[llvm] [VPlan] Add VPInstruction::StepVector and use it in VPWidenIntOrFpInductionRecipe (PR #129508)

[Florian Hahn via llvm-commits]

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@@ -1918,6 +1928,18 @@ class VPWidenIntOrFpInductionRecipe : public VPWidenInductionRecipe {
   VPValue *getVFValue() { return getOperand(2); }
   const VPValue *getVFValue() const { return getOperand(2); }
 
+  // TODO: Remove once VPWidenIntOrFpInduction is fully expanded in
+  // convertToConcreteRecipes.
+  VPValue *getStepVector() { return getOperand(3); }
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fhahn wrote:

At the moment, it always must be a `VPInstructionWithType`, right? Would changing the return type to `VPInstructionWithType` remove some casts at use sites?

Also asser that it is a `StepVector` opcode here, rather than at use sites?

https://github.com/llvm/llvm-project/pull/129508