Ref-count the filespecs used by diffcore

Rather than copy the filespecs when introducing new versions of them
(for rename or copy detection), use a refcount and increment the count
when reusing the diff_filespec.

This avoids unnecessary allocations, but the real reason behind this is
a future enhancement: we will want to track shared data across the
copy/rename detection.  In order to efficiently notice when a filespec
is used by a rename, the rename machinery wants to keep track of a
rename usage count which is shared across all different users of the
filespec.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/diff.c b/diff.c
index dfb8595b70..0b320f6b96 100644
--- a/diff.c
+++ b/diff.c
@@ -1440,9 +1440,18 @@ struct diff_filespec *alloc_filespec(const char *path)
 	memset(spec, 0, sizeof(*spec));
 	spec->path = (char *)(spec + 1);
 	memcpy(spec->path, path, namelen+1);
+	spec->count = 1;
 	return spec;
 }
 
+void free_filespec(struct diff_filespec *spec)
+{
+	if (!--spec->count) {
+		diff_free_filespec_data(spec);
+		free(spec);
+	}
+}
+
 void fill_filespec(struct diff_filespec *spec, const unsigned char *sha1,
 		   unsigned short mode)
 {
@@ -2435,10 +2444,8 @@ struct diff_filepair *diff_queue(struct diff_queue_struct *queue,
 
 void diff_free_filepair(struct diff_filepair *p)
 {
-	diff_free_filespec_data(p->one);
-	diff_free_filespec_data(p->two);
-	free(p->one);
-	free(p->two);
+	free_filespec(p->one);
+	free_filespec(p->two);
 	free(p);
 }