Gas Optimizations #211
Comments
2. Multiple accesses of a mapping/array should use a local variable cacheI seem to be getting between 20 and 40 gas savings in caching, I can't quite explain why this would happen for calldata. Will give it 20 gas per instance per calldata * 2 = 40 for Storage * 5 = 3. Caching Storage into MemoryFirst time saves 94 gas (100 - 6 - SLOAD + MLOAD), each subsequent is 97 (100 - 3 - SLOAD) 94+94+97+94 5 + 6 + 7Around 300 gas like other submissions Upgrade pragmaSkipping external calls will save about 100 gas per instance, however no instances were listed, giving it 100 gas In this case I don't think 1 is applicable, same for the last function as while it does save gas it's a trade-off All in all way better than average report, highly recommend the sponsor to follow the advice 1019 gas saved |
Overview
Table of Contents:
<array>.lengthshould not be looked up in every loop of afor-loop++icosts less gas compared toi++ori += 1(same for--ivsi--ori -= 1)payable1. Use EIP-1167 minimal proxies for 10x cheaper contract instantiation
When new contracts have to be instantiated frequently, it's much cheaper for it to be done via minimal proxies. The only downside is that they rely on
delegatecall()calls for every function, which adds an overhead of ~800 gas, but this is multiple orders of magnitude less than the amount saved during deployment.Due to the following note, this optimization seem relevant for
DepositReceiver:Affected code:
2. Multiple accesses of a mapping/array should use a local variable cache
Caching a mapping's value in a local
storageorcalldatavariable when the value is accessed multiple times saves ~42 gas per access due to not having to perform the same offset calculation every time.Affected code:
refundTokens[i](calldata)wrapped[axelarToken]andunwrapped[xc20Token](storage)3. Caching storage values in memory
The code can be optimized by minimizing the number of SLOADs (here, notably on the
gatewaystate variable).SLOADs are expensive (100 gas after the 1st one) compared to MLOADs/MSTOREs (3 gas each). Storage values read multiple times should instead be cached in memory the first time (costing 1 SLOAD) and then read from this cache to avoid multiple SLOADs.
4. Duplicated conditions should be refactored to a modifier or function to save deployment costs
5.
<array>.lengthshould not be looked up in every loop of afor-loopReading 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), the amount of gas wasted can be massive.
Here, consider storing the array's length in a variable before the for-loop, and use this new variable instead:
6.
++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).
7. 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
Consider wrapping with an
uncheckedblock here (around 25 gas saved per instance):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.8. Upgrade pragma
Using newer compiler versions and the optimizer give gas optimizations. Also, additional safety checks are available for free.
The advantages here are:
Consider upgrading from
0.8.9to at least0.8.10in the solution.9. (Not recommended, but true) 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: