Gas Optimizations #316

code423n4 · 2022-07-19T19:57:56Z

Returns variable ignored

Summary

Not using the named return variables when a function returns wastes deployment gas

Details

There are functions that includes returns(type variableName)
and then doesn't use that variableName that had been initialised.
This consumes gas.

Github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/NameWrapper.sol#L94-L96
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/NameWrapper.sol#L744-L752

Mitigation

returns variable ignored wastes extra gas, remove them or assigned them

use of custom errors rather than revert() / require()

summary

Custom errors reduce 38 gas if the condition is met and 22 gas otherwise.
Also reduces contract size and deployment costs.

details

Since version 0.8.4 the use of custom errors rather than revert() / require() saves gas as noticed in
https://blog.soliditylang.org/2021/04/21/custom-errors/
code-423n4/2022-04-pooltogether-findings#13

github permalinks

mitigation

replace each require by an error

use of > 0 costs more than != 0 on uints

summary

using > 0 costs 6 more gas than != 0 when used on a require() statement as negative numbers are not allowed in uint values

details

uint variables can't go negative so it can be improved the gas

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/BytesUtil.sol#L44
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L245
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/ETHRegistrarController.sol#L98

mitigation

replace > 0 to != 0 for extra gas savings by each time is called the condition

duplicated require() check should be refactored

summary

duplicated require() / revert() checks should be
refactored to a modifier or function to save gas

details

Event appears twice and can be reduced

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L12
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L235

mitigation

refactor this checks to different functions to save gas

Index initialised in for loop

summary

for loops doens't need to initialize loop indexes to 0 as it is the default uint value
this saves gas

details

Multiple initializations on loop's index to 0

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/ERC1155Fuse.sol#L92
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/ERC1155Fuse.sol#L205
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/StringUtils.sol#L14
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L56
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L266
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L313
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L310
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/ETHRegistrarController.sol#L256

mitigation

Don't initialise the index

variable initialised without need

summary

The default value of the uints is 0

details

Not initializing to 0 explicitly saves gas on variable declarations

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/StringUtils.sol#L12
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/INameWrapper.sol#L16
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L264
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L50
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L63
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L181
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L200

mitigation

Don't initialise uint variables to 0

variables in a struct should be ordered by same data type to improve gas and storage

summary

the order in structs affects memory and gas usage

details

there are several structs with no order on the variable types

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L73-L83
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L104-L112

mitigation

put together all the same data types

use of counter++ in loop rather than ++counter

summary

++i costs less gas than i++, especially when it's used in for loops

details

using ++i doesn't affect the flow of regular for loops and improves gas cost

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/StringUtils.sol#L12
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L266
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L313
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/ETHRegistrarController.sol#L256

mitigation

Substitute to ++variableName when posible

use of var-- where it can be substitute by --var

summary

--i costs less gas than i--

details

i-- is used within a while loop and can be optimised to --i

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L235
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/RRUtils.sol#L241

mitigation

replace i-- to --i

unchecked index in loop

summary

unchecked operations as the ++i on for loops are cheaper than checked one.
If they are not supposed to reach the maximum value, they don't need to check for overflow

details

Gas can be optimised

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/ERC1155Fuse.sol#L92-L94
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/ERC1155Fuse.sol#L205-L220
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/StringUtils.sol#L14-L31
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/BytesUtils.sol#L266-L275
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/ETHRegistrarController.sol#L256-L267

mitigation

add unchecked ++i at the end of all the for loop where it's not expected to overflow and remove them from the for header

loop length stored in local variable for performance

summary

loop length variables assigned to a local variable improves gas usage

details

loop length is used without a uint variable

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/ethregistrar/ETHRegistrarController.sol#L256

mitigation

assign lengths to local variable for loops or when they are used several times

variable should be declared constant

summary

variables that can be constant should be constant for gas usage

details

variable is only assigned 1 so should be constant

github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/DNSSEC.sol#L7

mitigation

assigned it to constant

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

Summary

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.

Details

The extra opcodes avoided are:
CALLVALUE (2), DUP1 (3), ISZERO (3), PUSH2 (3), JUMPI (10), PUSH1 (3), DUP1 (3), REVERT(0), JUMPDEST (1), POP (2), which costs an average of about 21 gas per call to the function, in addition to the extra deployment cost

Github permalinks

https://github.com/code-423n4/2022-07-ens/blob/main/contracts/wrapper/Controllable.sol#L11-L14
https://github.com/code-423n4/2022-07-ens/blob/main/contracts/dnssec-oracle/Owned.sol#L18-L20

Mitigation

It's suggested to add payable to functions guaranteed to revert when called by normal users to improve gas costs

code423n4 added bug Something isn't working G (Gas Optimization) old-submission-method labels Jul 19, 2022

code423n4 added a commit that referenced this issue Jul 19, 2022

Deivitto issue #316

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Gas Optimizations #316

Gas Optimizations #316

code423n4 commented Jul 19, 2022

Gas Optimizations #316

Gas Optimizations #316

Comments

code423n4 commented Jul 19, 2022

Returns variable ignored

Summary

Details

Github permalinks

Mitigation

use of custom errors rather than revert() / require()

summary

details

github permalinks

mitigation

use of > 0 costs more than != 0 on uints

summary

details

github permalinks

mitigation

duplicated require() check should be refactored

summary

details

github permalinks

mitigation

Index initialised in for loop

summary

details

github permalinks

mitigation

variable initialised without need

summary

details

github permalinks

mitigation

variables in a struct should be ordered by same data type to improve gas and storage

summary

details

github permalinks

mitigation

use of counter++ in loop rather than ++counter

summary

details

github permalinks

mitigation

use of var-- where it can be substitute by --var

summary

details

github permalinks

mitigation

unchecked index in loop

summary

details

github permalinks

mitigation

loop length stored in local variable for performance

summary

details

github permalinks

mitigation

variable should be declared constant

summary

details

github permalinks

mitigation

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

Summary

Details

Github permalinks

Mitigation