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

[Florian Hahn via llvm-commits]

================
@@ -1965,8 +1965,11 @@ void VPWidenIntOrFpInductionRecipe::execute(VPTransformState &State) {
   }
 
   Value *SplatStart = Builder.CreateVectorSplat(State.VF, Start);
-  Value *SteppedStart = getStepVector(SplatStart, Step, ID.getInductionOpcode(),
-                                      State.VF, State.Builder);
+  assert(cast<VPInstruction>(getStepVector())->getOpcode() ==
----------------
fhahn wrote:

`&& step vector operand must be a StepVector` VPInstruction.

Although that may be too restrictive, for fixed vectors it could just be a constant vector?

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