From b80b462d7cf2225c25959ce89727fdd3334c0afc Mon Sep 17 00:00:00 2001 From: Kristofer Karlsson Date: Sat, 16 May 2026 15:59:40 +0000 Subject: [PATCH 1/2] commit-reach: use object flags for tips_reachable_from_bases() tips_reachable_from_bases() walks the commit graph from a set of base commits to find which tip commits are reachable. The inner loop does a linear scan over the tips array to check whether each visited commit is a tip, making the overall cost O(C * T) where C is commits walked and T is the number of tips. Use the RESULT object flag to mark tip commits, replacing the linear scan with a single flag test per visited commit. This reduces the per-commit tip check from O(T) to O(1) and the overall cost from O(C * T) to O(C + T). When multiple refs point to the same commit, the shared object gets the flag once, so all duplicates are handled automatically. The early-termination advancement loop checks the flag on the sorted commits array directly, which naturally handles duplicates since the flag is on the shared commit object. This also removes the index field from struct commit_and_index, since the indirection through the original tips array is no longer needed. This function is called by `git for-each-ref --merged` and `git branch/tag --contains/--no-contains` via reach_filter() in ref-filter.c. Benchmark on a merge-heavy monorepo (2.3M commits, 10,000 refs): Command Before After Speedup for-each-ref --merged HEAD 6.57s 1.59s 4.1x for-each-ref --no-merged HEAD 6.67s 1.66s 4.0x branch --merged HEAD 0.68s 0.61s 10% branch --no-merged HEAD 0.65s 0.61s 8% tag --merged HEAD 0.12s 0.12s - On linux.git with 10,000 synthetic branches at the root commit (worst case for the DFS walk): Command Before After Speedup for-each-ref --merged HEAD 1.35s 0.35s 3.9x for-each-ref --no-merged HEAD 1.82s 0.31s 5.9x The large speedup for for-each-ref is because it checks all 10,000 refs as tips, making the O(T) inner loop expensive. The branch subcommand only checks local branches (fewer tips), so the improvement is smaller. Signed-off-by: Kristofer Karlsson Signed-off-by: Junio C Hamano --- commit-reach.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-) diff --git a/commit-reach.c b/commit-reach.c index d3a9b3ed6f..82614d2409 100644 --- a/commit-reach.c +++ b/commit-reach.c @@ -1125,7 +1125,6 @@ void ahead_behind(struct repository *r, struct commit_and_index { struct commit *commit; - unsigned int index; timestamp_t generation; }; @@ -1165,7 +1164,6 @@ void tips_reachable_from_bases(struct repository *r, for (size_t i = 0; i < tips_nr; i++) { commits[i].commit = tips[i]; - commits[i].index = i; commits[i].generation = commit_graph_generation(tips[i]); } @@ -1173,6 +1171,9 @@ void tips_reachable_from_bases(struct repository *r, QSORT(commits, tips_nr, compare_commit_and_index_by_generation); min_generation = commits[0].generation; + for (size_t i = 0; i < tips_nr; i++) + commits[i].commit->object.flags |= RESULT; + while (bases) { repo_parse_commit(r, bases->item); commit_list_insert(bases->item, &stack); @@ -1183,20 +1184,16 @@ void tips_reachable_from_bases(struct repository *r, int explored_all_parents = 1; struct commit_list *p; struct commit *c = stack->item; - timestamp_t c_gen = commit_graph_generation(c); /* Does it match any of our tips? */ - for (size_t j = min_generation_index; j < tips_nr; j++) { - if (c_gen < commits[j].generation) - break; + { + if (c->object.flags & RESULT) { + c->object.flags |= mark; - if (commits[j].commit == c) { - tips[commits[j].index]->object.flags |= mark; - - if (j == min_generation_index) { - unsigned int k = j + 1; + if (commits[min_generation_index].commit->object.flags & mark) { + unsigned int k = min_generation_index + 1; while (k < tips_nr && - (tips[commits[k].index]->object.flags & mark)) + (commits[k].commit->object.flags & mark)) k++; /* Terminate early if all found. */ @@ -1232,6 +1229,8 @@ void tips_reachable_from_bases(struct repository *r, } done: + for (size_t i = 0; i < tips_nr; i++) + commits[i].commit->object.flags &= ~RESULT; free(commits); repo_clear_commit_marks(r, SEEN); commit_list_free(stack); From a30f132bcb62bc44053b1dba0940c2d4041c797a Mon Sep 17 00:00:00 2001 From: Kristofer Karlsson Date: Sat, 16 May 2026 15:59:41 +0000 Subject: [PATCH 2/2] t6600: add tests for duplicate tips in tips_reachable_from_bases() When multiple refs point to the same commit, the reachability check must handle them correctly. Add three tests: - duplicate tips, all reachable - duplicate tips, none reachable - duplicate tips at the minimum generation (exercises the early-termination advancement logic) Suggested-by: Derrick Stolee Signed-off-by: Kristofer Karlsson Signed-off-by: Junio C Hamano --- t/t6600-test-reach.sh | 45 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 45 insertions(+) diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh index dc0421ed2f..9486002866 100755 --- a/t/t6600-test-reach.sh +++ b/t/t6600-test-reach.sh @@ -612,6 +612,51 @@ test_expect_success 'for-each-ref merged:none' ' --format="%(refname)" --stdin ' +test_expect_success 'for-each-ref merged:duplicate, all reachable' ' + git branch dup-a commit-3-3 && + git branch dup-b commit-3-3 && + cat >input <<-\EOF && + refs/heads/commit-1-1 + refs/heads/dup-a + refs/heads/dup-b + EOF + cat >expect <<-\EOF && + refs/heads/commit-1-1 + refs/heads/dup-a + refs/heads/dup-b + EOF + run_all_modes git for-each-ref --merged=commit-5-5 \ + --format="%(refname)" --stdin +' + +test_expect_success 'for-each-ref merged:duplicate, none reachable' ' + cat >input <<-\EOF && + refs/heads/dup-a + refs/heads/dup-b + refs/heads/commit-9-9 + EOF + >expect && + run_all_modes git for-each-ref --merged=commit-2-2 \ + --format="%(refname)" --stdin +' + +test_expect_success 'for-each-ref merged:duplicate at min generation' ' + git branch dup-c commit-1-1 && + git branch dup-d commit-1-1 && + cat >input <<-\EOF && + refs/heads/dup-c + refs/heads/dup-d + refs/heads/commit-5-5 + EOF + cat >expect <<-\EOF && + refs/heads/commit-5-5 + refs/heads/dup-c + refs/heads/dup-d + EOF + run_all_modes git for-each-ref --merged=commit-5-5 \ + --format="%(refname)" --stdin +' + # For get_branch_base_for_tip, we only care about # first-parent history. Here is the test graph with # second parents removed: