Derrick Stolee <dstolee@xxxxxxxxxxxxx> writes:
> 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 target commits.
You have "target" twice in above paragraph; one of those should probably
be something else.
>
> 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%
Nice...
>
> Reported-by: Jeff King <peff@xxxxxxxx>
> Signed-off-by: Derrick Stolee <dstolee@xxxxxxxxxxxxx>
> ---
> commit.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
...especially for so small changes.
>
> diff --git a/commit.c b/commit.c
> index a44899c733..bceb79c419 100644
> --- a/commit.c
> +++ b/commit.c
> @@ -1053,12 +1053,19 @@ 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 0;
Why not use "return ret;" instead of "return 0;", like the rest of the
code [cryptically] does, that is:
+ if (commit->generation > min_generation)
+ return ret;
>
> bases = paint_down_to_common(commit, nr_reference, reference);
> if (commit->object.flags & PARENT2)
Otherwise, it looks good to me.
