https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70526
--- Comment #23 from Richard Biener <rguenth at gcc dot gnu.org> --- A fix for your testcase would also be to do template<typename T> struct AlignedStorage2 { union U { char mBytes[sizeof(T)]; uint64_t mDummy; } u; typedef T _T __attribute__((may_alias)); const _T* addr() const { return reinterpret_cast<const _T*>(u.mBytes); } _T* addr() { return static_cast<_T*>(static_cast<void*>(u.mBytes)); } }; that is, making sure to return may_alias pointers (and use AlignedStorage2<>::_T for temporaries you save addr to and do other accesses). The stores done via that type are allowed to be accessed with an effective type of TypedOrValueRegister.