From 93e5b1680e30650ceca889a56429a055f17033bd Mon Sep 17 00:00:00 2001 From: Kristofer Karlsson Date: Mon, 11 May 2026 12:59:12 +0000 Subject: [PATCH] commit-reach: early exit paint_down_to_common for single merge-base Commits not in the commit-graph get GENERATION_NUMBER_INFINITY and sort to the top of the priority queue. After those, commits with finite generation numbers are popped in non-increasing order. When MERGE_BASE_FIND_ALL is not set the first doubly-painted commit with a finite generation is therefore a best merge-base: no commit still in the queue can be a descendant of it. Skip the expensive STALE drain in this case. Add MERGE_BASE_FIND_ALL to the merge_base_flags enum. Callers that need every merge-base (repo_get_merge_bases_many, repo_get_merge_bases, repo_in_merge_bases_many, remove_redundant_no_gen) pass the flag to preserve existing behavior. git merge-base (without --all) passes 0, triggering the early exit. On a 2.2M-commit merge-heavy monorepo with commit-graph: HEAD vs ~500: 5,229ms -> 24ms HEAD vs ~1000: 4,214ms -> 39ms HEAD vs ~5000: 3,799ms -> 46ms HEAD vs ~10000: 3,827ms -> 61ms Signed-off-by: Kristofer Karlsson Signed-off-by: Junio C Hamano --- builtin/merge-base.c | 3 ++- commit-reach.c | 19 +++++++++++++++---- commit-reach.h | 7 ++++++- t/t6600-test-reach.sh | 40 ++++++++++++++++++++++++++++++++++++++++ 4 files changed, 63 insertions(+), 6 deletions(-) diff --git a/builtin/merge-base.c b/builtin/merge-base.c index 9b50b4660e..a87011c6cd 100644 --- a/builtin/merge-base.c +++ b/builtin/merge-base.c @@ -11,11 +11,12 @@ static int show_merge_base(struct commit **rev, size_t rev_nr, int show_all) { + enum merge_base_flags flags = show_all ? MERGE_BASE_FIND_ALL : 0; struct commit_list *result = NULL, *r; if (repo_get_merge_bases_many_dirty(the_repository, rev[0], rev_nr - 1, rev + 1, - 0, &result) < 0) { + flags, &result) < 0) { commit_list_free(result); return -1; } diff --git a/commit-reach.c b/commit-reach.c index 766ba1156a..5a52be90a6 100644 --- a/commit-reach.c +++ b/commit-reach.c @@ -97,6 +97,14 @@ static int paint_down_to_common(struct repository *r, if (!(commit->object.flags & RESULT)) { commit->object.flags |= RESULT; tail = commit_list_append(commit, tail); + /* + * The queue is generation-ordered; no + * remaining common ancestor can be a + * descendant of this one. + */ + if (!(mb_flags & MERGE_BASE_FIND_ALL) && + generation < GENERATION_NUMBER_INFINITY) + break; } /* Mark parents of a found merge stale */ flags |= STALE; @@ -247,7 +255,8 @@ static int remove_redundant_no_gen(struct repository *r, min_generation = curr_generation; } if (paint_down_to_common(r, array[i], filled, - work, min_generation, 0, &common)) { + work, min_generation, + MERGE_BASE_FIND_ALL, &common)) { clear_commit_marks(array[i], all_flags); clear_commit_marks_many(filled, work, all_flags); commit_list_free(common); @@ -477,7 +486,8 @@ int repo_get_merge_bases_many(struct repository *r, struct commit **twos, struct commit_list **result) { - return get_merge_bases_many_0(r, one, n, twos, 1, 0, result); + return get_merge_bases_many_0(r, one, n, twos, 1, + MERGE_BASE_FIND_ALL, result); } int repo_get_merge_bases_many_dirty(struct repository *r, @@ -495,7 +505,8 @@ int repo_get_merge_bases(struct repository *r, struct commit *two, struct commit_list **result) { - return get_merge_bases_many_0(r, one, 1, &two, 1, 0, result); + return get_merge_bases_many_0(r, one, 1, &two, 1, + MERGE_BASE_FIND_ALL, result); } /* @@ -540,7 +551,7 @@ int repo_in_merge_bases_many(struct repository *r, struct commit *commit, struct commit_list *bases = NULL; int ret = 0, i; timestamp_t generation, max_generation = GENERATION_NUMBER_ZERO; - enum merge_base_flags mb_flags = 0; + enum merge_base_flags mb_flags = MERGE_BASE_FIND_ALL; if (ignore_missing_commits) mb_flags |= MERGE_BASE_IGNORE_MISSING_COMMITS; diff --git a/commit-reach.h b/commit-reach.h index a3f2cd80eb..3f3a563d8a 100644 --- a/commit-reach.h +++ b/commit-reach.h @@ -19,9 +19,14 @@ int repo_get_merge_bases_many(struct repository *r, struct commit_list **result); enum merge_base_flags { MERGE_BASE_IGNORE_MISSING_COMMITS = (1 << 0), + MERGE_BASE_FIND_ALL = (1 << 1), }; -/* To be used only when object flags after this call no longer matter */ +/* + * To be used only when object flags after this call no longer matter. + * Without MERGE_BASE_FIND_ALL and with generation numbers available, + * returns after finding the first merge-base, skipping the STALE drain. + */ int repo_get_merge_bases_many_dirty(struct repository *r, struct commit *one, size_t n, struct commit **twos, diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh index dc0421ed2f..51c23b7683 100755 --- a/t/t6600-test-reach.sh +++ b/t/t6600-test-reach.sh @@ -882,4 +882,44 @@ test_expect_success 'rev-list --maximal-only matches merge-base --independent' ' test_cmp expect.sorted actual.sorted ' +# The following tests verify the early-exit optimisation in +# paint_down_to_common when merge-base is invoked without --all. +# Each test checks all four commit-graph configurations. + +merge_base_all_modes () { + test_when_finished rm -rf .git/objects/info/commit-graph && + git merge-base "$@" >actual && + test_cmp expect actual && + cp commit-graph-full .git/objects/info/commit-graph && + git merge-base "$@" >actual && + test_cmp expect actual && + cp commit-graph-half .git/objects/info/commit-graph && + git merge-base "$@" >actual && + test_cmp expect actual && + cp commit-graph-no-gdat .git/objects/info/commit-graph && + git merge-base "$@" >actual && + test_cmp expect actual +} + +test_expect_success 'merge-base without --all (unique base)' ' + git rev-parse commit-5-3 >expect && + merge_base_all_modes commit-5-7 commit-8-3 +' + +test_expect_success 'merge-base without --all is one of --all results' ' + test_when_finished rm -rf .git/objects/info/commit-graph && + + cp commit-graph-full .git/objects/info/commit-graph && + git merge-base --all commit-5-7 commit-4-8 commit-6-6 commit-8-3 >all && + git merge-base commit-5-7 commit-4-8 commit-6-6 commit-8-3 >single && + test_line_count = 1 single && + grep -F -f single all && + + cp commit-graph-half .git/objects/info/commit-graph && + git merge-base --all commit-5-7 commit-4-8 commit-6-6 commit-8-3 >all && + git merge-base commit-5-7 commit-4-8 commit-6-6 commit-8-3 >single && + test_line_count = 1 single && + grep -F -f single all +' + test_done