gas-optimization

name	gas-optimization
description	Optimize Solidity smart contract gas costs — storage patterns, assembly, packing, and EVM-level tricks
allowed-tools	["Read","Grep"]
effort	high

When to activate

• Reducing gas costs for frequently-called functions
• Optimizing storage layout in Solidity contracts
• Implementing assembly (Yul) for performance-critical sections
• Reducing deployment costs for large contracts
• Optimizing NFT batch operations

When NOT to use

• For contracts with low transaction volume
• When readability matters more than gas savings
• For prototype/audit-phase contracts

Instructions

1. Profile gas usage. Use Hardhat gas reporter or Foundry gas snapshots. Identify hot functions.
2. Storage optimization. Pack variables (uint128 + uint128 = 1 slot). Use immutable and constant (compiled into bytecode).
3. Minimize SSTOREs. Batch state changes. Use memory for intermediate calculations. Write once, read many.
4. Calldata optimization. Use calldata over memory for function params. Shorter function selectors save gas.
5. Loop optimization. Avoid unbounded loops. Cache array length. Use unchecked arithmetic where safe.
6. Assembly (Yul). Inline assembly for critical paths. Custom error handling. Direct EVM operations.
7. External optimization. Multicall batching, permit (gasless approvals), meta-transactions.

Example

// Gas optimization: storage packing
contract Optimized {
    // BAD: 3 storage slots
    uint256 public valueA;    // slot 0
    uint8 public valueB;      // slot 1
    uint256 public valueC;    // slot 2
    
    // GOOD: 2 storage slots (packing)
    uint128 public valueA;    // slot 0 (first 128 bits)
    uint128 public valueC;    // slot 0 (last 128 bits)
    uint8 public valueB;      // slot 1
    
    // BEST: use constants and immutables (0 gas to read)
    uint256 public constant MAX_SUPPLY = 10000;
    address public immutable owner;
}

// Unchecked arithmetic (safe when overflow is impossible)
for (uint i; i < arr.length;) {
    sum += arr[i];
    unchecked { ++i; } // saves ~60 gas per iteration
}