src/conflicts.c

   1 /* Find and resolve or report look-ahead conflicts for bison,
   2    Copyright 1984, 1989, 1992, 2000, 2001 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 it
   7    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, but
  12    WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    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 the Free
  18    Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
  19    02111-1307, USA.  */
  20
  21 #include "system.h"
  22 #include "complain.h"
  23 #include "getargs.h"
  24 #include "files.h"
  25 #include "gram.h"
  26 #include "state.h"
  27 #include "lalr.h"
  28 #include "conflicts.h"
  29 #include "reader.h"
  30 #include "LR0.h"
  31
  32 errs **err_table = NULL;
  33 /* -1 stands for not specified. */
  34 int expected_conflicts = -1;
  35 static char *conflicts = NULL;
  36
  37 static unsigned *shiftset = NULL;
  38 static unsigned *lookaheadset = NULL;
  39 \f
  40
  41 static inline void
  42 log_resolution (int state, int LAno, int token, char *resolution)
  43 {
  44   obstack_fgrow4 (&output_obstack,
  45                   _("\
  46 Conflict in state %d between rule %d and token %s resolved as %s.\n"),
  47                   state, LAruleno[LAno], tags[token], resolution);
  48 }
  49
  50
  51 /*------------------------------------------------------------------.
  52 | Turn off the shift recorded for the specified token in the        |
  53 | specified state.  Used when we resolve a shift-reduce conflict in |
  54 | favor of the reduction.                                           |
  55 `------------------------------------------------------------------*/
  56
  57 static void
  58 flush_shift (int state, int token)
  59 {
  60   shifts *shiftp;
  61   int k, i;
  62
  63   shiftp = state_table[state].shift_table;
  64
  65   if (shiftp)
  66     {
  67       k = shiftp->nshifts;
  68       for (i = 0; i < k; i++)
  69         {
  70           if (shiftp->shifts[i]
  71               && token == state_table[shiftp->shifts[i]].accessing_symbol)
  72             (shiftp->shifts[i]) = 0;
  73         }
  74     }
  75 }
  76
  77
  78 /*------------------------------------------------------------------.
  79 | Attempt to resolve shift-reduce conflict for one rule by means of |
  80 | precedence declarations.  It has already been checked that the    |
  81 | rule has a precedence.  A conflict is resolved by modifying the   |
  82 | shift or reduce tables so that there is no longer a conflict.     |
  83 `------------------------------------------------------------------*/
  84
  85 static void
  86 resolve_sr_conflict (int state, int lookaheadnum)
  87 {
  88   int i;
  89   int mask;
  90   unsigned *fp1;
  91   unsigned *fp2;
  92   int redprec;
  93   errs *errp = (errs *) xcalloc (sizeof (errs) + ntokens * sizeof (short), 1);
  94   short *errtokens = errp->errs;
  95
  96   /* find the rule to reduce by to get precedence of reduction  */
  97   redprec = rprec[LAruleno[lookaheadnum]];
  98
  99   mask = 1;
 100   fp1 = LA + lookaheadnum * tokensetsize;
 101   fp2 = lookaheadset;
 102   for (i = 0; i < ntokens; i++)
 103     {
 104       if ((mask & *fp2 & *fp1) && sprec[i])
 105         /* Shift-reduce conflict occurs for token number i
 106            and it has a precedence.
 107            The precedence of shifting is that of token i.  */
 108         {
 109           if (sprec[i] < redprec)
 110             {
 111               log_resolution (state, lookaheadnum, i, _("reduce"));
 112               *fp2 &= ~mask;    /* flush the shift for this token */
 113               flush_shift (state, i);
 114             }
 115           else if (sprec[i] > redprec)
 116             {
 117               log_resolution (state, lookaheadnum, i, _("shift"));
 118               *fp1 &= ~mask;    /* flush the reduce for this token */
 119             }
 120           else
 121             {
 122               /* Matching precedence levels.
 123                  For left association, keep only the reduction.
 124                  For right association, keep only the shift.
 125                  For nonassociation, keep neither.  */
 126
 127               switch (sassoc[i])
 128                 {
 129                 case right_assoc:
 130                   log_resolution (state, lookaheadnum, i, _("shift"));
 131                   break;
 132
 133                 case left_assoc:
 134                   log_resolution (state, lookaheadnum, i, _("reduce"));
 135                   break;
 136
 137                 case non_assoc:
 138                   log_resolution (state, lookaheadnum, i, _("an error"));
 139                   break;
 140                 }
 141
 142               if (sassoc[i] != right_assoc)
 143                 {
 144                   *fp2 &= ~mask;        /* flush the shift for this token */
 145                   flush_shift (state, i);
 146                 }
 147               if (sassoc[i] != left_assoc)
 148                 {
 149                   *fp1 &= ~mask;        /* flush the reduce for this token */
 150                 }
 151               if (sassoc[i] == non_assoc)
 152                 {
 153                   /* Record an explicit error for this token.  */
 154                   *errtokens++ = i;
 155                 }
 156             }
 157         }
 158
 159       mask <<= 1;
 160       if (mask == 0)
 161         {
 162           mask = 1;
 163           fp2++;
 164           fp1++;
 165         }
 166     }
 167   errp->nerrs = errtokens - errp->errs;
 168   if (errp->nerrs)
 169     {
 170       /* Some tokens have been explicitly made errors.  Allocate
 171          a permanent errs structure for this state, to record them.  */
 172       i = (char *) errtokens - (char *) errp;
 173       err_table[state] = (errs *) xcalloc ((unsigned int) i, 1);
 174       bcopy (errp, err_table[state], i);
 175     }
 176   else
 177     err_table[state] = 0;
 178   free (errp);
 179 }
 180
 181
 182 static void
 183 set_conflicts (int state)
 184 {
 185   int i;
 186   int k;
 187   shifts *shiftp;
 188   unsigned *fp2;
 189   unsigned *fp3;
 190   unsigned *fp4;
 191   unsigned *fp1;
 192   int symbol;
 193
 194   if (consistent[state])
 195     return;
 196
 197   for (i = 0; i < tokensetsize; i++)
 198     lookaheadset[i] = 0;
 199
 200   shiftp = state_table[state].shift_table;
 201   if (shiftp)
 202     {
 203       k = shiftp->nshifts;
 204       for (i = 0; i < k; i++)
 205         {
 206           symbol = state_table[shiftp->shifts[i]].accessing_symbol;
 207           if (ISVAR (symbol))
 208             break;
 209           SETBIT (lookaheadset, symbol);
 210         }
 211     }
 212
 213   k = lookaheads[state + 1];
 214   fp4 = lookaheadset + tokensetsize;
 215
 216   /* Loop over all rules which require lookahead in this state.  First
 217      check for shift-reduce conflict, and try to resolve using
 218      precedence */
 219   for (i = lookaheads[state]; i < k; i++)
 220     if (rprec[LAruleno[i]])
 221       {
 222         fp1 = LA + i * tokensetsize;
 223         fp2 = fp1;
 224         fp3 = lookaheadset;
 225
 226         while (fp3 < fp4)
 227           {
 228             if (*fp2++ & *fp3++)
 229               {
 230                 resolve_sr_conflict (state, i);
 231                 break;
 232               }
 233           }
 234       }
 235
 236
 237   /* Loop over all rules which require lookahead in this state.  Check
 238      for conflicts not resolved above.  */
 239   for (i = lookaheads[state]; i < k; i++)
 240     {
 241       fp1 = LA + i * tokensetsize;
 242       fp2 = fp1;
 243       fp3 = lookaheadset;
 244
 245       while (fp3 < fp4)
 246         if (*fp2++ & *fp3++)
 247           conflicts[state] = 1;
 248
 249       fp2 = fp1;
 250       fp3 = lookaheadset;
 251
 252       while (fp3 < fp4)
 253         *fp3++ |= *fp2++;
 254     }
 255 }
 256
 257 void
 258 solve_conflicts (void)
 259 {
 260   int i;
 261
 262   conflicts = XCALLOC (char, nstates);
 263   shiftset = XCALLOC (unsigned, tokensetsize);
 264   lookaheadset = XCALLOC (unsigned, tokensetsize);
 265
 266   err_table = XCALLOC (errs *, nstates);
 267
 268   for (i = 0; i < nstates; i++)
 269     set_conflicts (i);
 270 }
 271
 272
 273 /*---------------------------------------------.
 274 | Count the number of shift/reduce conflicts.  |
 275 `---------------------------------------------*/
 276
 277 static int
 278 count_sr_conflicts (int state)
 279 {
 280   int i;
 281   int k;
 282   int mask;
 283   shifts *shiftp;
 284   unsigned *fp1;
 285   unsigned *fp2;
 286   unsigned *fp3;
 287   int symbol;
 288
 289   int src_count = 0;
 290
 291   shiftp = state_table[state].shift_table;
 292   if (!shiftp)
 293     return 0;
 294
 295   for (i = 0; i < tokensetsize; i++)
 296     {
 297       shiftset[i] = 0;
 298       lookaheadset[i] = 0;
 299     }
 300
 301   k = shiftp->nshifts;
 302   for (i = 0; i < k; i++)
 303     {
 304       if (!shiftp->shifts[i])
 305         continue;
 306       symbol = state_table[shiftp->shifts[i]].accessing_symbol;
 307       if (ISVAR (symbol))
 308         break;
 309       SETBIT (shiftset, symbol);
 310     }
 311
 312   k = lookaheads[state + 1];
 313   fp3 = lookaheadset + tokensetsize;
 314
 315   for (i = lookaheads[state]; i < k; i++)
 316     {
 317       fp1 = LA + i * tokensetsize;
 318       fp2 = lookaheadset;
 319
 320       while (fp2 < fp3)
 321         *fp2++ |= *fp1++;
 322     }
 323
 324   fp1 = shiftset;
 325   fp2 = lookaheadset;
 326
 327   while (fp2 < fp3)
 328     *fp2++ &= *fp1++;
 329
 330   mask = 1;
 331   fp2 = lookaheadset;
 332   for (i = 0; i < ntokens; i++)
 333     {
 334       if (mask & *fp2)
 335         src_count++;
 336
 337       mask <<= 1;
 338       if (mask == 0)
 339         {
 340           mask = 1;
 341           fp2++;
 342         }
 343     }
 344
 345   return src_count;
 346 }
 347
 348
 349 /*----------------------------------------------.
 350 | Count the number of reduce/reduce conflicts.  |
 351 `----------------------------------------------*/
 352
 353 static int
 354 count_rr_conflicts (int state)
 355 {
 356   int i;
 357   unsigned mask;
 358   unsigned *baseword;
 359
 360   int rrc_count = 0;
 361
 362   int m = lookaheads[state];
 363   int n = lookaheads[state + 1];
 364
 365   if (n - m < 2)
 366     return 0;
 367
 368   mask = 1;
 369   baseword = LA + m * tokensetsize;
 370   for (i = 0; i < ntokens; i++)
 371     {
 372       unsigned *wordp = baseword;
 373
 374       int count = 0;
 375       int j;
 376       for (j = m; j < n; j++)
 377         {
 378           if (mask & *wordp)
 379             count++;
 380
 381           wordp += tokensetsize;
 382         }
 383
 384       if (count >= 2)
 385         rrc_count++;
 386
 387       mask <<= 1;
 388       if (mask == 0)
 389         {
 390           mask = 1;
 391           baseword++;
 392         }
 393     }
 394
 395   return rrc_count;
 396 }
 397
 398 /*--------------------------------------------------------------.
 399 | Return a human readable string which reports shift/reduce and |
 400 | reduce/reduce conflict numbers (SRC_NUM, RRC_NUM).            |
 401 `--------------------------------------------------------------*/
 402
 403 static const char *
 404 conflict_report (int src_num, int rrc_num)
 405 {
 406   static char res[4096];
 407   char *cp = res;
 408
 409   if (src_num >= 1)
 410     {
 411       sprintf (cp, ngettext ("%d shift/reduce conflict",
 412                              "%d shift/reduce conflicts", src_num), src_num);
 413       cp += strlen (cp);
 414     }
 415
 416   if (src_num > 0 && rrc_num > 0)
 417     {
 418       sprintf (cp, " %s ", _("and"));
 419       cp += strlen (cp);
 420     }
 421
 422   if (rrc_num >= 1)
 423     {
 424       sprintf (cp, ngettext ("%d reduce/reduce conflict",
 425                              "%d reduce/reduce conflicts", rrc_num), rrc_num);
 426       cp += strlen (cp);
 427     }
 428
 429   *cp++ = '.';
 430   *cp++ = '\n';
 431   *cp++ = '\0';
 432
 433   return res;
 434 }
 435
 436
 437 /*-----------------------------------------------------------.
 438 | Output the detailed description of states with conflicts.  |
 439 `-----------------------------------------------------------*/
 440
 441 void
 442 conflicts_output (FILE *out)
 443 {
 444   int i;
 445   for (i = 0; i < nstates; i++)
 446     if (conflicts[i])
 447       {
 448         fprintf (out, _("State %d contains "), i);
 449         fputs (conflict_report (count_sr_conflicts (i),
 450                                 count_rr_conflicts (i)), out);
 451       }
 452 }
 453
 454
 455 /*------------------------------------------.
 456 | Reporting the total number of conflicts.  |
 457 `------------------------------------------*/
 458
 459 void
 460 conflicts_print (void)
 461 {
 462   int i;
 463
 464   int src_total = 0;
 465   int rrc_total = 0;
 466
 467   /* Conflicts by state.  */
 468   for (i = 0; i < nstates; i++)
 469     if (conflicts[i])
 470       {
 471         src_total += count_sr_conflicts (i);
 472         rrc_total += count_rr_conflicts (i);
 473       }
 474
 475   /* Report the total number of conflicts on STDERR.  */
 476   if (src_total || rrc_total)
 477     {
 478       if (yacc_flag)
 479         {
 480           /* If invoked with `--yacc', use the output format specified by
 481              POSIX.  */
 482           fprintf (stderr, _("conflicts: "));
 483           if (src_total > 0)
 484             fprintf (stderr, _(" %d shift/reduce"), src_total);
 485           if (src_total > 0 && rrc_total > 0)
 486             fprintf (stderr, ",");
 487           if (rrc_total > 0)
 488             fprintf (stderr, _(" %d reduce/reduce"), rrc_total);
 489           putc ('\n', stderr);
 490         }
 491       else
 492         {
 493           fprintf (stderr, _("%s contains "), infile);
 494           fputs (conflict_report (src_total, rrc_total), stderr);
 495         }
 496     }
 497
 498   if (expected_conflicts != -1
 499       && src_total != expected_conflicts)
 500     {
 501       complain_message_count++;
 502       fprintf (stderr, ngettext ("expected %d shift/reduce conflict",
 503                                  "expected %d shift/reduce conflicts",
 504                                  expected_conflicts),
 505                expected_conflicts);
 506     }
 507 }
 508
 509
 510 void
 511 print_reductions (FILE *out, int state)
 512 {
 513   int i;
 514   int j;
 515   int k;
 516   unsigned *fp1;
 517   unsigned *fp2;
 518   unsigned *fp3;
 519   unsigned *fp4;
 520   int rule;
 521   int symbol;
 522   unsigned mask;
 523   int m;
 524   int n;
 525   int default_LA;
 526   int default_rule = 0;
 527   int cmax;
 528   int count;
 529   shifts *shiftp;
 530   errs *errp;
 531   int nodefault = 0;
 532
 533   for (i = 0; i < tokensetsize; i++)
 534     shiftset[i] = 0;
 535
 536   shiftp = state_table[state].shift_table;
 537   if (shiftp)
 538     {
 539       k = shiftp->nshifts;
 540       for (i = 0; i < k; i++)
 541         {
 542           if (!shiftp->shifts[i])
 543             continue;
 544           symbol = state_table[shiftp->shifts[i]].accessing_symbol;
 545           if (ISVAR (symbol))
 546             break;
 547           /* if this state has a shift for the error token,
 548              don't use a default rule.  */
 549           if (symbol == error_token_number)
 550             nodefault = 1;
 551           SETBIT (shiftset, symbol);
 552         }
 553     }
 554
 555   errp = err_table[state];
 556   if (errp)
 557     {
 558       k = errp->nerrs;
 559       for (i = 0; i < k; i++)
 560         {
 561           if (!errp->errs[i])
 562             continue;
 563           symbol = errp->errs[i];
 564           SETBIT (shiftset, symbol);
 565         }
 566     }
 567
 568   m = lookaheads[state];
 569   n = lookaheads[state + 1];
 570
 571   if (n - m == 1 && !nodefault)
 572     {
 573       default_rule = LAruleno[m];
 574
 575       fp1 = LA + m * tokensetsize;
 576       fp2 = shiftset;
 577       fp3 = lookaheadset;
 578       fp4 = lookaheadset + tokensetsize;
 579
 580       while (fp3 < fp4)
 581         *fp3++ = *fp1++ & *fp2++;
 582
 583       mask = 1;
 584       fp3 = lookaheadset;
 585
 586       for (i = 0; i < ntokens; i++)
 587         {
 588           if (mask & *fp3)
 589             fprintf (out, _("    %-4s\t[reduce using rule %d (%s)]\n"),
 590                      tags[i], default_rule, tags[rlhs[default_rule]]);
 591
 592           mask <<= 1;
 593           if (mask == 0)
 594             {
 595               mask = 1;
 596               fp3++;
 597             }
 598         }
 599
 600       fprintf (out, _("    $default\treduce using rule %d (%s)\n\n"),
 601                default_rule, tags[rlhs[default_rule]]);
 602     }
 603   else if (n - m >= 1)
 604     {
 605       cmax = 0;
 606       default_LA = -1;
 607       fp4 = lookaheadset + tokensetsize;
 608
 609       if (!nodefault)
 610         for (i = m; i < n; i++)
 611           {
 612             fp1 = LA + i * tokensetsize;
 613             fp2 = shiftset;
 614             fp3 = lookaheadset;
 615
 616             while (fp3 < fp4)
 617               *fp3++ = *fp1++ & (~(*fp2++));
 618
 619             count = 0;
 620             mask = 1;
 621             fp3 = lookaheadset;
 622             for (j = 0; j < ntokens; j++)
 623               {
 624                 if (mask & *fp3)
 625                   count++;
 626
 627                 mask <<= 1;
 628                 if (mask == 0)
 629                   {
 630                     mask = 1;
 631                     fp3++;
 632                   }
 633               }
 634
 635             if (count > cmax)
 636               {
 637                 cmax = count;
 638                 default_LA = i;
 639                 default_rule = LAruleno[i];
 640               }
 641
 642             fp2 = shiftset;
 643             fp3 = lookaheadset;
 644
 645             while (fp3 < fp4)
 646               *fp2++ |= *fp3++;
 647           }
 648
 649       for (i = 0; i < tokensetsize; i++)
 650         shiftset[i] = 0;
 651
 652       if (shiftp)
 653         {
 654           k = shiftp->nshifts;
 655           for (i = 0; i < k; i++)
 656             {
 657               if (!shiftp->shifts[i])
 658                 continue;
 659               symbol = state_table[shiftp->shifts[i]].accessing_symbol;
 660               if (ISVAR (symbol))
 661                 break;
 662               SETBIT (shiftset, symbol);
 663             }
 664         }
 665
 666       mask = 1;
 667       fp1 = LA + m * tokensetsize;
 668       fp2 = shiftset;
 669       for (i = 0; i < ntokens; i++)
 670         {
 671           int defaulted = 0;
 672
 673           if (mask & *fp2)
 674             count = 1;
 675           else
 676             count = 0;
 677
 678           fp3 = fp1;
 679           for (j = m; j < n; j++)
 680             {
 681               if (mask & *fp3)
 682                 {
 683                   if (count == 0)
 684                     {
 685                       if (j != default_LA)
 686                         {
 687                           rule = LAruleno[j];
 688                           fprintf (out,
 689                                    _("    %-4s\treduce using rule %d (%s)\n"),
 690                                    tags[i], rule, tags[rlhs[rule]]);
 691                         }
 692                       else
 693                         defaulted = 1;
 694
 695                       count++;
 696                     }
 697                   else
 698                     {
 699                       if (defaulted)
 700                         {
 701                           rule = LAruleno[default_LA];
 702                           fprintf (out,
 703                                    _("    %-4s\treduce using rule %d (%s)\n"),
 704                                    tags[i], rule, tags[rlhs[rule]]);
 705                           defaulted = 0;
 706                         }
 707                       rule = LAruleno[j];
 708                       fprintf (out,
 709                                _("    %-4s\t[reduce using rule %d (%s)]\n"),
 710                                tags[i], rule, tags[rlhs[rule]]);
 711                     }
 712                 }
 713
 714               fp3 += tokensetsize;
 715             }
 716
 717           mask <<= 1;
 718           if (mask == 0)
 719             {
 720               mask = 1;
 721               /* We tried incrementing just fp1, and just fp2; both seem wrong.
 722                  It seems necessary to increment both in sync.  */
 723               fp1++;
 724               fp2++;
 725             }
 726         }
 727
 728       if (default_LA >= 0)
 729         fprintf (out, _("    $default\treduce using rule %d (%s)\n"),
 730                  default_rule, tags[rlhs[default_rule]]);
 731     }
 732 }
 733
 734
 735 void
 736 free_conflicts (void)
 737 {
 738   XFREE (conflicts);
 739   XFREE (shiftset);
 740   XFREE (lookaheadset);
 741 }