Gas Optimizations #167
Labels
Comments
|
Missing the immutables, this will save at most 3k gas |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Table of Contents:
> 0is less efficient than!= 0for unsigned integers (with proof)>=is cheaper than>(and<=cheaper than<)require()statements that use&&saves gas++icosts less gas compared toi++ori += 1(same for--ivsi--ori -= 1)abi.encode()is less efficient thanabi.encodePacked()payableCheap Contract Deployment Through Clones
See
@audittag:There's a way to save a significant amount of gas on deployment using Clones: https://www.youtube.com/watch?v=3Mw-pMmJ7TA .
This is a solution that was adopted, as an example, by Porter Finance. They realized that deploying using clones was 10x cheaper:
I suggest applying a similar pattern.
SafeMath is not needed when using Solidity version 0.8+
Solidity version 0.8+ already implements overflow and underflow checks by default.
Using the SafeMath library from OpenZeppelin (which is more gas expensive than the 0.8+ overflow checks) is therefore redundant.
I suggest using the built-in checks instead of SafeMath and remove SafeMath here:
Boolean comparisons
Comparing to a constant (
trueorfalse) is a bit more expensive than directly checking the returned boolean value.I suggest using
if(directValue)instead ofif(directValue == true)andif(!directValue)instead ofif(directValue == false)here:> 0is less efficient than!= 0for unsigned integers (with proof)!= 0costs less gas compared to> 0for unsigned integers inrequirestatements with the optimizer enabled (6 gas)Proof: While it may seem that
> 0is cheaper than!=, this is only true without the optimizer enabled and outside a require statement. If you enable the optimizer at 10k AND you're in arequirestatement, this will save gas. You can see this tweet for more proofs: https://twitter.com/gzeon/status/1485428085885640706I suggest changing
> 0with!= 0here:Also, please enable the Optimizer.
>=is cheaper than>(and<=cheaper than<)Strict inequalities (
>) are more expensive than non-strict ones (>=). This is due to some supplementary checks (ISZERO, 3 gas). This also holds true between<=and<.Consider replacing strict inequalities with non-strict ones to save some gas here:
Splitting
require()statements that use&&saves gasIf you're using the Optimizer at 200, instead of using the
&&operator in a single require statement to check multiple conditions, I suggest using multiple require statements with 1 condition per require statement:Please, note that this might not hold true at a higher number of runs for the Optimizer (10k). However, it indeed is true at 200.
Use shift right/left instead of division/multiplication if possible
While the
DIV/MULopcode uses 5 gas, theSHR/SHLopcode 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.>> 1instead of/ 2>> 2instead of/ 4<< 3instead of* 8Affected code:
An array's length should be cached to save gas in for-loops
Reading array length at each iteration of the loop consumes more gas than necessary.
In the best case scenario (length read on a memory variable), caching the array length in the stack saves around 3 gas per iteration.
In the worst case scenario (external calls at each iteration, like at
VE3DRewardPool.sol:148orVE3DRewardPool.sol:281), the amount of gas wasted can be massive.Here, I suggest storing the array's length in a variable before the for-loop, and use this new variable instead:
++icosts less gas compared toi++ori += 1(same for--ivsi--ori -= 1)Pre-increments and pre-decrements are cheaper.
For a
uint256 ivariable, the following is true with the Optimizer enabled at 10k:Increment:
i += 1is the most expensive formi++costs 6 gas less thani += 1++icosts 5 gas less thani++(11 gas less thani += 1)Decrement:
i -= 1is the most expensive formi--costs 11 gas less thani -= 1--icosts 5 gas less thani--(16 gas less thani -= 1)Note that post-increments (or post-decrements) return the old value before incrementing or decrementing, hence the name post-increment:
However, pre-increments (or pre-decrements) return the new value:
In the pre-increment case, the compiler has to create a temporary variable (when used) for returning
1instead of2.Affected code:
Consider using pre-increments and pre-decrements where they are relevant (meaning: not where post-increments/decrements logic are relevant).
Increments/decrements can be unchecked in for-loops
In Solidity 0.8+, there's a default overflow check on unsigned integers. It's possible to uncheck this in for-loops and save some gas at each iteration, but at the cost of some code readability, as this uncheck cannot be made inline.
ethereum/solidity#10695
Affected code:
The change would be:
The same can be applied with decrements (which should use
breakwheni == 0).The risk of overflow is non-existant for
uint256here.abi.encode()is less efficient thanabi.encodePacked()Changing
abi.encodefunction toabi.encodePackedcan save gas since theabi.encodefunction pads extra null bytes at the end of the call data, which is unnecessary. Also, in general,abi.encodePackedis more gas-efficient (see Solidity-Encode-Gas-Comparison).Consider using
abi.encodePacked()here:Public functions to external
An external call cost is less expensive than one of a public function.
The following functions could be set external to save gas and improve code quality (extracted from Slither).
No need to explicitly initialize variables with default values
If a variable is not set/initialized, it is assumed to have the default value (
0foruint,falseforbool,address(0)for address...). Explicitly initializing it with its default value is an anti-pattern and wastes gas.As an example:
for (uint256 i = 0; i < numIterations; ++i) {should be replaced withfor (uint256 i; i < numIterations; ++i) {Affected code:
I suggest removing explicit initializations for default values.
Variable that should be constant
This variable is never edited:
Consider marking it as constant.
Reduce the size of error messages (Long revert Strings)
Shortening revert strings to fit in 32 bytes will decrease deployment time gas and will decrease runtime gas when the revert condition is met.
Revert strings that are longer than 32 bytes require at least one additional mstore, along with additional overhead for computing memory offset, etc.
Revert strings > 32 bytes:
I suggest shortening the revert strings to fit in 32 bytes.
Use Custom Errors instead of Revert Strings to save Gas
Solidity 0.8.4 introduced custom errors. They are more gas efficient than revert strings, when it comes to deploy cost as well as runtime cost when the revert condition is met. Use custom errors instead of revert strings for gas savings.
Custom errors from Solidity 0.8.4 are cheaper than revert strings (cheaper deployment cost and runtime cost when the revert condition is met)
Source: https://blog.soliditylang.org/2021/04/21/custom-errors/:
Custom errors are defined using the
errorstatement, which can be used inside and outside of contracts (including interfaces and libraries).I suggest replacing all revert strings with custom errors in the solution. Affected files:
Functions guaranteed to revert when called by normal users can be marked
payableIf a function modifier such as
onlyOwneris used, the function will revert if a normal user tries to pay the function. Marking the function aspayablewill lower the gas cost for legitimate callers because the compiler will not include checks for whether a payment was provided.The text was updated successfully, but these errors were encountered: