[RISCV][TTI] Add vp.cmp intrinsic cost with functionalOPC. (llvm#107504)

This patch make the instruction cost of VP compare intrinsics as same as
their non-VP counterpart.

Author: ElvisWang123

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -1033,6 +1033,21 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
                             TTI::CastContextHint::None, CostKind);
     break;
   }
+
+  // vp compare
+  case Intrinsic::vp_icmp:
+  case Intrinsic::vp_fcmp: {
+    Intrinsic::ID IID = ICA.getID();
+    std::optional<unsigned> FOp = VPIntrinsic::getFunctionalOpcodeForVP(IID);
+    auto *UI = dyn_cast<VPCmpIntrinsic>(ICA.getInst());
+
+    // We can only handle vp_cmp intrinsics with underlying instructions.
+    if (!UI)
+      break;
+    assert(FOp);
+    return getCmpSelInstrCost(*FOp, ICA.getArgTypes()[0], ICA.getReturnType(),
+                              UI->getPredicate(), CostKind);
+  }
   }
 
   if (ST->hasVInstructions() && RetTy->isVectorTy()) {