[Bug sanitizer/93246] [9/10 Regression] Unexpected program behavior when -fsanitize=address and -O2/O3 used

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93246

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note that the 'using' make it work is another wrong-code issue I think.  But
clearly somehow the TYPE_TYPELESS_STORAGE handling is responsible here
(it works with 'short' padding for example).  More reduced:

template <typename = void> struct Optional {
  auto is_present() const { return inner.present; }
  auto set_present() { if (not is_present()) inner.present = true; }
  struct InnerType {
    bool present = false;
    char padding[1] = {0};
  };
  using inner_t = InnerType;
  //InnerType inner = {}; // this works as expected!
  inner_t inner = {}; // this doesn't!
};

template <typename WrappedType> struct Wrapper {
  auto operator-> () { return value; }
  WrappedType *value;
};

void __attribute__((noipa)) foo(Optional<>& x) {}

int main()
{
  Optional<> buf{};
  foo(buf);
  Wrapper<Optional<>> wo = {&buf};
  wo->set_present();
  auto x = wo->is_present();
  if (!x)
    __builtin_abort ();
}