--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/builtin-object-size-18.c	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+/* __stpncpy_chk could return buf up to buf + 64, so
+   the minimum object size might be far smaller than 64.  */
+/* { dg-final { scan-tree-dump-not "return 64;" "optimized" } } */
+
+typedef __SIZE_TYPE__ size_t;
+
+size_t
+foo (const char *p, size_t s, size_t t)
+{
+  char buf[64];
+  char *q = __builtin___stpncpy_chk (buf, p, s, t);
+  return __builtin_object_size (q, 2);
+}