[VPlan] Remove remaining references to VPScalarPHIRecipe (NFC).

VPScalarPHIRecipe has been replaced by VPInstructions with PHI opcodes.
Strip remaining dead references to VPScalarPHIRecipe.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -532,7 +532,6 @@ class VPSingleDefRecipe : public VPRecipeBase, public VPValue {
     case VPRecipeBase::VPWidenPointerInductionSC:
     case VPRecipeBase::VPReductionPHISC:
     case VPRecipeBase::VPScalarCastSC:
-    case VPRecipeBase::VPScalarPHISC:
     case VPRecipeBase::VPPartialReductionSC:
       return true;
     case VPRecipeBase::VPBranchOnMaskSC:
@@ -2819,8 +2818,8 @@ class VPCanonicalIVPHIRecipe : public VPHeaderPHIRecipe {
   VP_CLASSOF_IMPL(VPDef::VPCanonicalIVPHISC)
 
   void execute(VPTransformState &State) override {
-    llvm_unreachable(
-        "cannot execute this recipe, should be replaced by VPScalarPHIRecipe");
+    llvm_unreachable("cannot execute this recipe, should be replaced by a "
+                     "scalar phi recipe");
   }
 
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
@@ -2905,8 +2904,8 @@ class VPEVLBasedIVPHIRecipe : public VPHeaderPHIRecipe {
   VP_CLASSOF_IMPL(VPDef::VPEVLBasedIVPHISC)
 
   void execute(VPTransformState &State) override {
-    llvm_unreachable(
-        "cannot execute this recipe, should be replaced by VPScalarPHIRecipe");
+    llvm_unreachable("cannot execute this recipe, should be replaced by a "
+                     "scalar phi recipe");
   }
 
   /// Return the cost of this VPEVLBasedIVPHIRecipe.

llvm/lib/Transforms/Vectorize/VPlanValue.h

@@ -360,7 +360,6 @@ class VPDef {
     VPFirstOrderRecurrencePHISC,
     VPWidenIntOrFpInductionSC,
     VPWidenPointerInductionSC,
-    VPScalarPHISC,
     VPReductionPHISC,
     // END: SubclassID for recipes that inherit VPHeaderPHIRecipe
     // END: Phi-like recipes