https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93843
--- Comment #7 from Matthias Kretz (Vir) <kretz at kde dot org> --- This one exhibits the issue without -ftree-vectorize (`-O1` suffices) (cf. https://godbolt.org/z/Swx-jW): using M [[gnu::vector_size(2)]] = char; using MM [[gnu::vector_size(4)]] = short; MM cvt(M x) { return MM{short(x[0]), short(x[1])}; }