https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122414
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> --- The macro is documented in XLC documentation since this is compatibility for XLC: https://www.ibm.com/docs/en/xl-c-and-cpp-aix/13.1.0?topic=features-macros-related-architecture-settings
