https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70299
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> --- Using the __builtin_powi* functions was done for PR11706, I believe because they can be a lot more efficient than the general powl(double, double) implementations. So it seems that for C++11 and later we provide more accuracy, but probably via slower functions than we use for C++03.
