[llvm] [IR][RISCV] Remove @llvm.experimental.vp.splat (PR #171084)

[Luke Lau via llvm-commits]

lukel97 wrote:

> > Do we need to add AutoUpgrade support for compatibility with old bitcode?
> 
> 
> 
> If we are to add this AutoUpgrade, what would we substitute the scalable vector version of this intrinsic with?
> 
> I can only think of store + zero-stride load, or multiple layers of vector.interleave

The disabled lanes are poison so we can just replace them with whatever right? I think we can just replace it with the usual insertelement + shufflevector idiom if we need to

https://github.com/llvm/llvm-project/pull/171084