[Bug c++/95950] New: Call to pseudo-destructor does not end the lifetime until C++20

["kutdanila at yandex dot ru" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95950

            Bug ID: 95950
           Summary: Call to pseudo-destructor does not end the lifetime
                    until C++20
           Product: gcc
           Version: 9.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kutdanila at yandex dot ru
  Target Milestone: ---

#include <optional>

int main() {
  std::optional<int> t = 2;
  using T = std::optional<int>;
  t.~T();
  return t.has_value();
}

g++ test.cpp -O1 -o test


This code should not return 0 until C++20, see
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0593r4.html and
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0593r4.html#c5-c-and-iso-c-2017-diffcpp17

In that case, std::optional<int> has a trivial destructor and should have no
effect

The regression started somewhere in the 9th version of gcc in any optimized
builds (O1-O3, with O0 still ok)

Yet, static_assert works fine

#include <optional>

int main() {
  constexpr std::optional<int> t = 2;
  using T = std::optional<int>;
  t.~T();
  static_assert(t.has_value());
}