[Bug middle-end/69553] [6 Regression] Optimizations O1/O2 makes std::array value incorrect when passed to function

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69553

--- Comment #6 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
markus@x4 tmp % cat array.ii
template <typename _Tp, long _Nm> struct A {
  typedef _Tp _Type[_Nm];
  static _Tp &_S_ref(const _Type &p1, int p2) {
    return const_cast<_Tp &>(p1[p2]);
  }
};
template <typename _Tp, long _Nm> struct B {
  typedef A<_Tp, _Nm> _AT_Type;
  typename _AT_Type::_Type _M_elems;
  _Tp &operator[](long p1) const { return _AT_Type::_S_ref(_M_elems, p1); }
};
int t;
void foo(int p1, int &p2) {
  if ((t & 1) == 0) {
    if (p1 != 1)
      __builtin_abort();
    if (p2 != 2)
      __builtin_abort();
  }
  t++;
}
 __attribute__((noinline))
void test1(const B<int, 2> &p1) { foo(p1[0], p1[1]); }
void test(B<B<int, 2>, 2> &p1) {
  test1(p1[0]);
  test1(p1[1]);
  foo(p1[0][0], p1[0][1]);
}
int main() {
  B<B<int, 2>, 2> t;
  t[0][0] = 1;
  t[0][1] = 2;
  test(t);
}