[Bug middle-end/78044] -Wmaybe-uninitialized and -O2: false positive with boost::optional

[akrzemi1 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78044

--- Comment #7 from Andrzej Krzemienski <akrzemi1 at gmail dot com> ---
This still reproduces in version 7.2. Here is a Wandbox link:
https://wandbox.org/permlink/5uCAr5u0xpynljhQ

Here is the code, you need to compile it with -DNDEBUG -O2:

```
#include <cassert>

class O
{
    int _val;
    bool _init = false;
public:
    O() = default;
    O(const int& i) : _val(i), _init(true) {}
    explicit operator bool () const { return _init; }
    const int& operator*() const { assert (_init); return _val; }
    void operator=(int const& i) { _init = true; _val = i; }
};

bool equal_pointees ( O const& x, O const& y )
{
  return (!x) != (!y) ? false : ( !x ? true : (*x) == (*y) ) ;
}

O getitem();

int main(int argc, const char *[])
{
  O a = getitem();
  O b;

  if (argc > 0)
    b = argc;

  if (equal_pointees(a, b))
    return 1;

  return 0;
}
```

Is there a way to give a hint to the compiler (like with an attribute) so that
the warning is silenced?