Yeah, I end up using __attribute__((packed)) for this at work. For tortured reasons, part of our codebase allocates memory with only 8-byte alignment, but the buffer is cast to a type that would have 16-byte alignment without __attribute__((packed)). As a result Clang wants to generate VMOVDQAs that require 16-byte alignment, unless you use packed, in which case it generates VMOVDQU.