Gas Optimizations

[code423n4]

C4-001 : Use of _msgSender()

Impact

The use of _msgSender() when there is no implementation of a meta transaction mechanism that uses it, such as EIP-2771, very slightly increases gas consumption.

Proof of Concept

_msgSender() is utilized three times where msg.sender could have been used in the following function.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/base/ERC721Time.sol#L155

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/base/ERC721Time.sol#L177

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/base/ERC721Time.sol#L203

Tools Used

None

Recommended Mitigation Steps

Replace _msgSender() with msg.sender if there is no mechanism to support meta-transactions like EIP-2771 implemented.

C4-002 : Immutable variables

Impact

'immutable' greatly reduces gas costs. There are variables that do not change so they can be marked as immutable to greatly improve the gas costs.

Proof of Concept

1. For instance : https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L21

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/CollectNFT.sol#L22

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/FollowNFT.sol#L42

Tools Used

Code Review

Recommended Mitigation Steps

Mark variables as immutable.

C4-003 : # Adding unchecked directive can save gas

Impact

For the arithmetic operations that will never over/underflow, using the unchecked directive (Solidity v0.8 has default overflow/underflow checks) can save some gas from the unnecessary internal over/underflow checks.

Proof of Concept

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/modules/collect/TimedFeeCollectModule.sol#L71

Tools Used

None

Mitigation Steps

Consider applying unchecked arithmetic where overflow/underflow is not possible.

C4-004 : Revert String Size Optimization

Impact - Gas Optimization

Shortening revert strings to fit in 32 bytes will decrease deploy time gas and will decrease runtime gas when the revert condition has been met. Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.

Proof of Concept

1. Navigate to the following contract function and lines.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/base/ERC721Time.sol#L458

Tools Used

Code Review

Recommended Mitigation Steps

Shorten the revert strings to fit in 32 bytes. That will affect gas optimization.

C4-005 : Less than 256 uints are not gas efficient

Impact - Gas Optimization

Lower than uint256 size storage instance variables are actually less gas efficient. E.g. using uint16 does not give any efficiency, actually, it is the opposite as EVM operates on default of 256-bit values so uint16 is more expensive in this case as it needs a conversion. It only gives improvements in cases where you can pack variables together, e.g. structs.

Proof of Concept

1. Navigate to the following contract function line.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/modules/ModuleGlobals.sol#L110

Tools Used

Code Review

Recommended Mitigation Steps

Consider to review all uint types. Change them with uint256 If the integer is not necessary to present with uint16.

C4-006 : Changing function visibility from public to external can save gas

Impact - Gas Optimization

There is a function declared as public that are never called internally within the contract. It is best practice to mark such functions as external instead, as this saves gas (especially in the case where the function takes arguments, as external functions can read arguments directly from calldata instead of having to allocate memory).

Proof of Concept

1. Navigate to the following contract function line.

https://github.com/code-423n4/2022-02-aave-lens/blob/aaf6c116345f3647e11a35010f28e3b90e7b4862/contracts/core/LensHub.sol#L493

Tools Used

Slither

Recommended Mitigation Steps

All of the public functions in the contract are not called internally, so access can be changed to external to reduce gas.

[Zer0dot]

So I think this is largely valid but we won't be acting on it, except the unchecked increments which are included in lens-protocol/core#80. A lot of this is relating to the ERC721Time contract which is largely a CC of the OpenZeppelin implementation, we don't want to change that much.

The reason we keep the burn function public is because we override it in certain inheriting contracts.