Gas Optimizations

[code423n4]

1)X = X + Y IS CHEAPER THAN X += Y

File: 2022-10-zksync\ethereum\contracts\zksync\facets\DiamondCut.sol 29,47: s.diamondCutStorage.currentProposalId += 1;

2)USE A MORE RECENT VERSION OF SOLIDITY

Use a solidity version of at least 0.8.2 to get 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

File: 2022-10-zksync\ethereum\contracts\bridge\L1ERC20Bridge.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\bridge\L1EthBridge.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\bridge\interfaces\IL1Bridge.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\bridge\interfaces\IL2Bridge.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\Config.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\DiamondInit.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\DiamondProxy.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\Storage.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Base.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\DiamondCut.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Executor.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Getters.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Governance.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Mailbox.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IDiamondCut.sol: 2
3: pragma solidity ^0.8; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IExecutor.sol: 2
3: pragma solidity ^0.8; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IGetters.sol: 2
3: pragma solidity ^0.8.0; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IGovernance.sol: 2
3: pragma solidity ^0.8; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IMailbox.sol: 2
3: pragma solidity ^0.8; 4

File: 2022-10-zksync\ethereum\contracts\zksync\interfaces\IZkSync.sol: 2
3: pragma solidity ^0.8; 4

3)Splitting require() statements that use && saves gas

File: 2022-10-zksync\ethereum\contracts\common\AllowList.sol: 96 require( 97: callersLength == _targets.length && 98: callersLength == _functionSigs.length && 99 callersLength == _enables.length, 100: "yw" 101: );

4)Use assembly to check for address(0) Impact

File: 2022-10-zksync\ethereum\contracts\common\AllowList.sol 33,27: require(_owner != address(0), "kq"); 161,44: emit NewPendingOwner(newOwner, address(0));

File: 2022-10-zksync\ethereum\contracts\zksync\DiamondProxy.sol 29,33: require(facetAddress != address(0), "F"); // Proxy has no facet for this selector

File: 2022-10-zksync\ethereum\contracts\zksync\facets\Getters.sol 148,63: require(ds.selectorToFacet[_selector].facetAddress != address(0), "g2");

File: 2022-10-zksync\ethereum\contracts\zksync\libraries\Diamond.sol 126,27: require(_facet != address(0), "G"); // facet with zero address cannot be added 135,46: require(oldFacet.facetAddress == address(0), "J"); // facet for this selector already exists 150,27: require(_facet != address(0), "K"); // cannot replace facet with zero address 156,46: require(oldFacet.facetAddress != address(0), "L"); // it is impossible to replace the facet with zero address 170,27: require(_facet == address(0), "a1"); // facet address must be zero 176,46: require(oldFacet.facetAddress != address(0), "a2"); // Can't delete a non-existent facet 278,22: if (_init == address(0)) {

5)Multiple address mappings can be combined into a single mapping of an address to a struct

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.

File: 2022-10-zksync\ethereum\contracts\bridge\L1ERC20Bridge.sol: 37
38: /// @dev A mapping L2 block number => message number => flag 39 /// @dev Used to indicate that zkSync L2 -> L1 message was already processed 40: mapping(uint256 => mapping(uint256 => bool)) public isWithdrawalFinalized; 41
42: /// @dev A mapping account => L1 token address => L2 deposit transaction hash => amount 43 /// @dev Used for saving the number of deposited funds, to claim them in case the deposit transaction will fail 44: mapping(address => mapping(address => mapping(bytes32 => uint256))) depositAmount; 45

File: 2022-10-zksync\ethereum\contracts\bridge\L1EthBridge.sol: 34
35: /// @dev A mapping L2 block number => message number => flag 36 /// @dev Used to indicate that zkSync L2 -> L1 message was already processed 37: mapping(uint256 => mapping(uint256 => bool)) public isWithdrawalFinalized; 38
39: /// @dev A mapping account => L1 token address => L2 deposit transaction hash => amount 40 /// @dev Used for saving the number of deposited funds, to claim them in case the deposit transaction will fail 41: mapping(address => mapping(bytes32 => uint256)) depositAmount; 42

File: 2022-10-zksync\ethereum\contracts\common\AllowList.sol: 24
25: /// @notice mapping of the addresses that everyone has permission to call 26: mapping(address => bool) public isAccessPublic; 27
28: /// @notice The mapping that stores permissions to call the function on the target address by the caller 29 /// @dev caller => target => function signature => permission to call target function for the given caller address 30: mapping(address => mapping(address => mapping(bytes4 => bool))) public hasSpecialAccessToCall; 31

File: 2022-10-zksync\ethereum\contracts\zksync\Storage.sol: 14 /// @param securityCouncilMembers The set of the trusted addresses that can instantly finish upgrade (diamond cut) 15: /// @param securityCouncilMemberLastApprovedProposalId The mapping of the security council addresses and the last diamond cut that they approved 16 /// @param securityCouncilEmergencyApprovals The number of received upgrade approvals from the security council

21 uint256 currentProposalId; 22: mapping(address => bool) securityCouncilMembers; 23: mapping(address => uint256) securityCouncilMemberLastApprovedProposalId; 24 uint256 securityCouncilEmergencyApprovals;

76 /// @notice List of permitted validators 77: mapping(address => bool) validators; 78 /// @dev Verifier contract. Used to verify aggregated proof for blocks

86 /// @dev Stored hashed StoredBlock for block number 87: mapping(uint256 => bytes32) storedBlockHashes; 88 /// @dev Stored root hashes of L2 -> L1 logs 89: mapping(uint256 => bytes32) l2LogsRootHashes; 90 /// @dev Container that stores transactions requested from L1

[GalloDaSballo]

2)USE A MORE RECENT VERSION OF SOLIDITY

200

3 of the mappings could be bulked, saving around 120 gas

320

[c4-judge]

GalloDaSballo marked the issue as grade-c