!fixup address latest comments

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1026,19 +1026,22 @@ class VPInstruction : public VPRecipeWithIRFlags,
 };
 
 /// A recipe to wrap on original IR instruction not to be modified during
-/// execution, execept for PHIs. For PHIs, a single VPValue operand is allowed,
-/// and it is used to add a new incoming value for the single predecessor VPBB.
+/// execution, except for PHIs. PHIs are modeled via the VPIRPhi subclass.
 /// Expect PHIs, VPIRInstructions cannot have any operands.
 class VPIRInstruction : public VPRecipeBase {
   Instruction &I;
 
 protected:
+  /// VPIRInstruction::create() should be used to create VPIRInstructions, as
+  /// subclasses may need to be created, e.g. VPIRPhi.
   VPIRInstruction(Instruction &I)
       : VPRecipeBase(VPDef::VPIRInstructionSC, ArrayRef<VPValue *>()), I(I) {}
 
 public:
   ~VPIRInstruction() override = default;
 
+  /// Create a new VPIRPhi for \p \I, if it is a PHINode, otherwise create a
+  /// VPIRInstruction.
   static VPIRInstruction *create(Instruction &I);
 
   VP_CLASSOF_IMPL(VPDef::VPIRInstructionSC)
@@ -1089,7 +1092,9 @@ class VPIRInstruction : public VPRecipeBase {
 };
 
 /// An overlay for VPIRInstructions wrapping PHI nodes enabling convenient use
-/// cast/dyn_cast/isa and execute() implementation.
+/// cast/dyn_cast/isa and execute() implementation. A single VPValue operand is
+/// allowed, and it is used to add a new incoming value for the single
+/// predecessor VPBB.
 struct VPIRPhi : public VPIRInstruction {
   VPIRPhi(PHINode &PN) : VPIRInstruction(PN) {}
 

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -1106,6 +1106,7 @@ void VPIRInstruction::print(raw_ostream &O, const Twine &Indent,
 #endif
 
 void VPIRPhi::execute(VPTransformState &State) {
+  assert(getNumOperands() > 0 && "VPIRPhi recipes must have operands");
   PHINode *Phi = &getIRPhi();
   for (const auto &[Idx, Op] : enumerate(operands())) {
     VPValue *ExitValue = Op;

llvm/lib/Transforms/Vectorize/VPlanVerifier.cpp

@@ -208,10 +208,9 @@ bool VPlanVerifier::verifyVPBasicBlock(const VPBasicBlock *VPBB) {
       for (const VPUser *U : V->users()) {
         auto *UI = cast<VPRecipeBase>(U);
         // TODO: check dominance of incoming values for phis properly.
-        if (!UI || isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe,
-                       VPIRPhi>(UI))
         if (!UI ||
-            isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe>, VPIRPhi(UI) ||
+            isa<VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPredInstPHIRecipe,
+                VPIRPhi>(UI) ||
             (isa<VPInstruction>(UI) &&
              cast<VPInstruction>(UI)->getOpcode() == Instruction::PHI))
           continue;