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

[Pengcheng Wang via llvm-commits]

wangpc-pp wrote:

> > > > And we don't seem to currently check if it's supported anyway?
> > > 
> > > 
> > > Yes, because we never emit strided ops in LV for now. To emit it, need to correctly implement legality checks and cost model
> > 
> > 
> > I meant as in we don't check if llvm.experimental.vp.reverse is supported, and it doesn't look like there's a default expansion for it
> 
> It is not correct and should be checked

I am not so familiar with current LV infrastructure, how should I check the legality and cost model here?

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