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

[Luke Lau via llvm-commits]

================
@@ -1836,6 +1841,7 @@ class VPWidenIntOrFpInductionRecipe : public VPWidenInductionRecipe {
                                Step, IndDesc, DL),
         Trunc(nullptr) {
     addOperand(VF);
+    addOperand(VF); // Dummy StepVector replaced in convertToConcreteRecipes
----------------
lukel97 wrote:

Oh good idea, I've changed it to poison in e73e9944eedd280f9b3b2f959affc61425aa6e59

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