[VPlan] Pass NumUnrolledElems as operand to VPWidenPointerInductionRecipe. NFC (#119859)

Similarly to VPWidenIntOrFpInductionRecipe, if we want to support it in
EVL tail folding we need to increment the induction by EVL steps instead
of VF*UF steps, but currently this is hard-wired in
VPWidenPointerInductionRecipe.

This adds an operand for the number of elements unrolled and plumbs it
through, so that we can swap it out in
VPlanTransforms::tryAddExplicitVectorLength further down the line.

Author: lukel97

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -7826,7 +7826,7 @@ VPHeaderPHIRecipe *VPRecipeBuilder::tryToOptimizeInductionPHI(
     VPValue *Step = vputils::getOrCreateVPValueForSCEVExpr(Plan, II->getStep(),
                                                            *PSE.getSE());
     return new VPWidenPointerInductionRecipe(
-        Phi, Operands[0], Step, *II,
+        Phi, Operands[0], Step, &Plan.getVFxUF(), *II,
         LoopVectorizationPlanner::getDecisionAndClampRange(
             [&](ElementCount VF) {
               return CM.isScalarAfterVectorization(Phi, VF);

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -2034,25 +2034,30 @@ class VPWidenIntOrFpInductionRecipe : public VPWidenInductionRecipe {
 };
 
 class VPWidenPointerInductionRecipe : public VPWidenInductionRecipe,
-                                      public VPUnrollPartAccessor<3> {
+                                      public VPUnrollPartAccessor<4> {
   bool IsScalarAfterVectorization;
 
 public:
   /// Create a new VPWidenPointerInductionRecipe for \p Phi with start value \p
-  /// Start.
+  /// Start and the number of elements unrolled \p NumUnrolledElems, typically
+  /// VF*UF.
   VPWidenPointerInductionRecipe(PHINode *Phi, VPValue *Start, VPValue *Step,
+                                VPValue *NumUnrolledElems,
                                 const InductionDescriptor &IndDesc,
                                 bool IsScalarAfterVectorization, DebugLoc DL)
       : VPWidenInductionRecipe(VPDef::VPWidenPointerInductionSC, Phi, Start,
                                Step, IndDesc, DL),
-        IsScalarAfterVectorization(IsScalarAfterVectorization) {}
+        IsScalarAfterVectorization(IsScalarAfterVectorization) {
+    addOperand(NumUnrolledElems);
+  }
 
   ~VPWidenPointerInductionRecipe() override = default;
 
   VPWidenPointerInductionRecipe *clone() override {
     return new VPWidenPointerInductionRecipe(
         cast<PHINode>(getUnderlyingInstr()), getOperand(0), getOperand(1),
-        getInductionDescriptor(), IsScalarAfterVectorization, getDebugLoc());
+        getOperand(2), getInductionDescriptor(), IsScalarAfterVectorization,
+        getDebugLoc());
   }
 
   VP_CLASSOF_IMPL(VPDef::VPWidenPointerInductionSC)
@@ -2067,7 +2072,7 @@ class VPWidenPointerInductionRecipe : public VPWidenInductionRecipe,
   /// the first unrolled part, if it exists. Returns itself if unrolling did not
   /// take place.
   VPValue *getFirstUnrolledPartOperand() {
-    return getUnrollPart(*this) == 0 ? this : getOperand(2);
+    return getUnrollPart(*this) == 0 ? this : getOperand(3);
   }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -3544,8 +3544,7 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
   if (CurrentPart == 0) {
     // The recipe represents the first part of the pointer induction. Create the
     // GEP to increment the phi across all unrolled parts.
-    Value *NumUnrolledElems =
-        State.get(&getParent()->getPlan()->getVFxUF(), true);
+    Value *NumUnrolledElems = State.get(getOperand(2), true);
 
     Value *InductionGEP = GetElementPtrInst::Create(
         State.Builder.getInt8Ty(), NewPointerPhi,
@@ -3581,19 +3580,21 @@ void VPWidenPointerInductionRecipe::execute(VPTransformState &State) {
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 void VPWidenPointerInductionRecipe::print(raw_ostream &O, const Twine &Indent,
                                           VPSlotTracker &SlotTracker) const {
-  assert((getNumOperands() == 2 || getNumOperands() == 4) &&
+  assert((getNumOperands() == 3 || getNumOperands() == 5) &&
          "unexpected number of operands");
   O << Indent << "EMIT ";
   printAsOperand(O, SlotTracker);
   O << " = WIDEN-POINTER-INDUCTION ";
   getStartValue()->printAsOperand(O, SlotTracker);
   O << ", ";
   getStepValue()->printAsOperand(O, SlotTracker);
-  if (getNumOperands() == 4) {
-    O << ", ";
-    getOperand(2)->printAsOperand(O, SlotTracker);
+  O << ", ";
+  getOperand(2)->printAsOperand(O, SlotTracker);
+  if (getNumOperands() == 5) {
     O << ", ";
     getOperand(3)->printAsOperand(O, SlotTracker);
+    O << ", ";
+    getOperand(4)->printAsOperand(O, SlotTracker);
   }
 }
 #endif