Saintcode_-G.md

USE CALLDATA INSTEAD OF MEMORY

When a function with a memory array is called externally, the abi.decode() step has to use a for-loop to copy each index of the calldata to the memory index. Each iteration of this for-loop costs at least 60 gas (i.e. 60 * <mem_array>.length). Using calldata directly, obliviates the need for such a loop in the contract code and runtime execution.

When arguments are read-only on external functions, the data location should be calldata

-L1ERC20Bridge.sol line 260 -L1EthBridge.sol line 214 -L2ContractHelper.sol lines 43, 47 -Executor lines 152, 190 -Mailbox lines 43, 53 -Diamond.sol lines 89, 119

.LENGTH SHOULD NOT BE LOOKED UP IN EVERY LOOP OF A FOR-LOOP

Reading array length at each iteration of the loop consumes more gas than necessary. In the best case scenario (length read on a memory variable), caching the array length in the stack saves around 3 gas per iteration. In the worst case scenario (external calls at each iteration), the amount of gas wasted can be massive.

Consider storing the array’s length in a variable before the for-loop, and use this new variable instead

Instances: -Executor.sol line 111

+= COSTS MORE GAS THAN = + FOR STATE VARIABLES

-DiamondCut.sol line 29

USE MULTIPLE REQUIRE() STATMENTS INSTEAD OF REQUIRE(EXPRESSION && EXPRESSION && ...)

-AllowList.sol line 96 -L2ContractHelper.sol line 65

>= COSTS LESS GAS THAN >

The compiler uses opcodes GT and ISZERO for solidity code that uses >, but only requires LT for >=, which saves 3 gas

Instances: -L1ERC20Bridge.sol lines 117, 210 -DiamondCut.sol line 16 -Diamond.sol line 100 -Merkle.sol line 23

++I/I++ SHOULD BE UNCHECKED{++I}/UNCHECKED{I++} WHEN IT IS NOT POSSIBLE FOR THEM TO OVERFLOW, AS IS THE CASE WHEN USED IN FOR- AND WHILE-LOOPS

The unchecked keyword is new in solidity version 0.8.0, so this only applies to that version or higher, which these instances are. This saves 30-40 gas per loop for (uint256 i = 0; i < orders.length; /** NOTE: Removed i++ **/ ) { // Do the thing // Unchecked pre-increment is cheapest unchecked { ++i; } }

Instances: -Diamond.sol lines 94, 132, 153, 173

USING PRIVATE RATHER THAN PUBLIC FOR CONSTANTS, SAVES GAS

If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table

USE CUSTOM ERRORS RATHER THAN REVERT()/REQUIRE() STRINGS TO SAVE GAS

Custom errors are available from solidity version 0.8.4. Custom errors save ~50 gas each time they’re hitby avoiding having to allocate and store the revert string. Not defining the strings also save deployment gas