C# 'is' 结构类型检查 - 奇怪的 .NET 4.0 x86 优化行为

Question

更新:我已经提交了 bug report Microsoft Connect，请为它投票!

更新 2:Microsoft 已将错误报告标记为已修复

Posted by Microsoft on 18/08/2010 at 17:25

This bug will be fixed in afuture version of the runtime. I'mafraid it's too early to tell if thatwill be in a service pack or the nextmajor release.

自升级到 VS2010 后，“is”关键字出现了一些非常奇怪的行为。

下面的程序 (test.cs) 在 Debug模式下编译时(对于 x86)输出 True，在优化编译时输出 False(对于 x86)。在 x64 或 AnyCPU 中编译所有组合会给出预期的结果，True。

在 .NET 3.5 下编译的所有组合都给出了预期的结果，True。

我正在使用下面的批处理文件 (runtest.bat) 来编译和测试使用编译器 .NET 框架的各种组合的代码。

• 还有其他人在 .NET 4.0 下遇到过这类问题吗？
• 当运行 runtests.bat 时，其他人是否在他们的计算机上看到与我相同的行为？

• @$@#$??

• 有解决办法吗？

测试.cs

using System;

public class Program
{
    public static bool IsGuid(object item)
    {
        return item is Guid;
    } 

    public static void Main()
    {
        Console.Write(IsGuid(Guid.NewGuid()));
    }
}

运行测试.bat

@echo off

rem Usage:
rem   runtest         -- runs with csc.exe x86 .NET 4.0
rem   runtest 64      -- runs with csc.exe x64 .NET 4.0
rem   runtest v3.5    -- runs with csc.exe x86 .NET 3.5
rem   runtest v3.5 64 -- runs with csc.exe x64 .NET 3.5

set version=v4.0.30319
set platform=Framework

for %%a in (%*) do (
  if "%%a" == "64" (set platform=Framework64)
  if "%%a" == "v3.5" (set version=v3.5)
)

echo Compiler: %platform%\%version%\csc.exe
set csc="C:\Windows\Microsoft.NET\%platform%\%version%\csc.exe"

set make=%csc% /nologo /nowarn:1607 test.cs
rem CS1607: Referenced assembly targets a different processor
rem This happens if you compile for x64 using csc32, or x86 using csc64

%make% /platform:x86
test.exe
echo  =^> x86

%make% /platform:x86 /optimize
test.exe
echo  =^> x86 (Optimized)

%make% /platform:x86 /debug
test.exe
echo  =^> x86 (Debug)

%make% /platform:x86 /debug /optimize
test.exe
echo  =^> x86 (Debug + Optimized)

%make% /platform:x64
test.exe
echo  =^> x64

%make% /platform:x64 /optimize
test.exe
echo  =^> x64 (Optimized)

%make% /platform:x64 /debug
test.exe
echo  =^> x64 (Debug)

%make% /platform:x64 /debug /optimize
test.exe
echo  =^> x64 (Debug + Optimized)

%make% /platform:AnyCPU
test.exe
echo  =^> AnyCPU

%make% /platform:AnyCPU /optimize
test.exe
echo  =^> AnyCPU (Optimized)

%make% /platform:AnyCPU /debug
test.exe
echo  =^> AnyCPU (Debug)

%make% /platform:AnyCPU /debug /optimize
test.exe
echo  =^> AnyCPU (Debug + Optimized)

测试结果

运行 runtest.bat 时，我在 Win7 x64 安装上得到以下结果。

> runtest 32 v4.0
Compiler: Framework\v4.0.30319\csc.exe
False => x86
False => x86 (Optimized)
True => x86 (Debug)
False => x86 (Debug + Optimized)
True => x64
True => x64 (Optimized)
True => x64 (Debug)
True => x64 (Debug + Optimized)
True => AnyCPU
True => AnyCPU (Optimized)
True => AnyCPU (Debug)
True => AnyCPU (Debug + Optimized)

> runtest 64 v4.0
Compiler: Framework64\v4.0.30319\csc.exe
False => x86
False => x86 (Optimized)
True => x86 (Debug)
False => x86 (Debug + Optimized)
True => x64
True => x64 (Optimized)
True => x64 (Debug)
True => x64 (Debug + Optimized)
True => AnyCPU
True => AnyCPU (Optimized)
True => AnyCPU (Debug)
True => AnyCPU (Debug + Optimized)

> runtest 32 v3.5
Compiler: Framework\v3.5\csc.exe
True => x86
True => x86 (Optimized)
True => x86 (Debug)
True => x86 (Debug + Optimized)
True => x64
True => x64 (Optimized)
True => x64 (Debug)
True => x64 (Debug + Optimized)
True => AnyCPU
True => AnyCPU (Optimized)
True => AnyCPU (Debug)
True => AnyCPU (Debug + Optimized)

> runtest 64 v3.5
Compiler: Framework64\v3.5\csc.exe
True => x86
True => x86 (Optimized)
True => x86 (Debug)
True => x86 (Debug + Optimized)
True => x64
True => x64 (Optimized)
True => x64 (Debug)
True => x64 (Debug + Optimized)
True => AnyCPU
True => AnyCPU (Optimized)
True => AnyCPU (Debug)
True => AnyCPU (Debug + Optimized)

tl;dr

Answer 1

我设计了一个类似的例子，但以同样的方式失败了:

using System;
using System.Runtime.CompilerServices;

public class Program {
  static void Main() {
    Console.Write(Verify(Test.Create()));
    Console.ReadLine();
  }
  //[MethodImpl(MethodImplOptions.NoInlining)]
  static bool Verify(IDisposable item) {
    return item is Test;
  }
  struct Test : IDisposable {
    public void Dispose() { }
    public static Test Create() { return new Test(); }
  }
}

这是一个 JIT 优化器错误。不能完全指责它，它大量优化了代码。但在我看来，它在优化装箱转换时遇到了麻烦。坦率地说，这是一个非常严重的错误。

---

此错误已修复，我无法再重现它。我当前的 clrjit.dll 版本是 4.0.30319.237，日期为 2011 年 5 月 17 日。我无法确切地说出是哪个更新修复了它。我在 2011 年 8 月 5 日收到了一个安全更新，将 clrjit.dll 更新为修订版 235，日期为 4 月 12 日，那将是最早的。