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

[Florian Hahn via llvm-commits]

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@@ -795,11 +795,17 @@ static void legalizeAndOptimizeInductions(VPlan &Plan) {
       continue;
 
     const InductionDescriptor &ID = WideIV->getInductionDescriptor();
+    // We can preserve nuw when the step is non-negative.
+    VPIRFlags::WrapFlagsTy WrapFlags;
+    ConstantInt *Step = ID.getConstIntStepValue();
+    if (Step && !Step->isNegative())
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fhahn wrote:

can we check `getStepValue`, which is what is passed below as well? 

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