Gas Optimizations

[code423n4]

[G-1] Variable == false|0 -> !variable or variable == true -> variable

L1GraphTokenGateway.sol:214:                    extraData.length == 0 || callhookWhitelist[msg.sender] == true,
GraphTokenUpgradeable.sol:95:        require(_deadline == 0 || block.timestamp <= _deadline, "GRT: expired permit");
L2GraphTokenGateway.sol:147:        require(msg.value == 0, "INVALID_NONZERO_VALUE");
L2GraphTokenGateway.sol:153:        require(outboundCalldata.extraData.length == 0, "CALL_HOOK_DATA_NOT_ALLOWED");
L2GraphTokenGateway.sol:234:        require(msg.value == 0, "INVALID_NONZERO_VALUE");

[G-2] Use != 0 instead of > 0

L1GraphTokenGateway.sol:201:        require(_amount > 0, "INVALID_ZERO_AMOUNT");
L1GraphTokenGateway.sol:217:                require(maxSubmissionCost > 0, "NO_SUBMISSION_COST");
IStaking.sol:15:     * - Active = not Null && tokens > 0
L2GraphTokenGateway.sol:146:        require(_amount > 0, "INVALID_ZERO_AMOUNT");
L2GraphTokenGateway.sol:238:        if (_data.length > 0) {

[G-3] Use abi.encodePacked for gas optimization

Changing the abi.encode function to abi.encodePacked can save gas since the abi.encode function pads extra null bytes at the end of the call data, which is unnecessary. Also, in general, abi.encodePacked is more gas-efficient.

L1GraphTokenGateway.sol:249:        return abi.encode(seqNum);
L1GraphTokenGateway.sol:342:                abi.encode(emptyBytes, _data)
GraphTokenUpgradeable.sol:88:                    abi.encode(PERMIT_TYPEHASH, _owner, _spender, _value, nonces[_owner], _deadline)
GraphTokenUpgradeable.sol:162:            abi.encode(
L2GraphTokenGateway.sol:174:        return abi.encode(id);
L2GraphTokenGateway.sol:275:                abi.encode(0, _data) // we don't need to track exitNums (b/c we have no fast exits) so we always use 0