[Bug c++/66355] defining a constructor inhibits optimization

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66355

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
If you make the constructors and operator+ constexpr and compile with
-std=gnu++14 then you remove the overhead.