[llvm] [SLP][REVEC] SubVectorsMask should be transformed into vector form. (PR #120398)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> I think we can fix `ShuffleCostEstimator::finalize` in another PR.

I think this incorrect approach at all. You need to operate with the original length masks everywhere

https://github.com/llvm/llvm-project/pull/120398