smatch_comparison.c

   1 /*
   2  * smatch/smatch_comparison.c
   3  *
   4  * Copyright (C) 2012 Oracle.
   5  *
   6  * Licensed under the Open Software License version 1.1
   7  *
   8  */
   9
  10 /*
  11  * The point here is to store the relationships between two variables.
  12  * Ie:  y > x.
  13  * To do that we create a state with the two variables in alphabetical order:
  14  * ->name = "x vs y" and the state would be "<".  On the false path the state
  15  * would be ">=".
  16  *
  17  * Part of the trick of it is that if x or y is modified then we need to reset
  18  * the state.  We need to keep a list of all the states which depend on x and
  19  * all the states which depend on y.  The link_id code handles this.
  20  *
  21  * Future work:  If we know that x is greater than y and y is greater than z
  22  * then we know that x is greater than z.
  23  */
  24
  25 #include "smatch.h"
  26 #include "smatch_extra.h"
  27 #include "smatch_slist.h"
  28
  29 static int compare_id;
  30 static int link_id;
  31
  32 struct compare_data {
  33         const char *var1;
  34         struct symbol *sym1;
  35         int comparison;
  36         const char *var2;
  37         struct symbol *sym2;
  38 };
  39 ALLOCATOR(compare_data, "compare data");
  40
  41 int var_sym_eq(const char *a, struct symbol *a_sym, const char *b, struct symbol *b_sym)
  42 {
  43         if (a_sym != b_sym)
  44                 return 0;
  45         if (strcmp(a, b) == 0)
  46                 return 1;
  47         return 0;
  48 }
  49
  50 static struct smatch_state *alloc_compare_state(
  51                 const char *var1, struct symbol *sym1,
  52                 int comparison,
  53                 const char *var2, struct symbol *sym2)
  54 {
  55         struct smatch_state *state;
  56         struct compare_data *data;
  57
  58         state = __alloc_smatch_state(0);
  59         state->name = alloc_sname(show_special(comparison));
  60         data = __alloc_compare_data(0);
  61         data->var1 = alloc_sname(var1);
  62         data->sym1 = sym1;
  63         data->comparison = comparison;
  64         data->var2 = alloc_sname(var2);
  65         data->sym2 = sym2;
  66         state->data = data;
  67         return state;
  68 }
  69
  70 static int state_to_comparison(struct smatch_state *state)
  71 {
  72         if (!state || !state->data)
  73                 return 0;
  74         return ((struct compare_data *)state->data)->comparison;
  75 }
  76
  77 /*
  78  * flip_op() reverses the op left and right.  So "x >= y" becomes "y <= x".
  79  */
  80 static int flip_op(int op)
  81 {
  82         switch (op) {
  83         case 0:
  84                 return 0;
  85         case '<':
  86                 return '>';
  87         case SPECIAL_UNSIGNED_LT:
  88                 return SPECIAL_UNSIGNED_GT;
  89         case SPECIAL_LTE:
  90                 return SPECIAL_GTE;
  91         case SPECIAL_UNSIGNED_LTE:
  92                 return SPECIAL_UNSIGNED_GTE;
  93         case SPECIAL_EQUAL:
  94                 return SPECIAL_EQUAL;
  95         case SPECIAL_NOTEQUAL:
  96                 return SPECIAL_NOTEQUAL;
  97         case SPECIAL_GTE:
  98                 return SPECIAL_LTE;
  99         case SPECIAL_UNSIGNED_GTE:
 100                 return SPECIAL_UNSIGNED_LTE;
 101         case '>':
 102                 return '<';
 103         case SPECIAL_UNSIGNED_GT:
 104                 return SPECIAL_UNSIGNED_LT;
 105         default:
 106                 sm_msg("internal smatch bug.  unhandled comparison %d", op);
 107                 return op;
 108         }
 109 }
 110
 111 static int falsify_op(int op)
 112 {
 113         switch (op) {
 114         case 0:
 115                 return 0;
 116         case '<':
 117                 return SPECIAL_GTE;
 118         case SPECIAL_UNSIGNED_LT:
 119                 return SPECIAL_UNSIGNED_GTE;
 120         case SPECIAL_LTE:
 121                 return '>';
 122         case SPECIAL_UNSIGNED_LTE:
 123                 return SPECIAL_UNSIGNED_GT;
 124         case SPECIAL_EQUAL:
 125                 return SPECIAL_NOTEQUAL;
 126         case SPECIAL_NOTEQUAL:
 127                 return SPECIAL_EQUAL;
 128         case SPECIAL_GTE:
 129                 return '<';
 130         case SPECIAL_UNSIGNED_GTE:
 131                 return SPECIAL_UNSIGNED_LT;
 132         case '>':
 133                 return SPECIAL_LTE;
 134         case SPECIAL_UNSIGNED_GT:
 135                 return SPECIAL_UNSIGNED_LTE;
 136         default:
 137                 sm_msg("internal smatch bug.  unhandled comparison %d", op);
 138                 return op;
 139         }
 140 }
 141
 142 static int rl_comparison(struct range_list *left_rl, struct range_list *right_rl)
 143 {
 144         sval_t left_min, left_max, right_min, right_max;
 145
 146         if (!left_rl || !right_rl)
 147                 return 0;
 148
 149         left_min = rl_min(left_rl);
 150         left_max = rl_max(left_rl);
 151         right_min = rl_min(right_rl);
 152         right_max = rl_max(right_rl);
 153
 154         if (left_min.value == left_max.value &&
 155             right_min.value == right_max.value &&
 156             left_min.value == right_min.value)
 157                 return SPECIAL_EQUAL;
 158
 159         if (sval_cmp(left_max, right_min) < 0)
 160                 return '<';
 161         if (sval_cmp(left_max, right_min) == 0)
 162                 return SPECIAL_LTE;
 163         if (sval_cmp(left_min, right_max) > 0)
 164                 return '>';
 165         if (sval_cmp(left_min, right_max) == 0)
 166                 return SPECIAL_GTE;
 167
 168         return 0;
 169 }
 170
 171 static struct range_list *get_orig_rl(struct symbol *sym)
 172 {
 173         struct smatch_state *state;
 174
 175         if (!sym || !sym->ident)
 176                 return NULL;
 177         state = get_orig_estate(sym->ident->name, sym);
 178         return estate_rl(state);
 179 }
 180
 181 static struct smatch_state *unmatched_comparison(struct sm_state *sm)
 182 {
 183         struct compare_data *data = sm->state->data;
 184         struct range_list *left_rl, *right_rl;
 185         int op;
 186
 187         if (!data)
 188                 return &undefined;
 189
 190         if (strstr(data->var1, " orig"))
 191                 left_rl = get_orig_rl(data->sym1);
 192         else if (!get_implied_rl_var_sym(data->var1, data->sym1, &left_rl))
 193                 return &undefined;
 194         if (strstr(data->var2, " orig"))
 195                 right_rl = get_orig_rl(data->sym2);
 196         else if (!get_implied_rl_var_sym(data->var2, data->sym2, &right_rl))
 197                 return &undefined;
 198
 199         op = rl_comparison(left_rl, right_rl);
 200         if (op)
 201                 return alloc_compare_state(data->var1, data->sym1, op, data->var2, data->sym2);
 202
 203         return &undefined;
 204 }
 205
 206 /* remove_unsigned_from_comparison() is obviously a hack. */
 207 static int remove_unsigned_from_comparison(int op)
 208 {
 209         switch (op) {
 210         case SPECIAL_UNSIGNED_LT:
 211                 return '<';
 212         case SPECIAL_UNSIGNED_LTE:
 213                 return SPECIAL_LTE;
 214         case SPECIAL_UNSIGNED_GTE:
 215                 return SPECIAL_GTE;
 216         case SPECIAL_UNSIGNED_GT:
 217                 return '>';
 218         default:
 219                 return op;
 220         }
 221 }
 222
 223 /*
 224  * This is for when you merge states "a < b" and "a == b", the result is that
 225  * we can say for sure, "a <= b" after the merge.
 226  */
 227 static int merge_comparisons(int one, int two)
 228 {
 229         int LT, EQ, GT;
 230
 231         one = remove_unsigned_from_comparison(one);
 232         two = remove_unsigned_from_comparison(two);
 233
 234         LT = EQ = GT = 0;
 235
 236         switch (one) {
 237         case '<':
 238                 LT = 1;
 239                 break;
 240         case SPECIAL_LTE:
 241                 LT = 1;
 242                 EQ = 1;
 243                 break;
 244         case SPECIAL_EQUAL:
 245                 EQ = 1;
 246                 break;
 247         case SPECIAL_GTE:
 248                 GT = 1;
 249                 EQ = 1;
 250                 break;
 251         case '>':
 252                 GT = 1;
 253         }
 254
 255         switch (two) {
 256         case '<':
 257                 LT = 1;
 258                 break;
 259         case SPECIAL_LTE:
 260                 LT = 1;
 261                 EQ = 1;
 262                 break;
 263         case SPECIAL_EQUAL:
 264                 EQ = 1;
 265                 break;
 266         case SPECIAL_GTE:
 267                 GT = 1;
 268                 EQ = 1;
 269                 break;
 270         case '>':
 271                 GT = 1;
 272         }
 273
 274         if (LT && EQ && GT)
 275                 return 0;
 276         if (LT && EQ)
 277                 return SPECIAL_LTE;
 278         if (LT && GT)
 279                 return SPECIAL_NOTEQUAL;
 280         if (LT)
 281                 return '<';
 282         if (EQ && GT)
 283                 return SPECIAL_GTE;
 284         if (GT)
 285                 return '>';
 286         return 0;
 287 }
 288
 289 /*
 290  * This is for if you have "a < b" and "b <= c".  Or in other words,
 291  * "a < b <= c".  You would call this like get_combined_comparison('<', '<=').
 292  * The return comparison would be '<'.
 293  *
 294  * This function is different from merge_comparisons(), for example:
 295  * merge_comparison('<', '==') returns '<='
 296  * get_combined_comparison('<', '==') returns '<'
 297  */
 298 static int combine_comparisons(int left_compare, int right_compare)
 299 {
 300         int LT, EQ, GT;
 301
 302         left_compare = remove_unsigned_from_comparison(left_compare);
 303         right_compare = remove_unsigned_from_comparison(right_compare);
 304
 305         LT = EQ = GT = 0;
 306
 307         switch (left_compare) {
 308         case '<':
 309                 LT++;
 310                 break;
 311         case SPECIAL_LTE:
 312                 LT++;
 313                 EQ++;
 314                 break;
 315         case SPECIAL_EQUAL:
 316                 return right_compare;
 317         case SPECIAL_GTE:
 318                 GT++;
 319                 EQ++;
 320                 break;
 321         case '>':
 322                 GT++;
 323         }
 324
 325         switch (right_compare) {
 326         case '<':
 327                 LT++;
 328                 break;
 329         case SPECIAL_LTE:
 330                 LT++;
 331                 EQ++;
 332                 break;
 333         case SPECIAL_EQUAL:
 334                 return left_compare;
 335         case SPECIAL_GTE:
 336                 GT++;
 337                 EQ++;
 338                 break;
 339         case '>':
 340                 GT++;
 341         }
 342
 343         if (LT == 2) {
 344                 if (EQ == 2)
 345                         return SPECIAL_LTE;
 346                 return '<';
 347         }
 348
 349         if (GT == 2) {
 350                 if (EQ == 2)
 351                         return SPECIAL_GTE;
 352                 return '>';
 353         }
 354         return 0;
 355 }
 356
 357 static struct smatch_state *merge_compare_states(struct smatch_state *s1, struct smatch_state *s2)
 358 {
 359         struct compare_data *data = s1->data;
 360         int op;
 361
 362         op = merge_comparisons(state_to_comparison(s1), state_to_comparison(s2));
 363         if (op)
 364                 return alloc_compare_state(data->var1, data->sym1, op, data->var2, data->sym2);
 365         return &undefined;
 366 }
 367
 368 struct smatch_state *alloc_link_state(struct string_list *links)
 369 {
 370         struct smatch_state *state;
 371         static char buf[256];
 372         char *tmp;
 373         int i;
 374
 375         state = __alloc_smatch_state(0);
 376
 377         i = 0;
 378         FOR_EACH_PTR(links, tmp) {
 379                 if (!i++)
 380                         snprintf(buf, sizeof(buf), "%s", tmp);
 381                 else
 382                         snprintf(buf, sizeof(buf), "%s, %s", buf, tmp);
 383         } END_FOR_EACH_PTR(tmp);
 384
 385         state->name = alloc_sname(buf);
 386         state->data = links;
 387         return state;
 388 }
 389
 390 static void save_start_states(struct statement *stmt)
 391 {
 392         struct symbol *param;
 393         char orig[64];
 394         char state_name[128];
 395         struct smatch_state *state;
 396         struct string_list *links;
 397         char *link;
 398
 399         FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
 400                 if (!param->ident)
 401                         continue;
 402                 snprintf(orig, sizeof(orig), "%s orig", param->ident->name);
 403                 snprintf(state_name, sizeof(state_name), "%s vs %s", param->ident->name, orig);
 404                 state = alloc_compare_state(param->ident->name, param, SPECIAL_EQUAL, alloc_sname(orig), param);
 405                 set_state(compare_id, state_name, NULL, state);
 406
 407                 link = alloc_sname(state_name);
 408                 links = NULL;
 409                 insert_string(&links, link);
 410                 state = alloc_link_state(links);
 411                 set_state(link_id, param->ident->name, param, state);
 412         } END_FOR_EACH_PTR(param);
 413 }
 414
 415 static struct smatch_state *merge_links(struct smatch_state *s1, struct smatch_state *s2)
 416 {
 417         struct smatch_state *ret;
 418         struct string_list *links;
 419
 420         links = combine_string_lists(s1->data, s2->data);
 421         ret = alloc_link_state(links);
 422         return ret;
 423 }
 424
 425 static void save_link_var_sym(const char *var, struct symbol *sym, const char *link)
 426 {
 427         struct smatch_state *old_state, *new_state;
 428         struct string_list *links;
 429         char *new;
 430
 431         old_state = get_state(link_id, var, sym);
 432         if (old_state)
 433                 links = clone_str_list(old_state->data);
 434         else
 435                 links = NULL;
 436
 437         new = alloc_sname(link);
 438         insert_string(&links, new);
 439
 440         new_state = alloc_link_state(links);
 441         set_state(link_id, var, sym, new_state);
 442 }
 443
 444 static void match_inc(struct sm_state *sm)
 445 {
 446         struct string_list *links;
 447         struct smatch_state *state;
 448         char *tmp;
 449
 450         links = sm->state->data;
 451
 452         FOR_EACH_PTR(links, tmp) {
 453                 state = get_state(compare_id, tmp, NULL);
 454
 455                 switch (state_to_comparison(state)) {
 456                 case SPECIAL_EQUAL:
 457                 case SPECIAL_GTE:
 458                 case SPECIAL_UNSIGNED_GTE:
 459                 case '>':
 460                 case SPECIAL_UNSIGNED_GT: {
 461                         struct compare_data *data = state->data;
 462                         struct smatch_state *new;
 463
 464                         new = alloc_compare_state(data->var1, data->sym1, '>', data->var2, data->sym2);
 465                         set_state(compare_id, tmp, NULL, new);
 466                         break;
 467                         }
 468                 default:
 469                         set_state(compare_id, tmp, NULL, &undefined);
 470                 }
 471         } END_FOR_EACH_PTR(tmp);
 472 }
 473
 474 static void match_dec(struct sm_state *sm)
 475 {
 476         struct string_list *links;
 477         struct smatch_state *state;
 478         char *tmp;
 479
 480         links = sm->state->data;
 481
 482         FOR_EACH_PTR(links, tmp) {
 483                 state = get_state(compare_id, tmp, NULL);
 484
 485                 switch (state_to_comparison(state)) {
 486                 case SPECIAL_EQUAL:
 487                 case SPECIAL_LTE:
 488                 case SPECIAL_UNSIGNED_LTE:
 489                 case '<':
 490                 case SPECIAL_UNSIGNED_LT: {
 491                         struct compare_data *data = state->data;
 492                         struct smatch_state *new;
 493
 494                         new = alloc_compare_state(data->var1, data->sym1, '<', data->var2, data->sym2);
 495                         set_state(compare_id, tmp, NULL, new);
 496                         break;
 497                         }
 498                 default:
 499                         set_state(compare_id, tmp, NULL, &undefined);
 500                 }
 501         } END_FOR_EACH_PTR(tmp);
 502 }
 503
 504 static int match_inc_dec(struct sm_state *sm, struct expression *mod_expr)
 505 {
 506         if (!mod_expr)
 507                 return 0;
 508         if (mod_expr->type != EXPR_PREOP && mod_expr->type != EXPR_POSTOP)
 509                 return 0;
 510
 511         if (mod_expr->op == SPECIAL_INCREMENT) {
 512                 match_inc(sm);
 513                 return 1;
 514         }
 515         if (mod_expr->op == SPECIAL_DECREMENT) {
 516                 match_dec(sm);
 517                 return 1;
 518         }
 519         return 0;
 520 }
 521
 522 static void match_modify(struct sm_state *sm, struct expression *mod_expr)
 523 {
 524         struct string_list *links;
 525         char *tmp;
 526
 527         if (match_inc_dec(sm, mod_expr))
 528                 return;
 529
 530         links = sm->state->data;
 531
 532         FOR_EACH_PTR(links, tmp) {
 533                 set_state(compare_id, tmp, NULL, &undefined);
 534         } END_FOR_EACH_PTR(tmp);
 535         set_state(link_id, sm->name, sm->sym, &undefined);
 536 }
 537
 538 static char *chunk_to_var_sym(struct expression *expr, struct symbol **sym)
 539 {
 540         char *name, *left_name, *right_name;
 541         struct symbol *tmp;
 542         char buf[128];
 543
 544         expr = strip_expr(expr);
 545         if (sym)
 546                 *sym = NULL;
 547
 548         name = expr_to_var_sym(expr, &tmp);
 549         if (name && tmp) {
 550                 if (sym)
 551                         *sym = tmp;
 552                 return name;
 553         }
 554         if (name)
 555                 free_string(name);
 556
 557         if (expr->type != EXPR_BINOP)
 558                 return NULL;
 559         if (expr->op != '-' && expr->op != '+')
 560                 return NULL;
 561
 562         left_name = expr_to_var(expr->left);
 563         if (!left_name)
 564                 return NULL;
 565         right_name = expr_to_var(expr->right);
 566         if (!right_name) {
 567                 free_string(left_name);
 568                 return NULL;
 569         }
 570         snprintf(buf, sizeof(buf), "%s %s %s", left_name, show_special(expr->op), right_name);
 571         free_string(left_name);
 572         free_string(right_name);
 573         return alloc_string(buf);
 574 }
 575
 576 static char *chunk_to_var(struct expression *expr)
 577 {
 578         return chunk_to_var_sym(expr, NULL);
 579 }
 580
 581 static void save_link(struct expression *expr, char *link)
 582 {
 583         char *var;
 584         struct symbol *sym;
 585
 586         expr = strip_expr(expr);
 587         if (expr->type == EXPR_BINOP) {
 588                 char *chunk;
 589
 590                 chunk = chunk_to_var(expr);
 591                 if (!chunk)
 592                         return;
 593
 594                 save_link(expr->left, link);
 595                 save_link(expr->right, link);
 596                 save_link_var_sym(chunk, NULL, link);
 597                 return;
 598         }
 599
 600         var = expr_to_var_sym(expr, &sym);
 601         if (!var || !sym)
 602                 goto done;
 603
 604         save_link_var_sym(var, sym, link);
 605 done:
 606         free_string(var);
 607 }
 608
 609
 610
 611 static void update_tf_links(struct state_list *pre_slist,
 612                             const char *left_var, struct symbol *left_sym,
 613                             int left_comparison,
 614                             const char *mid_var, struct symbol *mid_sym,
 615                             struct string_list *links)
 616 {
 617         struct smatch_state *state;
 618         struct smatch_state *true_state, *false_state;
 619         struct compare_data *data;
 620         const char *right_var;
 621         struct symbol *right_sym;
 622         int right_comparison;
 623         int true_comparison;
 624         int false_comparison;
 625         char *tmp;
 626         char state_name[256];
 627
 628         FOR_EACH_PTR(links, tmp) {
 629                 state = get_state_slist(pre_slist, compare_id, tmp, NULL);
 630                 if (!state || !state->data)
 631                         continue;
 632                 data = state->data;
 633                 right_comparison = data->comparison;
 634                 right_var = data->var2;
 635                 right_sym = data->sym2;
 636                 if (var_sym_eq(mid_var, mid_sym, right_var, right_sym)) {
 637                         right_var = data->var1;
 638                         right_sym = data->sym1;
 639                         right_comparison = flip_op(right_comparison);
 640                 }
 641                 true_comparison = combine_comparisons(left_comparison, right_comparison);
 642                 false_comparison = combine_comparisons(falsify_op(left_comparison), right_comparison);
 643
 644                 if (strcmp(left_var, right_var) > 0) {
 645                         struct symbol *tmp_sym = left_sym;
 646                         const char *tmp_var = left_var;
 647
 648                         left_var = right_var;
 649                         left_sym = right_sym;
 650                         right_var = tmp_var;
 651                         right_sym = tmp_sym;
 652                         true_comparison = flip_op(true_comparison);
 653                         false_comparison = flip_op(false_comparison);
 654                 }
 655
 656                 if (!true_comparison && !false_comparison)
 657                         continue;
 658
 659                 if (true_comparison)
 660                         true_state = alloc_compare_state(left_var, left_sym, true_comparison, right_var, right_sym);
 661                 else
 662                         true_state = NULL;
 663                 if (false_comparison)
 664                         false_state = alloc_compare_state(left_var, left_sym, false_comparison, right_var, right_sym);
 665                 else
 666                         false_state = NULL;
 667
 668                 snprintf(state_name, sizeof(state_name), "%s vs %s", left_var, right_var);
 669                 set_true_false_states(compare_id, state_name, NULL, true_state, false_state);
 670                 save_link_var_sym(left_var, left_sym, state_name);
 671                 save_link_var_sym(right_var, right_sym, state_name);
 672         } END_FOR_EACH_PTR(tmp);
 673 }
 674
 675 static void update_tf_data(struct state_list *pre_slist, struct compare_data *tdata)
 676 {
 677         struct smatch_state *state;
 678
 679         state = get_state_slist(pre_slist, link_id, tdata->var2, tdata->sym2);
 680         if (state)
 681                 update_tf_links(pre_slist, tdata->var1, tdata->sym1, tdata->comparison, tdata->var2, tdata->sym2, state->data);
 682
 683         state = get_state_slist(pre_slist, link_id, tdata->var1, tdata->sym1);
 684         if (state)
 685                 update_tf_links(pre_slist, tdata->var2, tdata->sym2, flip_op(tdata->comparison), tdata->var1, tdata->sym1, state->data);
 686 }
 687
 688 static void match_compare(struct expression *expr)
 689 {
 690         char *left = NULL;
 691         char *right = NULL;
 692         struct symbol *left_sym, *right_sym;
 693         int op, false_op;
 694         struct smatch_state *true_state, *false_state;
 695         char state_name[256];
 696         struct state_list *pre_slist;
 697
 698         if (expr->type != EXPR_COMPARE)
 699                 return;
 700         left = chunk_to_var_sym(expr->left, &left_sym);
 701         if (!left)
 702                 goto free;
 703         right = chunk_to_var_sym(expr->right, &right_sym);
 704         if (!right)
 705                 goto free;
 706
 707         if (strcmp(left, right) > 0) {
 708                 struct symbol *tmp_sym = left_sym;
 709                 char *tmp_name = left;
 710
 711                 left = right;
 712                 left_sym = right_sym;
 713                 right = tmp_name;
 714                 right_sym = tmp_sym;
 715                 op = flip_op(expr->op);
 716         } else {
 717                 op = expr->op;
 718         }
 719         false_op = falsify_op(op);
 720         snprintf(state_name, sizeof(state_name), "%s vs %s", left, right);
 721         true_state = alloc_compare_state(left, left_sym, op, right, right_sym);
 722         false_state = alloc_compare_state(left, left_sym, false_op, right, right_sym);
 723
 724         pre_slist = clone_slist(__get_cur_slist());
 725         update_tf_data(pre_slist, true_state->data);
 726         free_slist(&pre_slist);
 727
 728         set_true_false_states(compare_id, state_name, NULL, true_state, false_state);
 729         save_link(expr->left, state_name);
 730         save_link(expr->right, state_name);
 731 free:
 732         free_string(left);
 733         free_string(right);
 734 }
 735
 736 static void add_comparison_var_sym(const char *left_name, struct symbol *left_sym, int comparison, const char *right_name, struct symbol *right_sym)
 737 {
 738         struct smatch_state *state;
 739         char state_name[256];
 740
 741         if (strcmp(left_name, right_name) > 0) {
 742                 struct symbol *tmp_sym = left_sym;
 743                 const char *tmp_name = left_name;
 744
 745                 left_name = right_name;
 746                 left_sym = right_sym;
 747                 right_name = tmp_name;
 748                 right_sym = tmp_sym;
 749                 comparison = flip_op(comparison);
 750         }
 751         snprintf(state_name, sizeof(state_name), "%s vs %s", left_name, right_name);
 752         state = alloc_compare_state(left_name, left_sym, comparison, right_name, right_sym);
 753
 754         set_state(compare_id, state_name, NULL, state);
 755         save_link_var_sym(left_name, left_sym, state_name);
 756         save_link_var_sym(right_name, right_sym, state_name);
 757 }
 758
 759 static void add_comparison(struct expression *left, int comparison, struct expression *right)
 760 {
 761         char *left_name = NULL;
 762         char *right_name = NULL;
 763         struct symbol *left_sym, *right_sym;
 764
 765         left_name = chunk_to_var_sym(left, &left_sym);
 766         if (!left_name)
 767                 goto free;
 768         right_name = chunk_to_var_sym(right, &right_sym);
 769         if (!right_name)
 770                 goto free;
 771
 772         add_comparison_var_sym(left_name, left_sym, comparison, right_name, right_sym);
 773
 774 free:
 775         free_string(left_name);
 776         free_string(right_name);
 777 }
 778
 779 static void match_assign_add(struct expression *expr)
 780 {
 781         struct expression *right;
 782         struct expression *r_left, *r_right;
 783         sval_t left_tmp, right_tmp;
 784
 785         right = strip_expr(expr->right);
 786         r_left = strip_expr(right->left);
 787         r_right = strip_expr(right->right);
 788
 789         get_absolute_min(r_left, &left_tmp);
 790         get_absolute_min(r_right, &right_tmp);
 791
 792         if (left_tmp.value > 0)
 793                 add_comparison(expr->left, '>', r_right);
 794         else if (left_tmp.value == 0)
 795                 add_comparison(expr->left, SPECIAL_GTE, r_right);
 796
 797         if (right_tmp.value > 0)
 798                 add_comparison(expr->left, '>', r_left);
 799         else if (right_tmp.value == 0)
 800                 add_comparison(expr->left, SPECIAL_GTE, r_left);
 801 }
 802
 803 static void match_assign_sub(struct expression *expr)
 804 {
 805         struct expression *right;
 806         struct expression *r_left, *r_right;
 807         int comparison;
 808         sval_t min;
 809
 810         right = strip_expr(expr->right);
 811         r_left = strip_expr(right->left);
 812         r_right = strip_expr(right->right);
 813
 814         if (get_absolute_min(r_right, &min) && sval_is_negative(min))
 815                 return;
 816
 817         comparison = get_comparison(r_left, r_right);
 818
 819         switch (comparison) {
 820         case '>':
 821         case SPECIAL_GTE:
 822                 if (implied_not_equal(r_right, 0))
 823                         add_comparison(expr->left, '>', r_left);
 824                 else
 825                         add_comparison(expr->left, SPECIAL_GTE, r_left);
 826                 return;
 827         }
 828 }
 829
 830 static void match_assign_divide(struct expression *expr)
 831 {
 832         struct expression *right;
 833         struct expression *r_left, *r_right;
 834         sval_t min;
 835
 836         right = strip_expr(expr->right);
 837         r_left = strip_expr(right->left);
 838         r_right = strip_expr(right->right);
 839         if (!get_implied_min(r_right, &min) || min.value <= 1)
 840                 return;
 841
 842         add_comparison(expr->left, '<', r_left);
 843 }
 844
 845 static void match_binop_assign(struct expression *expr)
 846 {
 847         struct expression *right;
 848
 849         right = strip_expr(expr->right);
 850         if (right->op == '+')
 851                 match_assign_add(expr);
 852         if (right->op == '-')
 853                 match_assign_sub(expr);
 854         if (right->op == '/')
 855                 match_assign_divide(expr);
 856 }
 857
 858 static void copy_comparisons(struct expression *left, struct expression *right)
 859 {
 860         struct string_list *links;
 861         struct smatch_state *state;
 862         struct compare_data *data;
 863         struct symbol *left_sym, *right_sym;
 864         char *left_var = NULL;
 865         char *right_var = NULL;
 866         const char *var;
 867         struct symbol *sym;
 868         int comparison;
 869         char *tmp;
 870
 871         left_var = chunk_to_var_sym(left, &left_sym);
 872         if (!left_var)
 873                 goto done;
 874         right_var = chunk_to_var_sym(right, &right_sym);
 875         if (!right_var)
 876                 goto done;
 877
 878         state = get_state(link_id, right_var, right_sym);
 879         if (!state)
 880                 return;
 881         links = state->data;
 882
 883         FOR_EACH_PTR(links, tmp) {
 884                 state = get_state(compare_id, tmp, NULL);
 885                 if (!state || !state->data)
 886                         continue;
 887                 data = state->data;
 888                 comparison = data->comparison;
 889                 var = data->var2;
 890                 sym = data->sym2;
 891                 if (var_sym_eq(var, sym, right_var, right_sym)) {
 892                         var = data->var1;
 893                         sym = data->sym1;
 894                         comparison = flip_op(comparison);
 895                 }
 896                 add_comparison_var_sym(left_var, left_sym, comparison, var, sym);
 897         } END_FOR_EACH_PTR(tmp);
 898
 899 done:
 900         free_string(right_var);
 901 }
 902
 903 static void match_assign(struct expression *expr)
 904 {
 905         struct expression *right;
 906
 907         if (expr->op != '=')
 908                 return;
 909
 910         copy_comparisons(expr->left, expr->right);
 911         add_comparison(expr->left, SPECIAL_EQUAL, expr->right);
 912
 913         right = strip_expr(expr->right);
 914         if (right->type == EXPR_BINOP)
 915                 match_binop_assign(expr);
 916 }
 917
 918 static int get_comparison_strings(char *one, char *two)
 919 {
 920         char buf[256];
 921         struct smatch_state *state;
 922         int invert = 0;
 923         int ret = 0;
 924
 925         if (strcmp(one, two) > 0) {
 926                 char *tmp = one;
 927
 928                 one = two;
 929                 two = tmp;
 930                 invert = 1;
 931         }
 932
 933         snprintf(buf, sizeof(buf), "%s vs %s", one, two);
 934         state = get_state(compare_id, buf, NULL);
 935         if (state)
 936                 ret = state_to_comparison(state);
 937
 938         if (invert)
 939                 ret = flip_op(ret);
 940
 941         return ret;
 942 }
 943
 944 int get_comparison(struct expression *a, struct expression *b)
 945 {
 946         char *one = NULL;
 947         char *two = NULL;
 948         int ret = 0;
 949
 950         one = chunk_to_var(a);
 951         if (!one)
 952                 goto free;
 953         two = chunk_to_var(b);
 954         if (!two)
 955                 goto free;
 956
 957         ret = get_comparison_strings(one, two);
 958 free:
 959         free_string(one);
 960         free_string(two);
 961         return ret;
 962 }
 963
 964 void __add_comparison_info(struct expression *expr, struct expression *call, const char *range)
 965 {
 966         struct expression *arg;
 967         int comparison;
 968         const char *c = range;
 969
 970         if (!str_to_comparison_arg(c, call, &comparison, &arg))
 971                 return;
 972         add_comparison(expr, comparison, arg);
 973 }
 974
 975 static char *range_comparison_to_param_helper(struct expression *expr, char starts_with)
 976 {
 977         struct symbol *param;
 978         char *var = NULL;
 979         char buf[256];
 980         char *ret_str = NULL;
 981         int compare;
 982         int i;
 983
 984         var = chunk_to_var(expr);
 985         if (!var)
 986                 goto free;
 987
 988         i = -1;
 989         FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
 990                 i++;
 991                 if (!param->ident)
 992                         continue;
 993                 snprintf(buf, sizeof(buf), "%s orig", param->ident->name);
 994                 compare = get_comparison_strings(var, buf);
 995                 if (!compare)
 996                         continue;
 997                 if (show_special(compare)[0] != starts_with)
 998                         continue;
 999                 snprintf(buf, sizeof(buf), "[%sp%d]", show_special(compare), i);
1000                 ret_str = alloc_sname(buf);
1001                 break;
1002         } END_FOR_EACH_PTR(param);
1003
1004 free:
1005         free_string(var);
1006         return ret_str;
1007 }
1008
1009 char *expr_equal_to_param(struct expression *expr)
1010 {
1011         return range_comparison_to_param_helper(expr, '=');
1012 }
1013
1014 char *expr_lte_to_param(struct expression *expr)
1015 {
1016         return range_comparison_to_param_helper(expr, '<');
1017 }
1018
1019 static void free_data(struct symbol *sym)
1020 {
1021         if (__inline_fn)
1022                 return;
1023         clear_compare_data_alloc();
1024 }
1025
1026 void register_comparison(int id)
1027 {
1028         compare_id = id;
1029         add_hook(&match_compare, CONDITION_HOOK);
1030         add_hook(&match_assign, ASSIGNMENT_HOOK);
1031         add_hook(&save_start_states, AFTER_DEF_HOOK);
1032         add_unmatched_state_hook(compare_id, unmatched_comparison);
1033         add_merge_hook(compare_id, &merge_compare_states);
1034         add_hook(&free_data, AFTER_FUNC_HOOK);
1035 }
1036
1037 void register_comparison_links(int id)
1038 {
1039         link_id = id;
1040         add_merge_hook(link_id, &merge_links);
1041         add_modification_hook(link_id, &match_modify);
1042 }