rev-list: use merge-base --independent algorithm when possible

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);
 

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

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

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