计算代码执行的时间

1.第一种方法
let start = CFAbsoluteTimeGetCurrent()
let data = try! Data(contentsOf: url)
let end = CFAbsoluteTimeGetCurrent()
print(end - start)

2. let start = Date()
    let data = try! Data(contentsOf: url)
    let end = Date()
    print(end.timeIntervalSince(start))