Gas optimization: Struct layout

[code423n4]

Handle

gzeon

Vulnerability details

Impact

Detailed description of the impact of this finding.

Proof of Concept

https://github.com/code-423n4/2021-10-mochi/blob/main/projects/mochi-core/contracts/interfaces/IMochiVault.sol
L6-L12: the struct can be reordered into
struct Detail {
Status status;
address referrer;
uint256 collateral;
uint256 debt;
uint256 debtIndex;
}

such that status and referrer are put into the same slot, should save ~2000 gas per borrow

Tools Used

None

Recommended Mitigation Steps

Reorder the struct as suggested, and modify impacted code at
IMochiVault.sol L28-L34
DutchAuctionLiquidator.sol L77

Extra

Realistically, the range of debtIndex (start at 1e18 and increase by fee per year) probably fit in a uint88(11bytes) so you can pack (status(1byte), referrer(20bytes), debtIndex(11bytes)) all in 32 bytes, saving another storage slot.