PoolTogether contest - Madalad's results

Gas Optimisations

1. Clean up relayed mapping after calls are processed

The processCalls() function in the EthereumToArbitrumRelayer contract does not reset the value in the relayed mapping to false after processing the calls. Doing so provides a gas refund, and so implementing this results in a gas saving. Simply alter the processCalls() function slightly as follows:

function processCalls(...) external payable returns (uint256) {
    bytes32 _txHash = _getTxHash(_nonce, _calls, _sender, _gasLimit);
    require(relayed[_txHash], "Relayer/calls-not-relayed");

    delete relayed[_txHash];

    // ...

    return _ticketID;
}

This results in a gas saving of 1319 (16%):

Instances: 1

https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L101

2. Use unchecked for nonce incrementation

Use unchecked{ ++nonce } instead of nonce++. The automated gas report mentioned that ++nonce is cheaper than nonce++, however did not mention to use unchecked{}. This is safe because the operation cannot overflow.

Gas saving per call of relayCalls():

• EthereumToArbitrumRelayer.sol - 130 gas
• EthereumToOptimismRelayer.sol - 124 gas
• EthereumToPolygonRelayer.sol - 146 gas

Instances: 3

https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L78 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-optimism/EthereumToOptimismRelayer.sol#L60 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-polygon/EthereumToPolygonRelayer.sol#L56

3. Cache msg.sender variable

function relayCalls(...) external payable returns (uint256) {

    // ...

    address _msgSender = msg.sender;

    _sendMessageToChild(abi.encode(_nonce, msg.sender, _calls));

    emit RelayedCalls(_nonce, msg.sender, _calls, _gasLimit);

    return _nonce;
}

Gas saving per call of relayCalls():

• EthereumToArbitrumRelayer.sol - 14 gas
• EthereumToOptimismRelayer.sol - 11 gas
• EthereumToPolygonRelayer.sol - 36 gas

Instances: 3

https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L82-L84 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-optimism/EthereumToOptimismRelayer.sol#L64-L75 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-polygon/EthereumToPolygonRelayer.sol#L60-L62

4. Use getter function for mappings instead of public keyword

Gas saving per call to view executed[nonce]:

• EthereumToArbitrumExecutor.sol - 77 gas
• EthereumToOptimismExecutor.sol - 77 gas
• EthereumToPolygonExecutor.sol - 99 gas

Instances: 4

https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-arbitrum/EthereumToArbitrumExecutor.sol#L26 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-optimism/EthereumToOptimismExecutor.sol#L29 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-polygon/EthereumToPolygonExecutor.sol#L31 https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L47

5. Use unchecked { _callIndex++ } in for loop body in CallLib.executeCalls()

For loop index cannot overflow and so it is safe to use unchecked to save gas. Also, replace _callIndex < _callsLength with _callIndex != _callsLength. Using != instead of < was mentioned in the automated report, however this instance was missed.

function executeCalls(...) internal {

    //...

    for (uint256 _callIndex; _callIndex != _callsLength; ) {

        //...

        unchecked{
            ++_callIndex;
        }
    }
}

Gas saved: - 69 gas per iteration

Deployment saving - 47 gas

Instances: 1

https://github.com/pooltogether/ERC5164/blob/5647bd84f2a6d1a37f41394874d567e45a97bf48/src/libraries/CallLib.sol#L61

6. Remove/Replace require() statements in constructor

The team has mentioned the willingness to re-deploy the contracts if setExecutor() or setRelayer() are front-run. Similarly, they could do the same if they mistakenly pass the zero address/zero uint to the constructor. Removing the require() statement will save gas on deployment and sacrifice very little (misclicking constructor arguments is very unlikely). Alternatively, the checks could be performed off chain prior to deployment. However if they are to be kept, replacing them with custom errors would also save gas.

Deployment gas savings:

• EthereumToArbitrumRelayer.sol - 171
• EthereumToOptimismExecutor.sol - 98
• EthereumToOptimismRelayer.sol - 171
• EthereumToPolygonRelayer.sol - 86

Instances: 4

https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L57-L58 https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-optimism/EthereumToOptimismRelayer.sol#L39-L40 https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-optimism/EthereumToOptimismExecutor.sol#L38 https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-polygon/EthereumToPolygonRelayer.sol#L38

7. Initialize nonce to 1 instead of 0 to save gas on the first call

Incrementing from zero to non-zero is more expensive than from non-zero to non-zero.

Gas saving on first call to relayCalls():

• EthereumToArbitrumExecutor.sol - 17100 gas
• EthereumToOptimismExecutor.sol - 21900 gas
• EthereumToPolygonExecutor.sol - 21900 gas

Instances: 3

https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-arbitrum/EthereumToArbitrumRelayer.sol#L40 https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-optimism/EthereumToOptimismRelayer.sol#L29 https://github.com/pooltogether/ERC5164/blob/851d1fe82f301ebe0e35e6f1f98bf8113135a9d2/src/ethereum-polygon/EthereumToPolygonRelayer.sol#L23