在CLR数组边界检查消除？ [英] Array Bounds Check Elimination in the CLR?

问题描述

我最近读<一个href=\"http://blogs.msdn.com/b/clr$c$cgeneration/archive/2009/08/13/array-bounds-check-elimination-in-the-clr.aspx\"相对=nofollow>本文由Dave Detlefs 他在presents少数情况下CLR执行数组边界检查消除。我决定把这个测​​试自己，所以我做了以下内容：

I was recently reading this article by Dave Detlefs in which he presents a few cases where the CLR performs array bounds check elimination. I decided to test this myself, so I did the following:

• 开业的Visual Studio 2010 SP1旗舰版


• 创建类型控制台应用程序的一个新的C＃项目（针对默认.NET 4客户端配置文件）



• 增加了以下code（所有的子方法是直接从文章所）：

• Opened Visual Studio 2010 Ultimate SP1
• Created a new C# project of type Console Application (targeting .NET 4 Client Profile by default)

• Added the following code (all sub-methods are taken directly from the article):

class Program {
    static void Main(string[] args) {
        int[] array = new int[30];
        Test_SimpleAscend(array);
        Test_SimpleRedundant(array, 3);

        foreach (int i in array) {
            Console.WriteLine(i);
        }
    }

    static void Test_SimpleAscend(int[] a) {
        for (int i = 0; i < a.Length; i++)
            a[i] = i;
    }

    static void Test_SimpleRedundant(int[] a, int i) {
        int k = a[i];
        k = k + a[i];
    }
}

切换到发布模式;验证了优化code，在构建选项被选中

Switched to Release mode; verified that "Optimize Code" is checked in the Build options

因此​​，这里是一个为在dissassembly [我] =我;在Test_SimpleAscend：

So here's the dissassembly for a[i] = i; in Test_SimpleAscend:

                a[i] = i;
00000024  mov         eax,dword ptr [ebp-4] 
00000027  mov         edx,dword ptr [ebp-8] 
0000002a  cmp         eax,dword ptr [edx+4] 
0000002d  jb          00000034 
0000002f  call        64FD6E08 
00000034  mov         ecx,dword ptr [ebp-4] 
00000037  mov         dword ptr [edx+eax*4+8],ecx 

在CMP / JB /呼叫边界检查，竟迫使通话将被执行，则会引发IndexOutOfRangeException。

The cmp/jb/call is bounds checking, actually forcing the call to be executed throws an IndexOutOfRangeException.

对于所有阵列同样的事情的访问，包括Test_SimpleRedundant冗余访问。那么，有什么错我的测试方法，或者CLR实际上并没有消除边界检查？我希望我是错的，如果是这样，我想知道我怎么才能真正得到数组边界检查消除。

Same thing for all array accesses, including the redundant access in Test_SimpleRedundant. So is there something wrong with my testing methodology, or the CLR doesn't actually eliminate bounds checking? I hope I'm wrong and if so I'd like to know how I can really get array bounds checking elimination.

推荐答案

多亏了科迪灰色评论，我已经成功地回答我的问题：

Thanks to a comment by Cody Gray, I've managed to answer my own question:

在默认情况下，JIT优化调试时被禁用。为了解决这个问题，可以到调试 - >选项和设置 - >调试 - >常规，并取消这两个启用仅我的code和燮$ P模块负载$ PSS JIT优化。

By default, JIT Optimizations are disabled when debugging. To fix this, one can go to Debug -> Options and Settings -> Debugging -> General, and uncheck both "Enable Just My Code" and "Suppress JIT Optimization on module load".

另请参见 http://msdn.microsoft.com/en-us/库/ ms241594.aspx

启用优化，边界检查被移除像广告。

With optimization enabled, the bounds check are removed as advertised.

在这里我要离开这个以作记录。

I'll leave this here for documentation purposes.

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