c# - 运行 C# 代码仅在发布版本中失败(可能是因为 JIT 编译器优化)

Question

下面的代码在调试版本中运行成功，但在发布版本中显示“开始”后停滞不前。只要我研究过它，在 JIT 编译器中优化编译该方法似乎需要花费很多时间。

它为什么停滞不前，解决方法是什么？

我检查了 visual studio 2017 社区版。

已编辑:
它仅在 CPU=AnyCPU(删除首选 32 位)或 CPU=x64 时失败。

我刚刚安装了 .Net Framework 4.7.1。 (目标框架是 .Net Framework 4。)
即使安装了.Net Framework 4.7.1，问题依然存在。

将useLegacyJit设置到注册表后，就解决了。 (去掉useLegacyJit，问题又来了。)好像是RyuJIT的bug。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApp1
{
    class Program
    {
        static void Main(string[] args) {
            Console.WriteLine("start");
            Calculation calc = new Calculation();
            calc.Run();
            Console.WriteLine("end");
        }
    }

    class Calculation
    {
        double[] V0 = new double[1];
        double[] V1 = new double[1];
        double[] V2 = new double[1];
        double[] V3 = new double[1];
        double[] V4 = new double[1];
        double[] V5 = new double[1];
        double[] V6 = new double[1];
        double[] V7 = new double[1];
        double[] V8 = new double[1];
        double[] V9 = new double[1];
        double[] V10 = new double[1];
        double[] V11 = new double[1];
        double[] V12 = new double[1];
        double[] V13 = new double[1];
        double[] V14 = new double[1];
        double[] V15 = new double[1];
        double[] V16 = new double[1];
        double[] V17 = new double[1];
        double[] V18 = new double[1];
        double[] V19 = new double[1];
        double[] V20 = new double[1];
        double[] V21 = new double[1];
        double[] V22 = new double[1];
        double[] V23 = new double[1];
        double[] V24 = new double[1];
        double[] V25 = new double[1];
        double[] V26 = new double[1];
        double[] V27 = new double[1];
        double[] V28 = new double[1];
        double[] V29 = new double[1];
        double[] V30 = new double[1];
        double[] V31 = new double[1];
        double[] V32 = new double[1];
        double[] V33 = new double[1];
        double[] V34 = new double[1];
        double[] V35 = new double[1];
        double[] V36 = new double[1];
        double[] V37 = new double[1];
        double[] V38 = new double[1];
        double[] V39 = new double[1];
        double[] V40 = new double[1];
        double[] V41 = new double[1];
        double[] V42 = new double[1];
        double[] V43 = new double[1];
        double[] V44 = new double[1];
        double[] V45 = new double[1];
        double[] V46 = new double[1];
        double[] V47 = new double[1];
        double[] V48 = new double[1];
        double[] V49 = new double[1];

        public void Run()
        {
        for (int x = 0; x < 1; x++){V0[x] = 0.0;}
        for (int x = 0; x < 1; x++){V1[x] = 0.0;}
        for (int x = 0; x < 1; x++){V2[x] = 0.0;}
        for (int x = 0; x < 1; x++){V3[x] = 0.0;}
        for (int x = 0; x < 1; x++){V4[x] = 0.0;}
        for (int x = 0; x < 1; x++){V5[x] = 0.0;}
        for (int x = 0; x < 1; x++){V6[x] = 0.0;}
        for (int x = 0; x < 1; x++){V7[x] = 0.0;}
        for (int x = 0; x < 1; x++){V8[x] = 0.0;}
        for (int x = 0; x < 1; x++){V9[x] = 0.0;}
        for (int x = 0; x < 1; x++){V10[x] = 0.0;}
        for (int x = 0; x < 1; x++){V11[x] = 0.0;}
        for (int x = 0; x < 1; x++){V12[x] = 0.0;}
        for (int x = 0; x < 1; x++){V13[x] = 0.0;}
        for (int x = 0; x < 1; x++){V14[x] = 0.0;}
        for (int x = 0; x < 1; x++){V15[x] = 0.0;}
        for (int x = 0; x < 1; x++){V16[x] = 0.0;}
        for (int x = 0; x < 1; x++){V17[x] = 0.0;}
        for (int x = 0; x < 1; x++){V18[x] = 0.0;}
        for (int x = 0; x < 1; x++){V19[x] = 0.0;}
        for (int x = 0; x < 1; x++){V20[x] = 0.0;}
        for (int x = 0; x < 1; x++){V21[x] = 0.0;}
        for (int x = 0; x < 1; x++){V22[x] = 0.0;}
        for (int x = 0; x < 1; x++){V23[x] = 0.0;}
        for (int x = 0; x < 1; x++){V24[x] = 0.0;}
        for (int x = 0; x < 1; x++){V25[x] = 0.0;}
        for (int x = 0; x < 1; x++){V26[x] = 0.0;}
        for (int x = 0; x < 1; x++){V27[x] = 0.0;}
        for (int x = 0; x < 1; x++){V28[x] = 0.0;}
        for (int x = 0; x < 1; x++){V29[x] = 0.0;}
        for (int x = 0; x < 1; x++){V30[x] = 0.0;}
        for (int x = 0; x < 1; x++){V31[x] = 0.0;}
        for (int x = 0; x < 1; x++){V32[x] = 0.0;}
        for (int x = 0; x < 1; x++){V33[x] = 0.0;}
        for (int x = 0; x < 1; x++){V34[x] = 0.0;}
        for (int x = 0; x < 1; x++){V35[x] = 0.0;}
        for (int x = 0; x < 1; x++){V36[x] = 0.0;}
        for (int x = 0; x < 1; x++){V37[x] = 0.0;}
        for (int x = 0; x < 1; x++){V38[x] = 0.0;}
        for (int x = 0; x < 1; x++){V39[x] = 0.0;}
        for (int x = 0; x < 1; x++){V40[x] = 0.0;}
        for (int x = 0; x < 1; x++){V41[x] = 0.0;}
        for (int x = 0; x < 1; x++){V42[x] = 0.0;}
        for (int x = 0; x < 1; x++){V43[x] = 0.0;}
        for (int x = 0; x < 1; x++){V44[x] = 0.0;}
        for (int x = 0; x < 1; x++){V45[x] = 0.0;}
        for (int x = 0; x < 1; x++){V46[x] = 0.0;}
        for (int x = 0; x < 1; x++){V47[x] = 0.0;}
        for (int x = 0; x < 1; x++){V48[x] = 0.0;}
        for (int x = 0; x < 1; x++){V49[x] = 0.0;}
        }

    }
}

Answer 1

这确实似乎是 RyuJIT 的问题，可以通过暂时禁用它来验证:

Set-ItemProperty -Path HKLM:\Software\Microsoft\.NETFramework -名称 useLegacyJit -Type DWord -Value 1

但是，如果我们构建 coreclr v2.0.5，跟踪实际问题会更加复杂一些。 (最新稳定版)，并使用 /v 详细标志和 COMPlus_JitDump=* 设置环境变量运行它，一段时间后它开始打印出很多这样的日志:

  AX2: $f5b != $1c0 ==> select([$277]store($dae, $1c0, $276), $f5b) ==> select($dae, $f5b).
  AX2: $f5b != $1c0 ==> select([$277]store($dae, $1c0, $276), $f5b) ==> select($dae, $f5b).
  AX2: $f5b != $1c0 ==> select([$279]store($dbd, $1c0, $278), $f5b) ==> select($dbd, $f5b).
  AX2: $f5b != $1c0 ==> select([$277]store($dae, $1c0, $276), $f5b) ==> select($dae, $f5b).
  AX2: $f5b != $1c0 ==> select([$277]store($dae, $1c0, $276), $f5b) ==> select($dae, $f5b).
  AX2: $f5b != $1c0 ==> select([$279]store($dbd, $1c0, $278), $f5b) ==> select($dbd, $f5b).
  AX2: $f5b != $1c0 ==> select([$27b]store($e0f, $1c0, $27a), $f5b) ==> select($e0f, $f5b).
  AX2: $f5b != $1c0 ==> select([$27d]store($e21, $1c0, $27c), $f5b) ==> select($e21, $f5b).
  AX2: $f5b != $1c0 ==> select([$27f]store($e32, $1c0, $27e), $f5b) ==> select($e32, $f5b).

打印log的方法可以引用https://github.com/dotnet/coreclr/blob/v2.0.5/src/jit/valuenum.cpp#L1377

这个问题很可能是由于 budget 变量溢出或由于某种原因没有减少引起的。不幸的是，没有太多时间进一步研究它，但对该方法进行了一些更改 here ，当我尝试使用 master 运行示例时核心 CLR 的构建问题似乎已经解决。

根据 Roadmap ，它将于 2018 年第一季度发布。不过，我不确定它何时会包含在实际的 .NET Framework 版本中。

作为解决方法，也许您可​​以尝试将循环重构为它们自己的方法:

public void RunLoop(double[] arr)
{
    for (int x = 0; x < 1; x++)
    {
        arr[x] = 0.0;
        // etc...
    }
}

这似乎也解决了这个问题(如果在您的实际代码中这样做有意义的话)。