re PR tree-optimization/87415 (wrong code at -O1 and above on x86_64-linux-gnu)

	PR tree-optimization/87415
	* tree-vrp.c (set_value_range_with_overflow): Special case one bit
	precision fields.

From-SVN: r264817

gcc/ChangeLog

+2018-10-03  Aldy Hernandez  <aldyh@redhat.com>
+
+	PR tree-optimization/87415
+	* tree-vrp.c (set_value_range_with_overflow): Special case one bit
+	precision fields.
+
 2018-10-02  Jeff Law  <law@redhat.com>
 
 	* gimple-fold.c (get_range_strlen): Only set *nonstr when

gcc/testsuite/gcc.dg/pr87415.c

+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+struct A
+{
+  int b:1;
+};
+
+int d;
+
+int main ()
+{
+  struct A e = { 0 };
+  if (!d)
+    e.b = -1;
+  if (!e.b)
+    __builtin_abort ();
+
+  return 0;
+}

gcc/tree-vrp.c

@@ -1116,6 +1116,15 @@ set_value_range_with_overflow (value_range &vr,
   const unsigned int prec = TYPE_PRECISION (type);
   vr.type = VR_RANGE;
   vr.equiv = NULL;
+
+  /* For one bit precision if max < min, then the swapped
+     range covers all values.  */
+  if (prec == 1 && wi::lt_p (wmax, wmin, sgn))
+    {
+      set_value_range_to_varying (&vr);
+      return;
+    }
+
   if (TYPE_OVERFLOW_WRAPS (type))
     {
       /* If overflow wraps, truncate the values and adjust the