[committed] Add testcase for already fixed PR (PR tree-optimization/83283)

[Jakub Jelinek]

Hi!

This testcase has been fixed by r253146 but that testcase is quite different
from this one, so I've committed this to trunk as obvious.

2017-12-05  Jakub Jelinek  <ja...@redhat.com>

        PR tree-optimization/83283
        * g++.dg/torture/pr83283.C: New test.

--- gcc/testsuite/g++.dg/torture/pr83283.C.jj   2017-12-05 13:01:03.432144366 
+0100
+++ gcc/testsuite/g++.dg/torture/pr83283.C      2017-12-05 13:00:55.926238921 
+0100
@@ -0,0 +1,26 @@
+// PR tree-optimization/83283
+// { dg-do run }
+// { dg-additional-options "-std=c++11" }
+
+enum E : unsigned char { X = 0, Y = 1 };
+
+void __attribute__((noinline))
+foo (E *v, int size)
+{
+  for (int i = 0; i < size; ++i)
+    {
+      const bool b = (v[i] == E::Y);
+      v[i] = static_cast<E>(static_cast<unsigned char>(b));
+    }
+}
+
+int
+main ()
+{
+  constexpr int items = 32;
+  E vals[items] = {X};
+  vals[3] = Y;
+  foo (vals, items);
+  if (vals[3] != 1)
+    __builtin_abort ();
+}

        Jakub