https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61591
--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> --- I think it is a gimple-fold/ipa-devirt etc. bug. __builtin_unreachable doesn't have any arguments, so pretending it has is broken and also a missed optimization, in the IL we think those arguments are used when they aren't. So IMNSHO we should just never generate such bogus __builtin_unreachable calls.
