[llvm] [LV] Fix a crash on SELECT masks with a one element vector. (PR #83332)

[Florian Hahn via llvm-commits]

fhahn wrote:

So the issue here is that we are interleaving with VF=1, but creating an active-lane-mask, which provides `<1 x i1>`? IIUC this would be the only case where we could generate vectors with a single element. does it make sense to use active-lane-mask in this case? Seems like a simple compare would suffice in this case. If not, could the active-lane-mask recipes set the scalar-per-part instead of the vector value?

https://github.com/llvm/llvm-project/pull/83332