[RISCV][NFC] Combine the control flow for different RetOp of interrupt function

[Jim]

ping? Thanks.

[frasercrmck]

LGTM

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

RISCVTargetLowering::LowerReturn(SDValue Chain, CallingConv::ID CallConv,
 
   RetOps[0] = Chain; // Update chain.
 
   // Add the glue node if we have it.
   if (Glue.getNode()) {
     RetOps.push_back(Glue);
   }
 
+  unsigned RetOpc = RISCVISD::RET_FLAG;
   // Interrupt service routines use different return instructions.
   const Function &Func = DAG.getMachineFunction().getFunction();
   if (Func.hasFnAttribute("interrupt")) {
     if (!Func.getReturnType()->isVoidTy())
       report_fatal_error(
           "Functions with the interrupt attribute must have void return type!");
 
     MachineFunction &MF = DAG.getMachineFunction();
     StringRef Kind =
       MF.getFunction().getFnAttribute("interrupt").getValueAsString();
 
-    unsigned RetOpc;
     if (Kind == "user")
       RetOpc = RISCVISD::URET_FLAG;
     else if (Kind == "supervisor")
       RetOpc = RISCVISD::SRET_FLAG;
     else
       RetOpc = RISCVISD::MRET_FLAG;
-
-    return DAG.getNode(RetOpc, DL, MVT::Other, RetOps);
   }
 
-  return DAG.getNode(RISCVISD::RET_FLAG, DL, MVT::Other, RetOps);
+  return DAG.getNode(RetOpc, DL, MVT::Other, RetOps);
 }
 
 void RISCVTargetLowering::validateCCReservedRegs(
     const SmallVectorImpl<std::pair<llvm::Register, llvm::SDValue>> &Regs,
     MachineFunction &MF) const {
   const Function &F = MF.getFunction();
   const RISCVSubtarget &STI = MF.getSubtarget<RISCVSubtarget>();