Description:
Functions that read state variables more than once can catch it into a local variable for repeated reads saving gas by converting expensive SLOADs into much cheaper MLOADs.
Recommendation:
It's best to catch the state variables into memory when read more than once.
[NAZ-G2] In require(), Use != 0 Instead of > 0 With Uint Values
Description:
(This is only relevant if you are using the default solidity checked arithmetic). i++ involves checked arithmetic, which is not required. This is because the value of i is always strictly less than length <= 2256 - 1. Therefore, the theoretical maximum value of i to enter the for-loop body is `2256 - 2. This means that thei++` in the for loop can never overflow. Regardless, the overflow checks are performed by the compiler.
Unfortunately, the Solidity optimizer is not smart enough to detect this and remove the checks. One can manually do this by:
for (uint i = 0; i < length; ) {
// do something that doesn't change the value of i
unchecked {
++i;
}
}
Recommendation:
Consider doing the increment in the for loop post condition in an unchecked block.
Description:
One can save gas by caching the array length (in stack) and using that set variable in the loop. Replace state variable reads and writes within loops with local variable reads and writes. This is done by assigning state variable values to new local variables, reading and/or writing the local variables in a loop, then after the loop assigning any changed local variables to their equivalent state variables.
Recommendation:
Simply do something like so before the for loop: uint length = variable.length. Then add length in place of variable.length in the for loop.
Description:
You can cut out 10 opcodes in the creation-time EVM bytecode if you declare a constructor payable. Making the constructor payable eliminates the need for an initial check of msg.value == 0 and saves 21 gas on deployment with no security risks.
Description:
To save some gas the use of custom errors leads to cheaper deploy time cost and run time cost. The run time cost is only relevant when the revert condition is met.
Recommendation:
Use Custom Errors instead of strings.
Description:
Contracts most called functions could simply save gas by function ordering via Method ID. Calling a function at runtime will be cheaper if the function is positioned earlier in the order (has a relatively lower Method ID) because 22 gas are added to the cost of a function for every position that came before it. The caller can save on gas if you prioritize most called functions. One could use This tool to help find alternative function names with lower Method IDs while keeping the original name intact.
Recommendation:
Find a lower method ID name for the most called functions for example mostCalled() vs. mostCalled_41q() is cheaper by 44 gas.
Description:
Using newer compiler versions and the optimizer gives gas
optimizations and additional safety checks for free!
The advantages of versions =0.8.*= over =<0.8.0= are:
Safemath by default from =0.8.0= (can be more gas efficient than /some/
library based safemath).
Low level inliner from =0.8.2=, leads to cheaper runtime gas.
Especially relevant when the contract has small functions. For
example, OpenZeppelin libraries typically have a lot of small
helper functions and if they are not inlined, they cost an
additional 20 to 40 gas because of 2 extra =jump= instructions and
additional stack operations needed for function calls.
Optimizer improvements in packed structs: Before =0.8.3=, storing
packed structs, in some cases used an additional storage read
operation. After EIP-2929, if the slot was already cold, this
means unnecessary stack operations and extra deploy time costs.
However, if the slot was already warm, this means additional cost
of =100= gas alongside the same unnecessary stack operations and
extra deploy time costs.
Custom errors from =0.8.4=, leads to cheaper deploy time cost and
run time cost. Note: the run time cost is only relevant when the
revert condition is met. In short, replace revert strings by
custom errors.
Recommendation:
Upgrade to at least 0.8.4 for the additional benefits.
[NAZ-G1] Same State Variable Read More Than Once
Context:
frxETHMinter.sol#L95-L96 (withholdRatio)Description: Functions that read state variables more than once can catch it into a local variable for repeated reads saving gas by converting expensive
SLOADs into much cheaperMLOADs.Recommendation: It's best to catch the state variables into memory when read more than once.
[NAZ-G2] In
require(), Use!= 0Instead of> 0With Uint ValuesContext:
frxETHMinter.sol#L79,frxETHMinter.sol#L126Description: In a require, when checking a uint, using
!= 0instead of> 0saves 6 gas. This will jump over or avoid an extraISZEROopcode.Recommendation: Use
!= 0instead of> 0with uint values but only inrequire()statements.[NAZ-G] Use
++indexinstead ofindex++to increment a loop counterContext:
ERC20PermitPermissionedMint.sol#L84Description: Due to reduced stack operations, using
++indexsaves 5 gas per iteration.Recommendation: Use
++indexto increment a loop counter.[NAZ-G3] The Increment In For Loop Post Condition Can Be Made Unchecked
Context:
ERC20PermitPermissionedMint.sol#L84,frxETHMinter.sol#L129,OperatorRegistry.sol#L63,OperatorRegistry.sol#L84,OperatorRegistry.sol#L114Description: (This is only relevant if you are using the default solidity checked arithmetic).
i++involves checked arithmetic, which is not required. This is because the value ofiis always strictly less than length <= 2256 - 1. Therefore, the theoretical maximum value ofito enter the for-loop body is `2256 - 2. This means that thei++` in the for loop can never overflow. Regardless, the overflow checks are performed by the compiler.Unfortunately, the Solidity optimizer is not smart enough to detect this and remove the checks. One can manually do this by:
Recommendation: Consider doing the increment in the for loop post condition in an unchecked block.
[NAZ-G4] Catching The Array Length Prior To Loop
Context:
ERC20PermitPermissionedMint.sol#L84,OperatorRegistry.sol#L114Description: One can save gas by caching the array length (in stack) and using that set variable in the loop. Replace state variable reads and writes within loops with local variable reads and writes. This is done by assigning state variable values to new local variables, reading and/or writing the local variables in a loop, then after the loop assigning any changed local variables to their equivalent state variables.
Recommendation: Simply do something like so before the for loop:
uint length = variable.length. Then addlengthin place ofvariable.lengthin the for loop.[NAZ-G5] Setting The Constructor To Payable
Context:
All ContractsDescription: You can cut out 10 opcodes in the creation-time EVM bytecode if you declare a constructor payable. Making the constructor payable eliminates the need for an initial check of
msg.value == 0and saves 21 gas on deployment with no security risks.Recommendation: Set the constructor to payable.
[NAZ-G6] Use of Custom Errors Instead of String
Context:
All ContractsDescription: To save some gas the use of custom errors leads to cheaper deploy time cost and run time cost. The run time cost is only relevant when the revert condition is met.
Recommendation: Use Custom Errors instead of strings.
[NAZ-G7] Function Ordering via Method ID
Context:
All ContractsDescription: Contracts most called functions could simply save gas by function ordering via Method ID. Calling a function at runtime will be cheaper if the function is positioned earlier in the order (has a relatively lower Method ID) because 22 gas are added to the cost of a function for every position that came before it. The caller can save on gas if you prioritize most called functions. One could use
This toolto help find alternative function names with lower Method IDs while keeping the original name intact.Recommendation: Find a lower method ID name for the most called functions for example
mostCalled()vs.mostCalled_41q()is cheaper by 44 gas.[NAZ-G8] Upgrade To At Least 0.8.4
Context:
All ContractsDescription: Using newer compiler versions and the optimizer gives gas optimizations and additional safety checks for free!
The advantages of versions =0.8.*= over =<0.8.0= are:
Low level inlinerfrom =0.8.2=, leads to cheaper runtime gas. Especially relevant when the contract has small functions. For example, OpenZeppelin libraries typically have a lot of small helper functions and if they are not inlined, they cost an additional 20 to 40 gas because of 2 extra =jump= instructions and additional stack operations needed for function calls.Optimizer improvements in packed structs: Before =0.8.3=, storing packed structs, in some cases used an additional storage read operation. AfterEIP-2929, if the slot was already cold, this means unnecessary stack operations and extra deploy time costs. However, if the slot was already warm, this means additional cost of =100= gas alongside the same unnecessary stack operations and extra deploy time costs.Custom errorsfrom =0.8.4=, leads to cheaper deploy time cost and run time cost. Note: the run time cost is only relevant when the revert condition is met. In short, replace revert strings by custom errors.Recommendation: Upgrade to at least 0.8.4 for the additional benefits.