The Graph L2 bridge contest - Tomio's results

Title: Using != in require statement is more gas efficient

Proof of Concept: L1GraphTokenGateway.sol#L201 L1GraphTokenGateway.sol#L217

Recommended Mitigation Steps: Change > 0 to != 0

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Title: Using multiple require instead && can save gas

Proof of Concept: L1GraphTokenGateway.sol#L142 Governed.sol#L54-L56

Recommended Mitigation Steps: Change to:

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

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Title: Boolean comparison

Proof of Concept: L1GraphTokenGateway.sol#L214

Recommended Mitigation Steps: Change from callhookWhitelist[msg.sender] == true to callhookWhitelist[msg.sender]

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Title: abi.encode() is less efficient than abi.encodePacked()

Proof of Concept: GraphTokenUpgradeable.sol#L162 L1GraphTokenGateway.sol#L249 L2GraphTokenGateway.sol#L174

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Title: Gas improvement on returning from and extraData value

Proof of Concept: L2GraphTokenGateway.sol#L286

Recommended Mitigation Steps: by set from and extraData in returns L#286 and delete L#287-288 can save gas

function parseOutboundData(bytes memory _data) private view returns (address from, bytes memory extraData) { //@audit-info: set here
        if (msg.sender == l2Router) {
            (from, extraData) = abi.decode(_data, (address, bytes));
        } else {
            from = msg.sender;
            extraData = _data;
        }
        return (from, extraData);
    }

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Title: Gas improvement on returning id value

Proof of Concept: GraphTokenUpgradeable.sol#L195

Recommended Mitigation Steps: by set id in returns L#195 and delete L#196 can save gas

function _getChainID() private pure returns (uint256 id) { //@audit-info: set here
        // solhint-disable-next-line no-inline-assembly
        assembly {
            id := chainid()
        }
        return id;
    }

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Title: Expression for constant values such as a call to keccak256(), should use immutable rather than constant

Proof of Concept: GraphTokenUpgradeable.sol#L34-L37 GraphTokenUpgradeable.sol#L42-L45

Recommended Mitigation Steps: Change from constant to immutable reference: here

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