prePO contest - rjs's results

Introduction

The PrePO code base is well-written and employs many common gas optimizations in sensible places. It was quite a challenge to find improvements 👍.

Summary

Gas Optimization Findings

[G-01] Single-child inheritance hierarchies can be flattened

Deployment Gas saved: ✔ Transaction Gas saved: ✔

NFTScoreRequirement has only one descendant

DepositHook is the only class to inherit from NFTScoreRequirement. While it is good practice to separate concerns like this, it could be argued that this is a premature optimization until a second child contract has actually been implemented. Given that DepositHook is a hot path for PrePO, and hooks cannot be set by 3rd parties, I would consider flattening this hierarchy for the deployment and transaction (JUMP/stack) gas savings until there is a second descendant of NFTScoreRequirement.

• packages/prepo-shared-contracts/contracts/NFTScoreRequirement.sol

7: contract NFTScoreRequirement is INFTScoreRequirement {

• apps/smart-contracts/core/contracts/DepositHook.sol

12: contract DepositHook is IDepositHook, AccountListCaller, NFTScoreRequirement, TokenSenderCaller, SafeAccessControlEnumerable {

---

[G-02] x = x + y is more efficient than x += y;

Deployment Gas saved: ✔ Transaction Gas saved: ❌

• apps/smart-contracts/core/contracts/DepositRecord.sol

31:     globalNetDepositAmount += _amount;
32:     userToDeposits[_sender] += _amount;

• apps/smart-contracts/core/contracts/WithdrawHook.sol

64:       globalAmountWithdrawnThisPeriod += _amountBeforeFee;

• apps/smart-contracts/core/contracts/WithdrawHook.sol

71:       userToAmountWithdrawnThisPeriod[_sender] += _amountBeforeFee;

• packages/prepo-shared-contracts/contracts/NFTScoreRequirement.sol

60:       score += IERC721(collection).balanceOf(account) > 0 ? collectionScore : 0;

---

[G-03] Use named variables in function returns

Deployment Gas saved: ✔ Transaction Gas saved: ❌

Declaring additional variables rather than using named return variables is a waste of deployment gas.

• apps/smart-contracts/core/contracts/Collateral.sol

45:   function deposit(address _recipient, uint256 _amount) external override nonReentrant returns (uint256) {
...
60:     uint256 _collateralMintAmount = (_amountAfterFee * 1e18) / baseTokenDenominator;
...
63:     return _collateralMintAmount;
64:   }

• packages/prepo-shared-contracts/contracts/NFTScoreRequirement.sol

55:   function getAccountScore(address account) public view virtual override returns (uint256) {
56:     uint256 score;
...
65:     return score;
66:   }

---

[G-04] Redundant return statement

Deployment Gas saved: ✔ Transaction Gas saved: ❌

If you set values for all named variable in a function return, it is not necessary to use the return statement, see line 71 below:

• apps/smart-contracts/core/contracts/PrePOMarketFactory.sol

59:   function _createPairTokens(
...
64:   ) internal returns (LongShortToken _newLongToken, LongShortToken _newShortToken) {
...
69:     _newLongToken = new LongShortToken{salt: _longTokenSalt}(_longTokenName, _longTokenSymbol);
70:     _newShortToken = new LongShortToken{salt: _shortTokenSalt}(_shortTokenName, _shortTokenSymbol);
71:     return (_newLongToken, _newShortToken); // <-- remove
72:   }

Alternatively, if you are just returning the default value, it is also redundant:

• packages/prepo-shared-contracts/contracts/NFTScoreRequirement.sol

50:   function getCollectionScore(IERC721 collection) external view virtual override returns (uint256) {
51:     if (_collectionToScore.contains(address(collection))) return _collectionToScore.get(address(collection));
52:     return 0; // <-- remove
53:   }

---

[G-05] Cache variables in hot loops

Deployment Gas saved: ✔ Transaction Gas saved: ✔

• packages/prepo-shared-contracts/contracts/NFTScoreRequirement.sol

Before:

25:     for (uint256 i = 0; i < numCollections; ) {
26:       require(scores[i] > 0, "score == 0");
27:       _collectionToScore.set(address(collections[i]), scores[i]);
28:       unchecked {
29:         ++i;
30:       }
31:     }

·-----------------------------------------------------------|---------------------------|-------------|-----------------------------·
|                    Solc version: 0.8.7                    ·  Optimizer enabled: true  ·  Runs: 200  ·  Block limit: 30000000 gas  │
····························································|···························|·············|······························
|  Methods                                                                                                                          │
························|···································|·············|·············|·············|···············|··············
|  Contract             ·  Method                           ·  Min        ·  Max        ·  Avg        ·  # calls      ·  eur (avg)  │
························|···································|·············|·············|·············|···············|··············
|  DepositHook          ·  setCollectionScores              ·     118079  ·     118307  ·     118155  ·            3  ·          -  │
························|···································|·············|·············|·············|···············|··············

After:

25:     uint256 score;
26:     for (uint256 i = 0; i < numCollections; ) {
27:       score = scores[i];
28:       require(score > 0, "score == 0");
29:       _collectionToScore.set(address(collections[i]), score);
30:       unchecked {
31:         ++i;
32:       }
33:     }

·-----------------------------------------|---------------------------|-------------|-----------------------------·
|           Solc version: 0.8.7           ·  Optimizer enabled: true  ·  Runs: 200  ·  Block limit: 30000000 gas  │
··········································|···························|·············|······························
|  Methods                                                                                                        │
··················|·······················|·············|·············|·············|···············|··············
|  Contract       ·  Method               ·  Min        ·  Max        ·  Avg        ·  # calls      ·  eur (avg)  │
··················|·······················|·············|·············|·············|···············|··············
|  DepositHook    ·  setCollectionScores  ·     118043  ·     118271  ·     118119  ·            3  ·          -  │
··················|·······················|·············|·············|·············|···············|··············