Merge branch 'rs/merge-base-optim'

The code to walk revision graph to compute merge base has been
optimized.

* rs/merge-base-optim:
  commit-reach: avoid commit_list_insert_by_date()

commit-reach.c

@@ -60,6 +60,7 @@ static int paint_down_to_common(struct repository *r,
 	struct prio_queue queue = { compare_commits_by_gen_then_commit_date };
 	int i;
 	timestamp_t last_gen = GENERATION_NUMBER_INFINITY;
+	struct commit_list **tail = result;
 
 	if (!min_generation && !corrected_commit_dates_enabled(r))
 		queue.compare = compare_commits_by_commit_date;
@@ -95,7 +96,7 @@ static int paint_down_to_common(struct repository *r,
 		if (flags == (PARENT1 | PARENT2)) {
 			if (!(commit->object.flags & RESULT)) {
 				commit->object.flags |= RESULT;
-				commit_list_insert_by_date(commit, result);
+				tail = commit_list_append(commit, tail);
 			}
 			/* Mark parents of a found merge stale */
 			flags |= STALE;
@@ -128,6 +129,7 @@ static int paint_down_to_common(struct repository *r,
 	}
 
 	clear_prio_queue(&queue);
+	commit_list_sort_by_date(result);
 	return 0;
 }
 
@@ -136,7 +138,7 @@ static int merge_bases_many(struct repository *r,
 			    struct commit **twos,
 			    struct commit_list **result)
 {
-	struct commit_list *list = NULL;
+	struct commit_list *list = NULL, **tail = result;
 	int i;
 
 	for (i = 0; i < n; i++) {
@@ -171,8 +173,9 @@ static int merge_bases_many(struct repository *r,
 	while (list) {
 		struct commit *commit = pop_commit(&list);
 		if (!(commit->object.flags & STALE))
-			commit_list_insert_by_date(commit, result);
+			tail = commit_list_append(commit, tail);
 	}
+	commit_list_sort_by_date(result);
 	return 0;
 }
 
@@ -425,7 +428,7 @@ static int get_merge_bases_many_0(struct repository *r,
 				  int cleanup,
 				  struct commit_list **result)
 {
-	struct commit_list *list;
+	struct commit_list *list, **tail = result;
 	struct commit **rslt;
 	size_t cnt, i;
 	int ret;
@@ -461,7 +464,8 @@ static int get_merge_bases_many_0(struct repository *r,
 		return -1;
 	}
 	for (i = 0; i < cnt; i++)
-		commit_list_insert_by_date(rslt[i], result);
+		tail = commit_list_append(rslt[i], tail);
+	commit_list_sort_by_date(result);
 	free(rslt);
 	return 0;
 }

t/perf/p6010-merge-base.sh

@@ -0,0 +1,101 @@
+#!/bin/sh
+
+test_description='Test git merge-base'
+
+. ./perf-lib.sh
+
+test_perf_fresh_repo
+
+#
+# Creates lots of merges to make history traversal costly.  In
+# particular it creates 2^($max_level-1)-1 2-way merges on top of
+# 2^($max_level-1) root commits.  E.g., the commit history looks like
+# this for a $max_level of 3:
+#
+#     _1_
+#    /   \
+#   2     3
+#  / \   / \
+# 4   5 6   7
+#
+# The numbers are the fast-import marks, which also are the commit
+# messages.  1 is the HEAD commit and a merge, 2 and 3 are also merges,
+# 4-7 are the root commits.
+#
+build_history () {
+	local max_level="$1" &&
+	local level="${2:-1}" &&
+	local mark="${3:-1}" &&
+	if test $level -eq $max_level
+	then
+		echo "reset refs/heads/master" &&
+		echo "from $ZERO_OID" &&
+		echo "commit refs/heads/master" &&
+		echo "mark :$mark" &&
+		echo "committer C <c@example.com> 1234567890 +0000" &&
+		echo "data <<EOF" &&
+		echo "$mark" &&
+		echo "EOF"
+	else
+		local level1=$((level+1)) &&
+		local mark1=$((2*mark)) &&
+		local mark2=$((2*mark+1)) &&
+		build_history $max_level $level1 $mark1 &&
+		build_history $max_level $level1 $mark2 &&
+		echo "commit refs/heads/master" &&
+		echo "mark :$mark" &&
+		echo "committer C <c@example.com> 1234567890 +0000" &&
+		echo "data <<EOF" &&
+		echo "$mark" &&
+		echo "EOF" &&
+		echo "from :$mark1" &&
+		echo "merge :$mark2"
+	fi
+}
+
+#
+# Creates a new merge history in the same shape as build_history does,
+# while reusing the same root commits.  This way the two top commits
+# have 2^($max_level-1) merge bases between them.
+#
+build_history2 () {
+	local max_level="$1" &&
+	local level="${2:-1}" &&
+	local mark="${3:-1}" &&
+	if test $level -lt $max_level
+	then
+		local level1=$((level+1)) &&
+		local mark1=$((2*mark)) &&
+		local mark2=$((2*mark+1)) &&
+		build_history2 $max_level $level1 $mark1 &&
+		build_history2 $max_level $level1 $mark2 &&
+		echo "commit refs/heads/master" &&
+		echo "mark :$mark" &&
+		echo "committer C <c@example.com> 1234567890 +0000" &&
+		echo "data <<EOF" &&
+		echo "$mark II" &&
+		echo "EOF" &&
+		echo "from :$mark1" &&
+		echo "merge :$mark2"
+	fi
+}
+
+test_expect_success 'setup' '
+	max_level=15 &&
+	build_history $max_level | git fast-import --export-marks=marks &&
+	git tag one &&
+	build_history2 $max_level | git fast-import --import-marks=marks --force &&
+	git tag two &&
+	git gc &&
+	git log --format=%H --no-merges >expect
+'
+
+test_perf 'git merge-base' '
+	git merge-base --all one two >actual
+'
+
+test_expect_success 'verify result' '
+	test_cmp expect actual
+'
+
+test_done