x86 SIMD suffers from register aliasing. xmm0 is actually the low-half of ymm0, so you need to explicitly tell the processor what your input type is to properly

x86 SIMD suffers from register aliasing. xmm0 is actually the low-half of ymm0, so you need to explicitly tell the processor what your input type is to properly handle overflow and signing. Actual vectorized instructions don’t have this problem but you also can’t change it now.