commit-reach.c

   1 #include "cache.h"
   2 #include "commit.h"
   3 #include "commit-graph.h"
   4 #include "decorate.h"
   5 #include "prio-queue.h"
   6 #include "tree.h"
   7 #include "ref-filter.h"
   8 #include "revision.h"
   9 #include "tag.h"
  10 #include "commit-reach.h"
  11
  12 /* Remember to update object flag allocation in object.h */
  13 #define PARENT1         (1u<<16)
  14 #define PARENT2         (1u<<17)
  15 #define STALE           (1u<<18)
  16 #define RESULT          (1u<<19)
  17
  18 static const unsigned all_flags = (PARENT1 | PARENT2 | STALE | RESULT);
  19
  20 static int queue_has_nonstale(struct prio_queue *queue)
  21 {
  22         int i;
  23         for (i = 0; i < queue->nr; i++) {
  24                 struct commit *commit = queue->array[i].data;
  25                 if (!(commit->object.flags & STALE))
  26                         return 1;
  27         }
  28         return 0;
  29 }
  30
  31 /* all input commits in one and twos[] must have been parsed! */
  32 static struct commit_list *paint_down_to_common(struct repository *r,
  33                                                 struct commit *one, int n,
  34                                                 struct commit **twos,
  35                                                 int min_generation)
  36 {
  37         struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
  38         struct commit_list *result = NULL;
  39         int i;
  40         uint32_t last_gen = GENERATION_NUMBER_INFINITY;
  41
  42         if (!min_generation)
  43                 queue.compare = compare_commits_by_commit_date;
  44
  45         one->object.flags |= PARENT1;
  46         if (!n) {
  47                 commit_list_append(one, &result);
  48                 return result;
  49         }
  50         prio_queue_put(&queue, one);
  51
  52         for (i = 0; i < n; i++) {
  53                 twos[i]->object.flags |= PARENT2;
  54                 prio_queue_put(&queue, twos[i]);
  55         }
  56
  57         while (queue_has_nonstale(&queue)) {
  58                 struct commit *commit = prio_queue_get(&queue);
  59                 struct commit_list *parents;
  60                 int flags;
  61
  62                 if (min_generation && commit->generation > last_gen)
  63                         BUG("bad generation skip %8x > %8x at %s",
  64                             commit->generation, last_gen,
  65                             oid_to_hex(&commit->object.oid));
  66                 last_gen = commit->generation;
  67
  68                 if (commit->generation < min_generation)
  69                         break;
  70
  71                 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);
  72                 if (flags == (PARENT1 | PARENT2)) {
  73                         if (!(commit->object.flags & RESULT)) {
  74                                 commit->object.flags |= RESULT;
  75                                 commit_list_insert_by_date(commit, &result);
  76                         }
  77                         /* Mark parents of a found merge stale */
  78                         flags |= STALE;
  79                 }
  80                 parents = commit->parents;
  81                 while (parents) {
  82                         struct commit *p = parents->item;
  83                         parents = parents->next;
  84                         if ((p->object.flags & flags) == flags)
  85                                 continue;
  86                         if (repo_parse_commit(r, p))
  87                                 return NULL;
  88                         p->object.flags |= flags;
  89                         prio_queue_put(&queue, p);
  90                 }
  91         }
  92
  93         clear_prio_queue(&queue);
  94         return result;
  95 }
  96
  97 static struct commit_list *merge_bases_many(struct repository *r,
  98                                             struct commit *one, int n,
  99                                             struct commit **twos)
 100 {
 101         struct commit_list *list = NULL;
 102         struct commit_list *result = NULL;
 103         int i;
 104
 105         for (i = 0; i < n; i++) {
 106                 if (one == twos[i])
 107                         /*
 108                          * We do not mark this even with RESULT so we do not
 109                          * have to clean it up.
 110                          */
 111                         return commit_list_insert(one, &result);
 112         }
 113
 114         if (repo_parse_commit(r, one))
 115                 return NULL;
 116         for (i = 0; i < n; i++) {
 117                 if (repo_parse_commit(r, twos[i]))
 118                         return NULL;
 119         }
 120
 121         list = paint_down_to_common(r, one, n, twos, 0);
 122
 123         while (list) {
 124                 struct commit *commit = pop_commit(&list);
 125                 if (!(commit->object.flags & STALE))
 126                         commit_list_insert_by_date(commit, &result);
 127         }
 128         return result;
 129 }
 130
 131 struct commit_list *get_octopus_merge_bases(struct commit_list *in)
 132 {
 133         struct commit_list *i, *j, *k, *ret = NULL;
 134
 135         if (!in)
 136                 return ret;
 137
 138         commit_list_insert(in->item, &ret);
 139
 140         for (i = in->next; i; i = i->next) {
 141                 struct commit_list *new_commits = NULL, *end = NULL;
 142
 143                 for (j = ret; j; j = j->next) {
 144                         struct commit_list *bases;
 145                         bases = get_merge_bases(i->item, j->item);
 146                         if (!new_commits)
 147                                 new_commits = bases;
 148                         else
 149                                 end->next = bases;
 150                         for (k = bases; k; k = k->next)
 151                                 end = k;
 152                 }
 153                 ret = new_commits;
 154         }
 155         return ret;
 156 }
 157
 158 static int remove_redundant(struct repository *r, struct commit **array, int cnt)
 159 {
 160         /*
 161          * Some commit in the array may be an ancestor of
 162          * another commit.  Move such commit to the end of
 163          * the array, and return the number of commits that
 164          * are independent from each other.
 165          */
 166         struct commit **work;
 167         unsigned char *redundant;
 168         int *filled_index;
 169         int i, j, filled;
 170
 171         work = xcalloc(cnt, sizeof(*work));
 172         redundant = xcalloc(cnt, 1);
 173         ALLOC_ARRAY(filled_index, cnt - 1);
 174
 175         for (i = 0; i < cnt; i++)
 176                 repo_parse_commit(r, array[i]);
 177         for (i = 0; i < cnt; i++) {
 178                 struct commit_list *common;
 179                 uint32_t min_generation = array[i]->generation;
 180
 181                 if (redundant[i])
 182                         continue;
 183                 for (j = filled = 0; j < cnt; j++) {
 184                         if (i == j || redundant[j])
 185                                 continue;
 186                         filled_index[filled] = j;
 187                         work[filled++] = array[j];
 188
 189                         if (array[j]->generation < min_generation)
 190                                 min_generation = array[j]->generation;
 191                 }
 192                 common = paint_down_to_common(r, array[i], filled,
 193                                               work, min_generation);
 194                 if (array[i]->object.flags & PARENT2)
 195                         redundant[i] = 1;
 196                 for (j = 0; j < filled; j++)
 197                         if (work[j]->object.flags & PARENT1)
 198                                 redundant[filled_index[j]] = 1;
 199                 clear_commit_marks(array[i], all_flags);
 200                 clear_commit_marks_many(filled, work, all_flags);
 201                 free_commit_list(common);
 202         }
 203
 204         /* Now collect the result */
 205         COPY_ARRAY(work, array, cnt);
 206         for (i = filled = 0; i < cnt; i++)
 207                 if (!redundant[i])
 208                         array[filled++] = work[i];
 209         for (j = filled, i = 0; i < cnt; i++)
 210                 if (redundant[i])
 211                         array[j++] = work[i];
 212         free(work);
 213         free(redundant);
 214         free(filled_index);
 215         return filled;
 216 }
 217
 218 static struct commit_list *get_merge_bases_many_0(struct repository *r,
 219                                                   struct commit *one,
 220                                                   int n,
 221                                                   struct commit **twos,
 222                                                   int cleanup)
 223 {
 224         struct commit_list *list;
 225         struct commit **rslt;
 226         struct commit_list *result;
 227         int cnt, i;
 228
 229         result = merge_bases_many(r, one, n, twos);
 230         for (i = 0; i < n; i++) {
 231                 if (one == twos[i])
 232                         return result;
 233         }
 234         if (!result || !result->next) {
 235                 if (cleanup) {
 236                         clear_commit_marks(one, all_flags);
 237                         clear_commit_marks_many(n, twos, all_flags);
 238                 }
 239                 return result;
 240         }
 241
 242         /* There are more than one */
 243         cnt = commit_list_count(result);
 244         rslt = xcalloc(cnt, sizeof(*rslt));
 245         for (list = result, i = 0; list; list = list->next)
 246                 rslt[i++] = list->item;
 247         free_commit_list(result);
 248
 249         clear_commit_marks(one, all_flags);
 250         clear_commit_marks_many(n, twos, all_flags);
 251
 252         cnt = remove_redundant(r, rslt, cnt);
 253         result = NULL;
 254         for (i = 0; i < cnt; i++)
 255                 commit_list_insert_by_date(rslt[i], &result);
 256         free(rslt);
 257         return result;
 258 }
 259
 260 struct commit_list *repo_get_merge_bases_many(struct repository *r,
 261                                               struct commit *one,
 262                                               int n,
 263                                               struct commit **twos)
 264 {
 265         return get_merge_bases_many_0(r, one, n, twos, 1);
 266 }
 267
 268 struct commit_list *repo_get_merge_bases_many_dirty(struct repository *r,
 269                                                     struct commit *one,
 270                                                     int n,
 271                                                     struct commit **twos)
 272 {
 273         return get_merge_bases_many_0(r, one, n, twos, 0);
 274 }
 275
 276 struct commit_list *repo_get_merge_bases(struct repository *r,
 277                                          struct commit *one,
 278                                          struct commit *two)
 279 {
 280         return get_merge_bases_many_0(r, one, 1, &two, 1);
 281 }
 282
 283 /*
 284  * Is "commit" a descendant of one of the elements on the "with_commit" list?
 285  */
 286 static int repo_is_descendant_of(struct repository *r,
 287                                  struct commit *commit,
 288                                  struct commit_list *with_commit)
 289 {
 290         if (!with_commit)
 291                 return 1;
 292
 293         if (generation_numbers_enabled(the_repository)) {
 294                 struct commit_list *from_list = NULL;
 295                 int result;
 296                 commit_list_insert(commit, &from_list);
 297                 result = can_all_from_reach(from_list, with_commit, 0);
 298                 free_commit_list(from_list);
 299                 return result;
 300         } else {
 301                 while (with_commit) {
 302                         struct commit *other;
 303
 304                         other = with_commit->item;
 305                         with_commit = with_commit->next;
 306                         if (repo_in_merge_bases_many(r, other, 1, &commit))
 307                                 return 1;
 308                 }
 309                 return 0;
 310         }
 311 }
 312
 313 int is_descendant_of(struct commit *commit, struct commit_list *with_commit)
 314 {
 315         return repo_is_descendant_of(the_repository, commit, with_commit);
 316 }
 317
 318 /*
 319  * Is "commit" an ancestor of one of the "references"?
 320  */
 321 int repo_in_merge_bases_many(struct repository *r, struct commit *commit,
 322                              int nr_reference, struct commit **reference)
 323 {
 324         struct commit_list *bases;
 325         int ret = 0, i;
 326         uint32_t min_generation = GENERATION_NUMBER_INFINITY;
 327
 328         if (repo_parse_commit(r, commit))
 329                 return ret;
 330         for (i = 0; i < nr_reference; i++) {
 331                 if (repo_parse_commit(r, reference[i]))
 332                         return ret;
 333                 if (reference[i]->generation < min_generation)
 334                         min_generation = reference[i]->generation;
 335         }
 336
 337         if (commit->generation > min_generation)
 338                 return ret;
 339
 340         bases = paint_down_to_common(r, commit,
 341                                      nr_reference, reference,
 342                                      commit->generation);
 343         if (commit->object.flags & PARENT2)
 344                 ret = 1;
 345         clear_commit_marks(commit, all_flags);
 346         clear_commit_marks_many(nr_reference, reference, all_flags);
 347         free_commit_list(bases);
 348         return ret;
 349 }
 350
 351 /*
 352  * Is "commit" an ancestor of (i.e. reachable from) the "reference"?
 353  */
 354 int repo_in_merge_bases(struct repository *r,
 355                         struct commit *commit,
 356                         struct commit *reference)
 357 {
 358         int res;
 359         struct commit_list *list = NULL;
 360         struct commit_list **next = &list;
 361
 362         next = commit_list_append(commit, next);
 363         res = repo_is_descendant_of(r, reference, list);
 364         free_commit_list(list);
 365
 366         return res;
 367 }
 368
 369 struct commit_list *reduce_heads(struct commit_list *heads)
 370 {
 371         struct commit_list *p;
 372         struct commit_list *result = NULL, **tail = &result;
 373         struct commit **array;
 374         int num_head, i;
 375
 376         if (!heads)
 377                 return NULL;
 378
 379         /* Uniquify */
 380         for (p = heads; p; p = p->next)
 381                 p->item->object.flags &= ~STALE;
 382         for (p = heads, num_head = 0; p; p = p->next) {
 383                 if (p->item->object.flags & STALE)
 384                         continue;
 385                 p->item->object.flags |= STALE;
 386                 num_head++;
 387         }
 388         array = xcalloc(num_head, sizeof(*array));
 389         for (p = heads, i = 0; p; p = p->next) {
 390                 if (p->item->object.flags & STALE) {
 391                         array[i++] = p->item;
 392                         p->item->object.flags &= ~STALE;
 393                 }
 394         }
 395         num_head = remove_redundant(the_repository, array, num_head);
 396         for (i = 0; i < num_head; i++)
 397                 tail = &commit_list_insert(array[i], tail)->next;
 398         free(array);
 399         return result;
 400 }
 401
 402 void reduce_heads_replace(struct commit_list **heads)
 403 {
 404         struct commit_list *result = reduce_heads(*heads);
 405         free_commit_list(*heads);
 406         *heads = result;
 407 }
 408
 409 int ref_newer(const struct object_id *new_oid, const struct object_id *old_oid)
 410 {
 411         struct object *o;
 412         struct commit *old_commit, *new_commit;
 413         struct commit_list *old_commit_list = NULL;
 414         int ret;
 415
 416         /*
 417          * Both new_commit and old_commit must be commit-ish and new_commit is descendant of
 418          * old_commit.  Otherwise we require --force.
 419          */
 420         o = deref_tag(the_repository, parse_object(the_repository, old_oid),
 421                       NULL, 0);
 422         if (!o || o->type != OBJ_COMMIT)
 423                 return 0;
 424         old_commit = (struct commit *) o;
 425
 426         o = deref_tag(the_repository, parse_object(the_repository, new_oid),
 427                       NULL, 0);
 428         if (!o || o->type != OBJ_COMMIT)
 429                 return 0;
 430         new_commit = (struct commit *) o;
 431
 432         if (parse_commit(new_commit) < 0)
 433                 return 0;
 434
 435         commit_list_insert(old_commit, &old_commit_list);
 436         ret = is_descendant_of(new_commit, old_commit_list);
 437         free_commit_list(old_commit_list);
 438         return ret;
 439 }
 440
 441 /*
 442  * Mimicking the real stack, this stack lives on the heap, avoiding stack
 443  * overflows.
 444  *
 445  * At each recursion step, the stack items points to the commits whose
 446  * ancestors are to be inspected.
 447  */
 448 struct contains_stack {
 449         int nr, alloc;
 450         struct contains_stack_entry {
 451                 struct commit *commit;
 452                 struct commit_list *parents;
 453         } *contains_stack;
 454 };
 455
 456 static int in_commit_list(const struct commit_list *want, struct commit *c)
 457 {
 458         for (; want; want = want->next)
 459                 if (oideq(&want->item->object.oid, &c->object.oid))
 460                         return 1;
 461         return 0;
 462 }
 463
 464 /*
 465  * Test whether the candidate is contained in the list.
 466  * Do not recurse to find out, though, but return -1 if inconclusive.
 467  */
 468 static enum contains_result contains_test(struct commit *candidate,
 469                                           const struct commit_list *want,
 470                                           struct contains_cache *cache,
 471                                           uint32_t cutoff)
 472 {
 473         enum contains_result *cached = contains_cache_at(cache, candidate);
 474
 475         /* If we already have the answer cached, return that. */
 476         if (*cached)
 477                 return *cached;
 478
 479         /* or are we it? */
 480         if (in_commit_list(want, candidate)) {
 481                 *cached = CONTAINS_YES;
 482                 return CONTAINS_YES;
 483         }
 484
 485         /* Otherwise, we don't know; prepare to recurse */
 486         parse_commit_or_die(candidate);
 487
 488         if (candidate->generation < cutoff)
 489                 return CONTAINS_NO;
 490
 491         return CONTAINS_UNKNOWN;
 492 }
 493
 494 static void push_to_contains_stack(struct commit *candidate, struct contains_stack *contains_stack)
 495 {
 496         ALLOC_GROW(contains_stack->contains_stack, contains_stack->nr + 1, contains_stack->alloc);
 497         contains_stack->contains_stack[contains_stack->nr].commit = candidate;
 498         contains_stack->contains_stack[contains_stack->nr++].parents = candidate->parents;
 499 }
 500
 501 static enum contains_result contains_tag_algo(struct commit *candidate,
 502                                               const struct commit_list *want,
 503                                               struct contains_cache *cache)
 504 {
 505         struct contains_stack contains_stack = { 0, 0, NULL };
 506         enum contains_result result;
 507         uint32_t cutoff = GENERATION_NUMBER_INFINITY;
 508         const struct commit_list *p;
 509
 510         for (p = want; p; p = p->next) {
 511                 struct commit *c = p->item;
 512                 load_commit_graph_info(the_repository, c);
 513                 if (c->generation < cutoff)
 514                         cutoff = c->generation;
 515         }
 516
 517         result = contains_test(candidate, want, cache, cutoff);
 518         if (result != CONTAINS_UNKNOWN)
 519                 return result;
 520
 521         push_to_contains_stack(candidate, &contains_stack);
 522         while (contains_stack.nr) {
 523                 struct contains_stack_entry *entry = &contains_stack.contains_stack[contains_stack.nr - 1];
 524                 struct commit *commit = entry->commit;
 525                 struct commit_list *parents = entry->parents;
 526
 527                 if (!parents) {
 528                         *contains_cache_at(cache, commit) = CONTAINS_NO;
 529                         contains_stack.nr--;
 530                 }
 531                 /*
 532                  * If we just popped the stack, parents->item has been marked,
 533                  * therefore contains_test will return a meaningful yes/no.
 534                  */
 535                 else switch (contains_test(parents->item, want, cache, cutoff)) {
 536                 case CONTAINS_YES:
 537                         *contains_cache_at(cache, commit) = CONTAINS_YES;
 538                         contains_stack.nr--;
 539                         break;
 540                 case CONTAINS_NO:
 541                         entry->parents = parents->next;
 542                         break;
 543                 case CONTAINS_UNKNOWN:
 544                         push_to_contains_stack(parents->item, &contains_stack);
 545                         break;
 546                 }
 547         }
 548         free(contains_stack.contains_stack);
 549         return contains_test(candidate, want, cache, cutoff);
 550 }
 551
 552 int commit_contains(struct ref_filter *filter, struct commit *commit,
 553                     struct commit_list *list, struct contains_cache *cache)
 554 {
 555         if (filter->with_commit_tag_algo)
 556                 return contains_tag_algo(commit, list, cache) == CONTAINS_YES;
 557         return is_descendant_of(commit, list);
 558 }
 559
 560 static int compare_commits_by_gen(const void *_a, const void *_b)
 561 {
 562         const struct commit *a = *(const struct commit * const *)_a;
 563         const struct commit *b = *(const struct commit * const *)_b;
 564
 565         if (a->generation < b->generation)
 566                 return -1;
 567         if (a->generation > b->generation)
 568                 return 1;
 569         return 0;
 570 }
 571
 572 int can_all_from_reach_with_flag(struct object_array *from,
 573                                  unsigned int with_flag,
 574                                  unsigned int assign_flag,
 575                                  time_t min_commit_date,
 576                                  uint32_t min_generation)
 577 {
 578         struct commit **list = NULL;
 579         int i;
 580         int nr_commits;
 581         int result = 1;
 582
 583         ALLOC_ARRAY(list, from->nr);
 584         nr_commits = 0;
 585         for (i = 0; i < from->nr; i++) {
 586                 struct object *from_one = from->objects[i].item;
 587
 588                 if (!from_one || from_one->flags & assign_flag)
 589                         continue;
 590
 591                 from_one = deref_tag(the_repository, from_one,
 592                                      "a from object", 0);
 593                 if (!from_one || from_one->type != OBJ_COMMIT) {
 594                         /*
 595                          * no way to tell if this is reachable by
 596                          * looking at the ancestry chain alone, so
 597                          * leave a note to ourselves not to worry about
 598                          * this object anymore.
 599                          */
 600                         from->objects[i].item->flags |= assign_flag;
 601                         continue;
 602                 }
 603
 604                 list[nr_commits] = (struct commit *)from_one;
 605                 if (parse_commit(list[nr_commits]) ||
 606                     list[nr_commits]->generation < min_generation) {
 607                         result = 0;
 608                         goto cleanup;
 609                 }
 610
 611                 nr_commits++;
 612         }
 613
 614         QSORT(list, nr_commits, compare_commits_by_gen);
 615
 616         for (i = 0; i < nr_commits; i++) {
 617                 /* DFS from list[i] */
 618                 struct commit_list *stack = NULL;
 619
 620                 list[i]->object.flags |= assign_flag;
 621                 commit_list_insert(list[i], &stack);
 622
 623                 while (stack) {
 624                         struct commit_list *parent;
 625
 626                         if (stack->item->object.flags & (with_flag | RESULT)) {
 627                                 pop_commit(&stack);
 628                                 if (stack)
 629                                         stack->item->object.flags |= RESULT;
 630                                 continue;
 631                         }
 632
 633                         for (parent = stack->item->parents; parent; parent = parent->next) {
 634                                 if (parent->item->object.flags & (with_flag | RESULT))
 635                                         stack->item->object.flags |= RESULT;
 636
 637                                 if (!(parent->item->object.flags & assign_flag)) {
 638                                         parent->item->object.flags |= assign_flag;
 639
 640                                         if (parse_commit(parent->item) ||
 641                                             parent->item->date < min_commit_date ||
 642                                             parent->item->generation < min_generation)
 643                                                 continue;
 644
 645                                         commit_list_insert(parent->item, &stack);
 646                                         break;
 647                                 }
 648                         }
 649
 650                         if (!parent)
 651                                 pop_commit(&stack);
 652                 }
 653
 654                 if (!(list[i]->object.flags & (with_flag | RESULT))) {
 655                         result = 0;
 656                         goto cleanup;
 657                 }
 658         }
 659
 660 cleanup:
 661         clear_commit_marks_many(nr_commits, list, RESULT | assign_flag);
 662         free(list);
 663
 664         for (i = 0; i < from->nr; i++)
 665                 from->objects[i].item->flags &= ~assign_flag;
 666
 667         return result;
 668 }
 669
 670 int can_all_from_reach(struct commit_list *from, struct commit_list *to,
 671                        int cutoff_by_min_date)
 672 {
 673         struct object_array from_objs = OBJECT_ARRAY_INIT;
 674         time_t min_commit_date = cutoff_by_min_date ? from->item->date : 0;
 675         struct commit_list *from_iter = from, *to_iter = to;
 676         int result;
 677         uint32_t min_generation = GENERATION_NUMBER_INFINITY;
 678
 679         while (from_iter) {
 680                 add_object_array(&from_iter->item->object, NULL, &from_objs);
 681
 682                 if (!parse_commit(from_iter->item)) {
 683                         if (from_iter->item->date < min_commit_date)
 684                                 min_commit_date = from_iter->item->date;
 685
 686                         if (from_iter->item->generation < min_generation)
 687                                 min_generation = from_iter->item->generation;
 688                 }
 689
 690                 from_iter = from_iter->next;
 691         }
 692
 693         while (to_iter) {
 694                 if (!parse_commit(to_iter->item)) {
 695                         if (to_iter->item->date < min_commit_date)
 696                                 min_commit_date = to_iter->item->date;
 697
 698                         if (to_iter->item->generation < min_generation)
 699                                 min_generation = to_iter->item->generation;
 700                 }
 701
 702                 to_iter->item->object.flags |= PARENT2;
 703
 704                 to_iter = to_iter->next;
 705         }
 706
 707         result = can_all_from_reach_with_flag(&from_objs, PARENT2, PARENT1,
 708                                               min_commit_date, min_generation);
 709
 710         while (from) {
 711                 clear_commit_marks(from->item, PARENT1);
 712                 from = from->next;
 713         }
 714
 715         while (to) {
 716                 clear_commit_marks(to->item, PARENT2);
 717                 to = to->next;
 718         }
 719
 720         object_array_clear(&from_objs);
 721         return result;
 722 }
 723
 724 struct commit_list *get_reachable_subset(struct commit **from, int nr_from,
 725                                          struct commit **to, int nr_to,
 726                                          unsigned int reachable_flag)
 727 {
 728         struct commit **item;
 729         struct commit *current;
 730         struct commit_list *found_commits = NULL;
 731         struct commit **to_last = to + nr_to;
 732         struct commit **from_last = from + nr_from;
 733         uint32_t min_generation = GENERATION_NUMBER_INFINITY;
 734         int num_to_find = 0;
 735
 736         struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 737
 738         for (item = to; item < to_last; item++) {
 739                 struct commit *c = *item;
 740
 741                 parse_commit(c);
 742                 if (c->generation < min_generation)
 743                         min_generation = c->generation;
 744
 745                 if (!(c->object.flags & PARENT1)) {
 746                         c->object.flags |= PARENT1;
 747                         num_to_find++;
 748                 }
 749         }
 750
 751         for (item = from; item < from_last; item++) {
 752                 struct commit *c = *item;
 753                 if (!(c->object.flags & PARENT2)) {
 754                         c->object.flags |= PARENT2;
 755                         parse_commit(c);
 756
 757                         prio_queue_put(&queue, *item);
 758                 }
 759         }
 760
 761         while (num_to_find && (current = prio_queue_get(&queue)) != NULL) {
 762                 struct commit_list *parents;
 763
 764                 if (current->object.flags & PARENT1) {
 765                         current->object.flags &= ~PARENT1;
 766                         current->object.flags |= reachable_flag;
 767                         commit_list_insert(current, &found_commits);
 768                         num_to_find--;
 769                 }
 770
 771                 for (parents = current->parents; parents; parents = parents->next) {
 772                         struct commit *p = parents->item;
 773
 774                         parse_commit(p);
 775
 776                         if (p->generation < min_generation)
 777                                 continue;
 778
 779                         if (p->object.flags & PARENT2)
 780                                 continue;
 781
 782                         p->object.flags |= PARENT2;
 783                         prio_queue_put(&queue, p);
 784                 }
 785         }
 786
 787         clear_commit_marks_many(nr_to, to, PARENT1);
 788         clear_commit_marks_many(nr_from, from, PARENT2);
 789
 790         return found_commits;
 791 }