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 <p...@peff.net>
Signed-off-by: Derrick Stolee <dsto...@microsoft.com>
---
commit.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/commit.c b/commit.c
index 39a3749abd..7bb007f56a 100644
--- a/commit.c
+++ b/commit.c
@@ -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 (min_generation > reference[i]->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)
--
2.17.0.39.g685157f7fb
