Caching return values of external calls in local/memory variables avoids CALLs to save gas

[code423n4]

Handle

0xRajeev

Vulnerability details

Impact

There are places across contracts where the same external calls are made multiple times within a function. Caching return values of such calls in local/memory variables avoids CALLs to save gas. CALLs cost 2600 gas after Berlin upgrade. MLOADs cost only 3 gas units.

Proof of Concept

Cache factory.ownerSplit() return value to save 2600 gas in this function which gets called at every mint/burn.: https://github.com/code-423n4/2021-09-defiProtocol/blob/52b74824c42acbcd64248f68c40128fe3a82caf6/contracts/contracts/Basket.sol#L120-L121

Hoist basketAsERC20.totalSupply() external call out of the loop because it remains the same and each call costs 2600 gas: https://github.com/code-423n4/2021-09-defiProtocol/blob/52b74824c42acbcd64248f68c40128fe3a82caf6/contracts/contracts/Auction.sol#L96-L99

Tools Used

Manual Analysis

Recommended Mitigation Steps

Cache return values of external calls in local/memory variables

[GalloDaSballo]

The warden is pointing out to something important, which the importance of caching external calls

However the gas values do not seem to be up to date The cost of STATICCALL is not 2.6k additionally the repeated STATICCALL will cost about 100 gas

However, the warden is correct in saying that caching the value will save gas (as reading from memory only costs 3 gas)