[llvm] [LV] Limits the splat operations be hoisted must not be defined by a recipe. (PR #117138)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> > > I think it should be possible to organize the declarations in a better way to enable this (with the main other benefit being that it also reduces the size of VPlan.h): #124104
> > 
> > 
> > Thanks, #124104 help me a lot! I j already rebased this patch on that.:) But I just saw #124644, do we still need to use VPDominatorTree? In my opinion, the explicit splat is the best approach to resolve this issue.
> 
> It depends if anything is blocked on this at the moment. #124644 is the first step, there is a bit more follow-up work needed to completely remove `SafeToHoist`, but after that the VPDT shouldn't be needed.
> 
> If you need this fixed urgently to unblock follow-up patches then it may make sense to use the VPDT here for now.

Got it. #124644 is currently limited to LiveIn values, and further work is needed to support splatting non-LiveIn values. 
In that case, maybe we can proceed with the VPDT approach first. :)

https://github.com/llvm/llvm-project/pull/117138