[VPlan] Use VPDef for VPWidenSelectRecipe.

[fhahn]

Summary

This patch turns updates VPWidenSelectRecipe 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 VPWidenSelectRecipe 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 :)

[fhahn]

ping

[gilr]

How is the new test related to this change?

[fhahn]

In D90560#2454074, @gilr wrote:

How is the new test related to this change?

It exposed a crash in an earlier revision of the patches, but that has been fixed a while ago. I committed the test separately in 8a7e770638f0.

[gilr]

LGTM, tx!

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 select instructions.
-class VPWidenSelectRecipe : public VPRecipeBase, public VPValue, public VPUser {
+class VPWidenSelectRecipe : public VPRecipeBase,
+                            public VPDef,
+                            public VPUser,
+                            public VPValue {
 
   /// Is the condition of the select loop invariant?
   bool InvariantCond;
 
 public:
   template <typename IterT>
   VPWidenSelectRecipe(SelectInst &I, iterator_range<IterT> Operands,
                       bool InvariantCond)
-      : VPRecipeBase(VPRecipeBase::VPWidenSelectSC),
-        VPValue(VPValue::VPVWidenSelectSC, &I), VPUser(Operands),
+      : VPRecipeBase(VPRecipeBase::VPWidenSelectSC), VPUser(Operands),
+        VPValue(VPValue::VPVWidenSelectSC, &I, this),
         InvariantCond(InvariantCond) {}
 
   ~VPWidenSelectRecipe() override = default;
 
   /// Method to support type inquiry through isa, cast, and dyn_cast.
   static inline bool classof(const VPRecipeBase *V) {
     return V->getVPRecipeID() == VPRecipeBase::VPWidenSelectSC;
   }