https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114417
Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |mkretz at gcc dot gnu.org --- Comment #9 from Matthias Kretz (Vir) <mkretz at gcc dot gnu.org> --- Sorry for not noticing this PR earlier. Yes, this specific behavior of fixed_size follows a request from the C++ committee for the TS. It is not mandated by the TS wording, because the C++ spec has no means to require passing arguments via the stack or registers. That's beyond the abstract machine. It still asks for that behavior non-normatively, though. What you want to use instead is std::experimental::simd_abi::deduce_t<T, N>. That'll give you a not-fixed_size ABI if one exists. And those will likely be passed via registers (as long as the psABI allows).