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[G-01] Use storage instead memory

When fetching data from a storage location, assigning the data to a memory variable causes all fields of the struct/array to be read from storage, which incurs a Gcoldsload (2100 gas) for each field of the struct/array. If the fields are read from the new memory variable, they incur an additional MLOAD rather than a cheap stack read. Instead of declearing the variable with the memory keyword, declaring the variable with the storage keyword and caching any fields that need to be re-read in stack variables, will be much cheaper, only incuring the Gcoldsload for the fields actually read. The only time it makes sense to read the whole struct/array into a memory variable, is if the full struct/array is being returned by the function, is being passed to a function that requires memory, or if the array/struct is being read from another memory array/struct

code snipped

https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/DiamondProxy.sol#L26 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/libraries/Diamond.sol#L175

recommendation

use storage instead memory

[G-02] Use abi.encodePackage instead of abi.encode is more efficient

abi.encode encodes its parameters using the ABI specification. ABI is designed to make calls to contracts. Parameters filled up to 32 bytes. If you make calls to contracts you should probably use abi.encode if you are dealing with more than one dynamic data type as it prevents collisions. abi.encodePacked: abi.encodePacked encodes its parameters using the minimal space required by the type. Encoding that uint8 will use 1 byte. This is used when you want to save space, and not call contracts. Takes any type of data and any amount of input. so from the explanation above it will be more efficient to use abi.encodePacked.

code snipped

https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/DiamondInit.sol#L54 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/facets/DiamondCut.sol#L27 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/facets/DiamondCut.sol#L61 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/libraries/Merkle.sol#L30 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/libraries/Merkle.sol#L32 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L82 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L283

recommendation

use abi.encodePacked instead abi.encode

[G-03] Use private rather than for constants.

Using private rather than public for constants, saves gas 10 gas per instances. https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/Config.sol#L9 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/Config.sol#L12 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/Config.sol#L15 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/Config.sol#L23 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/Config.sol#L26 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L32 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/bridge/L1ERC20Bridge.sol#L36

recommendation

use private for constant variable states.

[G-04] Use calldata instead memory

code snipped

https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/facets/Mailbox.sol#L43 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/facets/Mailbox.sol#L53

recommendation

In the external functions where the function argument is read-only, the function() has an inputed parameter that using memory, if this function didnt change the parameter, its cheaper to use calldata then memory.

[G-05] Use require instead && (split require)

code snipped

https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/common/AllowList.sol#L96-L100 https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/common/L2ContractHelper.sol#L65

recommendation

When using logical conjunction (&&), make sure to order your functions correctly for optimal gas usage. we reccomend to use require instead of logical conjunction (&&) for save gas cost.

[G-06] Cache msg.data.length

code snipped

https://github.com/code-423n4/2022-10-zksync/blob/456078b53a6d09636b84522ac8f3e8049e4e3af5/ethereum/contracts/zksync/DiamondProxy.sol#L24

recommendation

caching the array length can reduce gas it caused access to a local variable is more cheap than query storage / calldata / memory in solidity. we recommend to cache the msg.data.length due to use multiple times. Caching a state variable replace each Gwarmaccess (100 gas) with cheaper stack read.