[Bug c++/80635] std::optional and bogus -Wmaybe-uninitialized warning

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80635

--- Comment #34 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Martin Sebor from comment #15)
> I think the following smaller test case independent of libstdc++ captures
> the same issue as the bigger test case in comment #4.  Again, declaring f()
> noexcept avoids the warning (but it's not a solution in general).  Zero
> initializing A::i first and then setting it to the result of f() also avoids
> the warning and seems like more viable solution/workaround until GCC gets
> smarter about exceptions.


In this example, if you add a useless pointer to t, then GCC doesn't warn:

template <class T>
struct C {
  C (): b(), t()  { }
  ~C () { if (b) t.~T (); }

  void f () {
    b = true;
    new (&t) T ();
    pt = &t;
  }
private:
  bool b;
  T * pt;
public:
  union {
    T t;
    char x[sizeof (T)];
  };
 };