Gas Optimization: Struct layout

[code423n4]

Handle

gzeon

Vulnerability details

Impact

Save storage slot by packing non-256 bit types.

./contracts/interfaces/IMigrator.sol:5

    struct MigrateDelegatorParams {
        // Address that is migrating from L1
        address l1Addr;
        // Address to use on L2
        // If null, l1Addr is used on L2
        address l2Addr;
        // Stake of l1Addr on L1
        uint256 stake;
        // Delegated stake of l1Addr on L1
        uint256 delegatedStake;
        // Fees of l1Addr on L1
        uint256 fees;
        // Delegate of l1Addr on L1
        address delegate;
    }

    struct MigrateUnbondingLocksParams {
        // Address that is migrating from L1
        address l1Addr;
        // Address to use on L2
        // If null, l1Addr is used on L2
        address l2Addr;
        // Total tokens in unbonding locks
        uint256 total;
        // IDs of unbonding locks being migrated
        uint256[] unbondingLockIds;
        // Delegate of l1Addr on L1
        address delegate;
    }

to

    struct MigrateDelegatorParams {
        // Address that is migrating from L1
        address l1Addr;
        // Address to use on L2
        // If null, l1Addr is used on L2
        address l2Addr;
        // Delegate of l1Addr on L1
        address delegate;
        // Stake of l1Addr on L1
        uint256 stake;
        // Delegated stake of l1Addr on L1
        uint256 delegatedStake;
        // Fees of l1Addr on L1
        uint256 fees;
    }

    struct MigrateUnbondingLocksParams {
        // Address that is migrating from L1
        address l1Addr;
        // Address to use on L2
        // If null, l1Addr is used on L2
        address l2Addr;
        // Delegate of l1Addr on L1
        address delegate;
        // Total tokens in unbonding locks
        uint256 total;
        // IDs of unbonding locks being migrated
        uint256[] unbondingLockIds;
    }

[yondonfu]

The suggested layout doesn't seem to support packing since the only types that are smaller than 32 bytes are addresses and two addresses cannot be packed into a single 32 byte slot.

[0xleastwood]

Agreed! address types always fill up an entire 32 byte slot.