Gas Optimizations

[code423n4]

C4-001 : Cache array length in for loops can save gas

Impact

Reading array length at each iteration of the loop takes 6 gas (3 for mload and 3 to place memory_offset) in the stack.

Caching the array length in the stack saves around 3 gas per iteration.

Proof of Concept

1. Navigate to the following smart contract line.

https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/LenderPool.sol#L670

Tools Used

None

Recommended Mitigation Steps

Consider to cache array length.

C4-002 : > 0 can be replaced with != 0 for gas optimization

Impact - Gas Optimization

!= 0 is a cheaper operation compared to > 0, when dealing with uint.

Proof of Concept

1. Navigate to the following contract function and lines.

https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/PooledCreditLine.sol#L1038

Tools Used

Code Review

Recommended Mitigation Steps

Use "!=0" instead of ">0" for the gas optimization.

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/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/LenderPool.sol#L295

Tools Used

None

Recommended Mitigation Steps

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

C4-004 : Free gas savings for using solidity 0.8.10+

Impact

Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks are available for free.

Proof of Concept

Solidity 0.8.10 has a useful change which reduced gas costs of external calls which expect a return value: https://blog.soliditylang.org/2021/11/09/solidity-0.8.10-release-announcement/

Code Generator: Skip existence check for external contract if return data is expected. In this case, the ABI decoder will revert if the contract does not exist

The advantages of versions 0.8.* over <0.8.0 are:

• Safemath by default from 0.8.0 (can be more gas efficient than
  library based safemath.)
• Low level inliner : from 0.8.2, leads to cheaper runtime gas. Especially relevant when the contract has small functions. For example, OpenZeppelin libraries typically have a lot of small helper functions and if they are not inlined, they cost an additional 20 to 40 gas because of 2 extra jump instructions and additional stack operations needed for function calls.
• Optimizer improvements in packed structs: Before 0.8.3, storing packed structs, in some cases used an
  additional storage read operation. After EIP-2929, if the slot was already cold, this means unnecessary stack operations and extra deploy time costs. However, if the slot was already warm, this means
  additional cost of 100 gas alongside the same unnecessary stack operations and extra deploy time costs.
• Custom errors from 0.8.4, leads to cheaper deploy time cost and run time cost. Note: the run time cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider to upgrade pragma to at least 0.8.10.

C4-005 : Check if amount > 0 before token transfer can save gas

Impact

Since _amount can be 0. Checking if (_amount != 0) before the transfer can potentially save an external call and the unnecessary gas cost of a 0 token transfer.

Proof of Concept

https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/LenderPool.sol#L295

All Contracts

Tools Used

None

Recommended Mitigation Steps

Consider checking amount != 0.

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

Impact

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

https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/PooledCreditLine.sol#L1189

Tools Used

Code Review

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.

C4-007 : Non-strict inequalities are cheaper than strict ones

Impact

Strict inequalities add a check of non equality which costs around 3 gas.

Proof of Concept

All Facets Directory Contracts
Examples :
https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/LenderPool.sol#L283

Tools Used

Code Review

Recommended Mitigation Steps

Use >= or <= instead of > and < when possible.

C4-008 : Delete - ABI Coder V2 For Gas Optimization

Impact

From Pragma 0.8.0, ABI coder v2 is activated by default. The pragma abicoder v2 can be deleted from the repository. That will provide gas optimization.

Proof of Concept

1. Navigate to the following code section.

"""
https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/LenderPool.sol#L3

https://github.com/sublime-finance/sublime-v1/blob/46536a6d25df4264c1b217bd3232af30355dcb95/contracts/PooledCreditLine/PooledCreditLine.sol#L3
"""

Tools Used

None

Recommended Mitigation Steps

ABI coder v2 is activated by default. It is recommended to delete redundant codes.

From Solidity v0.8.0 Breaking Changes https://docs.soliditylang.org/en/v0.8.0/080-breaking-changes.html

[ritik99]

All except C4-004 and C4-008 are not valid because we cannot upgrade to v0.8 because of a dependency (see #67 )

[HardlyDifficult]

Merging with #32