[llvm] [LV] Convert scatter w/uniform addr and mask being header mask to scalar store. (PR #172799)

[Luke Lau via llvm-commits]

lukel97 wrote:

It looks like in practice the scalar store will always be sunk into the middle block. Can we directly do that in this transform instead of leaving it in the vector body?

That way we wouldn't need to worry about costing it. Unless I'm missing something it should always be profitable to sink it out of the vector body?

https://github.com/llvm/llvm-project/pull/172799