bisect.c

   1 #include "cache.h"
   2 #include "commit.h"
   3 #include "diff.h"
   4 #include "revision.h"
   5 #include "sha1-lookup.h"
   6 #include "bisect.h"
   7
   8 static unsigned char (*skipped_sha1)[20];
   9 static int skipped_sha1_nr;
  10
  11 /* bits #0-15 in revision.h */
  12
  13 #define COUNTED         (1u<<16)
  14
  15 /*
  16  * This is a truly stupid algorithm, but it's only
  17  * used for bisection, and we just don't care enough.
  18  *
  19  * We care just barely enough to avoid recursing for
  20  * non-merge entries.
  21  */
  22 static int count_distance(struct commit_list *entry)
  23 {
  24         int nr = 0;
  25
  26         while (entry) {
  27                 struct commit *commit = entry->item;
  28                 struct commit_list *p;
  29
  30                 if (commit->object.flags & (UNINTERESTING | COUNTED))
  31                         break;
  32                 if (!(commit->object.flags & TREESAME))
  33                         nr++;
  34                 commit->object.flags |= COUNTED;
  35                 p = commit->parents;
  36                 entry = p;
  37                 if (p) {
  38                         p = p->next;
  39                         while (p) {
  40                                 nr += count_distance(p);
  41                                 p = p->next;
  42                         }
  43                 }
  44         }
  45
  46         return nr;
  47 }
  48
  49 static void clear_distance(struct commit_list *list)
  50 {
  51         while (list) {
  52                 struct commit *commit = list->item;
  53                 commit->object.flags &= ~COUNTED;
  54                 list = list->next;
  55         }
  56 }
  57
  58 #define DEBUG_BISECT 0
  59
  60 static inline int weight(struct commit_list *elem)
  61 {
  62         return *((int*)(elem->item->util));
  63 }
  64
  65 static inline void weight_set(struct commit_list *elem, int weight)
  66 {
  67         *((int*)(elem->item->util)) = weight;
  68 }
  69
  70 static int count_interesting_parents(struct commit *commit)
  71 {
  72         struct commit_list *p;
  73         int count;
  74
  75         for (count = 0, p = commit->parents; p; p = p->next) {
  76                 if (p->item->object.flags & UNINTERESTING)
  77                         continue;
  78                 count++;
  79         }
  80         return count;
  81 }
  82
  83 static inline int halfway(struct commit_list *p, int nr)
  84 {
  85         /*
  86          * Don't short-cut something we are not going to return!
  87          */
  88         if (p->item->object.flags & TREESAME)
  89                 return 0;
  90         if (DEBUG_BISECT)
  91                 return 0;
  92         /*
  93          * 2 and 3 are halfway of 5.
  94          * 3 is halfway of 6 but 2 and 4 are not.
  95          */
  96         switch (2 * weight(p) - nr) {
  97         case -1: case 0: case 1:
  98                 return 1;
  99         default:
 100                 return 0;
 101         }
 102 }
 103
 104 #if !DEBUG_BISECT
 105 #define show_list(a,b,c,d) do { ; } while (0)
 106 #else
 107 static void show_list(const char *debug, int counted, int nr,
 108                       struct commit_list *list)
 109 {
 110         struct commit_list *p;
 111
 112         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 113
 114         for (p = list; p; p = p->next) {
 115                 struct commit_list *pp;
 116                 struct commit *commit = p->item;
 117                 unsigned flags = commit->object.flags;
 118                 enum object_type type;
 119                 unsigned long size;
 120                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 121                 char *ep, *sp;
 122
 123                 fprintf(stderr, "%c%c%c ",
 124                         (flags & TREESAME) ? ' ' : 'T',
 125                         (flags & UNINTERESTING) ? 'U' : ' ',
 126                         (flags & COUNTED) ? 'C' : ' ');
 127                 if (commit->util)
 128                         fprintf(stderr, "%3d", weight(p));
 129                 else
 130                         fprintf(stderr, "---");
 131                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 132                 for (pp = commit->parents; pp; pp = pp->next)
 133                         fprintf(stderr, " %.*s", 8,
 134                                 sha1_to_hex(pp->item->object.sha1));
 135
 136                 sp = strstr(buf, "\n\n");
 137                 if (sp) {
 138                         sp += 2;
 139                         for (ep = sp; *ep && *ep != '\n'; ep++)
 140                                 ;
 141                         fprintf(stderr, " %.*s", (int)(ep - sp), sp);
 142                 }
 143                 fprintf(stderr, "\n");
 144         }
 145 }
 146 #endif /* DEBUG_BISECT */
 147
 148 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 149 {
 150         struct commit_list *p, *best;
 151         int best_distance = -1;
 152
 153         best = list;
 154         for (p = list; p; p = p->next) {
 155                 int distance;
 156                 unsigned flags = p->item->object.flags;
 157
 158                 if (flags & TREESAME)
 159                         continue;
 160                 distance = weight(p);
 161                 if (nr - distance < distance)
 162                         distance = nr - distance;
 163                 if (distance > best_distance) {
 164                         best = p;
 165                         best_distance = distance;
 166                 }
 167         }
 168
 169         return best;
 170 }
 171
 172 struct commit_dist {
 173         struct commit *commit;
 174         int distance;
 175 };
 176
 177 static int compare_commit_dist(const void *a_, const void *b_)
 178 {
 179         struct commit_dist *a, *b;
 180
 181         a = (struct commit_dist *)a_;
 182         b = (struct commit_dist *)b_;
 183         if (a->distance != b->distance)
 184                 return b->distance - a->distance; /* desc sort */
 185         return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
 186 }
 187
 188 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 189 {
 190         struct commit_list *p;
 191         struct commit_dist *array = xcalloc(nr, sizeof(*array));
 192         int cnt, i;
 193
 194         for (p = list, cnt = 0; p; p = p->next) {
 195                 int distance;
 196                 unsigned flags = p->item->object.flags;
 197
 198                 if (flags & TREESAME)
 199                         continue;
 200                 distance = weight(p);
 201                 if (nr - distance < distance)
 202                         distance = nr - distance;
 203                 array[cnt].commit = p->item;
 204                 array[cnt].distance = distance;
 205                 cnt++;
 206         }
 207         qsort(array, cnt, sizeof(*array), compare_commit_dist);
 208         for (p = list, i = 0; i < cnt; i++) {
 209                 struct name_decoration *r = xmalloc(sizeof(*r) + 100);
 210                 struct object *obj = &(array[i].commit->object);
 211
 212                 sprintf(r->name, "dist=%d", array[i].distance);
 213                 r->next = add_decoration(&name_decoration, obj, r);
 214                 p->item = array[i].commit;
 215                 p = p->next;
 216         }
 217         if (p)
 218                 p->next = NULL;
 219         free(array);
 220         return list;
 221 }
 222
 223 /*
 224  * zero or positive weight is the number of interesting commits it can
 225  * reach, including itself.  Especially, weight = 0 means it does not
 226  * reach any tree-changing commits (e.g. just above uninteresting one
 227  * but traversal is with pathspec).
 228  *
 229  * weight = -1 means it has one parent and its distance is yet to
 230  * be computed.
 231  *
 232  * weight = -2 means it has more than one parent and its distance is
 233  * unknown.  After running count_distance() first, they will get zero
 234  * or positive distance.
 235  */
 236 static struct commit_list *do_find_bisection(struct commit_list *list,
 237                                              int nr, int *weights,
 238                                              int find_all)
 239 {
 240         int n, counted;
 241         struct commit_list *p;
 242
 243         counted = 0;
 244
 245         for (n = 0, p = list; p; p = p->next) {
 246                 struct commit *commit = p->item;
 247                 unsigned flags = commit->object.flags;
 248
 249                 p->item->util = &weights[n++];
 250                 switch (count_interesting_parents(commit)) {
 251                 case 0:
 252                         if (!(flags & TREESAME)) {
 253                                 weight_set(p, 1);
 254                                 counted++;
 255                                 show_list("bisection 2 count one",
 256                                           counted, nr, list);
 257                         }
 258                         /*
 259                          * otherwise, it is known not to reach any
 260                          * tree-changing commit and gets weight 0.
 261                          */
 262                         break;
 263                 case 1:
 264                         weight_set(p, -1);
 265                         break;
 266                 default:
 267                         weight_set(p, -2);
 268                         break;
 269                 }
 270         }
 271
 272         show_list("bisection 2 initialize", counted, nr, list);
 273
 274         /*
 275          * If you have only one parent in the resulting set
 276          * then you can reach one commit more than that parent
 277          * can reach.  So we do not have to run the expensive
 278          * count_distance() for single strand of pearls.
 279          *
 280          * However, if you have more than one parents, you cannot
 281          * just add their distance and one for yourself, since
 282          * they usually reach the same ancestor and you would
 283          * end up counting them twice that way.
 284          *
 285          * So we will first count distance of merges the usual
 286          * way, and then fill the blanks using cheaper algorithm.
 287          */
 288         for (p = list; p; p = p->next) {
 289                 if (p->item->object.flags & UNINTERESTING)
 290                         continue;
 291                 if (weight(p) != -2)
 292                         continue;
 293                 weight_set(p, count_distance(p));
 294                 clear_distance(list);
 295
 296                 /* Does it happen to be at exactly half-way? */
 297                 if (!find_all && halfway(p, nr))
 298                         return p;
 299                 counted++;
 300         }
 301
 302         show_list("bisection 2 count_distance", counted, nr, list);
 303
 304         while (counted < nr) {
 305                 for (p = list; p; p = p->next) {
 306                         struct commit_list *q;
 307                         unsigned flags = p->item->object.flags;
 308
 309                         if (0 <= weight(p))
 310                                 continue;
 311                         for (q = p->item->parents; q; q = q->next) {
 312                                 if (q->item->object.flags & UNINTERESTING)
 313                                         continue;
 314                                 if (0 <= weight(q))
 315                                         break;
 316                         }
 317                         if (!q)
 318                                 continue;
 319
 320                         /*
 321                          * weight for p is unknown but q is known.
 322                          * add one for p itself if p is to be counted,
 323                          * otherwise inherit it from q directly.
 324                          */
 325                         if (!(flags & TREESAME)) {
 326                                 weight_set(p, weight(q)+1);
 327                                 counted++;
 328                                 show_list("bisection 2 count one",
 329                                           counted, nr, list);
 330                         }
 331                         else
 332                                 weight_set(p, weight(q));
 333
 334                         /* Does it happen to be at exactly half-way? */
 335                         if (!find_all && halfway(p, nr))
 336                                 return p;
 337                 }
 338         }
 339
 340         show_list("bisection 2 counted all", counted, nr, list);
 341
 342         if (!find_all)
 343                 return best_bisection(list, nr);
 344         else
 345                 return best_bisection_sorted(list, nr);
 346 }
 347
 348 struct commit_list *find_bisection(struct commit_list *list,
 349                                           int *reaches, int *all,
 350                                           int find_all)
 351 {
 352         int nr, on_list;
 353         struct commit_list *p, *best, *next, *last;
 354         int *weights;
 355
 356         show_list("bisection 2 entry", 0, 0, list);
 357
 358         /*
 359          * Count the number of total and tree-changing items on the
 360          * list, while reversing the list.
 361          */
 362         for (nr = on_list = 0, last = NULL, p = list;
 363              p;
 364              p = next) {
 365                 unsigned flags = p->item->object.flags;
 366
 367                 next = p->next;
 368                 if (flags & UNINTERESTING)
 369                         continue;
 370                 p->next = last;
 371                 last = p;
 372                 if (!(flags & TREESAME))
 373                         nr++;
 374                 on_list++;
 375         }
 376         list = last;
 377         show_list("bisection 2 sorted", 0, nr, list);
 378
 379         *all = nr;
 380         weights = xcalloc(on_list, sizeof(*weights));
 381
 382         /* Do the real work of finding bisection commit. */
 383         best = do_find_bisection(list, nr, weights, find_all);
 384         if (best) {
 385                 if (!find_all)
 386                         best->next = NULL;
 387                 *reaches = weight(best);
 388         }
 389         free(weights);
 390         return best;
 391 }
 392
 393 static int skipcmp(const void *a, const void *b)
 394 {
 395         return hashcmp(a, b);
 396 }
 397
 398 static void prepare_skipped(void)
 399 {
 400         qsort(skipped_sha1, skipped_sha1_nr, sizeof(*skipped_sha1), skipcmp);
 401 }
 402
 403 static const unsigned char *skipped_sha1_access(size_t index, void *table)
 404 {
 405         unsigned char (*skipped)[20] = table;
 406         return skipped[index];
 407 }
 408
 409 static int lookup_skipped(unsigned char *sha1)
 410 {
 411         return sha1_pos(sha1, skipped_sha1, skipped_sha1_nr,
 412                         skipped_sha1_access);
 413 }
 414
 415 struct commit_list *filter_skipped(struct commit_list *list,
 416                                    struct commit_list **tried,
 417                                    int show_all)
 418 {
 419         struct commit_list *filtered = NULL, **f = &filtered;
 420
 421         *tried = NULL;
 422
 423         if (!skipped_sha1_nr)
 424                 return list;
 425
 426         prepare_skipped();
 427
 428         while (list) {
 429                 struct commit_list *next = list->next;
 430                 list->next = NULL;
 431                 if (0 <= lookup_skipped(list->item->object.sha1)) {
 432                         /* Move current to tried list */
 433                         *tried = list;
 434                         tried = &list->next;
 435                 } else {
 436                         if (!show_all)
 437                                 return list;
 438                         /* Move current to filtered list */
 439                         *f = list;
 440                         f = &list->next;
 441                 }
 442                 list = next;
 443         }
 444
 445         return filtered;
 446 }