https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104208
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- That is certainly one option. Another option would be to move this diagnostics to rs6000_handle_option and diagnose if -mabi=ieeelongdouble or -mabi=ibmlongdouble is seen while -mlong-double-64 is in effect and not when -mlong-double-128 is in effect. So, in a compiler that defaults to -mlong-double-64, -mabi=ieeelongdouble or -mlong-double-128 -mlong-double-64 -mabi=ibmlongdouble would error, but -mlong-double-128 -mabi=ieeelongdouble would not. And in a compiler that defaults to -mlong-double128, -mabi=ieeelongdouble or -mabi=ibmlongdouble would be ok, but -mlong-double-64 -mabi=ibmlongdouble would not.
