[VPlan] Compute cost of replicating calls in VPlan. (NFCI)

Implement computing the scalarization overhead for replicating calls in
VPlan, matching the legacy cost model.

Depends on llvm#154126.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -3002,13 +3002,6 @@ InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
     // instruction cost.
     return 0;
   case Instruction::Call: {
-    if (!isSingleScalar()) {
-      // TODO: Handle remaining call costs here as well.
-      if (VF.isScalable())
-        return InstructionCost::getInvalid();
-      break;
-    }
-
     auto *CalledFn =
         cast<Function>(getOperand(getNumOperands() - 1)->getLiveInIRValue());
     if (CalledFn->isIntrinsic())
@@ -3017,8 +3010,43 @@ InstructionCost VPReplicateRecipe::computeCost(ElementCount VF,
     SmallVector<Type *, 4> Tys;
     for (VPValue *ArgOp : drop_end(operands()))
       Tys.push_back(Ctx.Types.inferScalarType(ArgOp));
+
     Type *ResultTy = Ctx.Types.inferScalarType(this);
-    return Ctx.TTI.getCallInstrCost(CalledFn, ResultTy, Tys, Ctx.CostKind);
+    InstructionCost ScalarCallCost =
+        Ctx.TTI.getCallInstrCost(CalledFn, ResultTy, Tys, Ctx.CostKind);
+    if (isSingleScalar())
+      return ScalarCallCost;
+
+    if (VF.isScalable())
+      return InstructionCost::getInvalid();
+
+    // Compute the cost of scalarizing the result and operands if needed.
+    InstructionCost ScalarizationCost = 0;
+    if (VF.isVector()) {
+      if (!ResultTy->isVoidTy()) {
+        for (Type *VectorTy : getContainedTypes(toVectorizedTy(ResultTy, VF))) {
+          ScalarizationCost += Ctx.TTI.getScalarizationOverhead(
+              cast<VectorType>(VectorTy), APInt::getAllOnes(VF.getFixedValue()),
+              /*Insert=*/true,
+              /*Extract=*/false, Ctx.CostKind);
+        }
+      }
+      // Skip operands that do not require extraction/scalarization and do not
+      // incur any overhead.
+      SmallVector<Type *> Tys;
+      SmallPtrSet<const VPValue *, 4> UniqueOperands;
+      for (auto *Op : drop_end(operands())) {
+        if (Op->isLiveIn() || isa<VPReplicateRecipe, VPPredInstPHIRecipe>(Op) ||
+            !UniqueOperands.insert(Op).second)
+          continue;
+        Tys.push_back(toVectorizedTy(Ctx.Types.inferScalarType(Op), VF));
+      }
+      ScalarizationCost +=
+          Ctx.TTI.getOperandsScalarizationOverhead(Tys, Ctx.CostKind);
+    }
+
+    return ScalarCallCost * (isSingleScalar() ? 1 : VF.getFixedValue()) +
+           ScalarizationCost;
   }
   case Instruction::Add:
   case Instruction::Sub: