Gas Optimizations

[code423n4]

1.Use Custom Error instead of Revert String to Save Gas

Custom error from solidity 0.8.4 are cheaper than revert strings, custom error are defined using the error statement can use inside and outside the contract.

source https://blog.soliditylang.org/2021/04/21/custom-errors/

i suggest replacing revert error strings with custom error

POC :

https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/facets/BaseConnextFacet.sol#L38
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/ConnextPriceOracle.sol#L72
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/ConnextPriceOracle.sol#L150
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/LPToken.sol#L35
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/LPToken.sol#L50
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L75
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L76
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L77
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L86
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L89
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L90
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L96
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L97
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L98
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L102
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L125
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L155
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L167
https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/StableSwap.sol#L177

2. > 0 is less efficient than != 0 for unsigned integers

!= 0 costs less gas compared to > 0 for unsigned integers in require statements with the optimizer enabled (6 gas)

While it may seem that > 0 is cheaper than !=, this is only true without the optimizer enabled and outside a require statement. If you enable the optimizer at 10k AND you’re in a require statement, this will save gas.

source : https://twitter.com/gzeon/status/1485428085885640706

I suggest changing > 0 with != 0

POC :

https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/helpers/ConnextPriceOracle.sol#L150

3. Consider making some constants as non-public to save gas

Reducing from public to private or internal can save gas when a constant isn’t used outside of its contract. I suggest changing the visibility from public to internal or private.

POC :

https://github.com/code-423n4/2022-06-connext/blob/main/contracts/contracts/core/connext/facets/BridgeFacet.sol#L68