WTF Gas Optimization

Solidity gas optimization techniques, verified with Foundry.

总结 Solidity 智能合约省 gas 技巧，并使用 Foundry 验证。

Lead by @0xKaso

Outline

1. use constant and immutable

2. use calldata over memory

3. use Bitmap

4. use unchecked

5. use uint256 over uint8

6. use custom error over require/assert

7. use local variable over storage

8. use clone over new/create2 to deploy contracts

9. packing storage slots

10. use ++i as better increment

11. use uint in reentrancy guard

12. use < over <=

13. optimized selector/method id

14. selector/method-id order matters

15. use shorter string in require()

16. use short circuit in logic operation || or &&

17. delete variables to get gas refund

18. do not initialize state variables with default values

19. swap 2 variables in 1 line with destructuring assignment

20. set constructor to payable to save gas

21. use bytes32 for short string

22. use fixed-size array over dynamic array

23. use event to store data when possible

24. use mapping over array when possible

1. use constant and immutable

Code | 文章

Testing

forge test --contracts 01_Constant/Constant.t.sol --gas-report

Gas report

Function Name	Gas Cost
varConstant	161 ✅
varImmutable	161 ✅
variable	2261

2. use calldata over memory

Code | 文章

Testing

forge test --contracts 02_CalldataAndMemory/CalldataAndMemory.T.sol --gas-report

Gas report

Function Name	Gas Cost
writeByCalldata	67905 ✅
writeByMemory	68456

3. use Bitmap

Code | 文章

Testing

forge test --contracts 03_Bitmap/Bitmap.T.sol --gas-report

Gas report

Function Name	Gas Cost
setDataWithBitmap	22366 ✅
setDataWithBoolArray	35729

4. use unchecked

Code | 文章

Testing

forge test --contracts 04_unchecked/Unchecked.T.sol --gas-report

Gas report

Function Name	Gas Cost
forNormal	1910309
forUnckecked	570287 ✅

5. use uint256 over uint8

Code | 文章

Testing

forge test --contracts 05_Uint/Uint.T.sol --gas-report

Gas report

Function Name	Gas Cost
read Uint8	2301
read Uint32	2301
read Uint256	2261 ✅
set Uint8	22234
set Uint128	22234
set Uint256	22238
UseUint8	53,427
UseUint32	53,895
UseUint256	42,950 ✅

6. use custom error over require/assert

Code | 文章

Testing

forge test --contracts 06_Error/Error.T.sol --gas-report

Gas report

Error Name	Gas Cost
Assert	180
Require	268
Revert	164 ✅

7. use local variable over storage

Code | 文章

Testing

forge test --contracts 07_LocalData/LocalData.T.sol --gas-report

Gas report

Data Type	Gas Cost
localData	1902339 ✅
storageData	4022155

8. use clone over new/create2 to deploy contract

Code | 文章

Testing

forge test --contracts 08_Clone/Clone.T.sol --gas-report

Gas report

Create Type	Gas Cost
clone	41493 ✅
create2	93031
new	79515

9. packing storage slots

Code | 文章

Testing

forge test --contracts 09_Packing/Packing.T.sol --gas-report

Gas report

Create Type	Gas Cost
normal	133521
packing	111351 ✅

10. use ++i as better increment

Code | 文章

forge test --contracts 10_Increment/Increment.T.sol --gas-report

Gas report

Increment	Gas Cost
i += 1	204
i = i +1	204
i++	198
++i	193 ✅

11. use Uint in Reentrancy Guard

Code | 文章

Testing

forge test --contracts 11_ReentrancyGuard/ReentrancyGuard.T.sol --gas-report

Gas report

ReentrancyGuard	Gas Cost	tips
Bool	27757
Uint01	27604	0 to non-zero -> 20000 gas
Uint12	13908 ✅	non-zero to non-zero -> 2900 gas

12. use < over <=

Code | 文章

Testing

forge test --contracts 12_LessThan/LessThan.t.sol --gas-report

Gas report

Operator	Gas Cost
<=	250
<	247 ✅

13 optimized selector

Code | 文章

Testing

forge test --contracts 13_MethodName/MethodName.t.sol --gas-report

Gas report

Operator	Gas Cost
regular selector 0xf8a8fd6d	5285
optimized selector 0x000073eb	5265 ✅

14 selector order

Code | 文章

Testing

forge test --contracts 14_MethodIdSort/MethodIdSort.t.sol --gas-report

Gas report

Operator	Gas Cost
test1 0x0dbe671f	164
test2 0x66e41cb7	142
test3 0x0a8e8e01	120
test_y2K 0x000073eb	98 ✅

15 shorter string in require()

Code

Testing

forge test --contracts 15_RequireString/RequireString.t.sol --gas-report

Gas report

Operator	Gas Cost
longString	2578
shortString	2347 ✅

16. short circuit in logic operation

Code

Testing

forge test --contracts 16_ShortCircuit/ShortCircuit.t.sol --gas-report

Gas report

Operator	Gas Cost
normal	191,282
shortCircuit	120 ✅

17. delete variables to get gas refund

Code

Testing

forge test --contracts 17_DeleteVar/DeleteVar.t.sol --gas-report

Gas report

Operator	Gas Cost
update	22,238
updateDefault	2360 ✅
updateDelete	2316 ✅

18. do not initialize state variables with default values

Code

Testing

forge test --contracts 18_InitDefault/InitDefault.t.sol --gas-report

Gas report

Operator	Gas Cost
testDefault	67,148 ✅
testInitDefault	69,376

19. swap 2 variables in 1 line with destructuring assignment

Code

Testing

forge test --contracts 19_SwapVars/SwapVars.t.sol --gas-report

Gas report

This technique will not save gas, but it makes your code look better :p

Operator	Gas Cost
swap	282
desSwap	282 ✅

20. set constructor to payable to save gas

You can cut out 10 opcodes in the creation-time EVM bytecode if you declare a constructor payable. The following opcodes are cut out:

CALLVALUE
DUP1
ISZERO
PUSH2
JUMPI
PUSH1
DUP1
REVERT
JUMPDEST
POP

In Solidity, this chunk of assembly would mean the following:

if(msg.value != 0) revert();

Code

Testing

forge test --contracts 20_PayableConstructor/PayableConstructor.t.sol --gas-report

Gas report

Operator	Gas Cost
default	67,171
payable constructor	67,102 ✅

21. use bytes32 for short string

Code

Testing

forge test --contracts 21_Bytes32String/Bytes32String.t.sol --gas-report

Gas report

Operator	Gas Cost
setBytes32	22,222 ✅
setString	22,682

22. use fixed-size array over dynamic array

Code

Testing

forge test --contracts 22_FixedSize/FixedSize.t.sol --gas-report

Gas report

Operator	Gas Cost
set dynamic-length array	2,224,770 gas ✅
set fixed-length array	2,182,608

23. use `event` to store data when possible

Code

Testing

forge test --contracts 23_Event/Event.t.sol --gas-report

Gas report

Operator	Gas Cost
useVar	22,216
useEvent	1,189 ✅

24. use `mapping` over `array` when possible

Code

Testing

forge test --contracts 24_MappingArray/MappingArray.t.sol --gas-report

Gas report

Operator	Gas Cost
Mapping get	451 ✅
Mapping insert	22,385 ✅
Mapping remove	305 ✅
Array get	710
Array insert	44,442
Array remove	748