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code-423n4 / 2022-04-backd-findings

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Gas Optimizations #129

Open code423n4 opened 2 years ago

code423n4 commented 2 years ago

1. i++ can be replaced with ++i

pre-increment consumes less gas compared to post-increment, if post-increment return value is not used, it can be replaced with pre-increment to save some gas

Proof of concept

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/Controller.sol#L117

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L260

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L188

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L456

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L479

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L506

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L891

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpKeeperHelper.sol#L43

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpKeeperHelper.sol#L46

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpKeeperHelper.sol#L72

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpKeeperHelper.sol#L93

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpKeeperHelper.sol#L165

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/access/RoleManager.sol#L80

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/strategies/ConvexStrategyBase.sol#L313

Mitigation

Replace post-increment with pre-increment

2. Initialising with default values

When variables are created it contains default values, initialising with default values is not necessary

Proof of concept

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/Controller.sol#L117

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L260

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L188

Mitigation

Initialising with default values can be avoided

3. Use unchecked to save gas

Using unchecked in expressions that wont overflow/underflow can avoid the default overflow/underflow checks and saves gas

Proof of concept

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L163-L164 

150        require(startingAllowance >= amount, Error.INSUFFICIENT_BALANCE);

153        require(srcTokens >= amount, Error.INSUFFICIENT_BALANCE);

163        uint256 allowanceNew = startingAllowance - amount;
164        uint256 srcTokensNew = srcTokens - amount;

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L231

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L125

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L444

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L452

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L591

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L595

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L605

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L756

Mitigation

unchecked can be placed in the expression

4. Avoid storage re-read and save gas

Storage variables that are re-read multiple times in a same code block can be cached in a temporary variable and re-used to save gas

Proof of concept

token in function stakeFor and unstakeFor

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L331-L339

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/StakerVault.sol#L376-L384

_rewardTokens.length() in

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/strategies/ConvexStrategyBase.sol#L313

Mitigation

Storage variables can be stored in temporary variables and re-used

5. Replace > 0 with != 0 to save gas

!= 0 is more efficient than > 0 for unsigned integers in require statements with optimizer enabled

Proof of concept

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpAction.sol#L210

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/actions/topup/TopUpActionFeeHandler.sol#L123

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/pool/LiquidityPool.sol#L401

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/pool/LiquidityPool.sol#L471

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/pool/LiquidityPool.sol#L473

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/pool/LiquidityPool.sol#L549

https://github.com/code-423n4/2022-04-backd/blob/c856714a50437cb33240a5964b63687c9876275b/backd/contracts/vault/Vault.sol#L164

Mitigation

> can be replaced with !=