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, 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 save_link(struct expression *expr, char *link)
 445 {
 446         char *var;
 447         struct symbol *sym;
 448
 449         var = expr_to_var_sym(expr, &sym);
 450         if (!var || !sym)
 451                 goto done;
 452
 453         save_link_var_sym(var, sym, link);
 454 done:
 455         free_string(var);
 456 }
 457
 458 static void match_inc(struct sm_state *sm)
 459 {
 460         struct string_list *links;
 461         struct smatch_state *state;
 462         char *tmp;
 463
 464         links = sm->state->data;
 465
 466         FOR_EACH_PTR(links, tmp) {
 467                 state = get_state(compare_id, tmp, NULL);
 468
 469                 switch (state_to_comparison(state)) {
 470                 case SPECIAL_EQUAL:
 471                 case SPECIAL_GTE:
 472                 case SPECIAL_UNSIGNED_GTE:
 473                 case '>':
 474                 case SPECIAL_UNSIGNED_GT: {
 475                         struct compare_data *data = state->data;
 476                         struct smatch_state *new;
 477
 478                         new = alloc_compare_state(data->var1, data->sym1, '>', data->var2, data->sym2);
 479                         set_state(compare_id, tmp, NULL, new);
 480                         break;
 481                         }
 482                 default:
 483                         set_state(compare_id, tmp, NULL, &undefined);
 484                 }
 485         } END_FOR_EACH_PTR(tmp);
 486 }
 487
 488 static void match_dec(struct sm_state *sm)
 489 {
 490         struct string_list *links;
 491         struct smatch_state *state;
 492         char *tmp;
 493
 494         links = sm->state->data;
 495
 496         FOR_EACH_PTR(links, tmp) {
 497                 state = get_state(compare_id, tmp, NULL);
 498
 499                 switch (state_to_comparison(state)) {
 500                 case SPECIAL_EQUAL:
 501                 case SPECIAL_LTE:
 502                 case SPECIAL_UNSIGNED_LTE:
 503                 case '<':
 504                 case SPECIAL_UNSIGNED_LT: {
 505                         struct compare_data *data = state->data;
 506                         struct smatch_state *new;
 507
 508                         new = alloc_compare_state(data->var1, data->sym1, '<', data->var2, data->sym2);
 509                         set_state(compare_id, tmp, NULL, new);
 510                         break;
 511                         }
 512                 default:
 513                         set_state(compare_id, tmp, NULL, &undefined);
 514                 }
 515         } END_FOR_EACH_PTR(tmp);
 516 }
 517
 518 static int match_inc_dec(struct sm_state *sm, struct expression *mod_expr)
 519 {
 520         if (!mod_expr)
 521                 return 0;
 522         if (mod_expr->type != EXPR_PREOP && mod_expr->type != EXPR_POSTOP)
 523                 return 0;
 524
 525         if (mod_expr->op == SPECIAL_INCREMENT) {
 526                 match_inc(sm);
 527                 return 1;
 528         }
 529         if (mod_expr->op == SPECIAL_DECREMENT) {
 530                 match_dec(sm);
 531                 return 1;
 532         }
 533         return 0;
 534 }
 535
 536 static void match_modify(struct sm_state *sm, struct expression *mod_expr)
 537 {
 538         struct string_list *links;
 539         char *tmp;
 540
 541         if (match_inc_dec(sm, mod_expr))
 542                 return;
 543
 544         links = sm->state->data;
 545
 546         FOR_EACH_PTR(links, tmp) {
 547                 set_state(compare_id, tmp, NULL, &undefined);
 548         } END_FOR_EACH_PTR(tmp);
 549         set_state(link_id, sm->name, sm->sym, &undefined);
 550 }
 551
 552 static void update_tf_links(const char *left_var, struct symbol *left_sym,
 553                             int left_comparison,
 554                             const char *mid_var, struct symbol *mid_sym,
 555                             struct string_list *links)
 556 {
 557         struct smatch_state *state;
 558         struct smatch_state *true_state, *false_state;
 559         struct compare_data *data;
 560         const char *right_var;
 561         struct symbol *right_sym;
 562         int right_comparison;
 563         int true_comparison;
 564         int false_comparison;
 565         char *tmp;
 566         char state_name[256];
 567
 568         FOR_EACH_PTR(links, tmp) {
 569                 state = get_state(compare_id, tmp, NULL);
 570                 if (!state || !state->data)
 571                         continue;
 572                 data = state->data;
 573                 right_comparison = data->comparison;
 574                 right_var = data->var2;
 575                 right_sym = data->sym2;
 576                 if (var_sym_eq(mid_var, mid_sym, right_var, right_sym)) {
 577                         right_var = data->var1;
 578                         right_sym = data->sym1;
 579                         right_comparison = flip_op(right_comparison);
 580                 }
 581                 true_comparison = combine_comparisons(left_comparison, right_comparison);
 582                 false_comparison = combine_comparisons(falsify_op(left_comparison), right_comparison);
 583
 584                 if (strcmp(left_var, right_var) > 0) {
 585                         struct symbol *tmp_sym = left_sym;
 586                         const char *tmp_var = left_var;
 587
 588                         left_var = right_var;
 589                         left_sym = right_sym;
 590                         right_var = tmp_var;
 591                         right_sym = tmp_sym;
 592                         true_comparison = flip_op(true_comparison);
 593                         false_comparison = flip_op(false_comparison);
 594                 }
 595
 596                 if (!true_comparison && !false_comparison)
 597                         continue;
 598
 599                 if (true_comparison)
 600                         true_state = alloc_compare_state(left_var, left_sym, true_comparison, right_var, right_sym);
 601                 else
 602                         true_state = NULL;
 603                 if (false_comparison)
 604                         false_state = alloc_compare_state(left_var, left_sym, false_comparison, right_var, right_sym);
 605                 else
 606                         false_state = NULL;
 607
 608                 snprintf(state_name, sizeof(state_name), "%s vs %s", left_var, right_var);
 609                 set_true_false_states(compare_id, state_name, NULL, true_state, false_state);
 610                 save_link_var_sym(left_var, left_sym, state_name);
 611                 save_link_var_sym(right_var, right_sym, state_name);
 612         } END_FOR_EACH_PTR(tmp);
 613 }
 614
 615 static void update_tf_data(struct compare_data *tdata)
 616 {
 617         struct smatch_state *state;
 618
 619         state = get_state(link_id, tdata->var2, tdata->sym2);
 620         if (state)
 621                 update_tf_links(tdata->var1, tdata->sym1, tdata->comparison, tdata->var2, tdata->sym2, state->data);
 622
 623         state = get_state(link_id, tdata->var1, tdata->sym1);
 624         if (state)
 625                 update_tf_links(tdata->var2, tdata->sym2, flip_op(tdata->comparison), tdata->var1, tdata->sym1, state->data);
 626 }
 627
 628 static void match_compare(struct expression *expr)
 629 {
 630         char *left = NULL;
 631         char *right = NULL;
 632         struct symbol *left_sym, *right_sym;
 633         int op, false_op;
 634         struct smatch_state *true_state, *false_state;
 635         char state_name[256];
 636
 637         if (expr->type != EXPR_COMPARE)
 638                 return;
 639         left = expr_to_var_sym(expr->left, &left_sym);
 640         if (!left || !left_sym)
 641                 goto free;
 642         right = expr_to_var_sym(expr->right, &right_sym);
 643         if (!right || !right_sym)
 644                 goto free;
 645
 646         if (strcmp(left, right) > 0) {
 647                 struct symbol *tmp_sym = left_sym;
 648                 char *tmp_name = left;
 649
 650                 left = right;
 651                 left_sym = right_sym;
 652                 right = tmp_name;
 653                 right_sym = tmp_sym;
 654                 op = flip_op(expr->op);
 655         } else {
 656                 op = expr->op;
 657         }
 658         false_op = falsify_op(op);
 659         snprintf(state_name, sizeof(state_name), "%s vs %s", left, right);
 660         true_state = alloc_compare_state(left, left_sym, op, right, right_sym);
 661         false_state = alloc_compare_state(left, left_sym, false_op, right, right_sym);
 662
 663         update_tf_data(true_state->data);
 664
 665         set_true_false_states(compare_id, state_name, NULL, true_state, false_state);
 666         save_link(expr->left, state_name);
 667         save_link(expr->right, state_name);
 668 free:
 669         free_string(left);
 670         free_string(right);
 671 }
 672
 673 static void add_comparison_var_sym(const char *left_name, struct symbol *left_sym, int comparison, const char *right_name, struct symbol *right_sym)
 674 {
 675         struct smatch_state *state;
 676         char state_name[256];
 677
 678         if (strcmp(left_name, right_name) > 0) {
 679                 struct symbol *tmp_sym = left_sym;
 680                 const char *tmp_name = left_name;
 681
 682                 left_name = right_name;
 683                 left_sym = right_sym;
 684                 right_name = tmp_name;
 685                 right_sym = tmp_sym;
 686                 comparison = flip_op(comparison);
 687         }
 688         snprintf(state_name, sizeof(state_name), "%s vs %s", left_name, right_name);
 689         state = alloc_compare_state(left_name, left_sym, comparison, right_name, right_sym);
 690
 691         set_state(compare_id, state_name, NULL, state);
 692         save_link_var_sym(left_name, left_sym, state_name);
 693         save_link_var_sym(right_name, right_sym, state_name);
 694 }
 695
 696 static void add_comparison(struct expression *left, int comparison, struct expression *right)
 697 {
 698         char *left_name = NULL;
 699         char *right_name = NULL;
 700         struct symbol *left_sym, *right_sym;
 701
 702         left_name = expr_to_var_sym(left, &left_sym);
 703         if (!left_name || !left_sym)
 704                 goto free;
 705         right_name = expr_to_var_sym(right, &right_sym);
 706         if (!right_name || !right_sym)
 707                 goto free;
 708
 709         add_comparison_var_sym(left_name, left_sym, comparison, right_name, right_sym);
 710
 711 free:
 712         free_string(left_name);
 713         free_string(right_name);
 714 }
 715
 716 static void match_assign_add(struct expression *expr)
 717 {
 718         struct expression *right;
 719         struct expression *r_left, *r_right;
 720         sval_t left_tmp, right_tmp;
 721
 722         right = strip_expr(expr->right);
 723         r_left = strip_expr(right->left);
 724         r_right = strip_expr(right->right);
 725
 726         get_absolute_min(r_left, &left_tmp);
 727         get_absolute_min(r_right, &right_tmp);
 728
 729         if (left_tmp.value > 0)
 730                 add_comparison(expr->left, '>', r_right);
 731         else if (left_tmp.value == 0)
 732                 add_comparison(expr->left, SPECIAL_GTE, r_right);
 733
 734         if (right_tmp.value > 0)
 735                 add_comparison(expr->left, '>', r_left);
 736         else if (right_tmp.value == 0)
 737                 add_comparison(expr->left, SPECIAL_GTE, r_left);
 738 }
 739
 740 static void match_assign_sub(struct expression *expr)
 741 {
 742         struct expression *right;
 743         struct expression *r_left, *r_right;
 744         int comparison;
 745         sval_t min;
 746
 747         right = strip_expr(expr->right);
 748         r_left = strip_expr(right->left);
 749         r_right = strip_expr(right->right);
 750
 751         if (get_absolute_min(r_right, &min) && sval_is_negative(min))
 752                 return;
 753
 754         comparison = get_comparison(r_left, r_right);
 755
 756         switch (comparison) {
 757         case '>':
 758         case SPECIAL_GTE:
 759                 if (implied_not_equal(r_right, 0))
 760                         add_comparison(expr->left, '>', r_left);
 761                 else
 762                         add_comparison(expr->left, SPECIAL_GTE, r_left);
 763                 return;
 764         }
 765 }
 766
 767 static void match_assign_divide(struct expression *expr)
 768 {
 769         struct expression *right;
 770         struct expression *r_left, *r_right;
 771         sval_t min;
 772
 773         right = strip_expr(expr->right);
 774         r_left = strip_expr(right->left);
 775         r_right = strip_expr(right->right);
 776         if (!get_implied_min(r_right, &min) || min.value <= 1)
 777                 return;
 778
 779         add_comparison(expr->left, '<', r_left);
 780 }
 781
 782 static void match_binop_assign(struct expression *expr)
 783 {
 784         struct expression *right;
 785
 786         right = strip_expr(expr->right);
 787         if (right->op == '+')
 788                 match_assign_add(expr);
 789         if (right->op == '-')
 790                 match_assign_sub(expr);
 791         if (right->op == '/')
 792                 match_assign_divide(expr);
 793 }
 794
 795 static void copy_comparisons(struct expression *left, struct expression *right)
 796 {
 797         struct string_list *links;
 798         struct smatch_state *state;
 799         struct compare_data *data;
 800         struct symbol *left_sym, *right_sym;
 801         char *left_var = NULL;
 802         char *right_var = NULL;
 803         const char *var;
 804         struct symbol *sym;
 805         int comparison;
 806         char *tmp;
 807
 808         left_var = expr_to_var_sym(left, &left_sym);
 809         if (!left_var || !left_sym)
 810                 goto done;
 811         right_var = expr_to_var_sym(right, &right_sym);
 812         if (!right_var || !right_sym)
 813                 goto done;
 814
 815         state = get_state_expr(link_id, right);
 816         if (!state)
 817                 return;
 818         links = state->data;
 819
 820         FOR_EACH_PTR(links, tmp) {
 821                 state = get_state(compare_id, tmp, NULL);
 822                 if (!state->data)
 823                         continue;
 824                 data = state->data;
 825                 comparison = data->comparison;
 826                 var = data->var2;
 827                 sym = data->sym2;
 828                 if (var_sym_eq(var, sym, right_var, right_sym)) {
 829                         var = data->var1;
 830                         sym = data->sym1;
 831                         comparison = flip_op(comparison);
 832                 }
 833                 add_comparison_var_sym(left_var, left_sym, comparison, var, sym);
 834         } END_FOR_EACH_PTR(tmp);
 835
 836 done:
 837         free_string(right_var);
 838 }
 839
 840 static void match_normal_assign(struct expression *expr)
 841 {
 842         copy_comparisons(expr->left, expr->right);
 843         add_comparison(expr->left, SPECIAL_EQUAL, expr->right);
 844 }
 845
 846 static void match_assign(struct expression *expr)
 847 {
 848         struct expression *right;
 849
 850         right = strip_expr(expr->right);
 851         if (right->type == EXPR_BINOP)
 852                 match_binop_assign(expr);
 853         else
 854                 match_normal_assign(expr);
 855 }
 856
 857 static int get_comparison_strings(char *one, char *two)
 858 {
 859         char buf[256];
 860         struct smatch_state *state;
 861         int invert = 0;
 862         int ret = 0;
 863
 864         if (strcmp(one, two) > 0) {
 865                 char *tmp = one;
 866
 867                 one = two;
 868                 two = tmp;
 869                 invert = 1;
 870         }
 871
 872         snprintf(buf, sizeof(buf), "%s vs %s", one, two);
 873         state = get_state(compare_id, buf, NULL);
 874         if (state)
 875                 ret = state_to_comparison(state);
 876
 877         if (invert)
 878                 ret = flip_op(ret);
 879
 880         return ret;
 881 }
 882
 883 int get_comparison(struct expression *a, struct expression *b)
 884 {
 885         char *one = NULL;
 886         char *two = NULL;
 887         int ret = 0;
 888
 889         one = expr_to_var(a);
 890         if (!one)
 891                 goto free;
 892         two = expr_to_var(b);
 893         if (!two)
 894                 goto free;
 895
 896         ret = get_comparison_strings(one, two);
 897 free:
 898         free_string(one);
 899         free_string(two);
 900         return ret;
 901 }
 902
 903 void __add_comparison_info(struct expression *expr, struct expression *call, const char *range)
 904 {
 905         struct expression *arg;
 906         int comparison;
 907         const char *c = range;
 908
 909         if (!str_to_comparison_arg(c, call, &comparison, &arg))
 910                 return;
 911         add_comparison(expr, comparison, arg);
 912 }
 913
 914 static char *range_comparison_to_param_helper(struct expression *expr, char starts_with)
 915 {
 916         struct symbol *param;
 917         char *var = NULL;
 918         char buf[256];
 919         char *ret_str = NULL;
 920         int compare;
 921         int i;
 922
 923         var = expr_to_var(expr);
 924         if (!var)
 925                 goto free;
 926
 927         i = -1;
 928         FOR_EACH_PTR(cur_func_sym->ctype.base_type->arguments, param) {
 929                 i++;
 930                 if (!param->ident)
 931                         continue;
 932                 snprintf(buf, sizeof(buf), "%s orig", param->ident->name);
 933                 compare = get_comparison_strings(var, buf);
 934                 if (!compare)
 935                         continue;
 936                 if (show_special(compare)[0] != starts_with)
 937                         continue;
 938                 snprintf(buf, sizeof(buf), "[%sp%d]", show_special(compare), i);
 939                 ret_str = alloc_sname(buf);
 940                 break;
 941         } END_FOR_EACH_PTR(param);
 942
 943 free:
 944         free_string(var);
 945         return ret_str;
 946 }
 947
 948 char *expr_equal_to_param(struct expression *expr)
 949 {
 950         return range_comparison_to_param_helper(expr, '=');
 951 }
 952
 953 char *expr_lte_to_param(struct expression *expr)
 954 {
 955         return range_comparison_to_param_helper(expr, '<');
 956 }
 957
 958 static void free_data(struct symbol *sym)
 959 {
 960         if (__inline_fn)
 961                 return;
 962         clear_compare_data_alloc();
 963 }
 964
 965 void register_comparison(int id)
 966 {
 967         compare_id = id;
 968         add_hook(&match_compare, CONDITION_HOOK);
 969         add_hook(&match_assign, ASSIGNMENT_HOOK);
 970         add_hook(&save_start_states, AFTER_DEF_HOOK);
 971         add_unmatched_state_hook(compare_id, unmatched_comparison);
 972         add_merge_hook(compare_id, &merge_compare_states);
 973         add_hook(&free_data, AFTER_FUNC_HOOK);
 974 }
 975
 976 void register_comparison_links(int id)
 977 {
 978         link_id = id;
 979         add_merge_hook(link_id, &merge_links);
 980         add_modification_hook(link_id, &match_modify);
 981 }