Gas Optimizations #71

code423n4 · 2022-09-08T16:14:27Z

Using storage instead of memory for struct/array saves gas

When fetching data from a storage location, assigning the data to a memory variable causes all fields of the struct/array to be read from storage, which incurs a Gcoldsload (2100 gas) for each field of the struct/array. If the fields are read from the new memory variable, they incur an additional MLOAD rather than a cheap stack read. Instead of declearing the variable with the memory keyword, declaring the variable with the storage keyword and caching any fields that need to be re-read in stack variables, will be much cheaper, only incuring the Gcoldsload for the fields actually read. The only time it makes sense to read the whole struct/array into a memory variable, is if the full struct/array is being returned by the function, is being passed to a function that requires memory, or if the array/struct is being read from another memory array/struct

Using calldata instead of memory for read-only arguments in external functions

When a function with a memory array is called externally, the abi.decode() step has to use a for-loop to copy each index of the calldata to the memoryindex. Each iteration of this for-loop costs at least 60 gas (i.e. 60 * <mem_array>.length). Using calldata directly, obliviates the need for such a loop in the contract code and runtime execution. Structs have the same overhead as an array of length one

When arguments are read-only on external functions, the data location should be calldata:

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L116
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L192
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L347
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L355
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L363
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/proxy/UUPS.sol#L55

Using cache to contain "array.length"

-storage arrays incur a Gwarmaccess (100 gas)
-memory arrays use MLOAD (3 gas)
-calldata arrays use CALLDATALOAD (3 gas)

Caching the length of the array changes it to a DUP (3 gas), and gets rid of the extra DUP needed to store the stack offset:

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L138
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L139
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/proxy/ERC1967Upgrade.sol#L61
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/utils/Address.sol#L50

Multiple accesses of a mapping/array should use a local variable cache

The instances below point to the second+ access of a value inside a mapping/array, within a function. Caching a mapping's value in a local storage variable when the value is accessed multiple times, saves ~42 gas per access due to not having to recalculate the key's keccak256 hash (Gkeccak256 - 30 gas) and that calculation's associated stack operations. Caching an array's struct avoids recalculating the array offsets into memory.

The result of external function calls should be cached rather than re-calling the function

The instances below point to the second call of the function within a single function.

internal functions only called once can be inlined to save gas

Not inlining costs 20 to 40 gas because of two extra JUMP instructions and additional stack operations needed for function calls.

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/Token.sol#L71
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/Token.sol#L130

It costs more gas to initialize variables with their default value than letting the default value be applied

If a variable is not set/initialized, it is assumed to have the default value (0 for uint, false for bool, address(0) for address...). Explicitly initializing it with its default value is an anti-pattern and wastes gas.

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/treasury/Treasury.sol#L162
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L119
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L133
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L189
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/metadata/MetadataRenderer.sol#L229

Make a decent gas savings by saving a storage variable's reference instead of repeatedly fetching it

Declare a storage type variable and use it instead of repeatedly fetching the reference in a map or an array.
Instead of repeatedly calling someMap[someIndex], save its reference like this: SomeStruct storage someStruct = someMap[someIndex] and use it.

File: Token.sol
+112: Founder storage _tokenRecipient = tokenRecipient[baseTokenId];
-113: tokenRecipient[baseTokenId] = newFounder;
+113: _tokenRecipient = newFounder;

File: Token.sol
+131: Founder storage _tokenRecipient = tokenRecipient[_tokenId];
-132: while (tokenRecipient[_tokenId].wallet != address(0)) ++_tokenId;
+132: while (_tokenRecipient.wallet != address(0)) ++_tokenId;

File: Token.sol
+181: Founder storage _tokenRecipient = tokenRecipient[baseTokenId];
-182: if (tokenRecipient[baseTokenId].wallet == address(0)) {
+182: if (_tokenRecipient.wallet == address(0)) {
-186: } else if (block.timestamp < tokenRecipient[baseTokenId].vestExpiry) {
+186: } else if (block.timestamp < _tokenRecipient.vestExpiry) {
-188: _mint(tokenRecipient[baseTokenId].wallet, _tokenId);
+188: _mint(_tokenRecipient.wallet, _tokenId);

keccak256() should only need to be called on a specific string literal once

It should be saved to an immutable variable, and the variable used instead. If the hash is being used as a part of a function selector, the cast to bytes should also only be done once

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L142

Using bools for storage incurs overhead

(https://github.com/OpenZeppelin/openzeppelin-contracts/blob/58f635312aa21f947cae5f8578638a85aa2519f5/contracts/security/ReentrancyGuard.sol#L23-L27)

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/auction/Auction.sol#L136
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/auction/Auction.sol#L349

11 ">=" and "<=" COSTS LESS GAS THAN ">" and "<"

This action saves 3 gas - https://gist.github.com/IllIllI000/3dc79d25acccfa16dee4e83ffdc6ffde
Add one to the amount and use ">=" instead of ">".

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/governance/governor/Governor.sol#L261
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/token/Token.sol#L88

"++x" and "--x" costs less gas than "x++" and "x--".

Saves 6 gas per instance:

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L207
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L222

Use shift right/left instead of division/multiplication if possible

While the DIV / MUL opcode uses 5 gas, the SHR / SHL opcode only uses 3 gas. Furthermore, beware that Solidity's division operation also includes a division-by-0 prevention which is bypassed using shifting. Eventually, overflow checks are never performed for shift operations as they are done for arithmetic operations. Instead, the result is always truncated.

-Use >> 1 instead of / 2
-Use >> 2 instead of / 4
-Use << 3 instead of * 8

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L95

Arithmetics: Unchecking arithmetic operations that cannot underflow/overflow

From Solidity v0.8 onwards, all arithmetic operations come with implicit overflow and underflow checks. In some instances, an overflow/underflow is impossible, such as:

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L75
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L112
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L213
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721Votes.sol#L228

Storage variables should be declared immutable when possible

If a storage variable is assigned only in the constructor, it should be declared as immutable. This would help to reduce gas costs as calls to immutable variables are much cheaper than regular state variables.

https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721.sol#L19
https://github.com/code-423n4/2022-09-nouns-builder/blob/7e9fddbbacdd7d7812e912a369cfd862ee67dc03/src/lib/token/ERC721.sol#L22

Functions guaranteed to revert when called by normal users can be marked payable

If a function modifier such as onlyOwner is used, the function will revert if a normal user tries to pay the function. Marking the function as payable will lower the gas cost for legitimate callers because the compiler will not include checks for whether a payment was provided.

GalloDaSballo · 2022-09-26T20:34:43Z

200 from Storage
500 from Memory -> Calldata
100 from caching length

400 by avoiding SLOADs

100 misc

1300

code423n4 added bug Something isn't working G (Gas Optimization) labels Sep 8, 2022

code423n4 added a commit that referenced this issue Sep 8, 2022

SnowMan issue #71

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SnowMan data for issue #71

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Report for issue #71 updated by SnowMan

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Report for issue #71 updated by SnowMan

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Report for issue #71 updated by SnowMan

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Gas Optimizations #71

Gas Optimizations #71

code423n4 commented Sep 8, 2022 •

edited

GalloDaSballo commented Sep 26, 2022

Gas Optimizations #71

Gas Optimizations #71

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code423n4 commented Sep 8, 2022 • edited

GalloDaSballo commented Sep 26, 2022

code423n4 commented Sep 8, 2022 •

edited