Gas Optimizations

[code423n4]

1) Efficient variable packing saves gas

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L104 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2StandardERC20.sol#L29

2) a+=b costs more gas than a=a+b

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/DiamondCut.sol#L29

3) Avoid redundant returns

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L26

4) Internal function can be inlined to save gas

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L163 (https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L80) https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L37 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L198 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/bridge/L1ERC20Bridge.sol#L116 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/bridge/L1ERC20Bridge.sol#L240 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/bridge/L1ERC20Bridge.sol#L119 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/bridge/L1ERC20Bridge.sol#L155 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2ERC20Bridge.sol#L62 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2ERC20Bridge.sol#L97 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2ETHBridge.sol#L67

5) Use calldata instead of memory on external functions to save gas

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Mailbox.sol#L43 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/ExternalDecoder.sol#L10 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/ExternalDecoder.sol#L15 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2StandardERC20.sol#L43

6) Usage of uint takes less gas than usage of uint of size less than 256 bits

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L40 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L54 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/libraries/Diamond.sol#L24 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/libraries/Diamond.sol#L33 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/libraries/PriorityQueue.sol#L12 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/libraries/PriorityQueue.sol#L13 https://github.com/code-423n4/2022-10-zksync/blob/main/zksync/contracts/bridge/L2StandardERC20.sol#L29

7) Multiple mappings can be combined to save gas

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L22 with https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L2 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L87 with https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/Storage.sol#L8

8) Don’t emit storage variable

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/DiamondCut.sol#L36-L38 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/DiamondCut.sol#L69 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/DiamondCut.sol#L100 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L269 https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/Executor.sol#L345

9) Use require instead of assert to save gas

https://github.com/code-423n4/2022-10-zksync/blob/main/ethereum/contracts/zksync/facets/DiamondCut.sol#L16

[c4-judge]

GalloDaSballo marked the issue as grade-c

[GalloDaSballo]

Low impact