Julia JIT 编译、@time 和分配数量

我刚刚开始评估 Julia（版本 0.6.0），并且测试了如何调整大小！和尺寸提示！可能会影响性能。我使用@time宏。

文档说“#运行一次进行 JIT 编译”，但如果我们检查分配数量，运行一次似乎还不够。

module Test

function test(x::Int64; hint::Bool=false, resize::Bool=false)
    A::Array{Int64} = []
    n::Int64 = x
    if resize
        resize!(A, n)
        for i in 1:n
            A[i]=i
        end
    else
        if hint sizehint!(A, n) end
        for i in 1:n
            push!(A, i)
        end
    end
    A[end]
end

end

import Test

#Test.test(1);  # (1)
#Test.test(1, hint=true);  # (2)
#Test.test(1, resize=true);  # (3)
@time Test.test(10_000_000)
@time Test.test(10_000_000, hint=true)
@time Test.test(10_000_000, resize=true)

对于不同的“JIT 预编译”调用，我得到了不同的结果：

上面代码的结果：

    0.494120 seconds (11.02 k allocations: 129.706 MiB, 22.77% gc time)
    0.141155 seconds (3.43 k allocations: 76.537 MiB, 41.94% gc time)
    0.068319 seconds (9 allocations: 76.294 MiB, 76.99% gc time)

如果 (1) 未注释：

    0.520939 seconds (112 allocations: 129.007 MiB, 21.79% gc time)
    0.140845 seconds (3.43 k allocations: 76.537 MiB, 42.35% gc time)
    0.068741 seconds (9 allocations: 76.294 MiB, 77.55% gc time)

如果 (1) && (2) 未注释：

    0.586479 seconds (112 allocations: 129.007 MiB, 19.28% gc time)
    0.117521 seconds (9 allocations: 76.294 MiB, 50.56% gc time)
    0.068275 seconds (9 allocations: 76.294 MiB, 76.84% gc time)

如果 (1) && (2) && (3) 未注释：

    0.509668 seconds (112 allocations: 129.007 MiB, 21.61% gc time)
    0.112276 seconds (9 allocations: 76.294 MiB, 50.58% gc time)
    0.065123 seconds (9 allocations: 76.294 MiB, 76.34% gc time)

如果 (3) 未注释：

    0.497802 seconds (240 allocations: 129.016 MiB, 22.53% gc time)
    0.117035 seconds (11 allocations: 76.294 MiB, 52.56% gc time)
    0.067170 seconds (11 allocations: 76.294 MiB, 76.93% gc time)

我的问题：

1. 这是错误吗？
2. 如果不是 bug 那么是否有可能调用完整的编译？

不，医生here https://docs.julialang.org/en/latest/manual/performance-tips/#Measure-performance-with-%5B@time%5D(@ref)-and-pay-attention-to-memory-allocation-1清楚地表明这是因为你正在跑步@time在全球范围内：

julia> function foo()
          Test.test(1)  # warm-up
          @time Test.test(10_000_000)
          @time Test.test(10_000_000, hint=true)
          @time Test.test(10_000_000, resize=true)
       end
foo (generic function with 1 method)

julia> foo()
  0.401256 seconds (26 allocations: 129.001 MiB, 47.38% gc time)
  0.185094 seconds (6 allocations: 76.294 MiB, 37.13% gc time)
  0.034649 seconds (6 allocations: 76.294 MiB, 30.99% gc time)