[llvm] [VPlan] Use DerivedIV in convertToStridedAccesses (PR #209611)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> It looks like the costing change is a regression. We used to correctly cost the individual VPInstructions but the PtrInduction DerivedIV is now always zero.
> 
> I understand there's a TODO here but is it still relevant? I'm not sure the complexity of the BinOpGEPFlagsTy is worth it.

I guess we need to fix the TODO in DerivedIV costing. The benefit of BinOpGEPFlagsTy is that we can use it in follow-ups to get GEP no-wrap flags in many places, which would be an improvement.

https://github.com/llvm/llvm-project/pull/209611