Gas Optimizations

[code423n4]

Summary

Gas Optimizations

	Issue	Instances
GAS‑1	Multiple Address Mappings Can Be Combined Into A Single Mapping Of An Address To A Struct, Where Appropriate	1
GAS‑2	require()/revert() Strings Longer Than 32 Bytes Cost Extra Gas	4
GAS‑3	Using Bools For Storage Incurs Overhead	2
GAS‑4	Using > 0 Costs More Gas Than != 0 When Used On A Uint In A require() Statement	3
GAS‑5	Splitting require() Statements That Use && Saves Gas	1
GAS‑6	abi.encode() Is Less Efficient Than abi.encodepacked()	6
GAS‑7	Use assembly to check for address(0)	18
GAS‑8	Public Functions To External	11
GAS‑9	Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead	3
GAS‑10	Use of Custom Errors Instead of String	55
GAS‑11	Optimize names to save gas	12

Total: 116 instances over 11 issues

Gas Optimizations

[GAS‑1] Multiple Address Mappings Can Be Combined Into A Single Mapping Of An Address To A Struct, Where Appropriate

Saves a storage slot for the mapping. Depending on the circumstances and sizes of types, can avoid a Gsset (20000 gas) per mapping combined. Reads and subsequent writes can also be cheaper when a function requires both values and they both fit in the same storage slot.

Proof Of Concept

mapping(address => bool) private _minters;
mapping(address => uint256) public nonces;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L51

[GAS‑2] require()/revert() Strings Longer Than 32 Bytes Cost Extra Gas

Proof Of Concept

require(msg.sender == controller.getGovernor(), "Caller must be Controller governor");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Managed.sol#L53

require(_newAdmin != address(0), "Cannot change the admin of a proxy to the zero address");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol#L105

require(Address.isContract(_pendingImplementation), "Implementation must be a contract");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol#L141

require(msg.sender != _admin(), "Cannot fallback to proxy target");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol#L157

[GAS‑3] Using Bools For Storage Incurs Overhead

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.

Proof Of Concept

    mapping(address => bool) public callhookWhitelist;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L35

    mapping(address => bool) private _minters;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L51

[GAS‑4] Using > 0 Costs More Gas Than != 0 When Used On A Uint In A require() Statement

This change saves 6 gas per instance

Proof Of Concept

require(_amount > 0, "INVALID_ZERO_AMOUNT");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L201

require(maxSubmissionCost > 0, "NO_SUBMISSION_COST");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L216

require(_amount > 0, "INVALID_ZERO_AMOUNT");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L144

[GAS‑5] Splitting require() Statements That Use && Saves Gas

See code-423n4/2022-01-xdefi-findings#128 which describes the fact that there is a larger deployment gas cost, but with enough runtime calls, the change ends up being cheaper

Proof Of Concept

require(_escrow != address(0) && Address.isContract(_escrow), "INVALID_ESCROW");

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L142

[GAS‑6] abi.encode() Is Less Efficient Than abi.encodepacked()

Proof Of Concept

return abi.encode(seqNum);

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L249

abi.encode(emptyBytes, _data)

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L342

return abi.encode(id);

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L174

abi.encode(0, _data));

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L275

abi.encode(PERMIT_TYPEHASH, _owner, _spender, _value, nonces[_owner], _deadline)

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L88

abi.encode(

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L161

[GAS‑7] Use assembly to check for address(0)

Save 6 gas per instance if using assembly to check for address(0)

e.g.
assembly {
if iszero(_addr) {
mstore(0x00, "AddressZero")
revert(0x00, 0x20)
}
}

Proof Of Concept

function setPauseGuardian(address _newPauseGuardian) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/GraphTokenGateway.sol#L30

function setArbitrumAddresses(address _inbox, address _l1Router) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L109

function setArbitrumAddresses(address _inbox, address _l1Router) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L109

function setL2TokenAddress(address _l2GRT) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L121

function setL2CounterpartAddress(address _l2Counterpart) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L131

function setEscrowAddress(address _escrow) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L141

function addToCallhookWhitelist(address _newWhitelisted) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L152

function removeFromCallhookWhitelist(address _notWhitelisted) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L164

function transferOwnership(address _newGovernor) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Governed.sol#L40

function _setController(address _controller) internal {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Managed.sol#L103

function setL2Router(address _l2Router) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L97

function setL1TokenAddress(address _l1GRT) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L107

function setL1CounterpartAddress(address _l1Counterpart) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L117

function addMinter(address _account) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L105

function initialize(address _owner) external onlyImpl {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/L2GraphToken.sol#L48

function setGateway(address _gw) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/L2GraphToken.sol#L59

function setL1Address(address _addr) external onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/L2GraphToken.sol#L69

function setAdmin(address _newAdmin) external ifAdmin {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol#L104

[GAS‑8] Public Functions To External

The following functions could be set external to save gas and improve code quality.
External call cost is less expensive than of public functions.

Proof Of Concept

function getOutboundCalldata(
        address _l1Token,
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _data
    ) public pure returns (bytes memory) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L326

function outboundTransfer(
        address _l1Token,
        address _to,
        uint256 _amount,
        uint256,         uint256,         bytes calldata _data
    ) public payable override notPaused nonReentrant returns (bytes memory) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L137

function calculateL2TokenAddress(address l1ERC20) public view override returns (address) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L203

function getOutboundCalldata(
        address _token,
        address _from,
        address _to,
        uint256 _amount,
        bytes memory _data
    ) public pure returns (bytes memory) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L261

function isMinter(address _account) public view returns (bool) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L141

function getProxyImplementation(IGraphProxy _proxy) public view returns (address) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L30

function getProxyPendingImplementation(IGraphProxy _proxy) public view returns (address) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L43

function getProxyAdmin(IGraphProxy _proxy) public view returns (address) {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L55

function changeProxyAdmin(IGraphProxy _proxy, address _newAdmin) public onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L68

function upgrade(IGraphProxy _proxy, address _implementation) public onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L77

function acceptProxy(GraphUpgradeable _implementation, IGraphProxy _proxy) public onlyGovernor {

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol#L86

[GAS‑9] Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead

When using elements that are smaller than 32 bytes, your contract’s gas usage may be higher. This is because the EVM operates on 32 bytes at a time. Therefore, if the element is smaller than that, the EVM must use more operations in order to reduce the size of the element from 32 bytes to the desired size.

https://docs.soliditylang.org/en/v0.8.11/internals/layout_in_storage.html
Each operation involving a uint8 costs an extra 22-28 gas (depending on whether the other operand is also a variable of type uint8) as compared to ones involving uint256, due to the compiler having to clear the higher bits of the memory word before operating on the uint8, as well as the associated stack operations of doing so. Use a larger size then downcast where needed

Proof Of Concept

uint32 cooldownBlocks;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/staking/IStakingData.sol#L37

uint32 indexingRewardCut;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/staking/IStakingData.sol#L38

uint32 queryFeeCut;

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/staking/IStakingData.sol#L39

[GAS‑10] Use of Custom Errors Instead of String

To save some gas the use of custom errors leads to cheaper deploy time cost and run time cost. The run time cost is only relevant when the revert condition is met.

Proof Of Concept

File: \2022-10-thegraph\contracts\gateway\GraphTokenGateway.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/GraphTokenGateway.sol#L40

File: \2022-10-thegraph\contracts\gateway\L1GraphTokenGateway.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/L1GraphTokenGateway.sol#L275

File: \2022-10-thegraph\contracts\governance\Governed.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Governed.sol#L41

File: \2022-10-thegraph\contracts\governance\Managed.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Managed.sol#L104

File: \2022-10-thegraph\contracts\l2\gateway\L2GraphTokenGateway.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol#L147

File: \2022-10-thegraph\contracts\l2\token\GraphTokenUpgradeable.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol#L123

File: \2022-10-thegraph\contracts\l2\token\L2GraphToken.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/L2GraphToken.sol#L70

File: \2022-10-thegraph\contracts\upgrades\GraphProxy.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol#L157

File: \2022-10-thegraph\contracts\upgrades\GraphProxyStorage.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyStorage.sol#L62

File: \2022-10-thegraph\contracts\upgrades\GraphUpgradeable.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphUpgradeable.sol#L32

Recommended Mitigation Steps

Use Custom Errors instead of strings.

[GAS‑11] Optimize names to save gas

public/external function names and public member variable names can be optimized to save gas. See this link for an example of how it works. Method IDs that have two leading zero bytes can save 128 gas each during deployment, and renaming functions to have lower method IDs will save 22 gas per call, per sorted position shifted

Proof Of Concept

File: \2022-10-thegraph\contracts\gateway\GraphTokenGateway.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/gateway/GraphTokenGateway.sol

File: \2022-10-thegraph\contracts\gateway\L1GraphTokenGateway.sol

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

File: \2022-10-thegraph\contracts\governance\Governed.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Governed.sol

File: \2022-10-thegraph\contracts\governance\Managed.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Managed.sol

File: \2022-10-thegraph\contracts\governance\Pausable.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/governance/Pausable.sol

File: \2022-10-thegraph\contracts\l2\gateway\L2GraphTokenGateway.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/gateway/L2GraphTokenGateway.sol

File: \2022-10-thegraph\contracts\l2\token\GraphTokenUpgradeable.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/GraphTokenUpgradeable.sol

File: \2022-10-thegraph\contracts\l2\token\L2GraphToken.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/l2/token/L2GraphToken.sol

File: \2022-10-thegraph\contracts\upgrades\GraphProxy.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxy.sol

File: \2022-10-thegraph\contracts\upgrades\GraphProxyAdmin.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyAdmin.sol

File: \2022-10-thegraph\contracts\upgrades\GraphProxyStorage.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphProxyStorage.sol

File: \2022-10-thegraph\contracts\upgrades\GraphUpgradeable.sol

https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/upgrades/GraphUpgradeable.sol

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