Avoid excessive rewrites in merge-recursive

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>
Signed-off-by: Junio C Hamano <junkio@cox.net>

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);
 			}
 		}
 	}