[llvm] [VPlan] Endow DerivedIV with IRFlags (PR #205908)

[Mel Chen via llvm-commits]

Mel-Chen wrote:

> I think I found one more case where we cannot preserve NUW when the IV counts down: https://alive2.llvm.org/ce/z/dRwiJb

It seems that the no-wrap flags for Add cannot be directly applied to Mul, and vice versa. Likewise, the no-wrap flags in InductionDescriptor cannot be directly applied when expanding VPDerivedIVRecipe.
Perhaps we should store the Add and Mul flags separately inside VPDerivedIVRecipe, and let its constructor properly infer the correct flags?

https://github.com/llvm/llvm-project/pull/205908