[llvm] [TTI][AArch64] Detect OperandInfo from scalable splats. (PR #122469)

[Sander de Smalen via llvm-commits]

https://github.com/sdesmalen-arm commented:

I agree that it makes sense to investigate why the cost for illegal types gets assigned a lower cost. In a way this regresses the cost-model because for some types it now assumes that a div of a legal type is more expensive than an illegal type that requires legalisation.

https://github.com/llvm/llvm-project/pull/122469