> scalar instructions can easily introduce performance issues because they leave the high bits of the registers untouched (i.e., introduce useless partial depen

> scalar instructions can easily introduce performance issues because they leave the high bits of the registers untouched (i.e., introduce useless partial dependencies) How's that? SSE scalar ops are all two-address, so they depend on the destination regardless. And AVX scalar ops are three-address, but zero the high bits of the register. Where you run into trouble is mixing sse with avx, as you can end up in the dirty high half state; but that can happen with vector or scalar ops.