Gas Optimizations

[code423n4]

Unnecessary equals boolean

Boolean variables can be checked within conditionals directly without the use of equality operators to true/false.

Code instances:

    GNS.sol, 717: require(legacySubgraphExists == true, "GNS: Subgraph does not exist");
    GNS.sol, 818: require(_isPublished(subgraphData) == true, "GNS: Must be active");
    GNS.sol, 506: require(subgraphData.disabled == true, "GNS: Must be disabled first");
    Staking.sol, 202: return msg.sender == _indexer || isOperator(msg.sender, _indexer) == true;
    ServiceRegistry.sol, 27: return msg.sender == _indexer || staking().isOperator(msg.sender, _indexer) == true;
    GNS.sol, 804: return _subgraphData.subgraphDeploymentID != 0 && _subgraphData.disabled == false;
    L1GraphTokenGateway.sol, 214: extraData.length == 0 || callhookWhitelist[msg.sender] == true,
    Staking.sol, 970: require(assetHolders[msg.sender] == true, "!assetHolder");

Unused state variables

Unused state variables are gas consuming at deployment (since they are located in storage) and are
a bad code practice. Removing those variables will decrease deployment gas cost and improve code quality.
This is a full list of all the unused storage variables we found in your code base.

Code instances:

    DisputeManagerStorage.sol, fishermanRewardPercentage
    L2ArbitrumMessenger.sol, ARB_SYS_ADDRESS
    EpochManagerStorage.sol, epochLength
    GNSStorage.sol, subgraphNFT
    RewardsManagerStorage.sol, tokenSupplySnapshot
    GraphGovernanceStorage.sol, proposals

Unnecessary array boundaries check when loading an array element twice

There are places in the code (especially in for-each loops) that loads the same array element more than once.
In such cases, only one array boundaries check should take place, and the rest are unnecessary.
Therefore, this array element should be cached in a local variable and then be loaded
again using this local variable, skipping the redundant second array boundaries check:

Code instance:

    Staking.sol.closeAllocationMany - double load of _requests[i]

Caching array length can save gas

Caching the array length is more gas efficient.
This is because access to a local variable in solidity is more efficient than query storage / calldata / memory.
We recommend to change from:

for (uint256 i=0; i<array.length; i++) { ... }

to:

uint len = array.length
for (uint256 i=0; i<len; i++) { ... }

Code instances:

    Multicall.sol, data, 19
    Base58Encoder.sol, source, 18
    Base58Encoder.sol, indices, 53
    Staking.sol, _requests, 924
    RewardsManager.sol, _subgraphDeploymentID, 161
    AllocationExchange.sol, _vouchers, 136
    Base58Encoder.sol, input, 45
    Staking.sol, _allocationID, 1050

Prefix increments are cheaper than postfix increments

Prefix increments are cheaper than postfix increments.
Further more, using unchecked {++x} is even more gas efficient, and the gas saving accumulates every iteration and can make a real change
There is no risk of overflow caused by increamenting the iteration index in for loops (the ++i in for (uint256 i = 0; i < numIterations; ++i)).
But increments perform overflow checks that are not necessary in this case.
These functions use not using prefix increments (++x) or not using the unchecked keyword:

Code instances:

    change to prefix increment and unchecked: RewardsManager.sol, i, 161
    change to prefix increment and unchecked: Base58Encoder.sol, i, 53
    change to prefix increment and unchecked: Staking.sol, i, 924
    change to prefix increment and unchecked: Base58Encoder.sol, i, 37
    change to prefix increment and unchecked: AllocationExchange.sol, i, 136
    change to prefix increment and unchecked: Multicall.sol, i, 19
    change to prefix increment and unchecked: Base58Encoder.sol, i, 45
    change to prefix increment and unchecked: Staking.sol, i, 1050
    just change to unchecked: Base58Encoder.sol, i, 18

Unnecessary index init

In for loops you initialize the index to start from 0, but it already initialized to 0 in default and this assignment cost gas.
It is more clear and gas efficient to declare without assigning 0 and will have the same meaning:

Code instances:

    AllocationExchange.sol, 136
    Staking.sol, 924
    Base58Encoder.sol, 37
    Base58Encoder.sol, 18
    Multicall.sol, 19
    Staking.sol, 1050
    Base58Encoder.sol, 45
    Base58Encoder.sol, 53
    RewardsManager.sol, 161

Storage double reading. Could save SLOAD

Reading a storage variable is gas costly (SLOAD). In cases of multiple read of a storage variable in the same scope, caching the first read (i.e saving as a local variable) can save gas and decrease the
overall gas uses. The following is a list of functions and the storage variables that you read twice:

Code instances:

    Staking.sol: MAX_PPM is read twice in _setDelegationParameters
    Staking.sol: MAX_PPM is read twice in _stake
    GNS.sol: MAX_PPM is read twice in _setOwnerTaxPercentage
    LibFixedMath.sol: FIXED_1 is read twice in ln

Unnecessary default assignment

Unnecessary default assignments, you can just declare and it will save gas and have the same meaning.

Code instance:

    LibFixedMath.sol (L#41) : int256 private constant EXP_MAX_VAL = 0;

Rearrange state variables

You can change the order of the storage variables to decrease memory uses.

Code instances:

In Pausable.sol,rearranging the storage fields can optimize to: 3 slots from: 4 slots.
The new order of types (you choose the actual variables):
1. uint256
2. uint256
3. address
4. bool
5. bool

In BancorFormula.sol,rearranging the storage fields can optimize to: 9 slots from: 10 slots.
The new order of types (you choose the actual variables):
1. uint256
2. uint256
3. uint256
4. uint256
5. uint256
6. uint256
7. uint256
8. uint256
9. uint32
10. uint16
11. uint8
12. uint8

In DisputeManagerStorage.sol,rearranging the storage fields can optimize to: 3 slots from: 4 slots.
The new order of types (you choose the actual variables):
1. bytes32
2. uint256
3. address
4. uint32
5. uint32
6. uint32

Use bytes32 instead of string to save gas whenever possible

Use bytes32 instead of string to save gas whenever possible.
String is a dynamic data structure and therefore is more gas consuming then bytes32.

Code instance:

    SubgraphNFT.sol (L153), string memory _subgraphURI = metadata > 0 ? HexStrings.toString(metadata) : "";

Short the following require messages

The following require messages are of length more than 32 and we think are short enough to short
them into exactly 32 characters such that it will be placed in one slot of memory and the require
function will cost less gas.
The list:

Code instances:

    Solidity file: Curation.sol, In line 195, Require message length to shorten: 35, The message: Caller must be the staking contract
    Solidity file: RewardsManager.sol, In line 95, Require message length to shorten: 35, The message: Issuance rate under minimum allowed
    Solidity file: GRTWithdrawHelper.sol, In line 63, Require message length to shorten: 33, The message: GRTWithdrawHelper: !returnAddress
    Solidity file: GNS.sol, In line 194, Require message length to shorten: 33, The message: Owner tax must be MAX_PPM or less
    Solidity file: GraphProxy.sol, In line 141, Require message length to shorten: 33, The message: Implementation must be a contract
    Solidity file: EthereumDIDRegistry.sol, In line 60, Require message length to shorten: 33, The message: Signer must be the identity owner

Use != 0 instead of > 0

Using != 0 is slightly cheaper than > 0. (see code-423n4/2021-12-maple-findings#75 for similar issue)

Code instances:

    BancorFormula.sol, 194: change '_reserveRatio > 0' to '_reserveRatio != 0'
    BancorFormula.sol, 289: change '_toReserveRatio > 0' to '_toReserveRatio != 0'
    LibFixedMath.sol, 404: change 'b > 0' to 'b != 0'
    BancorFormula.sol, 234: change '_supply > 0' to '_supply != 0'
    Staking.sol, 1119: change '_tokens > 0' to '_tokens != 0'
    BancorFormula.sol, 285: change '_fromReserveBalance > 0' to '_fromReserveBalance != 0'

Unnecessary cast

Code instances:

    DisputeType DisputeManager.sol._slashIndexer - unnecessary casting DisputeType(_disputeType)
    uint256 Staking.sol._collectCurationFees - unnecessary casting uint256(_curationPercentage)
    uint256 Staking.sol._collectTax - unnecessary casting uint256(_percentage)

Use unchecked to save gas for certain additive calculations that cannot overflow

You can use unchecked in the following calculations since there is no risk to overflow:

Code instances:

    EthereumDIDRegistry.sol (L#235) - emit DIDAttributeChanged( identity, name, value, block.timestamp + validity, changed[identity] );
    EthereumDIDRegistry.sol (L#118) - delegates[identity][keccak256(abi.encode(delegateType))][delegate] = block.timestamp + validity;
    EthereumDIDRegistry.sol (L#126) - block.timestamp + validity, changed[identity] );

Consider inline the following functions to save gas

You can inline the following functions instead of writing a specific function to save gas.
(see https://github.com/code-423n4/2021-11-nested-findings/issues/167 for a similar issue.)

Code instances

    LibFixedMath.sol, toInteger, { return f / FIXED_1; }
    MathUtils.sol, min, { return x <= y ? x : y; }
    MathUtils.sol, diffOrZero, { return (x > y) ? x.sub(y) : 0; }
    DisputeManager.sol, _isDisputeInConflict, { return _dispute.relatedDisputeID != 0; }

Inline one time use functions

The following functions are used exactly once. Therefore you can inline them and save gas and improve code clearness.

Code instances:

    BancorFormula.sol, floorLog2
    RewardsManager.sol, _pow
    Stakes.sol, tokensWithdrawable
    GNS.sol, _chargeOwnerTax
    GraphTokenUpgradeable.sol, _getChainID
    Base58Encoder.sol, reverse
    Base58Encoder.sol, toAlphabet
    GNS.sol, _nextAccountSeqID
    Stakes.sol, allocate
    DisputeManager.sol, _slashIndexer
    DisputeManager.sol, _onlyArbitrator
    DisputeManager.sol, _getSlashingPercentageForDisputeType
    GraphUpgradeable.sol, _implementation
    BancorFormula.sol, findPositionInMaxExpArray
    SubgraphNFT.sol, _setMinter
    Staking.sol, _getEffectiveAllocation
    GraphProxyStorage.sol, _pendingImplementation
    Staking.sol, _undelegate
    GNS.sol, _nextSubgraphID
    Base58Encoder.sol, truncate
    Curation.sol, _tokensToSignal
    HexStrings.sol, toHexString
    DisputeManager.sol, _toUint8
    Staking.sol, _collectCurationFees
    Staking.sol, _collectDelegationIndexingRewards
    Managed.sol, _onlyController
    BancorFormula.sol, generalExp
    Stakes.sol, unlockTokens
    Staking.sol, _distributeRewards
    Stakes.sol, tokensUsed
    Stakes.sol, tokensAvailableWithDelegation
    L1GraphTokenGateway.sol, parseOutboundData
    BancorFormula.sol, optimalExp
    DisputeManager.sol, _createIndexingDisputeWithAllocation
    SubgraphNFT.sol, _setTokenDescriptor
    Staking.sol, _collectDelegationQueryRewards
    Managed.sol, _notPartialPaused
    Managed.sol, _notPaused
    DisputeManager.sol, _getChainID
    L2GraphTokenGateway.sol, parseOutboundData
    BancorFormula.sol, optimalLog
    Rebates.sol, unclaimedFees
    GraphProxyStorage.sol, _implementation
    BancorFormula.sol, generalLog
    Stakes.sol, release
    GNS.sol, _burnNFT
    GraphTokenUpgradeable.sol, _initialize
    RewardsManager.sol, _setIssuanceRate
    GraphToken.sol, _getChainID
    Managed.sol, _onlyGovernor
    DisputeManager.sol, _recoverAttestationSigner

Change if -> revert pattern to require

Change if -> revert pattern to 'require' to save gas and improve code quality,
if (some_condition) {
revert(revert_message)
}

to: require(!some_condition, revert_message)

In the following locations:

Code instances:

    LibFixedMath.sol, 140
    LibFixedMath.sol, 153
    LibFixedMath.sol, 59
    LibFixedMath.sol, 386
    LibFixedMath.sol, 156
    LibFixedMath.sol, 88
    LibFixedMath.sol, 396
    LibFixedMath.sol, 405
    LibFixedMath.sol, 100
    LibFixedMath.sol, 267
    LibFixedMath.sol, 137
    LibFixedMath.sol, 393

Upgrade pragma to at least 0.8.4

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

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

    1. Safemath by default from 0.8.0 (can be more gas efficient than library based safemath.)
    2. 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.
    3. 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.
    4. 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.

Code instances:

    Managed.sol
    TokenUtils.sol
    IServiceRegistry.sol
    IRewardsManager.sol
    ISubgraphNFT.sol

Do not cache msg.sender

We recommend not to cache msg.sender since calling it is 2 gas while reading a variable is more.

Code instances:

    https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/discovery/GNS.sol#L325
    https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/disputes/DisputeManager.sol#L403
    https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/staking/Staking.sol#L825
    https://github.com/code-423n4/2022-10-thegraph/tree/main/contracts/discovery/GNS.sol#L445