[RISCV] Generalize cost model for vp_fneg. NFC. (#126915)

Move the cost model for vp_fneg from the riscv-specific implementation to the generic TTI layer.
This ensures consistent handling of vp_fneg across targets

Author: mikhailramalho

llvm/include/llvm/CodeGen/BasicTTIImpl.h

@@ -1675,7 +1675,8 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
           return thisT()->getMemoryOpCost(*FOp, ICA.getArgTypes()[0], Alignment,
                                           AS, CostKind);
         }
-        if (VPBinOpIntrinsic::isVPBinOp(ICA.getID())) {
+        if (VPBinOpIntrinsic::isVPBinOp(ICA.getID()) ||
+            ICA.getID() == Intrinsic::vp_fneg) {
           return thisT()->getArithmeticInstrCost(*FOp, ICA.getReturnType(),
                                                  CostKind);
         }

llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp

@@ -1356,13 +1356,6 @@ RISCVTTIImpl::getIntrinsicInstrCost(const IntrinsicCostAttributes &ICA,
       return Cost * LT.first;
     break;
   }
-  case Intrinsic::vp_fneg: {
-    std::optional<unsigned> FOp =
-        VPIntrinsic::getFunctionalOpcodeForVP(ICA.getID());
-    assert(FOp.has_value());
-    return getArithmeticInstrCost(*FOp, ICA.getReturnType(), CostKind);
-    break;
-  }
   case Intrinsic::vp_select: {
     Intrinsic::ID IID = ICA.getID();
     std::optional<unsigned> FOp = VPIntrinsic::getFunctionalOpcodeForVP(IID);