Ethos Reserve contest - banky's results

Multiple storage reads from yieldGenerator[collateral]

In the _rebalance function, we make multiple storage reads from yieldGenerator[collateral]. Storage is read in the following lines:

1. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/ActivePool.sol#L246
2. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/ActivePool.sol#L279
3. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/ActivePool.sol#L280
4. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/ActivePool.sol#L282

The address has already been stored in memory here and the IERC4626 vault has also been stored in memory here. By reading from memory instead of storage, we can save users gas.

No need to recalculate vars.yieldingAmount

We calculate yieldingAmount = yieldingAmount - toWithdraw

However, yieldingAmount = currentAllocated

We recalculate yieldingAmount here as yieldingAmount = yieldingAmount - toWithdraw

where toWithdraw = currentAllocated - finalYieldingAmount

Substituting values for toWithdraw,

yieldingAmount = currentAllocated - currentAllocated + finalYieldingAmount yieldingAmount = finalYieldingAmount

Thus, these extra computation steps are unnecessary and only waste gas. I suggest replacing this line with vars.yieldingAmount = vars.finalYieldingAmount

This same logic can be applied to the calculation here

Adjust trove should use > instead of !=

In the conditional check here, we can save 3 gas by using > instead of != since _collTopUp is a uint and thus must be >= 0

Prevent passing LUSD_GAS_COMPENSATION constant around

We are passing around the constant LUSD_GAS_COMPENSATION instead of just using the value where it is needed directly. This defeats some of the benefit of constants where the compiler will directly replace the values in code. The value is used in these locations

1. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/TroveManager.sol#L342
2. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/TroveManager.sol#L379
3. https://github.com/code-423n4/2023-02-ethos/blob/52aba524ede2e9becff9b8f0025b863c1029adac/Ethos-Core/contracts/TroveManager.sol#L500

I suggest not saving this value into memory and instead using the constant directly where it is needed.