[PATCH] Avoid excessive rewrites in merge-recursive

[Alex Riesen <raa.lkml@gmail.com>]

If a file is changed in one branch, and renamed and changed to the
same content in another branch than we can skip the rewrite of this
file in the working directory, as the content does not change.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---

Just as you may have thought merge-recursive cannot get any uglier
someone comes and does just this: puts another level of indentation.

It is a nice speed up, though. Besides, I had some directories moved
between branches, and the rewrites caused a rebuild of hefty 8000
objects, which in windows terms is around 2 hours.

 merge-recursive.c |   32 +++++++++++++++++++-------------
 1 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index 403a4c8..37f1ba9 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1342,20 +1342,26 @@ static int process_renames(struct path_list *a_renames,
 				mfi = merge_file(o, a, b,
 						a_branch, b_branch);
 
-				if (mfi.merge || !mfi.clean)
-					output(1, "Renamed %s => %s", ren1_src, ren1_dst);
-				if (mfi.merge)
-					output(2, "Auto-merged %s", ren1_dst);
-				if (!mfi.clean) {
-					output(1, "CONFLICT (rename/modify): Merge conflict in %s",
-					       ren1_dst);
-					clean_merge = 0;
-
-					if (!index_only)
-						update_stages(ren1_dst,
-								o, a, b, 1);
+				if (mfi.merge && mfi.clean &&
+				    sha_eq(mfi.sha, ren1->pair->two->sha1) &&
+				    mfi.mode == ren1->pair->two->mode)
+					output(3, "Skipped %s (merged same as existing)", ren1_dst);
+				else {
+					if (mfi.merge || !mfi.clean)
+						output(1, "Renamed %s => %s", ren1_src, ren1_dst);
+					if (mfi.merge)
+						output(2, "Auto-merged %s", ren1_dst);
+					if (!mfi.clean) {
+						output(1, "CONFLICT (rename/modify): Merge conflict in %s",
+						       ren1_dst);
+						clean_merge = 0;
+
+						if (!index_only)
+							update_stages(ren1_dst,
+								      o, a, b, 1);
+					}
+					update_file(mfi.clean, mfi.sha, mfi.mode, ren1_dst);
 				}
-				update_file(mfi.clean, mfi.sha, mfi.mode, ren1_dst);
 			}
 		}
 	}
-- 
1.5.2.rc0.63.gdfc8-dirty