From: Derrick Stolee Date: Mon, 6 Apr 2026 13:27:28 +0000 (+0000) Subject: rev-list: use reduce_heads() for --maximal-only X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b0ba57daa86dfba0a6551613452d1cb2301266a2;p=thirdparty%2Fgit.git 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 Signed-off-by: Junio C Hamano --- diff --git a/builtin/rev-list.c b/builtin/rev-list.c index 854d82ece3..8f63003709 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 d0a2a86610..a95ba576fa 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