shallow.c

   1 #include "cache.h"
   2 #include "tempfile.h"
   3 #include "lockfile.h"
   4 #include "commit.h"
   5 #include "tag.h"
   6 #include "pkt-line.h"
   7 #include "remote.h"
   8 #include "refs.h"
   9 #include "sha1-array.h"
  10 #include "diff.h"
  11 #include "revision.h"
  12 #include "commit-slab.h"
  13
  14 static int is_shallow = -1;
  15 static struct stat_validity shallow_stat;
  16 static char *alternate_shallow_file;
  17
  18 void set_alternate_shallow_file(const char *path, int override)
  19 {
  20         if (is_shallow != -1)
  21                 die("BUG: is_repository_shallow must not be called before set_alternate_shallow_file");
  22         if (alternate_shallow_file && !override)
  23                 return;
  24         free(alternate_shallow_file);
  25         alternate_shallow_file = xstrdup_or_null(path);
  26 }
  27
  28 int register_shallow(const unsigned char *sha1)
  29 {
  30         struct commit_graft *graft =
  31                 xmalloc(sizeof(struct commit_graft));
  32         struct commit *commit = lookup_commit(sha1);
  33
  34         hashcpy(graft->oid.hash, sha1);
  35         graft->nr_parent = -1;
  36         if (commit && commit->object.parsed)
  37                 commit->parents = NULL;
  38         return register_commit_graft(graft, 0);
  39 }
  40
  41 int is_repository_shallow(void)
  42 {
  43         FILE *fp;
  44         char buf[1024];
  45         const char *path = alternate_shallow_file;
  46
  47         if (is_shallow >= 0)
  48                 return is_shallow;
  49
  50         if (!path)
  51                 path = git_path_shallow();
  52         /*
  53          * fetch-pack sets '--shallow-file ""' as an indicator that no
  54          * shallow file should be used. We could just open it and it
  55          * will likely fail. But let's do an explicit check instead.
  56          */
  57         if (!*path || (fp = fopen(path, "r")) == NULL) {
  58                 stat_validity_clear(&shallow_stat);
  59                 is_shallow = 0;
  60                 return is_shallow;
  61         }
  62         stat_validity_update(&shallow_stat, fileno(fp));
  63         is_shallow = 1;
  64
  65         while (fgets(buf, sizeof(buf), fp)) {
  66                 unsigned char sha1[20];
  67                 if (get_sha1_hex(buf, sha1))
  68                         die("bad shallow line: %s", buf);
  69                 register_shallow(sha1);
  70         }
  71         fclose(fp);
  72         return is_shallow;
  73 }
  74
  75 struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
  76                 int shallow_flag, int not_shallow_flag)
  77 {
  78         int i = 0, cur_depth = 0;
  79         struct commit_list *result = NULL;
  80         struct object_array stack = OBJECT_ARRAY_INIT;
  81         struct commit *commit = NULL;
  82         struct commit_graft *graft;
  83
  84         while (commit || i < heads->nr || stack.nr) {
  85                 struct commit_list *p;
  86                 if (!commit) {
  87                         if (i < heads->nr) {
  88                                 commit = (struct commit *)
  89                                         deref_tag(heads->objects[i++].item, NULL, 0);
  90                                 if (!commit || commit->object.type != OBJ_COMMIT) {
  91                                         commit = NULL;
  92                                         continue;
  93                                 }
  94                                 if (!commit->util)
  95                                         commit->util = xmalloc(sizeof(int));
  96                                 *(int *)commit->util = 0;
  97                                 cur_depth = 0;
  98                         } else {
  99                                 commit = (struct commit *)
 100                                         stack.objects[--stack.nr].item;
 101                                 cur_depth = *(int *)commit->util;
 102                         }
 103                 }
 104                 parse_commit_or_die(commit);
 105                 cur_depth++;
 106                 if ((depth != INFINITE_DEPTH && cur_depth >= depth) ||
 107                     (is_repository_shallow() && !commit->parents &&
 108                      (graft = lookup_commit_graft(commit->object.oid.hash)) != NULL &&
 109                      graft->nr_parent < 0)) {
 110                         commit_list_insert(commit, &result);
 111                         commit->object.flags |= shallow_flag;
 112                         commit = NULL;
 113                         continue;
 114                 }
 115                 commit->object.flags |= not_shallow_flag;
 116                 for (p = commit->parents, commit = NULL; p; p = p->next) {
 117                         if (!p->item->util) {
 118                                 int *pointer = xmalloc(sizeof(int));
 119                                 p->item->util = pointer;
 120                                 *pointer =  cur_depth;
 121                         } else {
 122                                 int *pointer = p->item->util;
 123                                 if (cur_depth >= *pointer)
 124                                         continue;
 125                                 *pointer = cur_depth;
 126                         }
 127                         if (p->next)
 128                                 add_object_array(&p->item->object,
 129                                                 NULL, &stack);
 130                         else {
 131                                 commit = p->item;
 132                                 cur_depth = *(int *)commit->util;
 133                         }
 134                 }
 135         }
 136
 137         return result;
 138 }
 139
 140 static void check_shallow_file_for_update(void)
 141 {
 142         if (is_shallow == -1)
 143                 die("BUG: shallow must be initialized by now");
 144
 145         if (!stat_validity_check(&shallow_stat, git_path_shallow()))
 146                 die("shallow file has changed since we read it");
 147 }
 148
 149 #define SEEN_ONLY 1
 150 #define VERBOSE   2
 151
 152 struct write_shallow_data {
 153         struct strbuf *out;
 154         int use_pack_protocol;
 155         int count;
 156         unsigned flags;
 157 };
 158
 159 static int write_one_shallow(const struct commit_graft *graft, void *cb_data)
 160 {
 161         struct write_shallow_data *data = cb_data;
 162         const char *hex = oid_to_hex(&graft->oid);
 163         if (graft->nr_parent != -1)
 164                 return 0;
 165         if (data->flags & SEEN_ONLY) {
 166                 struct commit *c = lookup_commit(graft->oid.hash);
 167                 if (!c || !(c->object.flags & SEEN)) {
 168                         if (data->flags & VERBOSE)
 169                                 printf("Removing %s from .git/shallow\n",
 170                                        oid_to_hex(&c->object.oid));
 171                         return 0;
 172                 }
 173         }
 174         data->count++;
 175         if (data->use_pack_protocol)
 176                 packet_buf_write(data->out, "shallow %s", hex);
 177         else {
 178                 strbuf_addstr(data->out, hex);
 179                 strbuf_addch(data->out, '\n');
 180         }
 181         return 0;
 182 }
 183
 184 static int write_shallow_commits_1(struct strbuf *out, int use_pack_protocol,
 185                                    const struct sha1_array *extra,
 186                                    unsigned flags)
 187 {
 188         struct write_shallow_data data;
 189         int i;
 190         data.out = out;
 191         data.use_pack_protocol = use_pack_protocol;
 192         data.count = 0;
 193         data.flags = flags;
 194         for_each_commit_graft(write_one_shallow, &data);
 195         if (!extra)
 196                 return data.count;
 197         for (i = 0; i < extra->nr; i++) {
 198                 strbuf_addstr(out, sha1_to_hex(extra->sha1[i]));
 199                 strbuf_addch(out, '\n');
 200                 data.count++;
 201         }
 202         return data.count;
 203 }
 204
 205 int write_shallow_commits(struct strbuf *out, int use_pack_protocol,
 206                           const struct sha1_array *extra)
 207 {
 208         return write_shallow_commits_1(out, use_pack_protocol, extra, 0);
 209 }
 210
 211 static struct tempfile temporary_shallow;
 212
 213 const char *setup_temporary_shallow(const struct sha1_array *extra)
 214 {
 215         struct strbuf sb = STRBUF_INIT;
 216         int fd;
 217
 218         if (write_shallow_commits(&sb, 0, extra)) {
 219                 fd = xmks_tempfile(&temporary_shallow, git_path("shallow_XXXXXX"));
 220
 221                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 222                         die_errno("failed to write to %s",
 223                                   get_tempfile_path(&temporary_shallow));
 224                 close_tempfile(&temporary_shallow);
 225                 strbuf_release(&sb);
 226                 return get_tempfile_path(&temporary_shallow);
 227         }
 228         /*
 229          * is_repository_shallow() sees empty string as "no shallow
 230          * file".
 231          */
 232         return get_tempfile_path(&temporary_shallow);
 233 }
 234
 235 void setup_alternate_shallow(struct lock_file *shallow_lock,
 236                              const char **alternate_shallow_file,
 237                              const struct sha1_array *extra)
 238 {
 239         struct strbuf sb = STRBUF_INIT;
 240         int fd;
 241
 242         fd = hold_lock_file_for_update(shallow_lock, git_path_shallow(),
 243                                        LOCK_DIE_ON_ERROR);
 244         check_shallow_file_for_update();
 245         if (write_shallow_commits(&sb, 0, extra)) {
 246                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 247                         die_errno("failed to write to %s",
 248                                   get_lock_file_path(shallow_lock));
 249                 *alternate_shallow_file = get_lock_file_path(shallow_lock);
 250         } else
 251                 /*
 252                  * is_repository_shallow() sees empty string as "no
 253                  * shallow file".
 254                  */
 255                 *alternate_shallow_file = "";
 256         strbuf_release(&sb);
 257 }
 258
 259 static int advertise_shallow_grafts_cb(const struct commit_graft *graft, void *cb)
 260 {
 261         int fd = *(int *)cb;
 262         if (graft->nr_parent == -1)
 263                 packet_write(fd, "shallow %s\n", oid_to_hex(&graft->oid));
 264         return 0;
 265 }
 266
 267 void advertise_shallow_grafts(int fd)
 268 {
 269         if (!is_repository_shallow())
 270                 return;
 271         for_each_commit_graft(advertise_shallow_grafts_cb, &fd);
 272 }
 273
 274 /*
 275  * mark_reachable_objects() should have been run prior to this and all
 276  * reachable commits marked as "SEEN".
 277  */
 278 void prune_shallow(int show_only)
 279 {
 280         static struct lock_file shallow_lock;
 281         struct strbuf sb = STRBUF_INIT;
 282         int fd;
 283
 284         if (show_only) {
 285                 write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY | VERBOSE);
 286                 strbuf_release(&sb);
 287                 return;
 288         }
 289         fd = hold_lock_file_for_update(&shallow_lock, git_path_shallow(),
 290                                        LOCK_DIE_ON_ERROR);
 291         check_shallow_file_for_update();
 292         if (write_shallow_commits_1(&sb, 0, NULL, SEEN_ONLY)) {
 293                 if (write_in_full(fd, sb.buf, sb.len) != sb.len)
 294                         die_errno("failed to write to %s",
 295                                   get_lock_file_path(&shallow_lock));
 296                 commit_lock_file(&shallow_lock);
 297         } else {
 298                 unlink(git_path_shallow());
 299                 rollback_lock_file(&shallow_lock);
 300         }
 301         strbuf_release(&sb);
 302 }
 303
 304 struct trace_key trace_shallow = TRACE_KEY_INIT(SHALLOW);
 305
 306 /*
 307  * Step 1, split sender shallow commits into "ours" and "theirs"
 308  * Step 2, clean "ours" based on .git/shallow
 309  */
 310 void prepare_shallow_info(struct shallow_info *info, struct sha1_array *sa)
 311 {
 312         int i;
 313         trace_printf_key(&trace_shallow, "shallow: prepare_shallow_info\n");
 314         memset(info, 0, sizeof(*info));
 315         info->shallow = sa;
 316         if (!sa)
 317                 return;
 318         info->ours = xmalloc(sizeof(*info->ours) * sa->nr);
 319         info->theirs = xmalloc(sizeof(*info->theirs) * sa->nr);
 320         for (i = 0; i < sa->nr; i++) {
 321                 if (has_sha1_file(sa->sha1[i])) {
 322                         struct commit_graft *graft;
 323                         graft = lookup_commit_graft(sa->sha1[i]);
 324                         if (graft && graft->nr_parent < 0)
 325                                 continue;
 326                         info->ours[info->nr_ours++] = i;
 327                 } else
 328                         info->theirs[info->nr_theirs++] = i;
 329         }
 330 }
 331
 332 void clear_shallow_info(struct shallow_info *info)
 333 {
 334         free(info->ours);
 335         free(info->theirs);
 336 }
 337
 338 /* Step 4, remove non-existent ones in "theirs" after getting the pack */
 339
 340 void remove_nonexistent_theirs_shallow(struct shallow_info *info)
 341 {
 342         unsigned char (*sha1)[20] = info->shallow->sha1;
 343         int i, dst;
 344         trace_printf_key(&trace_shallow, "shallow: remove_nonexistent_theirs_shallow\n");
 345         for (i = dst = 0; i < info->nr_theirs; i++) {
 346                 if (i != dst)
 347                         info->theirs[dst] = info->theirs[i];
 348                 if (has_sha1_file(sha1[info->theirs[i]]))
 349                         dst++;
 350         }
 351         info->nr_theirs = dst;
 352 }
 353
 354 define_commit_slab(ref_bitmap, uint32_t *);
 355
 356 struct paint_info {
 357         struct ref_bitmap ref_bitmap;
 358         unsigned nr_bits;
 359         char **slab;
 360         char *free, *end;
 361         unsigned slab_count;
 362 };
 363
 364 static uint32_t *paint_alloc(struct paint_info *info)
 365 {
 366         unsigned nr = (info->nr_bits + 31) / 32;
 367         unsigned size = nr * sizeof(uint32_t);
 368         void *p;
 369         if (!info->slab_count || info->free + size > info->end) {
 370                 info->slab_count++;
 371                 REALLOC_ARRAY(info->slab, info->slab_count);
 372                 info->free = xmalloc(COMMIT_SLAB_SIZE);
 373                 info->slab[info->slab_count - 1] = info->free;
 374                 info->end = info->free + COMMIT_SLAB_SIZE;
 375         }
 376         p = info->free;
 377         info->free += size;
 378         return p;
 379 }
 380
 381 /*
 382  * Given a commit SHA-1, walk down to parents until either SEEN,
 383  * UNINTERESTING or BOTTOM is hit. Set the id-th bit in ref_bitmap for
 384  * all walked commits.
 385  */
 386 static void paint_down(struct paint_info *info, const unsigned char *sha1,
 387                        int id)
 388 {
 389         unsigned int i, nr;
 390         struct commit_list *head = NULL;
 391         int bitmap_nr = (info->nr_bits + 31) / 32;
 392         int bitmap_size = bitmap_nr * sizeof(uint32_t);
 393         uint32_t *tmp = xmalloc(bitmap_size); /* to be freed before return */
 394         uint32_t *bitmap = paint_alloc(info);
 395         struct commit *c = lookup_commit_reference_gently(sha1, 1);
 396         if (!c)
 397                 return;
 398         memset(bitmap, 0, bitmap_size);
 399         bitmap[id / 32] |= (1 << (id % 32));
 400         commit_list_insert(c, &head);
 401         while (head) {
 402                 struct commit_list *p;
 403                 struct commit *c = pop_commit(&head);
 404                 uint32_t **refs = ref_bitmap_at(&info->ref_bitmap, c);
 405
 406                 /* XXX check "UNINTERESTING" from pack bitmaps if available */
 407                 if (c->object.flags & (SEEN | UNINTERESTING))
 408                         continue;
 409                 else
 410                         c->object.flags |= SEEN;
 411
 412                 if (*refs == NULL)
 413                         *refs = bitmap;
 414                 else {
 415                         memcpy(tmp, *refs, bitmap_size);
 416                         for (i = 0; i < bitmap_nr; i++)
 417                                 tmp[i] |= bitmap[i];
 418                         if (memcmp(tmp, *refs, bitmap_size)) {
 419                                 *refs = paint_alloc(info);
 420                                 memcpy(*refs, tmp, bitmap_size);
 421                         }
 422                 }
 423
 424                 if (c->object.flags & BOTTOM)
 425                         continue;
 426
 427                 if (parse_commit(c))
 428                         die("unable to parse commit %s",
 429                             oid_to_hex(&c->object.oid));
 430
 431                 for (p = c->parents; p; p = p->next) {
 432                         uint32_t **p_refs = ref_bitmap_at(&info->ref_bitmap,
 433                                                           p->item);
 434                         if (p->item->object.flags & SEEN)
 435                                 continue;
 436                         if (*p_refs == NULL || *p_refs == *refs)
 437                                 *p_refs = *refs;
 438                         commit_list_insert(p->item, &head);
 439                 }
 440         }
 441
 442         nr = get_max_object_index();
 443         for (i = 0; i < nr; i++) {
 444                 struct object *o = get_indexed_object(i);
 445                 if (o && o->type == OBJ_COMMIT)
 446                         o->flags &= ~SEEN;
 447         }
 448
 449         free(tmp);
 450 }
 451
 452 static int mark_uninteresting(const char *refname, const struct object_id *oid,
 453                               int flags, void *cb_data)
 454 {
 455         struct commit *commit = lookup_commit_reference_gently(oid->hash, 1);
 456         if (!commit)
 457                 return 0;
 458         commit->object.flags |= UNINTERESTING;
 459         mark_parents_uninteresting(commit);
 460         return 0;
 461 }
 462
 463 static void post_assign_shallow(struct shallow_info *info,
 464                                 struct ref_bitmap *ref_bitmap,
 465                                 int *ref_status);
 466 /*
 467  * Step 6(+7), associate shallow commits with new refs
 468  *
 469  * info->ref must be initialized before calling this function.
 470  *
 471  * If used is not NULL, it's an array of info->shallow->nr
 472  * bitmaps. The n-th bit set in the m-th bitmap if ref[n] needs the
 473  * m-th shallow commit from info->shallow.
 474  *
 475  * If used is NULL, "ours" and "theirs" are updated. And if ref_status
 476  * is not NULL it's an array of ref->nr ints. ref_status[i] is true if
 477  * the ref needs some shallow commits from either info->ours or
 478  * info->theirs.
 479  */
 480 void assign_shallow_commits_to_refs(struct shallow_info *info,
 481                                     uint32_t **used, int *ref_status)
 482 {
 483         unsigned char (*sha1)[20] = info->shallow->sha1;
 484         struct sha1_array *ref = info->ref;
 485         unsigned int i, nr;
 486         int *shallow, nr_shallow = 0;
 487         struct paint_info pi;
 488
 489         trace_printf_key(&trace_shallow, "shallow: assign_shallow_commits_to_refs\n");
 490         shallow = xmalloc(sizeof(*shallow) * (info->nr_ours + info->nr_theirs));
 491         for (i = 0; i < info->nr_ours; i++)
 492                 shallow[nr_shallow++] = info->ours[i];
 493         for (i = 0; i < info->nr_theirs; i++)
 494                 shallow[nr_shallow++] = info->theirs[i];
 495
 496         /*
 497          * Prepare the commit graph to track what refs can reach what
 498          * (new) shallow commits.
 499          */
 500         nr = get_max_object_index();
 501         for (i = 0; i < nr; i++) {
 502                 struct object *o = get_indexed_object(i);
 503                 if (!o || o->type != OBJ_COMMIT)
 504                         continue;
 505
 506                 o->flags &= ~(UNINTERESTING | BOTTOM | SEEN);
 507         }
 508
 509         memset(&pi, 0, sizeof(pi));
 510         init_ref_bitmap(&pi.ref_bitmap);
 511         pi.nr_bits = ref->nr;
 512
 513         /*
 514          * "--not --all" to cut short the traversal if new refs
 515          * connect to old refs. If not (e.g. force ref updates) it'll
 516          * have to go down to the current shallow commits.
 517          */
 518         head_ref(mark_uninteresting, NULL);
 519         for_each_ref(mark_uninteresting, NULL);
 520
 521         /* Mark potential bottoms so we won't go out of bound */
 522         for (i = 0; i < nr_shallow; i++) {
 523                 struct commit *c = lookup_commit(sha1[shallow[i]]);
 524                 c->object.flags |= BOTTOM;
 525         }
 526
 527         for (i = 0; i < ref->nr; i++)
 528                 paint_down(&pi, ref->sha1[i], i);
 529
 530         if (used) {
 531                 int bitmap_size = ((pi.nr_bits + 31) / 32) * sizeof(uint32_t);
 532                 memset(used, 0, sizeof(*used) * info->shallow->nr);
 533                 for (i = 0; i < nr_shallow; i++) {
 534                         const struct commit *c = lookup_commit(sha1[shallow[i]]);
 535                         uint32_t **map = ref_bitmap_at(&pi.ref_bitmap, c);
 536                         if (*map)
 537                                 used[shallow[i]] = xmemdupz(*map, bitmap_size);
 538                 }
 539                 /*
 540                  * unreachable shallow commits are not removed from
 541                  * "ours" and "theirs". The user is supposed to run
 542                  * step 7 on every ref separately and not trust "ours"
 543                  * and "theirs" any more.
 544                  */
 545         } else
 546                 post_assign_shallow(info, &pi.ref_bitmap, ref_status);
 547
 548         clear_ref_bitmap(&pi.ref_bitmap);
 549         for (i = 0; i < pi.slab_count; i++)
 550                 free(pi.slab[i]);
 551         free(pi.slab);
 552         free(shallow);
 553 }
 554
 555 struct commit_array {
 556         struct commit **commits;
 557         int nr, alloc;
 558 };
 559
 560 static int add_ref(const char *refname, const struct object_id *oid,
 561                    int flags, void *cb_data)
 562 {
 563         struct commit_array *ca = cb_data;
 564         ALLOC_GROW(ca->commits, ca->nr + 1, ca->alloc);
 565         ca->commits[ca->nr] = lookup_commit_reference_gently(oid->hash, 1);
 566         if (ca->commits[ca->nr])
 567                 ca->nr++;
 568         return 0;
 569 }
 570
 571 static void update_refstatus(int *ref_status, int nr, uint32_t *bitmap)
 572 {
 573         int i;
 574         if (!ref_status)
 575                 return;
 576         for (i = 0; i < nr; i++)
 577                 if (bitmap[i / 32] & (1 << (i % 32)))
 578                         ref_status[i]++;
 579 }
 580
 581 /*
 582  * Step 7, reachability test on "ours" at commit level
 583  */
 584 static void post_assign_shallow(struct shallow_info *info,
 585                                 struct ref_bitmap *ref_bitmap,
 586                                 int *ref_status)
 587 {
 588         unsigned char (*sha1)[20] = info->shallow->sha1;
 589         struct commit *c;
 590         uint32_t **bitmap;
 591         int dst, i, j;
 592         int bitmap_nr = (info->ref->nr + 31) / 32;
 593         struct commit_array ca;
 594
 595         trace_printf_key(&trace_shallow, "shallow: post_assign_shallow\n");
 596         if (ref_status)
 597                 memset(ref_status, 0, sizeof(*ref_status) * info->ref->nr);
 598
 599         /* Remove unreachable shallow commits from "theirs" */
 600         for (i = dst = 0; i < info->nr_theirs; i++) {
 601                 if (i != dst)
 602                         info->theirs[dst] = info->theirs[i];
 603                 c = lookup_commit(sha1[info->theirs[i]]);
 604                 bitmap = ref_bitmap_at(ref_bitmap, c);
 605                 if (!*bitmap)
 606                         continue;
 607                 for (j = 0; j < bitmap_nr; j++)
 608                         if (bitmap[0][j]) {
 609                                 update_refstatus(ref_status, info->ref->nr, *bitmap);
 610                                 dst++;
 611                                 break;
 612                         }
 613         }
 614         info->nr_theirs = dst;
 615
 616         memset(&ca, 0, sizeof(ca));
 617         head_ref(add_ref, &ca);
 618         for_each_ref(add_ref, &ca);
 619
 620         /* Remove unreachable shallow commits from "ours" */
 621         for (i = dst = 0; i < info->nr_ours; i++) {
 622                 if (i != dst)
 623                         info->ours[dst] = info->ours[i];
 624                 c = lookup_commit(sha1[info->ours[i]]);
 625                 bitmap = ref_bitmap_at(ref_bitmap, c);
 626                 if (!*bitmap)
 627                         continue;
 628                 for (j = 0; j < bitmap_nr; j++)
 629                         if (bitmap[0][j] &&
 630                             /* Step 7, reachability test at commit level */
 631                             !in_merge_bases_many(c, ca.nr, ca.commits)) {
 632                                 update_refstatus(ref_status, info->ref->nr, *bitmap);
 633                                 dst++;
 634                                 break;
 635                         }
 636         }
 637         info->nr_ours = dst;
 638
 639         free(ca.commits);
 640 }
 641
 642 /* (Delayed) step 7, reachability test at commit level */
 643 int delayed_reachability_test(struct shallow_info *si, int c)
 644 {
 645         if (si->need_reachability_test[c]) {
 646                 struct commit *commit = lookup_commit(si->shallow->sha1[c]);
 647
 648                 if (!si->commits) {
 649                         struct commit_array ca;
 650
 651                         memset(&ca, 0, sizeof(ca));
 652                         head_ref(add_ref, &ca);
 653                         for_each_ref(add_ref, &ca);
 654                         si->commits = ca.commits;
 655                         si->nr_commits = ca.nr;
 656                 }
 657
 658                 si->reachable[c] = in_merge_bases_many(commit,
 659                                                        si->nr_commits,
 660                                                        si->commits);
 661                 si->need_reachability_test[c] = 0;
 662         }
 663         return si->reachable[c];
 664 }