[llvm] [LV][EVL] Generate negative strided load/store for reversed load/store (PR #123608)

[Luke Lau via llvm-commits]

lukel97 wrote:

> I am wondering about the necessity of emitting vp.stride_load/store in the vectorizer stage. 

One benefit of emitting strided intrinsics earlier is that it allows us to use the strided memory op TTI hook in the cost model. 

Otherwise we would have to conservatively cost it as a wide load + reverse, which IIRC the reverse is still costed as a quadratic vrgather today

https://github.com/llvm/llvm-project/pull/123608