https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88840
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> --- LLVM seems to hit a case where this matters, and I'm not sure if it's invalid yet: https://bugzilla.opensuse.org/show_bug.cgi?id=1121591 The __use_relocate member of std::vector will check the exception-specification without checking if the expression is even valid at all: #if __cplusplus >= 201103L static constexpr bool __use_relocate = noexcept(std::__relocate_a(std::declval<pointer>(), std::declval<pointer>(), std::declval<pointer>(), std::declval<_Tp_alloc_type&>())); #endif If something depends on that boolean in a context where it isn't going to relocate, we might get an error from the ill-formed signature. We might want to only check that noexcept expression if the type is move constructible.
