[llvm] [LV] Avoid redundant SCEVChecks on active lane mask (PR #171605)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > > Why don't we need the pointer overflow checks when we have an active lane mask?
> > 
> > 
> > MemChecks are still needed, and this patch doesn't change that?
> 
> Yes but I'm not familiar with the pointer overflow checks/SCEV checks which this patch removes. How does the active lane mask defend against that?

I think while the tail-folding style is ActiveLaneMask(WithControlFlow), it inserts these checks (and they're missing in some diffs due to folding)? Sorry, I might be mis-reading VPlanTransforms::addActiveLaneMask?

https://github.com/llvm/llvm-project/pull/171605