Use Local Memory Type Variable Instead of Global Storage Type Variable in Event to Save Gas

[HighBe]

Hi, we recently have conducted a systematic study about Solidity event usage, evolution, and impact, and we are attempting to build a tool to improve the practice of Solidity event use based on our findings. We have tried our prototype tool on some of the most popular GitHub Solidity repositories, and for your repository, we find a potential optimization of gas consumption arisen from event use.

The point is that when we use emit operation to store the value of a certain variable, local memory type variable would be preferable to global storage type (state) variable if they hold the same value. The reason is that an extra SLOAD operation would be needed to access the variable if it is storage type, and the SLOAD operation costs 800 gas.

For your repository, we find that the following event use can be improved:

• FraxUniV3Farm_V2.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier  
          LockedStakeMaxMultiplierUpdated  
          veFXSPerFraxForMaxBoostUpdated  
          veFXSBoostScaleFactor
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier  
          lock_max_multiplier->_lock_max_multiplier  
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost  
          vefxs_boost_scale_factor->_vefxs_boost_scale_factor

    function setMultipliers(
        uint256 _lock_max_multiplier, 
        uint256 _vefxs_max_multiplier, 
        uint256 _vefxs_per_frax_for_max_boost,
        uint256 _vefxs_boost_scale_factor
    ) external onlyByOwnGov {
        require(_lock_max_multiplier >= MULTIPLIER_PRECISION, "Mult must be >= MULTIPLIER_PRECISION");
        require(_vefxs_max_multiplier >= 0, "veFXS mul must be >= 0");
        require(_vefxs_per_frax_for_max_boost > 0, "veFXS pct max must be >= 0");
        require(_vefxs_boost_scale_factor > 0, "veFXS boost scale factor must be >= 0");

        lock_max_multiplier = _lock_max_multiplier;
        vefxs_max_multiplier = _vefxs_max_multiplier;
        vefxs_per_frax_for_max_boost = _vefxs_per_frax_for_max_boost;
        vefxs_boost_scale_factor = _vefxs_boost_scale_factor;

        emit MaxVeFXSMultiplier(vefxs_max_multiplier);
        emit LockedStakeMaxMultiplierUpdated(lock_max_multiplier);
        emit veFXSPerFraxForMaxBoostUpdated(vefxs_per_frax_for_max_boost);
        emit veFXSBoostScaleFactor(vefxs_boost_scale_factor);
    }

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

    function setLockedStakeTimeForMinAndMaxMultiplier(uint256 _lock_time_for_max_multiplier, uint256 _lock_time_min) external onlyByOwnGov {
        require(_lock_time_for_max_multiplier >= 1, "Mul max time must be >= 1");
        require(_lock_time_min >= 1, "Mul min time must be >= 1");

        lock_time_for_max_multiplier = _lock_time_for_max_multiplier;
        lock_time_min = _lock_time_min;

        emit LockedStakeTimeForMaxMultiplier(lock_time_for_max_multiplier);
        emit LockedStakeMinTime(_lock_time_min);
    }

• veFXSYieldDistributor.sol
  function name: setYieldDuration
  event name:  YieldDurationUpdated
  variable:    yieldDuration->_yieldDuration

    function setYieldDuration(uint256 _yieldDuration) external onlyByOwnGov {
        require(periodFinish == 0 || block.timestamp > periodFinish, "Previous yield period must be complete before changing the duration for the new period");
        yieldDuration = _yieldDuration;
        emit YieldDurationUpdated(yieldDuration);
    }

• FraxCrossChainFarmSushi.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier  
          LockedStakeMaxMultiplierUpdated  
          veFXSPerFraxForMaxBoostUpdated  
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier  
          lock_max_multiplier->_lock_max_multiplier  
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost  

    function setMultipliers(uint256 _lock_max_multiplier, uint256 _vefxs_max_multiplier, uint256 _vefxs_per_frax_for_max_boost) external onlyByOwnGov {
        require(_lock_max_multiplier >= MULTIPLIER_PRECISION, "Mult must be >= MULTIPLIER_PRECISION");
        require(_vefxs_max_multiplier >= 0, "veFXS mul must be >= 0");
        require(_vefxs_per_frax_for_max_boost > 0, "veFXS pct max must be >= 0");

        lock_max_multiplier = _lock_max_multiplier;
        vefxs_max_multiplier = _vefxs_max_multiplier;
        vefxs_per_frax_for_max_boost = _vefxs_per_frax_for_max_boost;

        emit MaxVeFXSMultiplier(vefxs_max_multiplier);
        emit LockedStakeMaxMultiplierUpdated(lock_max_multiplier);
        emit veFXSPerFraxForMaxBoostUpdated(vefxs_per_frax_for_max_boost);
    }

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

    function setLockedStakeTimeForMinAndMaxMultiplier(uint256 _lock_time_for_max_multiplier, uint256 _lock_time_min) external onlyByOwnGov {
        require(_lock_time_for_max_multiplier >= 1, "Mul max time must be >= 1");
        require(_lock_time_min >= 1, "Mul min time must be >= 1");

        lock_time_for_max_multiplier = _lock_time_for_max_multiplier;
        lock_time_min = _lock_time_min;

        emit LockedStakeTimeForMaxMultiplier(lock_time_for_max_multiplier);
        emit LockedStakeMinTime(_lock_time_min);
    }

• StakingRewards.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

    function setRewardsDuration(uint256 _rewardsDuration) external onlyByOwnGov {
        require(
            periodFinish == 0 || block.timestamp > periodFinish,
            "Reward period incomplete"
        );
        rewardsDuration = _rewardsDuration;
        emit RewardsDurationUpdated(rewardsDuration);
    }

  function name: setMultipliers
  event name:  MaxCRBoostMultiplier
          LockedStakeMaxMultiplierUpdated
  variable:    cr_boost_max_multiplier->_cr_boost_max_multiplier
          locked_stake_max_multiplier->_locked_stake_max_multiplier

    function setMultipliers(uint256 _locked_stake_max_multiplier, uint256 _cr_boost_max_multiplier) external onlyByOwnGov {
        require(_locked_stake_max_multiplier >= 1, "Multiplier must be greater than or equal to 1");
        require(_cr_boost_max_multiplier >= 1, "Max CR Boost must be greater than or equal to 1");

        locked_stake_max_multiplier = _locked_stake_max_multiplier;
        cr_boost_max_multiplier = _cr_boost_max_multiplier;
        
        emit MaxCRBoostMultiplier(cr_boost_max_multiplier);
        emit LockedStakeMaxMultiplierUpdated(locked_stake_max_multiplier);
    }

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    locked_stake_time_for_max_multiplier->_locked_stake_time_for_max_multiplier

• StakingRewardsDualV2.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxCRBoostMultiplier
          LockedStakeMaxMultiplierUpdated
  variable:    cr_boost_max_multiplier->_cr_boost_max_multiplier
          locked_stake_max_multiplier->_locked_stake_max_multiplier

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    locked_stake_time_for_max_multiplier->_locked_stake_time_for_max_multiplier

• veFXSYieldDistributorV3.sol
  function name: setYieldDuration
  event name:  YieldDurationUpdated
  variable:    yieldDuration->_yieldDuration

• FraxUniV3Farm_Volatile.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedNFTMaxMultiplierUpdated
          veFXSPctForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedNFTTimeForMinAndMaxMultiplier
  event name:  LockedNFTTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• veFXSYieldDistributorV2.sol
  function name: setYieldDuration
  event name:  YieldDurationUpdated
  variable:    yieldDuration->_yieldDuration

• StakingRewardsDualV4.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• StakingRewardsDual.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxCRBoostMultiplier
          LockedStakeMaxMultiplierUpdated
  variable:    cr_boost_max_multiplier->_cr_boost_max_multiplier
          locked_stake_max_multiplier->_locked_stake_max_multiplier

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    locked_stake_time_for_max_multiplier->_locked_stake_time_for_max_multiplier

• StakingRewardsDualV3.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• FraxFarmBSC_Dual_V5.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  LockedStakeMaxMultiplierUpdated
  variable:    lock_max_multiplier->_lock_max_multiplier

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• MigratableFarmBSC.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  LockedStakeMaxMultiplierUpdated
  variable:    locked_stake_max_multiplier->_locked_stake_max_multiplier

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    locked_stake_time_for_max_multiplier->_locked_stake_time_for_max_multiplier

• AnyswapV4ERC20.sol
  function name: changeVault
  event name:  LogChangeVault
  variable:    pendingVault->newVault

  function name: changeMPCOwner
  event name:  LogChangeMPCOwner
  variable:    pendingVault->newVault

• FraxCrossChainFarm.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• FraxCrossChainFarmV2.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• veFXSYieldDistributorV4.sol
  function name: setYieldDuration
  event name:  YieldDurationUpdated
  variable:    yieldDuration->_yieldDuration

• CommunalFarm.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  LockedStakeMaxMultiplierUpdated
  variable:    lock_max_multiplier->_lock_max_multiplier

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• FraxUniV3Farm_Stable.sol
  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedNFTTimeForMinAndMaxMultiplier
  event name:  LockedNFTTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• StakingRewardsDualV5.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• FRAX3CRV_Curve_FXS_Distributor.sol
  function name: setPaused
  event name:  PauseChanged
  variable:    paused->_paused

  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

• StakingRewardsMultiGauge.sol
  function name: setRewardsDuration
  event name:  RewardsDurationUpdated
  variable:    rewardsDuration->_rewardsDuration

  function name: setMultipliers
  event name:  MaxVeFXSMultiplier
          LockedStakeMaxMultiplierUpdated
          veFXSPerFraxForMaxBoostUpdated
  variable:    vefxs_max_multiplier->_vefxs_max_multiplier
          lock_max_multiplier->_lock_max_multiplier
          vefxs_per_frax_for_max_boost->_vefxs_per_frax_for_max_boost

  function name: setLockedStakeTimeForMinAndMaxMultiplier
  event name:  LockedStakeTimeForMaxMultiplier
  variable:    lock_time_for_max_multiplier->_lock_time_for_max_multiplier

• celrFRAX.sol
  function name: updateBridge
  event name:  BridgeUpdated
  variable:    bridge->_bridge

• AnyswapV5ERC20.sol
  function name: changeVault
  event name:  LogChangeVault
  variable:    pendingVault->newVault

  function name: changeMPCOwner
  event name:  LogChangeMPCOwner
  variable:    pendingVault->newVault

• celrFXS.sol
  function name: updateBridge
  event name:  BridgeUpdated
  variable:    bridge->_bridge

• AnyswapV4ERC20.sol
  function name: changeVault
  event name:  LogChangeVault
  variable:    pendingVault->newVault

  function name: changeMPCOwner
  event name:  LogChangeMPCOwner
  variable:    pendingVault->newVault

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