> A language defined 128bit SIMD type would be fine for basically all
> architectures. Even though they support different operations on these
> registers, the size and allocation patterns are always the same across all
> architectures; 128 bits, 16byte aligned, etc. This allows at minimum
> platform independent expression of structures containing simd data, and
> calling of functions passing these types as args.

You forgot about AVX. It uses 256 bit registers and is supported in new Intel and AMD processors.