Mimo August 2022 contest - Aymen0909's results

1- NO NEED TO EXPLICITLY INITIALIZE VARIABLES WITH DEFAULT VALUES

If a variable is not set/initialized, it is assumed to have the default value (0 for uint or int, false for bool, address(0) for address…). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

File: contracts/proxy/MIMOProxy.sol

line 132 : for (uint256 i = 0; i < targets.length; i++)

2- USE OF ++i COST LESS GAS THAN i++ IN FOR LOOPS :

Prefix increments are cheaper than postfix increments, It saves 5 gas per iteration

File: contracts/proxy/MIMOProxy.sol

line 132 : for (uint256 i = 0; i < targets.length; i++)

3- ++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

File: contracts/proxy/MIMOProxy.sol

line 132 : for (uint256 i = 0; i < targets.length; i++)

4- UNCHECKED ARITHMETIC

PROBLEM

The default “checked” behavior costs more gas when adding/diving/multiplying, because under-the-hood those checks are implemented as a series of opcodes that, prior to performing the actual arithmetic, check for under/overflow and revert if it is detected.

if it can statically be determined there is no possible way for your arithmetic to under/overflow (such as a condition in an if statement), surrounding the arithmetic in an unchecked block will save gas

PROOF OF CONCEPT

Instances includes :

File: contracts/actions/automated/MIMOAutoAction.sol

line 101 : uint256 vaultVariation = (rebalanceValue - swapResultValue).wadDiv(rebalanceValue); 
// because of the condition line 97 , the underflow check is unnecessary

File: contracts/actions/managed/MIMOManagedAction.sol

line 124 : uint256 vaultVariation = (rebalanceValue - swapResultValue).wadDiv(rebalanceValue); 
// because of the condition line 120 , the underflow check is unnecessary

File: contracts/actions/MIMOLeverage.sol

line 133 : token.safeIncreaseAllowance(address(core), collateralBalanceAfter - flashloanRepayAmount);
line 134 : core.deposit(address(token), collateralBalanceAfter - flashloanRepayAmount);
// because of the condition line 132 & line 130 , the underflow check is unnecessary

MITIGATION

Place the arithmetic operations in an unchecked block