From 176d1606c824f58443d085c6f5a02ab17a16ca1c Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Wed, 18 Mar 2026 10:10:48 -0400 Subject: [PATCH 1/3] t6600: test --maximal-only and --independent Add a test that verifies the 'git rev-list --maximal-only' option produces the same set of commits as 'git merge-base --independent'. This equivalence was noted when the feature was first created, but we are about to update the implementation to use a common algorithm in this case where the user intention is identical. Signed-off-by: Derrick Stolee --- 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 2613075894282d..dc0421ed2f3726 100755 --- a/t/t6600-test-reach.sh +++ b/t/t6600-test-reach.sh @@ -837,4 +837,49 @@ test_expect_success 'rev-list --maximal-only (range)' ' --first-parent --exclude-first-parent-only ' +test_expect_success 'rev-list --maximal-only matches merge-base --independent' ' + # Mix of independent and dependent + git merge-base --independent \ + refs/heads/commit-5-2 \ + refs/heads/commit-3-2 \ + refs/heads/commit-2-5 >expect && + sort expect >expect.sorted && + git rev-list --maximal-only \ + refs/heads/commit-5-2 \ + refs/heads/commit-3-2 \ + refs/heads/commit-2-5 >actual && + sort actual >actual.sorted && + test_cmp expect.sorted actual.sorted && + + # All independent commits. + git merge-base --independent \ + refs/heads/commit-5-2 \ + refs/heads/commit-4-3 \ + refs/heads/commit-3-4 \ + refs/heads/commit-2-5 >expect && + sort expect >expect.sorted && + git rev-list --maximal-only \ + refs/heads/commit-5-2 \ + refs/heads/commit-4-3 \ + refs/heads/commit-3-4 \ + refs/heads/commit-2-5 >actual && + sort actual >actual.sorted && + test_cmp expect.sorted actual.sorted && + + # Only one independent. + git merge-base --independent \ + refs/heads/commit-1-1 \ + refs/heads/commit-4-2 \ + refs/heads/commit-4-4 \ + refs/heads/commit-8-4 >expect && + sort expect >expect.sorted && + git rev-list --maximal-only \ + refs/heads/commit-1-1 \ + refs/heads/commit-4-2 \ + refs/heads/commit-4-4 \ + refs/heads/commit-8-4 >actual && + sort actual >actual.sorted && + test_cmp expect.sorted actual.sorted +' + test_done From 40722d7d13c3f19bc6984c11583ff8136dbeea81 Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Wed, 18 Mar 2026 10:13:32 -0400 Subject: [PATCH 2/3] p6011: add perf test for rev-list --maximal-only Add a performance test that compares 'git rev-list --maximal-only' against 'git merge-base --independent'. These two commands are asking essentially the same thing, but the rev-list implementation is more generic and hence slower. These performance tests will demonstrate that in the current state and also be used to show the equivalence in the future. We also add a case with '--since' to force the generic walk logic for rev-list even when we make that future change to use the merge-base algorithm on a simple walk. When run on my copy of git.git, I see these results: Test HEAD ---------------------------------------------- 6011.2: merge-base --independent 0.03 6011.3: rev-list --maximal-only 0.06 6011.4: rev-list --maximal-only --since 0.06 These numbers are low, but the --independent calculation is interesting due to having a lot of local branches that are actually independent. Running the same test on a fresh clone of the Linux kernel repository shows a larger difference between the algorithms, especially because the --independent algorithm is extremely fast when there are no independent references selected: Test HEAD ---------------------------------------------- 6011.2: merge-base --independent 0.00 6011.3: rev-list --maximal-only 0.70 6011.4: rev-list --maximal-only --since 0.70 Signed-off-by: Derrick Stolee --- t/perf/p6011-rev-list-maximal.sh | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) create mode 100755 t/perf/p6011-rev-list-maximal.sh diff --git a/t/perf/p6011-rev-list-maximal.sh b/t/perf/p6011-rev-list-maximal.sh new file mode 100755 index 00000000000000..e868e83ff847b3 --- /dev/null +++ b/t/perf/p6011-rev-list-maximal.sh @@ -0,0 +1,29 @@ +#!/bin/sh + +test_description='Test --maximal-only and --independent options' + +. ./perf-lib.sh + +test_perf_default_repo + +test_expect_success 'setup' ' + git for-each-ref --format="%(*objecttype) %(objecttype) %(objectname)" \ + "refs/heads/*" "refs/tags/*" | + sed -n -e "s/^commit commit //p" -e "s/^ commit //p" | + head -n 50 >commits && + git commit-graph write --reachable +' + +test_perf 'merge-base --independent' ' + git merge-base --independent $(cat commits) >/dev/null +' + +test_perf 'rev-list --maximal-only' ' + git rev-list --maximal-only $(cat commits) >/dev/null +' + +test_perf 'rev-list --maximal-only --since' ' + git rev-list --maximal-only --since=2000-01-01 $(cat commits) >/dev/null +' + +test_done From 0bdb88c85eabfa88b97c83a8f20f76cb8ed0489d Mon Sep 17 00:00:00 2001 From: Derrick Stolee Date: Wed, 18 Mar 2026 10:10:42 -0400 Subject: [PATCH 3/3] rev-list: use reduce_heads() for --maximal-only The 'git rev-list --maximal-only' option filters the output to only independent commits. A commit is independent if it is not reachable from other listed commits. Currently this is implemented by doing a full revision walk and marking parents with CHILD_VISITED to skip non-maximal commits. The 'git merge-base --independent' command computes the same result using reduce_heads(), which uses the more efficient remove_redundant() algorithm. This is significantly faster because it avoids walking the entire commit graph. Add a fast path in rev-list that detects when --maximal-only is the only interesting option and all input commits are positive (no revision ranges). In this case, use reduce_heads() directly instead of doing a full revision walk. In order to preserve the rest of the output filtering, this computation is done opportunistically in a new prepare_maximal_independent() method when possible. If successful, it populates revs->commits with the list of independent commits and set revs->no_walk to prevent any other walk from occurring. This allows us to have any custom output be handled using the existing output code hidden inside traverse_commit_list_filtered(). A new test is added to demonstrate that this output is preserved. The fast path is only used when no other flags complicate the walk or output format: no UNINTERESTING commits, no limiting options (max-count, age filters, path filters, grep filters), no output formatting beyond plain OIDs, and no object listing flags. Running the p6011 performance test for my copy of git.git, I see the following improvement with this change: Test HEAD~1 HEAD ------------------------------------------------------------ 6011.2: merge-base --independent 0.03 0.03 +0.0% 6011.3: rev-list --maximal-only 0.06 0.03 -50.0% 6011.4: rev-list --maximal-only --since 0.06 0.06 +0.0% And for a fresh clone of the Linux kernel repository, I see: Test HEAD~1 HEAD ------------------------------------------------------------ 6011.2: merge-base --independent 0.00 0.00 = 6011.3: rev-list --maximal-only 0.70 0.00 -100.0% 6011.4: rev-list --maximal-only --since 0.70 0.70 +0.0% In both cases, the performance is indeed matching the behavior of 'git merge-base --independent', as expected. Signed-off-by: Derrick Stolee --- builtin/rev-list.c | 59 ++++++++++++++++++++++++++++++++++++++++ t/t6000-rev-list-misc.sh | 31 +++++++++++++++++++++ 2 files changed, 90 insertions(+) diff --git a/builtin/rev-list.c b/builtin/rev-list.c index 854d82ece368b3..8f63003709242e 100644 --- a/builtin/rev-list.c +++ b/builtin/rev-list.c @@ -25,6 +25,7 @@ #include "oidset.h" #include "oidmap.h" #include "packfile.h" +#include "commit-reach.h" #include "quote.h" #include "strbuf.h" @@ -633,6 +634,61 @@ static int try_bitmap_disk_usage(struct rev_info *revs, return 0; } +/* + * If revs->maximal_only is set and no other walk modifiers are provided, + * run a faster computation to filter the independent commits and prepare + * them for output. Set revs->no_walk to prevent later walking. + * + * If this algorithm doesn't apply, then no changes are made to revs. + */ +static void prepare_maximal_independent(struct rev_info *revs) +{ + struct commit_list *c; + + if (!revs->maximal_only) + return; + + for (c = revs->commits; c; c = c->next) { + if (c->item->object.flags & UNINTERESTING) + return; + } + + if (revs->limited || + revs->topo_order || + revs->first_parent_only || + revs->reverse || + revs->max_count >= 0 || + revs->skip_count >= 0 || + revs->min_age != (timestamp_t)-1 || + revs->max_age != (timestamp_t)-1 || + revs->min_parents > 0 || + revs->max_parents >= 0 || + revs->prune_data.nr || + revs->count || + revs->left_right || + revs->boundary || + revs->tag_objects || + revs->tree_objects || + revs->blob_objects || + revs->filter.choice || + revs->reflog_info || + revs->diff || + revs->grep_filter.pattern_list || + revs->grep_filter.header_list || + revs->verbose_header || + revs->print_parents || + revs->edge_hint || + revs->unpacked || + revs->no_kept_objects || + revs->line_level_traverse) + return; + + reduce_heads_replace(&revs->commits); + + /* Modify 'revs' to only output this commit list. */ + revs->no_walk = 1; +} + int cmd_rev_list(int argc, const char **argv, const char *prefix, @@ -875,6 +931,9 @@ int cmd_rev_list(int argc, if (prepare_revision_walk(&revs)) die("revision walk setup failed"); + + prepare_maximal_independent(&revs); + if (revs.tree_objects) mark_edges_uninteresting(&revs, show_edge, 0); diff --git a/t/t6000-rev-list-misc.sh b/t/t6000-rev-list-misc.sh index d0a2a866100d56..a95ba576fa24b2 100755 --- a/t/t6000-rev-list-misc.sh +++ b/t/t6000-rev-list-misc.sh @@ -263,4 +263,35 @@ test_expect_success 'rev-list --boundary incompatible with --maximal-only' ' test_grep "cannot be used together" err ' +test_expect_success 'rev-list --maximal-only and --pretty' ' + test_when_finished rm -rf repo && + + git init repo && + test_commit -C repo 1 && + oid1=$(git -C repo rev-parse HEAD) && + test_commit -C repo 2 && + oid2=$(git -C repo rev-parse HEAD) && + git -C repo checkout --detach HEAD~1 && + test_commit -C repo 3 && + oid3=$(git -C repo rev-parse HEAD) && + + cat >expect <<-EOF && + commit $oid3 + $oid3 + commit $oid2 + $oid2 + EOF + + git -C repo rev-list --pretty="%H" --maximal-only $oid1 $oid2 $oid3 >out && + test_cmp expect out && + + cat >expect <<-EOF && + $oid3 + $oid2 + EOF + + git -C repo log --pretty="%H" --maximal-only $oid1 $oid2 $oid3 >out && + test_cmp expect out +' + test_done