0)
 521         {
 522           sp = NEW2 (k + 1, short);
 523           new_R[i] = sp;
 524           temp_R[i] = sp;
 525           sp[k] = -1;
 526         }
 527     }
 528
 529   FREE (nedges);
 530
 531   for (i = 0; i < n; i++)
 532     {
 533       sp = R_arg[i];
 534       if (sp)
 535         {
 536           while (*sp >= 0)
 537             *temp_R[*sp++]++ = i;
 538         }
 539     }
 540
 541   FREE (temp_R);
 542
 543   return new_R;
 544 }
 545
 546
 547 static void
 548 build_relations (void)
 549 {
 550   int i;
 551   int j;
 552   int k;
 553   short *rulep;
 554   short *rp;
 555   shifts *sp;
 556   int length;
 557   int nedges;
 558   int done;
 559   int state1;
 560   int stateno;
 561   int symbol1;
 562   int symbol2;
 563   short *shortp;
 564   short *edge;
 565   short *states;
 566   short **new_includes;
 567
 568   includes = NEW2 (ngotos, short *);
 569   edge = NEW2 (ngotos + 1, short);
 570   states = NEW2 (maxrhs + 1, short);
 571
 572   for (i = 0; i < ngotos; i++)
 573     {
 574       nedges = 0;
 575       state1 = from_state[i];
 576       symbol1 = accessing_symbol[to_state[i]];
 577
 578       for (rulep = derives[symbol1]; *rulep > 0; rulep++)
 579         {
 580           length = 1;
 581           states[0] = state1;
 582           stateno = state1;
 583
 584           for (rp = ritem + rrhs[*rulep]; *rp > 0; rp++)
 585             {
 586               symbol2 = *rp;
 587               sp = shift_table[stateno];
 588               k = sp->nshifts;
 589
 590               for (j = 0; j < k; j++)
 591                 {
 592                   stateno = sp->shifts[j];
 593                   if (accessing_symbol[stateno] == symbol2)
 594                     break;
 595                 }
 596
 597               states[length++] = stateno;
 598             }
 599
 600           if (!consistent[stateno])
 601             add_lookback_edge (stateno, *rulep, i);
 602
 603           length--;
 604           done = 0;
 605           while (!done)
 606             {
 607               done = 1;
 608               rp--;
 609               /* JF added rp>=ritem &&   I hope to god its right! */
 610               if (rp >= ritem && ISVAR (*rp))
 611                 {
 612                   stateno = states[--length];
 613                   edge[nedges++] = map_goto (stateno, *rp);
 614                   if (nullable[*rp])
 615                     done = 0;
 616                 }
 617             }
 618         }
 619
 620       if (nedges)
 621         {
 622           includes[i] = shortp = NEW2 (nedges + 1, short);
 623           for (j = 0; j < nedges; j++)
 624             shortp[j] = edge[j];
 625           shortp[nedges] = -1;
 626         }
 627     }
 628
 629   new_includes = transpose (includes, ngotos);
 630
 631   for (i = 0; i < ngotos; i++)
 632     if (includes[i])
 633       FREE (includes[i]);
 634
 635   FREE (includes);
 636
 637   includes = new_includes;
 638
 639   FREE (edge);
 640   FREE (states);
 641 }
 642
 643
 644
 645 static void
 646 compute_FOLLOWS (void)
 647 {
 648   int i;
 649
 650   digraph (includes);
 651
 652   for (i = 0; i < ngotos; i++)
 653     {
 654       if (includes[i])
 655         FREE (includes[i]);
 656     }
 657
 658   FREE (includes);
 659 }
 660
 661
 662 static void
 663 compute_lookaheads (void)
 664 {
 665   int i;
 666   int n;
 667   unsigned *fp1;
 668   unsigned *fp2;
 669   unsigned *fp3;
 670   shorts *sp;
 671   unsigned *rowp;
 672   shorts *sptmp;                /* JF */
 673
 674   rowp = LA;
 675   n = lookaheads[nstates];
 676   for (i = 0; i < n; i++)
 677     {
 678       fp3 = rowp + tokensetsize;
 679       for (sp = lookback[i]; sp; sp = sp->next)
 680         {
 681           fp1 = rowp;
 682           fp2 = F + tokensetsize * sp->value;
 683           while (fp1 < fp3)
 684             *fp1++ |= *fp2++;
 685         }
 686
 687       rowp = fp3;
 688     }
 689
 690   for (i = 0; i < n; i++)
 691     {
 692       /* JF removed ref to freed storage */
 693       for (sp = lookback[i]; sp; sp = sptmp)
 694         {
 695           sptmp = sp->next;
 696           FREE (sp);
 697         }
 698     }
 699
 700   FREE (lookback);
 701   FREE (F);
 702 }
 703
 704
 705 void
 706 lalr (void)
 707 {
 708   tokensetsize = WORDSIZE (ntokens);
 709
 710   set_state_table ();
 711   set_accessing_symbol ();
 712   set_shift_table ();
 713   set_reduction_table ();
 714   set_maxrhs ();
 715   initialize_LA ();
 716   set_goto_map ();
 717   initialize_F ();
 718   build_relations ();
 719   compute_FOLLOWS ();
 720   compute_lookaheads ();
 721 }