Adding unchecked directive can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

For example:

1. https://github.com/code-423n4/2022-01-yield/blob/e946f40239b33812e54fafc700eb2298df1a2579/contracts/ConvexStakingWrapper.sol#L114-L114

uint256 startIndex = rewardsLength - 1;

rewardsLength - 1 will never underflow.

2. https://github.com/code-423n4/2022-01-yield/blob/e946f40239b33812e54fafc700eb2298df1a2579/contracts/ConvexYieldWrapper.sol#L82-L85

bool isLast = i == vaultsLength - 1;
if (!isLast) {
    vaults_[i] = vaults_[vaultsLength - 1];
}

[iamsahu]

From readme:

• In general, we are not going to change our code for small gas optimizations less than 100 gas

[GalloDaSballo]

Interestingly enough, while the specific link mentioned by the warden wouldn't save 100 gas, using unchecked on that code and the for loop would.

While I'm not a fan of unchecked due to syntax, I think the finding is valid and above the sponsors require of at last 100 gas

[alcueca]

Fair enough, thank you.