rerere: remove dubious "tail_optimization"

It is dubious if it is cheaper to shift entries repeatedly using memmove()
to collect entries that needs to be written out in front of an array than
simply marking the entries to be skipped.  In addition, the label called this
"tail optimization", but this obviously is not what people usually call
with that name.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rerere.c

@@ -66,8 +66,12 @@ static int write_rr(struct path_list *rr, int out_fd)
 {
 	int i;
 	for (i = 0; i < rr->nr; i++) {
-		const char *path = rr->items[i].path;
-		int length = strlen(path) + 1;
+		const char *path;
+		int length;
+		if (!rr->items[i].util)
+			continue;
+		path = rr->items[i].path;
+		length = strlen(path) + 1;
 		if (write_in_full(out_fd, rr->items[i].util, 40) != 40 ||
 		    write_in_full(out_fd, "\t", 1) != 1 ||
 		    write_in_full(out_fd, path, length) != length)
@@ -319,7 +323,7 @@ static int do_plain_rerere(struct path_list *rr, int fd)
 			if (!merge(name, path)) {
 				fprintf(stderr, "Resolved '%s' using "
 						"previous resolution.\n", path);
-				goto tail_optimization;
+				goto mark_resolved;
 			}
 		}
 
@@ -330,13 +334,8 @@ static int do_plain_rerere(struct path_list *rr, int fd)
 
 		fprintf(stderr, "Recorded resolution for '%s'.\n", path);
 		copy_file(rr_path(name, "postimage"), path, 0666);
-tail_optimization:
-		if (i < rr->nr - 1)
-			memmove(rr->items + i,
-				rr->items + i + 1,
-				sizeof(rr->items[0]) * (rr->nr - i - 1));
-		rr->nr--;
-		i--;
+	mark_resolved:
+		rr->items[i].util = NULL;
 	}
 
 	return write_rr(rr, fd);