Simd fixes

[iskamag]

No description provided.

[froggey]

What's happening here is (:object-unscaled ,object 0 ,index-unboxed) is still scaling the index by 8, as while the scale for the slot is 1 (because of :object-unscaled the scale of the index is 8 by default and separate from the slot scaling. index-unboxed can't be used as the slot here as it's non constant, hence slot 0. Setting the index scale to 1 is the right way to go here, and using either :object or :object-unscaled is fine, I think other parts of the compiler use :object for this case too. LGTM 👍