--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/builtin-object-size-9.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,31 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+typedef __SIZE_TYPE__ size_t;
+extern void *malloc (size_t);
+extern void free (void *);
+extern void abort (void);
+
+union U
+{
+  struct S { int a; int b; } s;
+  int t;
+};
+
+struct T
+{
+  int c;
+  char d[1];
+};
+
+int
+main (void)
+{
+  union U *u = malloc (sizeof (struct S) + sizeof (struct T) + 6);
+  struct T *t = (struct T *) (&u->s + 1);
+  if (__builtin_object_size (t->d, 1)
+      != sizeof (struct T) + 6 - __builtin_offsetof (struct T, d))
+    abort ();
+  free (u);
+  return 0;
+}