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commit: use generation numbers for in_merge_bases()

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The containment algorithm for 'git branch --contains' is different
from that for 'git tag --contains' in that it uses is_descendant_of()
instead of contains_tag_algo(). The expensive portion of the branch
algorithm is computing merge bases.

When a commit-graph file exists with generation numbers computed,
we can avoid this merge-base calculation when the target commit has
a larger generation number than the initial commits.

Performance tests were run on a copy of the Linux repository where
HEAD is contained in v4.13 but no earlier tag. Also, all tags were
copied to branches and 'git branch --contains' was tested:

Before: 60.0s
After:   0.4s
Rel %: -99.3%

Reported-by: Jeff King <peff@peff.net>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Derrick Stolee 2018-05-01 12:47:17 +00:00 committed by Junio C Hamano
parent 819807b33f
commit f9b8908b85
1 changed files with 8 additions and 1 deletions
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9
commit.c
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@ -1056,12 +1056,19 @@ int in_merge_bases_many(struct commit *commit, int nr_reference, struct commit *
{
struct commit_list *bases;
int ret = 0, i;
uint32_t min_generation = GENERATION_NUMBER_INFINITY;
if (parse_commit(commit))
return ret;
for (i = 0; i < nr_reference; i++)
for (i = 0; i < nr_reference; i++) {
if (parse_commit(reference[i]))
return ret;
if (reference[i]->generation < min_generation)
min_generation = reference[i]->generation;
}
if (commit->generation > min_generation)
return ret;
bases = paint_down_to_common(commit, nr_reference, reference);
if (commit->object.flags & PARENT2)