Rearranging the declaration order of state variables in Auction.sol by moving all 3 bool's next to each other will pack them in one slot because bool’s are represented as uint8 internally. This will save slots and gas if they're used together in functions by allowing optimizer to combine their SLOADs/SSTOREs. If they are not used together, this may increase gas costs due to the required masking of shared slot variables.
GalloDaSballo
commented
2 years ago
Handle
0xRajeev
Vulnerability details
Impact
Rearranging the declaration order of state variables in Auction.sol by moving all 3 bool's next to each other will pack them in one slot because bool’s are represented as uint8 internally. This will save slots and gas if they're used together in functions by allowing optimizer to combine their SLOADs/SSTOREs. If they are not used together, this may increase gas costs due to the required masking of shared slot variables.
Proof of Concept
https://github.com/code-423n4/2021-09-defiProtocol/blob/52b74824c42acbcd64248f68c40128fe3a82caf6/contracts/contracts/Auction.sol#L16-L21
Tools Used
Manual Analysis
Recommended Mitigation Steps
Rearrange state variable declaration order, by considering their usage in functions, to allow slot packing and save gas.