bisect.c

   1 #include "cache.h"
   2 #include "commit.h"
   3 #include "diff.h"
   4 #include "revision.h"
   5 #include "bisect.h"
   6
   7 static unsigned char (*skipped_sha1)[20];
   8 static int skipped_sha1_nr;
   9
  10 /* bits #0-15 in revision.h */
  11
  12 #define COUNTED         (1u<<16)
  13
  14 /*
  15  * This is a truly stupid algorithm, but it's only
  16  * used for bisection, and we just don't care enough.
  17  *
  18  * We care just barely enough to avoid recursing for
  19  * non-merge entries.
  20  */
  21 static int count_distance(struct commit_list *entry)
  22 {
  23         int nr = 0;
  24
  25         while (entry) {
  26                 struct commit *commit = entry->item;
  27                 struct commit_list *p;
  28
  29                 if (commit->object.flags & (UNINTERESTING | COUNTED))
  30                         break;
  31                 if (!(commit->object.flags & TREESAME))
  32                         nr++;
  33                 commit->object.flags |= COUNTED;
  34                 p = commit->parents;
  35                 entry = p;
  36                 if (p) {
  37                         p = p->next;
  38                         while (p) {
  39                                 nr += count_distance(p);
  40                                 p = p->next;
  41                         }
  42                 }
  43         }
  44
  45         return nr;
  46 }
  47
  48 static void clear_distance(struct commit_list *list)
  49 {
  50         while (list) {
  51                 struct commit *commit = list->item;
  52                 commit->object.flags &= ~COUNTED;
  53                 list = list->next;
  54         }
  55 }
  56
  57 #define DEBUG_BISECT 0
  58
  59 static inline int weight(struct commit_list *elem)
  60 {
  61         return *((int*)(elem->item->util));
  62 }
  63
  64 static inline void weight_set(struct commit_list *elem, int weight)
  65 {
  66         *((int*)(elem->item->util)) = weight;
  67 }
  68
  69 static int count_interesting_parents(struct commit *commit)
  70 {
  71         struct commit_list *p;
  72         int count;
  73
  74         for (count = 0, p = commit->parents; p; p = p->next) {
  75                 if (p->item->object.flags & UNINTERESTING)
  76                         continue;
  77                 count++;
  78         }
  79         return count;
  80 }
  81
  82 static inline int halfway(struct commit_list *p, int nr)
  83 {
  84         /*
  85          * Don't short-cut something we are not going to return!
  86          */
  87         if (p->item->object.flags & TREESAME)
  88                 return 0;
  89         if (DEBUG_BISECT)
  90                 return 0;
  91         /*
  92          * 2 and 3 are halfway of 5.
  93          * 3 is halfway of 6 but 2 and 4 are not.
  94          */
  95         switch (2 * weight(p) - nr) {
  96         case -1: case 0: case 1:
  97                 return 1;
  98         default:
  99                 return 0;
 100         }
 101 }
 102
 103 #if !DEBUG_BISECT
 104 #define show_list(a,b,c,d) do { ; } while (0)
 105 #else
 106 static void show_list(const char *debug, int counted, int nr,
 107                       struct commit_list *list)
 108 {
 109         struct commit_list *p;
 110
 111         fprintf(stderr, "%s (%d/%d)\n", debug, counted, nr);
 112
 113         for (p = list; p; p = p->next) {
 114                 struct commit_list *pp;
 115                 struct commit *commit = p->item;
 116                 unsigned flags = commit->object.flags;
 117                 enum object_type type;
 118                 unsigned long size;
 119                 char *buf = read_sha1_file(commit->object.sha1, &type, &size);
 120                 char *ep, *sp;
 121
 122                 fprintf(stderr, "%c%c%c ",
 123                         (flags & TREESAME) ? ' ' : 'T',
 124                         (flags & UNINTERESTING) ? 'U' : ' ',
 125                         (flags & COUNTED) ? 'C' : ' ');
 126                 if (commit->util)
 127                         fprintf(stderr, "%3d", weight(p));
 128                 else
 129                         fprintf(stderr, "---");
 130                 fprintf(stderr, " %.*s", 8, sha1_to_hex(commit->object.sha1));
 131                 for (pp = commit->parents; pp; pp = pp->next)
 132                         fprintf(stderr, " %.*s", 8,
 133                                 sha1_to_hex(pp->item->object.sha1));
 134
 135                 sp = strstr(buf, "\n\n");
 136                 if (sp) {
 137                         sp += 2;
 138                         for (ep = sp; *ep && *ep != '\n'; ep++)
 139                                 ;
 140                         fprintf(stderr, " %.*s", (int)(ep - sp), sp);
 141                 }
 142                 fprintf(stderr, "\n");
 143         }
 144 }
 145 #endif /* DEBUG_BISECT */
 146
 147 static struct commit_list *best_bisection(struct commit_list *list, int nr)
 148 {
 149         struct commit_list *p, *best;
 150         int best_distance = -1;
 151
 152         best = list;
 153         for (p = list; p; p = p->next) {
 154                 int distance;
 155                 unsigned flags = p->item->object.flags;
 156
 157                 if (flags & TREESAME)
 158                         continue;
 159                 distance = weight(p);
 160                 if (nr - distance < distance)
 161                         distance = nr - distance;
 162                 if (distance > best_distance) {
 163                         best = p;
 164                         best_distance = distance;
 165                 }
 166         }
 167
 168         return best;
 169 }
 170
 171 struct commit_dist {
 172         struct commit *commit;
 173         int distance;
 174 };
 175
 176 static int compare_commit_dist(const void *a_, const void *b_)
 177 {
 178         struct commit_dist *a, *b;
 179
 180         a = (struct commit_dist *)a_;
 181         b = (struct commit_dist *)b_;
 182         if (a->distance != b->distance)
 183                 return b->distance - a->distance; /* desc sort */
 184         return hashcmp(a->commit->object.sha1, b->commit->object.sha1);
 185 }
 186
 187 static struct commit_list *best_bisection_sorted(struct commit_list *list, int nr)
 188 {
 189         struct commit_list *p;
 190         struct commit_dist *array = xcalloc(nr, sizeof(*array));
 191         int cnt, i;
 192
 193         for (p = list, cnt = 0; p; p = p->next) {
 194                 int distance;
 195                 unsigned flags = p->item->object.flags;
 196
 197                 if (flags & TREESAME)
 198                         continue;
 199                 distance = weight(p);
 200                 if (nr - distance < distance)
 201                         distance = nr - distance;
 202                 array[cnt].commit = p->item;
 203                 array[cnt].distance = distance;
 204                 cnt++;
 205         }
 206         qsort(array, cnt, sizeof(*array), compare_commit_dist);
 207         for (p = list, i = 0; i < cnt; i++) {
 208                 struct name_decoration *r = xmalloc(sizeof(*r) + 100);
 209                 struct object *obj = &(array[i].commit->object);
 210
 211                 sprintf(r->name, "dist=%d", array[i].distance);
 212                 r->next = add_decoration(&name_decoration, obj, r);
 213                 p->item = array[i].commit;
 214                 p = p->next;
 215         }
 216         if (p)
 217                 p->next = NULL;
 218         free(array);
 219         return list;
 220 }
 221
 222 /*
 223  * zero or positive weight is the number of interesting commits it can
 224  * reach, including itself.  Especially, weight = 0 means it does not
 225  * reach any tree-changing commits (e.g. just above uninteresting one
 226  * but traversal is with pathspec).
 227  *
 228  * weight = -1 means it has one parent and its distance is yet to
 229  * be computed.
 230  *
 231  * weight = -2 means it has more than one parent and its distance is
 232  * unknown.  After running count_distance() first, they will get zero
 233  * or positive distance.
 234  */
 235 static struct commit_list *do_find_bisection(struct commit_list *list,
 236                                              int nr, int *weights,
 237                                              int find_all)
 238 {
 239         int n, counted;
 240         struct commit_list *p;
 241
 242         counted = 0;
 243
 244         for (n = 0, p = list; p; p = p->next) {
 245                 struct commit *commit = p->item;
 246                 unsigned flags = commit->object.flags;
 247
 248                 p->item->util = &weights[n++];
 249                 switch (count_interesting_parents(commit)) {
 250                 case 0:
 251                         if (!(flags & TREESAME)) {
 252                                 weight_set(p, 1);
 253                                 counted++;
 254                                 show_list("bisection 2 count one",
 255                                           counted, nr, list);
 256                         }
 257                         /*
 258                          * otherwise, it is known not to reach any
 259                          * tree-changing commit and gets weight 0.
 260                          */
 261                         break;
 262                 case 1:
 263                         weight_set(p, -1);
 264                         break;
 265                 default:
 266                         weight_set(p, -2);
 267                         break;
 268                 }
 269         }
 270
 271         show_list("bisection 2 initialize", counted, nr, list);
 272
 273         /*
 274          * If you have only one parent in the resulting set
 275          * then you can reach one commit more than that parent
 276          * can reach.  So we do not have to run the expensive
 277          * count_distance() for single strand of pearls.
 278          *
 279          * However, if you have more than one parents, you cannot
 280          * just add their distance and one for yourself, since
 281          * they usually reach the same ancestor and you would
 282          * end up counting them twice that way.
 283          *
 284          * So we will first count distance of merges the usual
 285          * way, and then fill the blanks using cheaper algorithm.
 286          */
 287         for (p = list; p; p = p->next) {
 288                 if (p->item->object.flags & UNINTERESTING)
 289                         continue;
 290                 if (weight(p) != -2)
 291                         continue;
 292                 weight_set(p, count_distance(p));
 293                 clear_distance(list);
 294
 295                 /* Does it happen to be at exactly half-way? */
 296                 if (!find_all && halfway(p, nr))
 297                         return p;
 298                 counted++;
 299         }
 300
 301         show_list("bisection 2 count_distance", counted, nr, list);
 302
 303         while (counted < nr) {
 304                 for (p = list; p; p = p->next) {
 305                         struct commit_list *q;
 306                         unsigned flags = p->item->object.flags;
 307
 308                         if (0 <= weight(p))
 309                                 continue;
 310                         for (q = p->item->parents; q; q = q->next) {
 311                                 if (q->item->object.flags & UNINTERESTING)
 312                                         continue;
 313                                 if (0 <= weight(q))
 314                                         break;
 315                         }
 316                         if (!q)
 317                                 continue;
 318
 319                         /*
 320                          * weight for p is unknown but q is known.
 321                          * add one for p itself if p is to be counted,
 322                          * otherwise inherit it from q directly.
 323                          */
 324                         if (!(flags & TREESAME)) {
 325                                 weight_set(p, weight(q)+1);
 326                                 counted++;
 327                                 show_list("bisection 2 count one",
 328                                           counted, nr, list);
 329                         }
 330                         else
 331                                 weight_set(p, weight(q));
 332
 333                         /* Does it happen to be at exactly half-way? */
 334                         if (!find_all && halfway(p, nr))
 335                                 return p;
 336                 }
 337         }
 338
 339         show_list("bisection 2 counted all", counted, nr, list);
 340
 341         if (!find_all)
 342                 return best_bisection(list, nr);
 343         else
 344                 return best_bisection_sorted(list, nr);
 345 }
 346
 347 struct commit_list *find_bisection(struct commit_list *list,
 348                                           int *reaches, int *all,
 349                                           int find_all)
 350 {
 351         int nr, on_list;
 352         struct commit_list *p, *best, *next, *last;
 353         int *weights;
 354
 355         show_list("bisection 2 entry", 0, 0, list);
 356
 357         /*
 358          * Count the number of total and tree-changing items on the
 359          * list, while reversing the list.
 360          */
 361         for (nr = on_list = 0, last = NULL, p = list;
 362              p;
 363              p = next) {
 364                 unsigned flags = p->item->object.flags;
 365
 366                 next = p->next;
 367                 if (flags & UNINTERESTING)
 368                         continue;
 369                 p->next = last;
 370                 last = p;
 371                 if (!(flags & TREESAME))
 372                         nr++;
 373                 on_list++;
 374         }
 375         list = last;
 376         show_list("bisection 2 sorted", 0, nr, list);
 377
 378         *all = nr;
 379         weights = xcalloc(on_list, sizeof(*weights));
 380
 381         /* Do the real work of finding bisection commit. */
 382         best = do_find_bisection(list, nr, weights, find_all);
 383         if (best) {
 384                 if (!find_all)
 385                         best->next = NULL;
 386                 *reaches = weight(best);
 387         }
 388         free(weights);
 389         return best;
 390 }
 391
 392 static int skipcmp(const void *a, const void *b)
 393 {
 394         return hashcmp(a, b);
 395 }
 396
 397 static void prepare_skipped(void)
 398 {
 399         qsort(skipped_sha1, skipped_sha1_nr, sizeof(*skipped_sha1), skipcmp);
 400 }
 401
 402 static int lookup_skipped(unsigned char *sha1)
 403 {
 404         int lo, hi;
 405         lo = 0;
 406         hi = skipped_sha1_nr;
 407         while (lo < hi) {
 408                 int mi = (lo + hi) / 2;
 409                 int cmp = hashcmp(sha1, skipped_sha1[mi]);
 410                 if (!cmp)
 411                         return mi;
 412                 if (cmp < 0)
 413                         hi = mi;
 414                 else
 415                         lo = mi + 1;
 416         }
 417         return -lo - 1;
 418 }
 419
 420 struct commit_list *filter_skipped(struct commit_list *list,
 421                                    struct commit_list **tried,
 422                                    int show_all)
 423 {
 424         struct commit_list *filtered = NULL, **f = &filtered;
 425
 426         *tried = NULL;
 427
 428         if (!skipped_sha1_nr)
 429                 return list;
 430
 431         prepare_skipped();
 432
 433         while (list) {
 434                 struct commit_list *next = list->next;
 435                 list->next = NULL;
 436                 if (0 <= lookup_skipped(list->item->object.sha1)) {
 437                         /* Move current to tried list */
 438                         *tried = list;
 439                         tried = &list->next;
 440                 } else {
 441                         if (!show_all)
 442                                 return list;
 443                         /* Move current to filtered list */
 444                         *f = list;
 445                         f = &list->next;
 446                 }
 447                 list = next;
 448         }
 449
 450         return filtered;
 451 }