@matheusbsbs / matheus-bagliano / commits / d7c1ec3efd

commit: add short-circuit to paint_down_to_common()

When running 'git branch --contains', the in_merge_bases_many() method calls paint_down_to_common() to discover if a specific commit is reachable from a set of branches. Commits with lower generation number are not needed to correctly answer the containment query of in_merge_bases_many(). Add a new parameter, min_generation, to paint_down_to_common() that prevents walking commits with generation number strictly less than min_generation. If 0 is given, then there is no functional change. For in_merge_bases_many(), we can pass commit->generation as the cutoff, and this saves time during 'git branch --contains' queries that would otherwise walk "around" the commit we are inspecting. For a copy of the Linux repository, where HEAD is checked out at v4.13~100, we get the following performance improvement for 'git branch --contains' over the previous commit: Before: 0.21s After: 0.13s Rel %: -38% Signed-off-by: Derrick Stolee <dstolee@microsoft.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>

Derrick Stolee committed May 1, 2018 at 12:47 UTC d7c1ec3efd0092ee665085cba4e8a2bcef95143b

1 file changed +16 -4

commit.c

+16 -4

@@ -808,11 +808,14 @@ static int queue_has_nonstale(struct prio_queue *queue)

808 }

809

810 /* all input commits in one and twos[] must have been parsed! */

811 -static struct commit_list *paint_down_to_common(struct commit *one, int n, struct commit **twos)

811 +static struct commit_list *paint_down_to_common(struct commit *one, int n,

812 + struct commit **twos,

813 + int min_generation)

814 {

815 struct prio_queue queue = { compare_commits_by_gen_then_commit_date };

816 struct commit_list *result = NULL;

817 int i;

818 + uint32_t last_gen = GENERATION_NUMBER_INFINITY;

819

820 one->object.flags |= PARENT1;

821 if (!n) {

@@ -831,6 +834,15 @@ static struct commit_list *paint_down_to_common(struct commit *one, int n, struc

834 struct commit_list *parents;

835 int flags;

836

837 + if (commit->generation > last_gen)

838 + BUG("bad generation skip %8x > %8x at %s",

839 + commit->generation, last_gen,

840 + oid_to_hex(&commit->object.oid));

841 + last_gen = commit->generation;

842 +

843 + if (commit->generation < min_generation)

844 + break;

845 +

846 flags = commit->object.flags & (PARENT1 | PARENT2 | STALE);

847 if (flags == (PARENT1 | PARENT2)) {

848 if (!(commit->object.flags & RESULT)) {

@@ -879,7 +891,7 @@ static struct commit_list *merge_bases_many(struct commit *one, int n, struct co

891 return NULL;

892 }

893

882 - list = paint_down_to_common(one, n, twos);

894 + list = paint_down_to_common(one, n, twos, 0);

895

896 while (list) {

897 struct commit *commit = pop_commit(&list);

@@ -946,7 +958,7 @@ static int remove_redundant(struct commit **array, int cnt)

958 filled_index[filled] = j;

959 work[filled++] = array[j];

960 }

949 - common = paint_down_to_common(array[i], filled, work);

961 + common = paint_down_to_common(array[i], filled, work, 0);

962 if (array[i]->object.flags & PARENT2)

963 redundant[i] = 1;

964 for (j = 0; j < filled; j++)

@@ -1070,7 +1082,7 @@ int in_merge_bases_many(struct commit *commit, int nr_reference, struct commit *

1082 if (commit->generation > min_generation)

1083 return ret;

1084

1073 - bases = paint_down_to_common(commit, nr_reference, reference);

1085 + bases = paint_down_to_common(commit, nr_reference, reference, commit->generation);

1086 if (commit->object.flags & PARENT2)

1087 ret = 1;

1088 clear_commit_marks(commit, all_flags);