https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116130
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Also there is "If possible, it is recommended that implementations diagnose if an attribute of this clause is applied to a function definition that does not have the corresponding property." so we'd want some warnings, maybe in the FE, or during gimplification.
