Gas Optimizations

[code423n4]

Table of contents

• [0x0] Disclaimer
• [G-01] Try ++i instead of i++
• [G-02] Consider a = a + b instead of a += b
• [G-03] Consider marking onlyOwner functions as payable
• [G-04] Use binary shifting instead of a / 2^x, x > 0
• [G-05] Cache state variables, MLOAD << SLOAD
• [G-06] Add require() before some computations, if it makes sense
• [G-07] Internal functions can be inlined
• [G-08] Use private/internal for constants/immutable variables instead of public
• [G-09] Use const values instead of type(uint256).max
• [G-10] Mark functions as external instead of public, if there are no internal calls
• [G-11] Use calldataload instead of mload
• **[G-12] Define state variables as immutable/const

Disclaimer

• Please, consider everything described below as a general recommendation. These notes will represent potential possibilities to optimize gas consumption. It's okay, if something is not suitable in your case. Just let me know the reason in the comments section. Enjoy!

[G-01] Try ++i instead of i++

Description:

• In case of i++, the compiler has to to create a temp variable to return i (if there's a need) and then i gets incremented.
• In case of ++i, the compiler just simply returns already incremented value.

All occurances:

• Contracts:

    file: src/utils/KernelUtils.sol
    ...............................
  
      // Lines: [63-63]
        unchecked {
            i++;
        }
  
      // Lines: [58-60]
        unchecked {
            i++;
        }

[G-02] Consider a = a + b instead of a += b

Description:

• It has an impact on the deployment cost and the cost for distinct transaction as well.

All occurances:

• Contracts:

    file: src/modules/PRICE.sol 
    ...............................
  
      // Lines: [136-136]
          _movingAverage += (currentPrice - earliestPrice) / numObs;
  
      // Lines: [138-138]
          _movingAverage -= (earliestPrice - currentPrice) / numObs; 
  
      // Lines: [222-222]
          total += startObservations_[i];
  
    file: src/modules/TRSRY.sol 
    ...............................
  
      // Lines: [96-97]
          reserveDebt[token_][msg.sender] += amount_;
          totalDebt[token_] += amount_;
  
      // Lines: [131-131]
          if (oldDebt < amount_) totalDebt[token_] += amount_ - oldDebt;
  
      // Lines: [115-116]
          reserveDebt[token_][msg.sender] -= received;
          totalDebt[token_] -= received;
  
      // Lines: [132-132]
          else totalDebt[token_] -= oldDebt - amount_;
  
    file: src/modules/VOTES.sol 
    ...............................
  
      // Lines: [58-58]
          balanceOf[to_] += amount_;
  
      // Lines: [56-56]
          balanceOf[from_] -= amount_;
  
    file: src/policies/BondCallback.sol 
    ...............................
  
      // Lines: [143-144]
          _amountsPerMarket[id_][0] += inputAmount_;
          _amountsPerMarket[id_][1] += outputAmount_;
  
    file: src/policies/Governance.sol 
    ...............................
  
      // Lines: [194-194]
          totalEndorsementsForProposal[proposalId_] -= previousEndorsement;
  
      // Lines: [198-198]
          totalEndorsementsForProposal[proposalId_] += userVotes;
  
      // Lines: [251-255]
          if (for_) {
              yesVotesForProposal[activeProposal.proposalId] += userVotes;
          } else {
              noVotesForProposal[activeProposal.proposalId] += userVotes;
          }
  
    file:  src/policies/Heart.sol
    ...............................
  
      // Lines: [103-103]
          lastBeat += frequency();
  
      // Lines: [138-138]
      // Lines: [138-138]
  

[G-03] Consider marking onlyOwner functions as payable

Description:

• This one is a bit questionable, but you can try that out. So, the compiler adds some extra conditions in case of non-payable, but we know that onlyOwner modifier will be reverted, if the user invoke following methods.

All occurances:

• Contracts:

    file:  src/Kernel.sol
    ...............................
  
      // Lines: [76-78]
          function changeKernel(Kernel newKernel_) external onlyKernel {
              kernel = newKernel_;
          }
  
      // Lines: [126-128]
          function setActiveStatus(bool activate_) external onlyKernel {
              isActive = activate_;
          }
  
      // Lines: [439-448]
          function grantRole(Role role_, address addr_) public onlyAdmin {}
  
      // Lines: [451-460]
          function revokeRole(Role role_, address addr_) public onlyAdmin {}
  
      // Lines: [235-260]
          function revokeRole(Role role_, address addr_) public onlyAdmin {}
  
    file: src/policies/BondCallback.sol 
    ...............................
  
      // Lines: [61-76]
          function requestPermissions()
              external
              view
              override
              onlyKernel
              returns (Permissions[] memory requests)
          {}
  
    file: src/policies/Governance.sol 
    ...............................
  
      // Lines: [61-76]
          function requestPermissions()
              external
              view
              override
              onlyKernel
              returns (Permissions[] memory requests)
          {}

*[G-04] Use binary shifting instead of a / 2^x, x > 0 or `a 2^x, x > 0`**

Description:

• It's also pretty impactful one, especially in loops.

All occurances:

• Contracts:

    file:  src/policies/Operator.sol
    ...............................
  
      // Lines: [372-372]
        int8 scaleAdjustment = int8(ohmDecimals) - int8(reserveDecimals) + (priceDecimals / 2);
  
      // Lines: [427-427]
        int8 scaleAdjustment = int8(reserveDecimals) - int8(ohmDecimals) + (priceDecimals / 2);
  
      // Lines: [419-420]
        uint256 invCushionPrice = 10**(oracleDecimals * 2) / range.cushion.low.price;
        uint256 invWallPrice = 10**(oracleDecimals * 2) / range.wall.low.price;
  

[G-05] Cache state variables, MLOAD << SLOAD

Description:

• MLOAD costs only 3 units of gas, SLOAD(warm access) is about 100 units. Therefore, cache, when it's possible.

All occurances:

• Contracts:

    file: src/policies/Governance.sol 
    ...............................
  
      // Lines: [240-262]
        // Comment: it is possible to cache `activeProposal.proposalId` in order to get MLOAD instead of warm access per each invoking.  
  
              function vote(bool for_) external {
                uint256 userVotes = VOTES.balanceOf(msg.sender);
  
                if (activeProposal.proposalId == 0) {
                    revert NoActiveProposalDetected();
                }
  
                if (userVotesForProposal[activeProposal.proposalId][msg.sender] > 0) {
                    revert UserAlreadyVoted();
                }
  
                if (for_) {
                    yesVotesForProposal[activeProposal.proposalId] += userVotes;
                } else {
                    noVotesForProposal[activeProposal.proposalId] += userVotes;
                }
  
                userVotesForProposal[activeProposal.proposalId][msg.sender] = userVotes;
  
                VOTES.transferFrom(msg.sender, address(this), userVotes);
  
                emit WalletVoted(activeProposal.proposalId, msg.sender, for_, userVotes);
            }
  
      // Lines: [265-289]
        // Comment: it is possible to cache `activeProposal.proposalId` in order to get MLOAD instead of warm access per each invoking.  
  
            function executeProposal() external {
                uint256 netVotes = yesVotesForProposal[activeProposal.proposalId] -
                    noVotesForProposal[activeProposal.proposalId];
                if (netVotes * 100 < VOTES.totalSupply() * EXECUTION_THRESHOLD) {
                    revert NotEnoughVotesToExecute();
                }
  
                if (block.timestamp < activeProposal.activationTimestamp + EXECUTION_TIMELOCK) {
                    revert ExecutionTimelockStillActive();
                }
  
                Instruction[] memory instructions = INSTR.getInstructions(activeProposal.proposalId);
  
                for (uint256 step; step < instructions.length; ) {
                    kernel.executeAction(instructions[step].action, instructions[step].target);
                    unchecked {
                        ++step;
                    }
                }
  
                emit ProposalExecuted(activeProposal.proposalId);
  
                // deactivate the active proposal
                activeProposal = ActivatedProposal(0, 0);
            }
  
    file:  src/modules/RANGE.sol
    ...............................
  
      // Lines: [158-178]
        // Comment: here you can allocate the result of `_range.wall.low.price` computation and etc into the memory, so in event you can simply pass that precomputed value instead of taking warm access to get `_range.wal.low.price again`. The same for all computation could be done.
  
            function updatePrices(uint256 movingAverage_) external permissioned {
                // Cache the spreads
                uint256 wallSpread = _range.wall.spread;
                uint256 cushionSpread = _range.cushion.spread;
  
                // Calculate new wall and cushion values from moving average and spread
                _range.wall.low.price = (movingAverage_ * (FACTOR_SCALE - wallSpread)) / FACTOR_SCALE;
                _range.wall.high.price = (movingAverage_ * (FACTOR_SCALE + wallSpread)) / FACTOR_SCALE;
  
                _range.cushion.low.price = (movingAverage_ * (FACTOR_SCALE - cushionSpread)) / FACTOR_SCALE;
                _range.cushion.high.price =
                    (movingAverage_ * (FACTOR_SCALE + cushionSpread)) /
                    FACTOR_SCALE;
  
                emit PricesChanged(
                    _range.wall.low.price,
                    _range.cushion.low.price,
                    _range.cushion.high.price,
                    _range.wall.high.price
                );
            }
  
    file: src/modules/PRICE.sol 
    ...............................
  
      // Lines: [97-100]
        // Comment: Also cache computation into memory, then assign the numObservations and after that just pass this cached result into allocating array. 
  
          numObservations = uint32(movingAverageDuration_ / observationFrequency_);
          observations = new uint256[](numObservations);
  
      // Lines: [144-144]
        // This line could be transformed a bit:
          nextObsIndex = (nextObsIndex + 1) % numObs;
  
          ++nextObsIndex %= numObs; 
  
      // Lines: [165-171]
        // Comment: cache `observationFrequency`
            if (updatedAt < block.timestamp - 3 * uint256(observationFrequency))
                revert Price_BadFeed(address(_ohmEthPriceFeed));
            ohmEthPrice = uint256(ohmEthPriceInt);
  
            int256 reserveEthPriceInt;
            (, reserveEthPriceInt, , updatedAt, ) = _reserveEthPriceFeed.latestRoundData();
            if (updatedAt < block.timestamp - uint256(observationFrequency))
  
      // Lines: [240-262]
  

[G-06] Add require() before some computations, if it makes sense

Description:

• Everyting above require() takes some gas for execution, therefore if the statement reverts gas will not be retrieved.

All occurances:

• Contracts:

    file: src/modules/INSTR.sol 
    ...............................
  
      // Lines: [48-48]
        // Comment: Put right after getting length in order to avoid unnecessary cold/warm accesses in case of the failure. 
  
          if (length == 0) revert INSTR_InstructionsCannotBeEmpty();
  
    file: src/policies/Governance.sol 
    ...............................
      // Lines: [183-185]
  
            if (proposalId_ == 0) {
                revert CannotEndorseNullProposal();
            }
  

[G-07] Internal functions can be inlined

Description:

• It takes some extra JUMPs which costs around 40-50 gas uints. In loops it will save significant amount of gas.

All occurances:

• Contracts:

    file:  src/policies/Operator.sol
    ...............................
  
      // Lines: [643-643]
        function _updateRangePrices() internal {}
  
      // Lines: [634-634]
          function _updateCapacity(bool high_, uint256 reduceBy_) internal {}
  

[G-08] Use private/internal for constants/immutable variables instead of public

Description:

• Optimization comes from not creating a getter function for each public instance. Try to define them as private/internal if it's possible in specific case.

All occurances:

• Contracts:

    file:  src/Kernel.sol
    ...............................
  
      // Lines: [155-158]
          address public executor;
          address public admin;
  
      // Lines: [165-197]
          Keycode[] public allKeycodes;
          mapping(Keycode => Module) public getModuleForKeycode;
          mapping(Module => Keycode) public getKeycodeForModule;
          mapping(Keycode => Policy[]) public moduleDependents;
          mapping(Keycode => mapping(Policy => uint256)) public getDependentIndex;
          mapping(Keycode => mapping(Policy => mapping(bytes4 => bool))) public modulePermissions;
          Policy[] public activePolicies;
          mapping(Policy => uint256) public getPolicyIndex;
          mapping(address => mapping(Role => bool)) public hasRole;
          mapping(Role => bool) public isRole;
  
    // Comment: I'll not include every single occurance, because the main message have been proposed. 

[G-09] Use const values instead of type(uint256).max

Description:

• Not sure about readability, but it might be tangible in loops.

All occurances:

• Contracts:

    file:  src/modules/RANGE.sol
    ...............................
  
      // Lines: [88-88]
        market: type(uint256).max
  
      // Lines: [95-95]
        market: type(uint256).max 
  
      // Lines: [221-221]
        if (market_ == type(uint256).max && marketCapacity_ != 0) revert RANGE_InvalidParams();
  
      // Lines: [230-230]
        if (market_ == type(uint256).max) {}
  
    file: src/modules/TRSRY.sol 
    ...............................
  
      // Lines: [147-151]
          if (approval != type(uint256).max) {
              unchecked {
                  withdrawApproval[withdrawer_][token_] = approval - amount_;
              }
          }
  
    file: src/policies/BondCallback.sol 
    ...............................
  
      // Lines: [57-57]
          ohm.safeApprove(address(MINTR), type(uint256).max);
  
      // Lines: [95-95]
          TRSRY.setApprovalFor(address(this), payoutToken, type(uint256).max);
  
    file:  src/policies/Operator.sol
    ...............................
  
      // Lines: [167-167]
          ohm.safeApprove(address(MINTR), type(uint256).max);
  
      // Lines: [477-477]
          RANGE.updateMarket(high_, type(uint256).max, 0);
  
      // Lines: [603-603]
          TRSRY.setApprovalFor(address(this), reserve, type(uint256).max);
  

[G-10] Mark functions as external instead of public, if there are no internal calls

Description:

• Functions marked by external use call data to read arguments, where public will first allocate in local memory and then load them.

All occurances:

• Contracts:

    file: src/modules/INSTR.sol 
    ...............................
  
      // Lines: [28-30]
        function VERSION() public pure override returns (uint8 major, uint8 minor) {
            return (1, 0);
        }
  
      // Lines: [37-39]
        function getInstructions(uint256 instructionsId_) public view returns (Instruction[] memory) {
            return storedInstructions[instructionsId_];
        }
  
    file: src/modules/MINTR.sol 
    ...............................
  
      // Lines: [20-22]
          function KEYCODE() public pure override returns (Keycode) {
              return toKeycode("MINTR");
          }
  
      // Lines: [33-39]
          function mintOhm(address to_, uint256 amount_) public permissioned {
              ohm.mint(to_, amount_);
          }
  
          function burnOhm(address from_, uint256 amount_) public permissioned {
              ohm.burnFrom(from_, amount_);
          }
  

  [G-11] Use calldataload instead of mload

Description:

• After Berlin hard fork, to load a non-zero byte from calldata dropped from 64 units of gas to 16 units, therefore if you do not modify args, use a calldata instead of memory. Here you need to explicitly specify calldataload, or replace memory with calldata. If the args are pretty huge, allocating args in memory will cost a lot.

All occurances:

• Contracts:

    file: src/Kernel.sol 
    ...............................
  
      // Lines: [391-395]
        // Comment: Permissions[] calldata requests_ instead of allocating into the memory.
  
          function _setPolicyPermissions(
              Policy policy_,
              Permissions[] memory requests_,
              bool grant_
          ) internal {}
  
    file: src/modules/PRICE.sol 
    ...............................
  
      // Lines: [205-205]
          function initialize(uint256[] memory startObservations_, uint48 lastObservationTime_){}
  
    file:  src/modules/RANGE.sol
    ...............................
  
      // Lines: [77-81]
          constructor(
              Kernel kernel_,
              ERC20[2] memory tokens_,
              uint256[3] memory rangeParams_ // [thresholdFactor, cushionSpread, wallSpread]
          ) Module(kernel_) {}
  
      // Lines: [275-277]
        // Comment: Calldata return
          function range() external view returns (Range memory) {
              return _range;
          }
  
    file: src/policies/BondCallback.sol 
    ...............................
  
      // Lines: [152-152]
          function batchToTreasury(ERC20[] memory tokens_) external onlyRole("callback_admin") {}
  
    file: src/policies/Governance.sol 
    ...............................
  
      // Lines: [159-163]
          function submitProposal(
              Instruction[] calldata instructions_,
              bytes32 title_,
              string memory proposalURI_
          ) external {}
  
    file:  src/policies/Operator.sol
    ...............................
  
      // Lines: [92-98]
          constructor(
              Kernel kernel_,
              IBondAuctioneer auctioneer_,
              IBondCallback callback_,
              ERC20[2] memory tokens_, // [ohm, reserve]
              uint32[8] memory configParams // [cushionFactor, cushionDuration, cushionDebtBuffer, cushionDepositInterval, reserveFactor, regenWait, regenThreshold, regenObserve]
          ) Policy(kernel_) {}
  
      // Lines: [793-801]
          function status() external view override returns (Status memory) {
              return _status;
          }
  
          /// @inheritdoc IOperator
          function config() external view override returns (Config memory) {
              return _config;
          }
      }
  
    file: src/policies/PriceConfig.sol 
    ...............................
  
      // Lines: [45-48]
          function initialize(uint256[] memory startObservations_, uint48 lastObservationTime_)
              external
              onlyRole("price_admin")
          {
  
      // Lines: [53-53]
          function revokePolicyApprovals(address policy_, ERC20[] memory tokens_) external {}
  

Kudos for the quality of the code! It's pretty easy to explore