Auction.sol: currentAuctionId should be cached in functions using it frequently

[code423n4]

Handle

harleythedog

Vulnerability details

Impact

In Auction.sol, the storage variable currentAuctionId is frequently used across the contract. In functions that read from this variable multiple times, it would save gas to copy it into a local memory variable first and then use the memory variable for calculations. This is because SLOAD operations are much more expensive than MLOAD operations.

Proof of Concept

For example, see _checkAuctionFinalization here: https://github.com/code-423n4/2021-11-malt/blob/c3a204a2c0f7c653c6c2dda9f4563fd1dc1cecf3/src/contracts/Auction.sol#L746

It would save a lot of gas if currentAuctionId was read from storage once at the start and then the local memory variable was used on subsequent reads.

Tools Used

Inspection

Recommended Mitigation Steps

Cache currentAuctionId reads when there are multiple reads in a function.

[0xScotch]

#89

[GalloDaSballo]

Duplicate of #89