Gas Optimizations

[code423n4]

[G-01] abi.encode() is less efficient than abi.encodePacked()

Impact

Consider using abi.encodePacked() instead for efficieny.

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L249        return abi.encode(seqNum);

contracts/gateway/L1GraphTokenGateway.sol:L342                abi.encode(emptyBytes, _data)

contracts/l2/token/GraphTokenUpgradeable.sol:L88                    abi.encode(PERMIT_TYPEHASH, _owner, _spender, _value, nonces[_owner], _deadline)

contracts/l2/token/GraphTokenUpgradeable.sol:L162            abi.encode(

contracts/l2/gateway/L2GraphTokenGateway.sol:L174        return abi.encode(id);

contracts/l2/gateway/L2GraphTokenGateway.sol:L275                abi.encode(0, _data) // we don't need to track exitNums (b/c we have no fast exits) so we always use 0

[G-02] Use assembly to check for zero address.

Impact

Save 6 gas when assembly is used to check for zero address. e.g:

assembly {
            if iszero(_addr) {
                mstore(0x00, "zero address")
                revert(0x00, 0x20)
            }

Findings:

contracts/upgrades/GraphProxy.sol:L105        require(_newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");

[G-03] Using bools for storage incurs overhead.

Impact

    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

https://github.com/OpenZeppelin/openzeppelin-contracts/blob/58f635312aa21f947cae5f8578638a85aa2519f5/contracts/security/ReentrancyGuard.sol#L23-L27 Use uint256(1) and uint256(2) for true/false to avoid a Gwarmaccess (100 gas), and to avoid Gsset (20000 gas) when changing from ‘false’ to ‘true’, after having been ‘true’ in the past

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L35    mapping(address => bool) public callhookWhitelist;

contracts/l2/token/GraphTokenUpgradeable.sol:L51    mapping(address => bool) private _minters;

[G-04] Use custom errors rather than revert()/require() string to save gas

Impact

Custom errors are available from solidity version 0.8.4, it saves around 50 gas each time they are hit by avoiding having to allocate and store the revert string.

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L74        require(inbox != address(0), "INBOX_NOT_SET");

contracts/gateway/L1GraphTokenGateway.sol:L78        require(msg.sender == address(bridge), "NOT_FROM_BRIDGE");

contracts/gateway/L1GraphTokenGateway.sol:L82        require(l2ToL1Sender == l2Counterpart, "ONLY_COUNTERPART_GATEWAY");

contracts/gateway/L1GraphTokenGateway.sol:L110        require(_inbox != address(0), "INVALID_INBOX");

contracts/gateway/L1GraphTokenGateway.sol:L111        require(_l1Router != address(0), "INVALID_L1_ROUTER");

contracts/gateway/L1GraphTokenGateway.sol:L122        require(_l2GRT != address(0), "INVALID_L2_GRT");

contracts/gateway/L1GraphTokenGateway.sol:L132        require(_l2Counterpart != address(0), "INVALID_L2_COUNTERPART");

contracts/gateway/L1GraphTokenGateway.sol:L142        require(_escrow != address(0) && Address.isContract(_escrow), "INVALID_ESCROW");

contracts/gateway/L1GraphTokenGateway.sol:L153        require(_newWhitelisted != address(0), "INVALID_ADDRESS");

contracts/gateway/L1GraphTokenGateway.sol:L154        require(!callhookWhitelist[_newWhitelisted], "ALREADY_WHITELISTED");

contracts/gateway/L1GraphTokenGateway.sol:L165        require(_notWhitelisted != address(0), "INVALID_ADDRESS");

contracts/gateway/L1GraphTokenGateway.sol:L166        require(callhookWhitelist[_notWhitelisted], "NOT_WHITELISTED");

contracts/gateway/L1GraphTokenGateway.sol:L200        require(_l1Token == address(token), "TOKEN_NOT_GRT");

contracts/gateway/L1GraphTokenGateway.sol:L201        require(_amount > 0, "INVALID_ZERO_AMOUNT");

contracts/gateway/L1GraphTokenGateway.sol:L202        require(_to != address(0), "INVALID_DESTINATION");

contracts/gateway/L1GraphTokenGateway.sol:L217                require(maxSubmissionCost > 0, "NO_SUBMISSION_COST");

contracts/gateway/L1GraphTokenGateway.sol:L224                    require(msg.value >= expectedEth, "WRONG_ETH_VALUE");

contracts/gateway/L1GraphTokenGateway.sol:L271        require(_l1Token == address(token), "TOKEN_NOT_GRT");

contracts/gateway/L1GraphTokenGateway.sol:L275        require(_amount <= escrowBalance, "BRIDGE_OUT_OF_FUNDS");

contracts/gateway/GraphTokenGateway.sol:L31        require(_newPauseGuardian != address(0), "PauseGuardian must be set");

contracts/gateway/GraphTokenGateway.sol:L40        require(!_paused, "Paused (contract)");

contracts/upgrades/GraphProxy.sol:L105        require(_newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");

contracts/upgrades/GraphProxy.sol:L141        require(Address.isContract(_pendingImplementation), "Implementation must be a contract");

contracts/upgrades/GraphProxy.sol:L157        require(msg.sender != _admin(), "Cannot fallback to proxy target");

contracts/upgrades/GraphUpgradeable.sol:L24        require(msg.sender == _proxy.admin(), "Caller must be the proxy admin");

contracts/upgrades/GraphUpgradeable.sol:L32        require(msg.sender == _implementation(), "Caller must be the implementation");

contracts/upgrades/GraphProxyStorage.sol:L62        require(msg.sender == _admin(), "Caller must be admin");

contracts/governance/Governed.sol:L24        require(msg.sender == governor, "Only Governor can call");

contracts/governance/Governed.sol:L41        require(_newGovernor != address(0), "Governor must be set");

contracts/governance/Managed.sol:L44        require(!controller.paused(), "Paused");

contracts/governance/Managed.sol:L45        require(!controller.partialPaused(), "Partial-paused");

contracts/governance/Managed.sol:L49        require(!controller.paused(), "Paused");

contracts/governance/Managed.sol:L53        require(msg.sender == controller.getGovernor(), "Caller must be Controller governor");

contracts/governance/Managed.sol:L57        require(msg.sender == address(controller), "Caller must be Controller");

contracts/governance/Managed.sol:L104        require(_controller != address(0), "Controller must be set");

contracts/l2/token/L2GraphToken.sol:L36        require(msg.sender == gateway, "NOT_GATEWAY");

contracts/l2/token/L2GraphToken.sol:L49        require(_owner != address(0), "Owner must be set");

contracts/l2/token/L2GraphToken.sol:L60        require(_gw != address(0), "INVALID_GATEWAY");

contracts/l2/token/L2GraphToken.sol:L70        require(_addr != address(0), "INVALID_L1_ADDRESS");

contracts/l2/token/GraphTokenUpgradeable.sol:L60        require(isMinter(msg.sender), "Only minter can call");

contracts/l2/token/GraphTokenUpgradeable.sol:L94        require(_owner == recoveredAddress, "GRT: invalid permit");

contracts/l2/token/GraphTokenUpgradeable.sol:L95        require(_deadline == 0 || block.timestamp <= _deadline, "GRT: expired permit");

contracts/l2/token/GraphTokenUpgradeable.sol:L106        require(_account != address(0), "INVALID_MINTER");

contracts/l2/token/GraphTokenUpgradeable.sol:L115        require(_minters[_account], "NOT_A_MINTER");

contracts/l2/token/GraphTokenUpgradeable.sol:L123        require(_minters[msg.sender], "NOT_A_MINTER");

contracts/l2/gateway/L2GraphTokenGateway.sol:L98        require(_l2Router != address(0), "INVALID_L2_ROUTER");

contracts/l2/gateway/L2GraphTokenGateway.sol:L108        require(_l1GRT != address(0), "INVALID_L1_GRT");

contracts/l2/gateway/L2GraphTokenGateway.sol:L118        require(_l1Counterpart != address(0), "INVALID_L1_COUNTERPART");

contracts/l2/gateway/L2GraphTokenGateway.sol:L145        require(_l1Token == l1GRT, "TOKEN_NOT_GRT");

contracts/l2/gateway/L2GraphTokenGateway.sol:L146        require(_amount > 0, "INVALID_ZERO_AMOUNT");

contracts/l2/gateway/L2GraphTokenGateway.sol:L147        require(msg.value == 0, "INVALID_NONZERO_VALUE");

contracts/l2/gateway/L2GraphTokenGateway.sol:L148        require(_to != address(0), "INVALID_DESTINATION");

contracts/l2/gateway/L2GraphTokenGateway.sol:L153        require(outboundCalldata.extraData.length == 0, "CALL_HOOK_DATA_NOT_ALLOWED");

contracts/l2/gateway/L2GraphTokenGateway.sol:L233        require(_l1Token == l1GRT, "TOKEN_NOT_GRT");

contracts/l2/gateway/L2GraphTokenGateway.sol:L234        require(msg.value == 0, "INVALID_NONZERO_VALUE");

[G-05] Public functions not called by the contract should be declared external instead

Impact

public functions that are never called by the contract should be declared external to save gas.

Findings:

contracts/upgrades/GraphProxyAdmin.sol:L68    function changeProxyAdmin(IGraphProxy _proxy, address _newAdmin) public onlyGovernor {

contracts/upgrades/GraphProxyAdmin.sol:L77    function upgrade(IGraphProxy _proxy, address _implementation) public onlyGovernor {

[G-06] Using > 0 costs more gas than != 0 when used on a uint in a require() statement.

Impact

When working with unsigned integer types, comparisons with != 0 are cheaper than with > 0 . This changes saves 6 gas per instance.

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L201        require(_amount > 0, "INVALID_ZERO_AMOUNT");

contracts/gateway/L1GraphTokenGateway.sol:L217                require(maxSubmissionCost > 0, "NO_SUBMISSION_COST");

contracts/l2/gateway/L2GraphTokenGateway.sol:L146        require(_amount > 0, "INVALID_ZERO_AMOUNT");

[G-07] Use a more recent version of solidity.

Impact

Use a solidity version of at least 0.8.2 to get simple compiler automatic inlining Use a solidity version of at least 0.8.3 to get better struct packing and cheaper multiple storage reads Use a solidity version of at least 0.8.4 to get custom errors, which are cheaper at deployment than revert()/require() strings Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value.

Findings:

contracts/token/IGraphToken.sol:L3      pragma solidity ^0.7.6;

contracts/staking/IStakingData.sol:L3      pragma solidity >=0.6.12 <0.8.0;

contracts/staking/IStaking.sol:L3      pragma solidity >=0.6.12 <0.8.0;

contracts/rewards/IRewardsManager.sol:L3      pragma solidity ^0.7.6;

contracts/gateway/L1GraphTokenGateway.sol:L3      pragma solidity ^0.7.6;

contracts/gateway/ICallhookReceiver.sol:L9      pragma solidity ^0.7.6;

contracts/gateway/GraphTokenGateway.sol:L3      pragma solidity ^0.7.6;

contracts/gateway/BridgeEscrow.sol:L3      pragma solidity ^0.7.6;

contracts/upgrades/GraphProxy.sol:L3      pragma solidity ^0.7.6;

contracts/upgrades/GraphUpgradeable.sol:L3      pragma solidity ^0.7.6;

contracts/upgrades/IGraphProxy.sol:L3      pragma solidity ^0.7.6;

contracts/upgrades/GraphProxyAdmin.sol:L3      pragma solidity ^0.7.6;

contracts/upgrades/GraphProxyStorage.sol:L3      pragma solidity ^0.7.6;

contracts/governance/Governed.sol:L3      pragma solidity ^0.7.6;

contracts/governance/Pausable.sol:L3      pragma solidity ^0.7.6;

contracts/governance/IController.sol:L3      pragma solidity >=0.6.12 <0.8.0;

contracts/governance/Managed.sol:L3      pragma solidity ^0.7.6;

contracts/epochs/IEpochManager.sol:L3      pragma solidity ^0.7.6;

contracts/curation/IGraphCurationToken.sol:L3      pragma solidity ^0.7.6;

contracts/curation/ICuration.sol:L3      pragma solidity ^0.7.6;

contracts/l2/token/L2GraphToken.sol:L3      pragma solidity ^0.7.6;

contracts/l2/token/GraphTokenUpgradeable.sol:L3      pragma solidity ^0.7.6;

contracts/l2/gateway/L2GraphTokenGateway.sol:L3      pragma solidity ^0.7.6;

[G-08] Functions guaranteed to revert when called by normal users can be declared as payable.

Impact

If a function modifier such as onlyOwner is used, the function will revert if a normal user tries to pay the function. Marking the function as payable will lower the gas cost for legitimate callers because the compiler will not include checks for whether a payment was provided. The extra opcodes avoided are CALLVALUE(2),DUP1(3),ISZERO(3),PUSH2(3),JUMPI(10),PUSH1(3),DUP1(3),REVERT(0),JUMPDEST(1),POP(2), which costs an average of about 21 gas per call to the function, in addition to the extra deployment cost.

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L99    function initialize(address _controller) external onlyImpl {

contracts/gateway/L1GraphTokenGateway.sol:L109    function setArbitrumAddresses(address _inbox, address _l1Router) external onlyGovernor {

contracts/gateway/L1GraphTokenGateway.sol:L121    function setL2TokenAddress(address _l2GRT) external onlyGovernor {

contracts/gateway/L1GraphTokenGateway.sol:L131    function setL2CounterpartAddress(address _l2Counterpart) external onlyGovernor {

contracts/gateway/L1GraphTokenGateway.sol:L141    function setEscrowAddress(address _escrow) external onlyGovernor {

contracts/gateway/L1GraphTokenGateway.sol:L152    function addToCallhookWhitelist(address _newWhitelisted) external onlyGovernor {

contracts/gateway/L1GraphTokenGateway.sol:L164    function removeFromCallhookWhitelist(address _notWhitelisted) external onlyGovernor {

contracts/gateway/GraphTokenGateway.sol:L30    function setPauseGuardian(address _newPauseGuardian) external onlyGovernor {

contracts/gateway/GraphTokenGateway.sol:L47    function setPaused(bool _newPaused) external onlyGovernorOrGuardian {

contracts/gateway/BridgeEscrow.sol:L20    function initialize(address _controller) external onlyImpl {

contracts/gateway/BridgeEscrow.sol:L28    function approveAll(address _spender) external onlyGovernor {

contracts/gateway/BridgeEscrow.sol:L36    function revokeAll(address _spender) external onlyGovernor {

contracts/upgrades/GraphUpgradeable.sol:L50    function acceptProxy(IGraphProxy _proxy) external onlyProxyAdmin(_proxy) {

contracts/upgrades/GraphProxyAdmin.sol:L68    function changeProxyAdmin(IGraphProxy _proxy, address _newAdmin) public onlyGovernor {

contracts/upgrades/GraphProxyAdmin.sol:L77    function upgrade(IGraphProxy _proxy, address _implementation) public onlyGovernor {

contracts/upgrades/GraphProxyAdmin.sol:L86    function acceptProxy(GraphUpgradeable _implementation, IGraphProxy _proxy) public onlyGovernor {

contracts/governance/Governed.sol:L40    function transferOwnership(address _newGovernor) external onlyGovernor {

contracts/governance/Managed.sol:L95    function setController(address _controller) external onlyController {

contracts/l2/token/L2GraphToken.sol:L48    function initialize(address _owner) external onlyImpl {

contracts/l2/token/L2GraphToken.sol:L59    function setGateway(address _gw) external onlyGovernor {

contracts/l2/token/L2GraphToken.sol:L69    function setL1Address(address _addr) external onlyGovernor {

contracts/l2/token/L2GraphToken.sol:L80    function bridgeMint(address _account, uint256 _amount) external override onlyGateway {

contracts/l2/token/L2GraphToken.sol:L90    function bridgeBurn(address _account, uint256 _amount) external override onlyGateway {

contracts/l2/token/GraphTokenUpgradeable.sol:L105    function addMinter(address _account) external onlyGovernor {

contracts/l2/token/GraphTokenUpgradeable.sol:L114    function removeMinter(address _account) external onlyGovernor {

contracts/l2/token/GraphTokenUpgradeable.sol:L132    function mint(address _to, uint256 _amount) external onlyMinter {

contracts/l2/gateway/L2GraphTokenGateway.sol:L87    function initialize(address _controller) external onlyImpl {

contracts/l2/gateway/L2GraphTokenGateway.sol:L97    function setL2Router(address _l2Router) external onlyGovernor {

contracts/l2/gateway/L2GraphTokenGateway.sol:L107    function setL1TokenAddress(address _l1GRT) external onlyGovernor {

contracts/l2/gateway/L2GraphTokenGateway.sol:L117    function setL1CounterpartAddress(address _l1Counterpart) external onlyGovernor {

[G-09] Revert message greater than 32 bytes

Impact

Keep revert message lower than or equal to 32 bytes to save gas.

Findings:

contracts/gateway/GraphTokenGateway.sol:L19        require(

contracts/upgrades/GraphProxy.sol:L105        require(_newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");

contracts/upgrades/GraphProxy.sol:L141        require(Address.isContract(_pendingImplementation), "Implementation must be a contract");

contracts/upgrades/GraphProxy.sol:L142        require(

contracts/upgrades/GraphUpgradeable.sol:L32        require(msg.sender == _implementation(), "Caller must be the implementation");

contracts/governance/Managed.sol:L53        require(msg.sender == controller.getGovernor(), "Caller must be Controller governor");

[G-10] Splitting require() statements that use && saves gas.

Impact

Consider splitting the require() statements to save gas.

Findings:

contracts/gateway/L1GraphTokenGateway.sol:L142        require(_escrow != address(0) && Address.isContract(_escrow), "INVALID_ESCROW");