--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/pr68835-2.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,23 @@
+/* PR tree-optimization/68835 */
+/* { dg-do run { target int128 } } */
+/* { dg-options "-O2" } */
+
+__attribute__((noinline, noclone)) unsigned __int128
+foo (void)
+{
+  unsigned __int128 x = (unsigned __int128) 0xffffffffffffffffULL;
+  struct { unsigned __int128 a : 65; } w;
+  w.a = x;
+  w.a += x;
+  return w.a;
+}
+
+int
+main ()
+{
+  unsigned __int128 x = foo ();
+  if ((unsigned long long) x != 0xfffffffffffffffeULL
+      || (unsigned long long) (x >> 64) != 1)
+    __builtin_abort ();
+  return 0;
+}