Use macros for generating code for most/all of the primitive SIMD natives. The MIR code should be annotated with the right TypePolicy for unboxing the inputs, and the output should be boxed after each SIMD instruction.
I think this is done. We insert explicit MSimdUnbox / MSimdBox instructions when inlining instead of relying on the TypePolicy, but the result is the same.
Sweet, first time I have the opportunity to close a meta bug as fixed \o/.