From: Linus Torvalds Date: Mon, 6 Jun 2005 21:01:58 +0000 (-0700) Subject: git-read-tree: simplify merge loops enormously X-Git-Tag: v0.99~337 X-Git-Url: https://git.verplant.org/?a=commitdiff_plain;h=d723c690637f2918d9861e8d602e592c5fa0bc5b;p=git.git git-read-tree: simplify merge loops enormously Stop trying to haev this stateful thing that keeps track of what it has seen, and use a much simpler "gather all the different stages with the same name together and just merge them in one go" approach. Makes it a lot more understandable, and allows the different merge algorithms to share the basic merge loop. --- diff --git a/read-tree.c b/read-tree.c index 63a1eb54..4acbb6b3 100644 --- a/read-tree.c +++ b/read-tree.c @@ -39,27 +39,11 @@ static int same(struct cache_entry *a, struct cache_entry *b) /* * This removes all trivial merges that don't change the tree * and collapses them to state 0. - * - * _Any_ other merge is left to user policy. That includes "both - * created the same file", and "both removed the same file" - which are - * trivial, but the user might still want to _note_ it. */ static struct cache_entry *merge_entries(struct cache_entry *a, struct cache_entry *b, struct cache_entry *c) { - int len = ce_namelen(a); - - /* - * Are they all the same filename? We won't do - * any name merging - */ - if (ce_namelen(b) != len || - ce_namelen(c) != len || - memcmp(a->name, b->name, len) || - memcmp(a->name, c->name, len)) - return NULL; - /* * Ok, all three entries describe the same * filename, but maybe the contents or file @@ -77,12 +61,14 @@ static struct cache_entry *merge_entries(struct cache_entry *a, * Here "a" is "original", and "b" and "c" are the two * trees we are merging. */ - if (same(b,c)) - return c; - if (same(a,b)) - return c; - if (same(a,c)) - return b; + if (a && b && c) { + if (same(b,c)) + return c; + if (same(a,b)) + return c; + if (same(a,c)) + return b; + } return NULL; } @@ -116,88 +102,54 @@ static void reject_merge(struct cache_entry *ce) die("Entry '%s' would be overwritten by merge. Cannot merge.", ce->name); } -#define CHECK_OLD(ce) if (old && same(old, ce)) { verify_uptodate(old); old = NULL; } - -static void trivially_merge_cache(struct cache_entry **src, int nr) +static int merged_entry(struct cache_entry *merge, struct cache_entry *old, struct cache_entry **dst) { - struct cache_entry **dst = src; - struct cache_entry *old = NULL; - - while (nr--) { - struct cache_entry *ce, *result; - - ce = *src++; - - /* We throw away original cache entries except for the stat information */ - if (!ce_stage(ce)) { - if (old) - reject_merge(old); - old = ce; - active_nr--; - continue; - } - if (old && !path_matches(old, ce)) - reject_merge(old); - if (nr > 1 && (result = merge_entries(ce, src[0], src[1])) != NULL) { - result->ce_flags |= htons(CE_UPDATE); - /* - * See if we can re-use the old CE directly? - * That way we get the uptodate stat info. - * - * This also removes the UPDATE flag on - * a match. - */ - if (old && same(old, result)) { - *result = *old; - old = NULL; - } - CHECK_OLD(ce); - CHECK_OLD(src[0]); - CHECK_OLD(src[1]); - ce = result; - ce->ce_flags &= ~htons(CE_STAGEMASK); - src += 2; - nr -= 2; - active_nr -= 2; - } - + merge->ce_flags |= htons(CE_UPDATE); + if (old) { /* - * If we had an old entry that we now effectively - * overwrite, make sure it wasn't dirty. + * See if we can re-use the old CE directly? + * That way we get the uptodate stat info. + * + * This also removes the UPDATE flag on + * a match. */ - CHECK_OLD(ce); - *dst++ = ce; + if (same(old, merge)) { + *merge = *old; + } else { + verify_uptodate(old); + } } - if (old) - reject_merge(old); + merge->ce_flags &= ~htons(CE_STAGEMASK); + *dst++ = merge; + return 1; } -/* - * When we find a "stage2" entry in the two-way merge, that's - * the one that will remain. If we have an exact old match, - * we don't care whether the file is up-to-date or not, we just - * re-use the thing directly. - * - * If we didn't have an exact match, then we want to make sure - * that we've seen a stage1 that matched the old, and that the - * old file was up-to-date. Because it will be gone after this - * merge.. - */ -static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_entry *ce) +static int threeway_merge(struct cache_entry *stages[4], struct cache_entry **dst) { - if (path_matches(old, ce)) { - /* - * This also removes the UPDATE flag on - * a match - */ - if (same(old, ce)) { - *ce = *old; - return; - } - if (!seen_stage1) - reject_merge(old); + struct cache_entry *old = stages[0]; + struct cache_entry *a = stages[1], *b = stages[2], *c = stages[3]; + struct cache_entry *merge; + int count; + + /* + * If we have an entry in the index cache ("old"), then we want + * to make sure that it matches any entries in stage 2 ("first + * branch", aka "b"). + */ + if (old) { + if (!b || !same(old, b)) + return -1; } - verify_uptodate(old); + merge = merge_entries(a, b, c); + if (merge) + return merged_entry(merge, old, dst); + if (old) + verify_uptodate(old); + count = 0; + if (a) { *dst++ = a; count++; } + if (b) { *dst++ = b; count++; } + if (c) { *dst++ = c; count++; } + return count; } /* @@ -208,79 +160,46 @@ static void twoway_check(struct cache_entry *old, int seen_stage1, struct cache_ * - if the current entry matches the new tree, we leave it * as-is. Otherwise we require that it be up-to-date. */ -static void twoway_merge(struct cache_entry **src, int nr) +static int twoway_merge(struct cache_entry **src, struct cache_entry **dst) { - int seen_stage1 = 0; - struct cache_entry *old = NULL; - struct cache_entry **dst = src; - - while (nr--) { - struct cache_entry *ce = *src++; - int stage = ce_stage(ce); + struct cache_entry *old = src[0]; + struct cache_entry *a = src[1], *b = src[2]; - switch (stage) { - case 0: - if (old) - reject_merge(old); - old = ce; - seen_stage1 = 0; - active_nr--; - continue; - - case 1: - active_nr--; - if (!old) - continue; - if (!path_matches(old, ce) || !same(old, ce)) - reject_merge(old); - seen_stage1 = 1; - continue; - - case 2: - ce->ce_flags |= htons(CE_UPDATE); - if (old) { - twoway_check(old, seen_stage1, ce); - old = NULL; - } - ce->ce_flags &= ~htons(CE_STAGEMASK); - *dst++ = ce; - continue; - } - die("impossible two-way stage"); - } + if (src[3]) + return -1; - /* - * Unmatched with a new entry? Make sure it was - * at least uptodate in the working directory _and_ - * the original tree.. - */ if (old) { - if (!seen_stage1) - reject_merge(old); - verify_uptodate(old); + if (!a || !same(old, a)) + return -1; } + if (b) + return merged_entry(b, old, dst); + if (old) + verify_uptodate(old); + return 0; } -static void merge_stat_info(struct cache_entry **src, int nr) +/* + * One-way merge. + * + * The rule is: + * - take the stat information from stage0, take the data from stage1 + */ +static int oneway_merge(struct cache_entry **src, struct cache_entry **dst) { - static struct cache_entry null_entry; - struct cache_entry **dst = src; - struct cache_entry *stat = &null_entry; + struct cache_entry *old = src[0]; + struct cache_entry *a = src[1]; - while (nr--) { - struct cache_entry *ce = *src++; + if (src[2] || src[3]) + return -1; - /* We throw away original cache entries except for the stat information */ - if (!ce_stage(ce)) { - stat = ce; - active_nr--; - continue; - } - if (path_matches(ce, stat) && same(ce, stat)) - *ce = *stat; - ce->ce_flags &= ~htons(CE_STAGEMASK); - *dst++ = ce; - } + if (!a) + return 0; + if (old && same(old, a)) + *a = *old; + a->ce_flags &= ~htons(CE_STAGEMASK); + *dst++ = a; + return 1; } static void check_updates(struct cache_entry **src, int nr) @@ -302,6 +221,35 @@ static void check_updates(struct cache_entry **src, int nr) } } +static void merge_cache(struct cache_entry **src, int nr, int (*fn)(struct cache_entry **, struct cache_entry **)) +{ + struct cache_entry **dst = src; + + while (nr) { + int entries; + struct cache_entry *name, *ce, *stages[4] = { NULL, }; + + name = ce = *src; + for (;;) { + int stage = ce_stage(ce); + stages[stage] = ce; + ce = *++src; + active_nr--; + if (!--nr) + break; + if (!path_matches(ce, name)) + break; + } + + entries = fn(stages, dst); + if (entries < 0) + reject_merge(name); + dst += entries; + active_nr += entries; + } + check_updates(active_cache, active_nr); +} + static char *read_tree_usage = "git-read-tree ( | -m [ []])"; static struct cache_file cache_file; @@ -350,15 +298,14 @@ int main(int argc, char **argv) if (merge) { switch (stage) { case 4: /* Three-way merge */ - trivially_merge_cache(active_cache, active_nr); - check_updates(active_cache, active_nr); + merge_cache(active_cache, active_nr, threeway_merge); break; case 3: /* Update from one tree to another */ - twoway_merge(active_cache, active_nr); + merge_cache(active_cache, active_nr, twoway_merge); check_updates(active_cache, active_nr); break; case 2: /* Just read a tree, merge with old cache contents */ - merge_stat_info(active_cache, active_nr); + merge_cache(active_cache, active_nr, oneway_merge); break; default: die("just how do you expect me to merge %d trees?", stage-1);