file.c: same timespec

* file.c (rb_file_s_utime): same timespec for same time object.
  assume time objects are static.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51926 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

file.c

@@ -2686,7 +2686,10 @@ rb_file_s_utime(int argc, VALUE *argv)
     if (!NIL_P(args.atime) || !NIL_P(args.mtime)) {
 	tsp = tss;
 	tsp[0] = rb_time_timespec(args.atime);
-	tsp[1] = rb_time_timespec(args.mtime);
+	if (args.atime == args.mtime)
+	    tsp[1] = tsp[0];
+	else
+	    tsp[1] = rb_time_timespec(args.mtime);
     }
     args.tsp = tsp;