bool LDVImpl::handleDebugValue(MachineInstr *MI, SlotIndex Idx) {
  // DBG_VALUE loc, offset, variable
  if (MI->getNumOperands() != 3 ||
      !MI->getOperand(1).isImm() || !MI->getOperand(2).isMetadata()) {
    DEBUG(dbgs() << "Can't handle " << *MI);
    return false;
  }

  // Get or create the UserValue for (variable,offset).
  unsigned Offset = MI->getOperand(1).getImm();
  const MDNode *Var = MI->getOperand(2).getMetadata();
  UserValue *UV = getUserValue(Var, Offset, MI->getDebugLoc());
  UV->addDef(Idx, MI->getOperand(0));
  return true;
}

void LDVImpl::
renameRegister(unsigned OldReg, unsigned NewReg, unsigned SubIdx) {
  UserValue *UV = lookupVirtReg(OldReg);
  if (!UV)
    return;

  if (TargetRegisterInfo::isVirtualRegister(NewReg))
    mapVirtReg(NewReg, UV);
  virtRegToEqClass.erase(OldReg);

  do {
    UV->renameRegister(OldReg, NewReg, SubIdx, TRI);
    UV = UV->getNext();
  } while (UV);
}

UserValue *LDVImpl::getUserValue(const MDNode *Var, const MDNode *Expr,
                                 bool IsIndirect, const DebugLoc &DL) {
  UserValue *&Leader = userVarMap[Var];
  if (Leader) {
    UserValue *UV = Leader->getLeader();
    Leader = UV;
    for (; UV; UV = UV->getNext())
      if (UV->match(Var, Expr, DL->getInlinedAt(), IsIndirect))
        return UV;
  }

  userValues.push_back(
      llvm::make_unique<UserValue>(Var, Expr, IsIndirect, DL, allocator));
  UserValue *UV = userValues.back().get();
  Leader = UserValue::merge(Leader, UV);
  return UV;
}

UserValue *LDVImpl::getUserValue(const MDNode *Var, unsigned Offset,
                                 bool IsIndirect, DebugLoc DL) {
  UserValue *&Leader = userVarMap[Var];
  if (Leader) {
    UserValue *UV = Leader->getLeader();
    Leader = UV;
    for (; UV; UV = UV->getNext())
      if (UV->match(Var, Offset, IsIndirect))
        return UV;
  }

  userValues.push_back(
      make_unique<UserValue>(Var, Offset, IsIndirect, DL, allocator));
  UserValue *UV = userValues.back().get();
  Leader = UserValue::merge(Leader, UV);
  return UV;
}

bool LDVImpl::handleDebugValue(MachineInstr &MI, SlotIndex Idx) {
  // DBG_VALUE loc, offset, variable
  if (MI.getNumOperands() != 4 ||
      !(MI.getOperand(1).isReg() || MI.getOperand(1).isImm()) ||
      !MI.getOperand(2).isMetadata()) {
    DEBUG(dbgs() << "Can't handle " << MI);
    return false;
  }

  // Get or create the UserValue for (variable,offset).
  bool IsIndirect = MI.isIndirectDebugValue();
  unsigned Offset = IsIndirect ? MI.getOperand(1).getImm() : 0;
  const MDNode *Var = MI.getDebugVariable();
  const MDNode *Expr = MI.getDebugExpression();
  //here.
  UserValue *UV = getUserValue(Var, Expr, Offset, IsIndirect, MI.getDebugLoc());
  UV->addDef(Idx, MI.getOperand(0));
  return true;
}