https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68908
--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> --- IMHO you should use the current code for _Bool atomic increments/decrements, _Bool has just doesn't behave like an integer. Only normal integers (with the precision the same as mode's precision, properly aligned; perhaps enums too) and pointer types should be optimized.
