G-01: Use a more recent version of solidity
Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value
Use a solidity version of at least 0.8.12 to get string.concat() instead of abi.encodePacked(,)
Use a solidity version of at least 0.8.13 to get the ability to use using for with a list of free functions
G-04 Using private rather than public for constants saves gas
If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table.
G-05 Use custom errors rather than revert()/require() strings to save deployment gas
Custom errors are available from solidity version 0.8.4. The instances below match or exceed that version.
G-06 Comparison operators
In the EVM, there is no opcode for >= or <=. When using greater than or equal, two operations are performed: > and =.
Using strict comparison operators hence saves gas.
G-01: Use a more recent version of solidity Use a solidity version of at least 0.8.10 to have external calls skip contract existence checks if the external call has a return value Use a solidity version of at least 0.8.12 to get string.concat() instead of abi.encodePacked(,)
Use a solidity version of at least 0.8.13 to get the ability to use using for with a list of free functions
Instances include: https://github.com/yieldprotocol/vault-interfaces/blob/cf12f06c3ac9a64e2ebfd4989b042f376ab72e48/src/DataTypes.sol#L2 https://github.com/yieldprotocol/vault-interfaces/blob/cf12f06c3ac9a64e2ebfd4989b042f376ab72e48/src/ICauldron.sol#L2 all contracts in https://github.com/yieldprotocol/vault-interfaces/tree/cf12f06c3ac9a64e2ebfd4989b042f376ab72e48/src all contracts in https://github.com/yieldprotocol/yield-utils-v2/tree/33b4f19bffa871d19e3cef9bfe43b8f5c3eef068/contracts
G-02 += costs more gas than = + for state variables (also -= vs = - )
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L204
G-03 Usage of uints/ints smaller than 32 bytes (256 bits) incurs overhead
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L44-L48 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L96-L100 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L217 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L241 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L582 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L584
G-04 Using private rather than public for constants saves gas If needed, the value can be read from the verified contract source code. Savings are due to the compiler not having to create non-payable getter functions for deployment calldata, and not adding another entry to the method ID table.
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L59 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L60
G-05 Use custom errors rather than revert()/require() strings to save deployment gas Custom errors are available from solidity version 0.8.4. The instances below match or exceed that version.
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L102 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L103 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L106 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L108 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L189 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L200 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L255 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L256 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L300 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L313 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L328 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L358 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L365 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L395 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L416 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L439
G-06 Comparison operators In the EVM, there is no opcode for >= or <=. When using greater than or equal, two operations are performed: > and =. Using strict comparison operators hence saves gas.
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L105 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L108 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L256 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L313 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L365 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L438
Mitigation: Replace <= with <, and >= with >. Do not forget to increment/decrement the compared variable.
G-07 Using > 0 costs more gas than != 0 when used on a uint in a require() statement
Instances include: https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L255 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L300 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L358 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L393 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L398 https://github.com/code-423n4/2022-07-yield/blob/6ab092b8c10e4dabb470918ae15c6451c861655f/contracts/Witch.sol#L416