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>

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);
+	free_filespec(p->one);
-	diff_free_filespec_data(p->two);
+	free_filespec(p->two);
-	free(p->one);
-	free(p->two);
 	free(p);
 }
 

diffcore-rename.c

@@ -209,21 +209,19 @@ static int estimate_similarity(struct diff_filespec *src,
 
 static void record_rename_pair(int dst_index, int src_index, int score)
 {
-	struct diff_filespec *one, *two, *src, *dst;
+	struct diff_filespec *src, *dst;
 	struct diff_filepair *dp;
 
 	if (rename_dst[dst_index].pair)
 		die("internal error: dst already matched.");
 
 	src = rename_src[src_index].one;
-	one = alloc_filespec(src->path);
+	src->count++;
-	fill_filespec(one, src->sha1, src->mode);
 
 	dst = rename_dst[dst_index].two;
-	two = alloc_filespec(dst->path);
+	dst->count++;
-	fill_filespec(two, dst->sha1, dst->mode);
 
-	dp = diff_queue(NULL, one, two);
+	dp = diff_queue(NULL, src, dst);
 	dp->renamed_pair = 1;
 	if (!strcmp(src->path, dst->path))
 		dp->score = rename_src[src_index].score;
@@ -526,10 +524,8 @@ void diffcore_rename(struct diff_options *options)
 		}
 	}
 
-	for (i = 0; i < rename_dst_nr; i++) {
+	for (i = 0; i < rename_dst_nr; i++)
-		diff_free_filespec_data(rename_dst[i].two);
+		free_filespec(rename_dst[i].two);
-		free(rename_dst[i].two);
-	}
 
 	free(rename_dst);
 	rename_dst = NULL;

diffcore.h

@@ -29,6 +29,7 @@ struct diff_filespec {
 	void *cnt_data;
 	const char *funcname_pattern_ident;
 	unsigned long size;
+	int count;               /* Reference count */
 	int xfrm_flags;		 /* for use by the xfrm */
 	unsigned short mode;	 /* file mode */
 	unsigned sha1_valid : 1; /* if true, use sha1 and trust mode;
@@ -43,6 +44,7 @@ struct diff_filespec {
 };
 
 extern struct diff_filespec *alloc_filespec(const char *);
+extern void free_filespec(struct diff_filespec *);
 extern void fill_filespec(struct diff_filespec *, const unsigned char *,
 			  unsigned short);