All this is true for compiling for the integer ALU as well. Exactly because the actual optimizations depend on the architecture, they should be done by the comp

All this is true for compiling for the integer ALU as well. Exactly because the actual optimizations depend on the architecture, they should be done by the compiler. Yes you can do much better by hand-writing assembly, but right now that's rarely done. So compilers try to vectorize scalar code we give it in languages like C, which is much harder than optimizing code that's already written in vectors like int32x4 or float64x2.