Fraxlend (Frax Finance) contest - Tomio's results

Title: calldata instead of memory for RO function parameters

Impact: If a reference type function parameter is read-only, it is cheaper in gas to use calldata instead of memory. Calldata is a non-modifiable, non-persistent area where function arguments are stored, and behaves mostly like memory.

Try to use calldata as a data location because it will avoid copies and also makes sure that the data cannot be modified.

Proof of Concept: VaultAccount.sol#L17 VaultAccount.sol#L34

Recommended Mitigation Steps: Replace memory with calldata

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Title: Using += or -= can save gas

Proof of Concept: VaultAccount.sol#L26 VaultAccount.sol#L43

Recommended Mitigation Steps: Change to:

    shares += 1;

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Title: Use of uint8 in for loop increases gas costs

Proof of Concept: SafeERC20.sol#L22

Recommended Mitigation Steps: Change uint8 to uint256

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Title: Default value initialization

Impact: If a variable is not set/initialized, it is assumed to have the default value (0, false, 0x0 etc depending on the data type). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

Proof of Concept: SafeERC20.sol#L22 FraxlendPair.sol#L289 FraxlendPair.sol#L308

Recommended Mitigation Steps: Remove explicit initialization for default values.

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Title: Using unchecked and prefix increment is more effective for gas saving:

Proof of Concept: SafeERC20.sol#L22 FraxlendPair.sol#L289 FraxlendPair.sol#L308 FraxlendPairCore.sol#L265-L270

Recommended Mitigation Steps: Change to:

for (i = 0; i < 32 && data[i] != 0;) {
  // ...
unchecked { ++i; }
}

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Title: Caching length for loop can save gas

Proof of Concept: FraxlendPair.sol#L289 FraxlendPair.sol#L308 FraxlendPairCore.sol#L265-L270

Recommended Mitigation Steps: Change to:

	uint256 Length = _lenders.length;
        for (uint256 i = 0; i < _lenders.Length; i++) {

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Title: Using storage instead of memory for struct can save gas

Proof of Concept: FraxlendPairCore.sol#L419 FraxlendPairCore.sol#L517

Recommended Mitigation Steps: Replace memory with storage

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Title: Unused lib

Proof of Concept: FraxlendPairDeployer.sol#L45

Recommended Mitigation Steps: remove unused can save gas

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Title: Set as constant can save gas

Proof of Concept: FraxlendPairDeployer.sol#L49-L51

Recommended Mitigation Steps: Change to constant and make it private or internal

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Title: Reduce the size of error messages (Long revert Strings)

Impact: Shortening revert strings to fit in 32 bytes will decrease deployment time gas and will decrease runtime gas when the revert condition is 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: FraxlendPairDeployer.sol#L205 FraxlendPairDeployer.sol#L228 FraxlendPairDeployer.sol#L253 FraxlendPairDeployer.sol#L365-L369

Recommended Mitigation Steps: Consider shortening the revert strings to fit in 32 bytes

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Title: Custom errors from Solidity 0.8.4 are cheaper than revert strings

Impact: Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met) while providing the same amount of information

Custom errors are defined using the error statement reference: https://blog.soliditylang.org/2021/04/21/custom-errors/

Proof of Concept: FraxlendPairDeployer.sol#L205 FraxlendPairDeployer.sol#L228 FraxlendPairDeployer.sol#L253 FraxlendPairDeployer.sol#L365-L369

Recommended Mitigation Steps: Replace require statements with custom errors.

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Title: Remove or replace unused state variable

Impact: Saves a storage slot. If the variable is assigned a non-zero value, saves Gsset (20000 gas). If it's assigned a zero value, saves Gsreset (2900 gas). If the variable remains unassigned, there is no gas savings. If the state variable is overriding an interface's public function, mark the variable as constant or immutable so that it does not use a storage slot, and manually add a getter function

Reference: here

Proof of Concept: FraxlendPairCore.sol#L51

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Title: Using multiple require instead && can save gas

Proof of Concept: LinearInterestRate.sol#L57-L68

Recommended Mitigation Steps: Change to:

	require(_minInterest < MAX_INT, "LinearInterestRate: _minInterest < MAX_INT");
	require( _minInterest <= _vertexInterest, "LinearInterestRate: _minInterest <= _vertexInterest");
 	require(_minInterest >= MIN_INT, "LinearInterestRate: _minInterest >= MIN_INT");

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Title: Using != is more gas efficient in require statement

Proof of Concept: LinearInterestRate.sol#L66

Recommended Mitigation Steps: Change from >0 to !=

	require(
            _vertexUtilization < MAX_VERTEX_UTIL && _vertexUtilization != 0,
            "LinearInterestRate: _vertexUtilization < MAX_VERTEX_UTIL && _vertexUtilization != 0"
        );

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