[llvm] [X86] isLoadBitCastBeneficial - its only beneficial to bitcast between vector types if the new type is legal (PR #171813)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@phoebewang Doesn't help with the missed store combines you mentioned, but it is related.

https://github.com/llvm/llvm-project/pull/171813