analyze-gas-optimization

技能：analyze-gas-optimization

分析并优化 Aptos Move 合约的 Gas 效率，找出高成本操作并提出优化建议。

适用场景

触发短语：

• “优化 Gas”“降低 Gas 成本”“Gas 分析”
• “降低合约成本”“Gas 效率”
• “分析 Gas 用量”“Gas 优化”
• “降低交易成本”

使用场景：

• 主网上部署前
• 交易成本较高时
• 针对高频操作进行优化时
• 构建交易频繁的 DeFi 协议时

Gas 优化核心原则

1. 存储优化

• 尽量减少存储数据的大小
• 使用高效的数据结构
• 高效地打包结构体字段
• 移除不必要的字段

2. 计算优化

• 避免遍历大型集合
• 缓存重复计算的结果
• 尽可能使用位运算
• 尽量减少 vector 操作

3. 引用优化

• 尽可能优先借用而非移动
• 高效使用 & 和 &mut
• 避免不必要的副本

Gas 成本分析

高成本操作

1. 全局存储操作

// EXPENSIVE: Writing to global storage
move_to(account, large_struct);

// EXPENSIVE: Reading and writing
let data = borrow_global_mut<LargeData>(addr);

// EXPENSIVE: Checking existence
if (exists<Resource>(addr)) { ... }

2. Vector 操作

// EXPENSIVE: Growing vectors dynamically
vector::push_back(&mut vec, item); // O(n) worst case

// EXPENSIVE: Searching vectors
vector::contains(&vec, &item); // O(n)

// EXPENSIVE: Removing from middle
vector::remove(&mut vec, index); // O(n)

3. 字符串操作

// EXPENSIVE: String concatenation
string::append(&mut s1, s2);

// EXPENSIVE: UTF8 validation
string::utf8(bytes);

优化模式

1. 批量操作

// BAD: Multiple storage accesses
public fun update_values(account: &signer, updates: vector<Update>) {
    let i = 0;
    while (i < vector::length(&updates)) {
        let update = vector::borrow(&updates, i);
        let data = borrow_global_mut<Data>(update.address);
        data.value = update.value;
        i = i + 1;
    }
}

// GOOD: Single storage access with batch update
public fun batch_update(account: &signer, updates: vector<Update>) {
    let data = borrow_global_mut<Data>(signer::address_of(account));
    let i = 0;
    while (i < vector::length(&updates)) {
        let update = vector::borrow(&updates, i);
        // Update in memory
        update_memory_data(data, update);
        i = i + 1;
    }
}

2. 存储打包

// BAD: Wasteful storage
struct UserData has key {
    active: bool,      // 1 byte used, 7 wasted
    level: u8,         // 1 byte used, 7 wasted
    score: u64,        // 8 bytes
    timestamp: u64,    // 8 bytes
    // Total: 32 bytes (50% wasted)
}

// GOOD: Packed storage
struct UserData has key {
    // Pack small fields together
    flags: u8,         // Bits: [active, reserved...]
    level: u8,
    reserved: u16,     // Future use
    score: u64,
    timestamp: u64,
    // Total: 20 bytes (37.5% saved)
}

3. 延迟求值

// BAD: Always compute expensive value
struct Pool has key {
    total_shares: u64,
    total_assets: u64,
    // Computed on every update
    share_price: u64,
}

// GOOD: Compute only when needed
struct Pool has key {
    total_shares: u64,
    total_assets: u64,
    // Don't store computed values
}

public fun get_share_price(pool_addr: address): u64 {
    let pool = borrow_global<Pool>(pool_addr);
    if (pool.total_shares == 0) {
        INITIAL_SHARE_PRICE
    } else {
        pool.total_assets * PRECISION / pool.total_shares
    }
}

4. 事件优化

// BAD: Large event data
struct TradeEvent has drop, store {
    pool: Object<Pool>,
    trader: address,
    token_in: Object<Token>,
    token_out: Object<Token>,
    amount_in: u64,
    amount_out: u64,
    fees: u64,
    timestamp: u64,
    metadata: vector<u8>, // Large metadata
}

// GOOD: Minimal event data
struct TradeEvent has drop, store {
    pool_id: u64,        // Use ID instead of Object
    trader: address,
    amounts: u128,       // Pack amount_in and amount_out
    fees: u64,
    // Compute other data from state
}

5. 集合优化

// BAD: Linear search
public fun find_item(items: &vector<Item>, id: u64): Option<Item> {
    let i = 0;
    while (i < vector::length(items)) {
        let item = vector::borrow(items, i);
        if (item.id == id) {
            return option::some(*item)
        };
        i = i + 1;
    }
    option::none()
}

// GOOD: Use Table for O(1) lookup
struct Storage has key {
    items: Table<u64, Item>,
}

public fun find_item(storage: &Storage, id: u64): Option<Item> {
    if (table::contains(&storage.items, id)) {
        option::some(*table::borrow(&storage.items, id))
    } else {
        option::none()
    }
}

Gas 测量

1. 交易模拟

# Simulate to get gas estimate
aptos move run-function \
    --function-id 0x1::module::function \
    --args ... \
    --simulate

# Output includes:
# - gas_unit_price
# - max_gas_amount
# - gas_used

2. Gas 性能分析

#[test]
public fun test_gas_usage() {
    // Measure gas for operation
    let gas_before = gas::remaining_gas();
    expensive_operation();
    let gas_used = gas_before - gas::remaining_gas();

    // Assert reasonable gas usage
    assert!(gas_used < MAX_ACCEPTABLE_GAS, E_TOO_EXPENSIVE);
}

优化检查清单

存储检查清单

• 打包结构体字段以尽量缩小体积
• 使用合适的整数大小（u8、u16、u32、u64）
• 移除不必要的字段
• 考虑将大型数据存储在链下
• 使用事件代替存储来记录日志

计算检查清单

• 缓存重复计算的结果
• 尽量减少对集合的遍历
• 使用提前返回跳过不必要的工作
• 批量执行相似操作
• 避免冗余检查

集合检查清单

• 使用 Table/TableWithLength 进行键值查找
• 对大型集合使用 SmartTable
• 限制 vector 大小
• 对大型结果考虑使用分页
• 使用合适的数据结构

最佳实践

• 优化前后都进行性能分析
• 在单元测试中测试 Gas 用量
• 记录公开函数的 Gas 成本
• 在合约设计中考虑 Gas 成本
• 监控主网 Gas 用量

常见 Gas 优化

1. 用 Table 替代 Vector

// Before: O(n) search
struct Registry has key {
    users: vector<User>,
}

// After: O(1) lookup
struct Registry has key {
    users: Table<address, User>,
    user_list: vector<address>, // If iteration needed
}

2. 尽量减少存储读取

// Before: Multiple reads
public fun transfer(from: &signer, to: address, amount: u64) {
    assert!(get_balance(signer::address_of(from)) >= amount, E_INSUFFICIENT);
    let from_balance = borrow_global_mut<Balance>(signer::address_of(from));
    let to_balance = borrow_global_mut<Balance>(to);
    // ...
}

// After: Single read with validation
public fun transfer(from: &signer, to: address, amount: u64) {
    let from_addr = signer::address_of(from);
    let from_balance = borrow_global_mut<Balance>(from_addr);
    assert!(from_balance.value >= amount, E_INSUFFICIENT);
    // ... rest of logic
}

3. 使用位标志

// Before: Multiple bool fields (8 bytes each)
struct Settings has copy, drop, store {
    is_active: bool,
    is_paused: bool,
    is_initialized: bool,
    allows_deposits: bool,
}

// After: Single u8 (1 byte)
struct Settings has copy, drop, store {
    flags: u8, // Bit 0: active, 1: paused, 2: initialized, 3: deposits
}

const FLAG_ACTIVE: u8 = 1;        // 0b00000001
const FLAG_PAUSED: u8 = 2;        // 0b00000010
const FLAG_INITIALIZED: u8 = 4;   // 0b00000100
const FLAG_DEPOSITS: u8 = 8;      // 0b00001000

public fun is_active(settings: &Settings): bool {
    (settings.flags & FLAG_ACTIVE) != 0
}

Gas 优化报告模板

# Gas Optimization Report

## Summary

- Current average gas: X units
- Optimized average gas: Y units
- Savings: Z% reduction

## Optimizations Applied

### 1. Storage Optimization

- Packed struct fields (saved X bytes)
- Replaced vectors with tables (O(n) → O(1))
- Removed redundant fields

### 2. Computation Optimization

- Cached price calculations (saved X operations)
- Batched updates (N calls → 1 call)
- Early returns in validation

### 3. Event Optimization

- Reduced event size from X to Y bytes
- Removed redundant event fields

## Measurements

| Function | Before | After  | Savings |
| -------- | ------ | ------ | ------- |
| mint     | 50,000 | 35,000 | 30%     |
| transfer | 30,000 | 25,000 | 17%     |
| swap     | 80,000 | 60,000 | 25%     |

## Recommendations

1. Consider further optimizations for high-frequency functions
2. Monitor mainnet usage patterns
3. Set up gas usage alerts

集成说明

• 与 security-audit 配合使用，确保优化不会损害安全性
• 与 generate-tests 配合使用，验证优化后仍保持正确性
• 主网部署前，在 deploy-contracts 之前应用
• 详细模式请参阅 STORAGE_OPTIMIZATION.md

绝对禁止事项

• ❌ 绝不移除安全检查（访问控制、输入验证）来进行优化
• ❌ 绝不在未重新测试的情况下部署优化后的代码
• ❌ Gas 分析期间绝不读取 .env 或 ~/.aptos/config.yaml（其中包含私钥）

参考资料

• Aptos Gas 费用表：https://github.com/aptos-labs/aptos-core/blob/main/aptos-move/aptos-gas-schedule
• Move VM Gas 计量：https://github.com/aptos-labs/aptos-core/tree/main/aptos-move/aptos-vm
• Gas 优化模式：查看 daily-move 仓库中的实际示例