[llvm] [LV][EVL]Support reversed loads/stores. (PR #88025)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> It's obviously safe for reverse to utilize an all-true mask - as does the non-EVL vectorizer. Question was if it is ever beneficial not to do so? I.e., if in practice the mask of reverse is an unused operand that only wastes a register.

Yes, always better from our perf data. Reducing dependencies increases the throughput, allows to execute instructions in parallel.

https://github.com/llvm/llvm-project/pull/88025