[VPlan] Move SCEV expansion for pointer induction to VPExpandSCEV (NFC).

Use VPExpandSCEVRecipe to expand the step of pointer inductions. This
cleanup addresses a corresponding FIXME.

It should be NFC, as steps for pointer induction must be constants,
which makes expansion trivial.

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -8197,9 +8197,12 @@ VPRecipeBase *VPRecipeBuilder::tryToOptimizeInductionPHI(
                                        *PSE.getSE(), *OrigLoop, Range);
 
   // Check if this is pointer induction. If so, build the recipe for it.
-  if (auto *II = Legal->getPointerInductionDescriptor(Phi))
-    return new VPWidenPointerInductionRecipe(Phi, Operands[0], *II,
-                                             *PSE.getSE());
+  if (auto *II = Legal->getPointerInductionDescriptor(Phi)) {
+    VPValue *Step = vputils::getOrCreateVPValueForSCEVExpr(Plan, II->getStep(),
+                                                           *PSE.getSE());
+    assert(isa<SCEVConstant>(II->getStep()));
+    return new VPWidenPointerInductionRecipe(Phi, Operands[0], Step, *II);
+  }
   return nullptr;
 }
 
@@ -9437,8 +9440,7 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
             PartStart, ConstantInt::get(PtrInd->getType(), Lane));
         Value *GlobalIdx = State.Builder.CreateAdd(PtrInd, Idx);
 
-        Value *Step = CreateStepValue(IndDesc.getStep(), SE,
-                                      State.CFG.PrevBB->getTerminator());
+        Value *Step = State.get(getOperand(1), VPIteration(0, Part));
         Value *SclrGep = emitTransformedIndex(
             State.Builder, GlobalIdx, IndDesc.getStartValue(), Step, IndDesc);
         SclrGep->setName("next.gep");
@@ -9465,9 +9467,7 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
   const DataLayout &DL = NewPointerPhi->getModule()->getDataLayout();
   Instruction *InductionLoc = &*State.Builder.GetInsertPoint();
 
-  const SCEV *ScalarStep = IndDesc.getStep();
-  SCEVExpander Exp(SE, DL, "induction");
-  Value *ScalarStepValue = Exp.expandCodeFor(ScalarStep, PhiType, InductionLoc);
+  Value *ScalarStepValue = State.get(getOperand(1), VPIteration(0, 0));
   Value *RuntimeVF = getRuntimeVF(State.Builder, PhiType, State.VF);
   Value *NumUnrolledElems =
       State.Builder.CreateMul(RuntimeVF, ConstantInt::get(PhiType, State.UF));
@@ -9495,6 +9495,8 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
     StartOffset = State.Builder.CreateAdd(
         StartOffset, State.Builder.CreateStepVector(VecPhiType));
 
+    assert(ScalarStepValue == State.get(getOperand(1), VPIteration(0, Part)) &&
+           "scalar step must be the same across all parts");
     Value *GEP = State.Builder.CreateGEP(
         IndDesc.getElementType(), NewPointerPhi,
         State.Builder.CreateMul(

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1183,21 +1183,16 @@ public:
 class VPWidenPointerInductionRecipe : public VPHeaderPHIRecipe {
   const InductionDescriptor &IndDesc;
 
-  /// SCEV used to expand step.
-  /// FIXME: move expansion of step to the pre-header, once it is modeled
-  /// explicitly.
-  ScalarEvolution &SE;
-
 public:
   /// Create a new VPWidenPointerInductionRecipe for \p Phi with start value \p
   /// Start.
-  VPWidenPointerInductionRecipe(PHINode *Phi, VPValue *Start,
-                                const InductionDescriptor &IndDesc,
-                                ScalarEvolution &SE)
+  VPWidenPointerInductionRecipe(PHINode *Phi, VPValue *Start, VPValue *Step,
+                                const InductionDescriptor &IndDesc)
       : VPHeaderPHIRecipe(VPVWidenPointerInductionSC, VPWidenPointerInductionSC,
                           Phi),
-        IndDesc(IndDesc), SE(SE) {
+        IndDesc(IndDesc) {
     addOperand(Start);
+    addOperand(Step);
   }
 
   ~VPWidenPointerInductionRecipe() override = default;