[VPlan] Use VPdef for VPWidenCall.

[fhahn]

Summary

This patch turns updates VPWidenREcipe to manage the value it defines
using VPDef. The VPValue is used during VPlan construction and
codegeneration instead of the plain IR reference where possible.

[fhahn]

Updated to keep VPWidenCall a VPValue which is then added to its VPDef. This simplifies things a bit.

[fhahn]

update after VPDef does not inherit from VPUser directly.

[fhahn]

Rebase after all dependent patches landed & ping :)

[fhahn]

ping :)

The main patches have already been approved (D90565, D90564) and this patch just updates VPWidenCallRecipe to be a single-value def.

[fhahn]

ping

llvm/lib/Transforms/Vectorize/VPlan.h

public:
   void execute(VPTransformState &State) override;
 
   /// Print the recipe.
   void print(raw_ostream &O, const Twine &Indent,
              VPSlotTracker &SlotTracker) const override;
 };
 
 /// A recipe for widening Call instructions.
-class VPWidenCallRecipe : public VPRecipeBase, public VPValue, public VPUser {
+class VPWidenCallRecipe : public VPRecipeBase, public VPDef, public VPValue {
 
 public:
   template <typename IterT>
   VPWidenCallRecipe(CallInst &I, iterator_range<IterT> CallArguments)
-      : VPRecipeBase(VPRecipeBase::VPWidenCallSC),
-        VPValue(VPValue::VPVWidenCallSC, &I), VPUser(CallArguments) {}
+      : VPRecipeBase(VPRecipeBase::VPWidenCallSC), VPDef(CallArguments),
+        VPValue(VPValue::VPVWidenCallSC, &I, this) {}
 
   ~VPWidenCallRecipe() override = default;
 
   /// Method to support type inquiry through isa, cast, and dyn_cast.
   static inline bool classof(const VPRecipeBase *V) {
     return V->getVPRecipeID() == VPRecipeBase::VPWidenCallSC;
   }