[Bug libstdc++/56785] std::tuple of two elements does not apply empty base class optimization when one of its elements is a std::tuple with two elements

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56785

--- Comment #9 from Marc Glisse <glisse at gcc dot gnu.org> ---
Try:
  struct X: std::tuple<Empty> { double d; };