Re: Performance problems in diffcore rename

Shawn Pearce [off-list ref] writes:

quoted

But looking at is_exact_match I'm now wondering why we bother
to open the working tree file at all here.

You are right.  When we _know_ both SHA-1 can be trusted, we
should be able to do just this, regardless of contents_too
(whose only purpose is to delay comparing a cache dirty working
tree file with something else):

diff --git a/diffcore-rename.c b/diffcore-rename.c
index 57a74b6..677db85 100644
--- a/diffcore-rename.c
+++ b/diffcore-rename.c

@@ -100,9 +100,8 @@ static int is_exact_match(struct diff_filespec *src,
 			  struct diff_filespec *dst,
 			  int contents_too)
 {
-	if (src->sha1_valid && dst->sha1_valid &&
-	    !hashcmp(src->sha1, dst->sha1))
-		return 1;
+	if (src->sha1_valid && dst->sha1_valid)
+		return !hashcmp(src->sha1, dst->sha1);
 	if (!contents_too)
 		return 0;
 	if (diff_populate_filespec(src, 1) || diff_populate_filespec(dst, 1))