Gas Optimizations

[code423n4]

[G-01] msg.sender CAN BE USED INSTEAD OF STATE VARIABLE IF POSSIBLE

Reading msg.sender costs 2 gas, which is much cheaper than reading a state variable because an sload operation costs 100 or 2100 gas depending on whether the accessed address is warm or not.

In the following acceptOwnership function, msg.sender can be used instead of pendingGovernor for setting oldPendingGovernor and updating governor. msg.sender can also be used instead of governor for emitting the NewOwnership event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/governance/Governed.sol#L53-L67

    function acceptOwnership() external {
        require(
            pendingGovernor != address(0) && msg.sender == pendingGovernor,
            "Caller must be pending governor"
        );

        address oldGovernor = governor;
        address oldPendingGovernor = pendingGovernor;

        governor = pendingGovernor;
        pendingGovernor = address(0);

        emit NewOwnership(oldGovernor, governor);
        emit NewPendingOwnership(oldPendingGovernor, pendingGovernor);
    }

[G-02] address(0) CAN BE USED INSTEAD OF STATE VARIABLE IF POSSIBLE

Executing address(0) instead of reading a state variable saves gas by avoiding the costly sload operation.

In the following acceptOwnership function, address(0) can be used instead of pendingGovernor for emitting the NewPendingOwnership event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/governance/Governed.sol#L53-L67

    function acceptOwnership() external {
        require(
            pendingGovernor != address(0) && msg.sender == pendingGovernor,
            "Caller must be pending governor"
        );

        address oldGovernor = governor;
        address oldPendingGovernor = pendingGovernor;

        governor = pendingGovernor;
        pendingGovernor = address(0);

        emit NewOwnership(oldGovernor, governor);
        emit NewPendingOwnership(oldPendingGovernor, pendingGovernor);
    }

[G-03] MEMORY VARIABLES CAN BE USED INSTEAD OF STATE VARIABLES IF POSSIBLE

Accessing a memory variable instead of a state variable replaces an sload operation with an mload operation. When this is possible, gas is saved.

In the following transferOwnership function, _newGovernor can be used instead of pendingGovernor for emitting the NewPendingOwnership event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/governance/Governed.sol#L40-L47

    function transferOwnership(address _newGovernor) external onlyGovernor {
        require(_newGovernor != address(0), "Governor must be set");

        address oldPendingGovernor = pendingGovernor;
        pendingGovernor = _newGovernor;

        emit NewPendingOwnership(oldPendingGovernor, pendingGovernor);
    }

In the following setGateway function, _gw can be used instead of gateway for emitting the GatewaySet event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/l2/token/L2GraphToken.sol#L59-L63

    function setGateway(address _gw) external onlyGovernor {
        require(_gw != address(0), "INVALID_GATEWAY");
        gateway = _gw;
        emit GatewaySet(gateway);
    }

In the following _setPaused function, _toPause can be used instead of _paused for emitting the PauseChanged event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/governance/Pausable.sol#L40-L49

    function _setPaused(bool _toPause) internal {
        if (_toPause == _paused) {
            return;
        }
        _paused = _toPause;
        if (_paused) {
            lastPauseTime = block.timestamp;
        }
        emit PauseChanged(_paused);
    }

In the following _setPauseGuardian function, newPauseGuardian can be used instead of pauseGuardian for emitting the NewPauseGuardian event. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/governance/Pausable.sol#L55-L59

    function _setPauseGuardian(address newPauseGuardian) internal {
        address oldPauseGuardian = pauseGuardian;
        pauseGuardian = newPauseGuardian;
        emit NewPauseGuardian(oldPauseGuardian, pauseGuardian);
    }

[G-04] STATE VARIABLE THAT IS ACCESSED FOR MULTIPLE TIMES CAN BE CACHED IN MEMORY

A state variable that is accessed for multiple times can be cached in memory, and the cached variable value can then be used. This can replace multiple sload operations with one sload, one mstore, and multiple mload operations to save gas.

In the following permit function, nonces[_owner] can be cached, and the cached value can then be used for setting digest and updating nonces[_owner]. https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/l2/token/GraphTokenUpgradeable.sol#L74-L99

    function permit(
        ...
    ) external {
        bytes32 digest = keccak256(
            abi.encodePacked(
                "\x19\x01",
                DOMAIN_SEPARATOR,
                keccak256(
                    abi.encode(PERMIT_TYPEHASH, _owner, _spender, _value, nonces[_owner], _deadline)
                )
            )
        );

        ...

        nonces[_owner] = nonces[_owner].add(1);
        ...
    }

[G-05] BOOLEAN EXPRESSION CAN BE USED INSTEAD OF COMPARING BOOLEAN VALUE TO BOOLEAN LITERAL

Comparing a boolean value to a boolean literal needs the iszero operation and costs more gas than using a boolean expression.

callhookWhitelist[msg.sender] can be used instead of callhookWhitelist[msg.sender] == true in the following code.

https://github.com/code-423n4/2022-10-thegraph/blob/main/contracts/gateway/L1GraphTokenGateway.sol#L214

      extraData.length == 0 || callhookWhitelist[msg.sender] == true,

[G-06] require REASON STRINGS CAN BE SHORTENED TO FIT IN 32 BYTES

require reason strings that are longer than 32 bytes need more memory space and more mstore operations than these that are shorter than 32 bytes when reverting. Please consider shortening the following require reason strings.

contracts\gateway\GraphTokenGateway.sol
  21: "Only Governor or Guardian can call"

contracts\governance\Managed.sol
  53: require(msg.sender == controller.getGovernor(), "Caller must be Controller governor");

contracts\upgrades\GraphUpgradeable.sol
  32: require(msg.sender == _implementation(), "Caller must be the implementation");

contracts\upgrades\GraphProxy.sol
  141: require(Address.isContract(_pendingImplementation), "Implementation must be a contract");
  144: "Caller must be the pending implementation"

[G-07] NEWER VERSION OF SOLIDITY CAN BE USED

The protocol can benefit from more gas-efficient features, such as custom errors starting from Solidity v0.8.4, by using a newer version of Solidity. For the following contracts, please consider using a newer Solidity version.

contracts\gateway\GraphTokenGateway.sol
  3: pragma solidity ^0.7.6;

contracts\gateway\L1GraphTokenGateway.sol
  3: pragma solidity ^0.7.6;

contracts\governance\Governed.sol
  3: pragma solidity ^0.7.6;

contracts\governance\Managed.sol
  3: pragma solidity ^0.7.6;

contracts\governance\Pausable.sol
  3: pragma solidity ^0.7.6;

contracts\l2\gateway\L2GraphTokenGateway.sol
  3: pragma solidity ^0.7.6;

contracts\l2\token\GraphTokenUpgradeable.sol
  3: pragma solidity ^0.7.6;

contracts\l2\token\L2GraphToken.sol
  3: pragma solidity ^0.7.6;

contracts\upgrades\GraphProxy.sol
  3: pragma solidity ^0.7.6;

contracts\upgrades\GraphProxyAdmin.sol
  3: pragma solidity ^0.7.6;

contracts\upgrades\GraphProxyStorage.sol
  3: pragma solidity ^0.7.6;

contracts\upgrades\GraphUpgradeable.sol
  3: pragma solidity ^0.7.6;