[PATCH 9/9] am: make a direct call to merge_recursive

[Johannes Schindelin <johannes.schindelin@gmx.de>]

From: Junio C Hamano <gitster@pobox.com>

Instead of spawning merge-recursive via run_command() in
run_fallback_merge_recursive(), make a direct call to the internal
merge_recursive_generic().

Here is a quick benchmark result, applying a patch for b4391657
(merge: drop 'git merge <message> HEAD <commit>' syntax, 2015-03-25)
that was still cooking in 'next' on 4b1fd356 (git-multimail: update
to release 1.2.0, 2015-10-11) which was the tip of 'master' at some
stage, on an x86-64 running Ubuntu:

      real    0m0.169s                      real    0m0.163s
      user    0m0.108s                      user    0m0.134s
      sys     0m0.068s                      sys     0m0.033s

      real    0m0.175s                      real    0m0.161s
      user    0m0.110s                      user    0m0.120s
      sys     0m0.066s                      sys     0m0.047s

      real    0m0.168s                      real    0m0.162s
      user    0m0.124s                      user    0m0.114s
      sys     0m0.045s                      sys     0m0.051s

      real    0m0.167s                      real    0m0.152s
      user    0m0.124s                      user    0m0.122s
      sys     0m0.045s                      sys     0m0.031s

      real    0m0.169s                      real    0m0.164s
      user    0m0.131s                      user    0m0.129s
      sys     0m0.043s                      sys     0m0.041s

Left-hand side shows the original, right-hand side shows the result
of this optimization.

Timings on Windows:

original:
0.00user 0.01system 0:00.29elapsed
0.00user 0.00system 0:00.25elapsed
0.01user 0.00system 0:00.24elapsed
0.01user 0.00system 0:00.26elapsed
0.00user 0.01system 0:00.23elapsed

with optimization:
0.00user 0.01system 0:00.22elapsed
0.00user 0.00system 0:00.25elapsed
0.00user 0.01system 0:00.22elapsed
0.00user 0.00system 0:00.22elapsed
0.01user 0.00system 0:00.21elapsed

Signed-off-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---

	It feels *slightly* wrong to submit your own patch to review,
	however, please keep in mind that

	1) I changed the patch (o.gently does not exist anymore, so I do
	   not set it), and

	2) I added my own timings performed on Windows.

 builtin/am.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/builtin/am.c b/builtin/am.c
index 3dfe70b..dd41154 100644
--- a/builtin/am.c
+++ b/builtin/am.c
@@ -1587,25 +1587,26 @@ static int run_fallback_merge_recursive(const struct am_state *state,
 					unsigned char *our_tree,
 					unsigned char *his_tree)
 {
-	struct child_process cp = CHILD_PROCESS_INIT;
+	const unsigned char *bases[1] = {orig_tree};
+	struct merge_options o;
+	struct commit *result;
+	char *his_tree_name;
 	int status;
 
-	cp.git_cmd = 1;
+	init_merge_options(&o);
+
+	o.branch1 = "HEAD";
+	his_tree_name = xstrfmt("%.*s", linelen(state->msg), state->msg);
+	o.branch2 = his_tree_name;
 
-	argv_array_pushf(&cp.env_array, "GITHEAD_%s=%.*s",
-			 sha1_to_hex(his_tree), linelen(state->msg), state->msg);
 	if (state->quiet)
-		argv_array_push(&cp.env_array, "GIT_MERGE_VERBOSITY=0");
+		o.verbosity = 0;
 
-	argv_array_push(&cp.args, "merge-recursive");
-	argv_array_push(&cp.args, sha1_to_hex(orig_tree));
-	argv_array_push(&cp.args, "--");
-	argv_array_push(&cp.args, sha1_to_hex(our_tree));
-	argv_array_push(&cp.args, sha1_to_hex(his_tree));
+	status = merge_recursive_generic(&o, our_tree, his_tree, 1, bases, &result);
+	if (status < 0)
+		exit(128);
+	free(his_tree_name);
 
-	status = run_command(&cp) ? (-1) : 0;
-	discard_cache();
-	read_cache();
 	return status;
 }
 
-- 
2.9.0.268.gcabc8b0