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C＃编译与尾递归优化？

分类: 技术问答 • 2022-04-30 08:34:13
问题描述：

基于stackoverflow的丰富的财富，我一直在关于是否尾递归优化是专门为c＃代码做的答案。

Based on the rich wealth of stackoverflow, I've been getting on and off answers on whether the tail recursive optimization is done to specifically c# code. A few of the questions appeared to talk about


  1. 在发布的.net新版本中推测优化

  2. 将应用程序构建为x64bit应用程序以实现优化

  3. 在Visual Studio中从调试版本切换到发布版本以实现优化

  4. 根本没有优化，微软社区声称他们不会为安全问题执行尾递归优化（真的不理解这一点）。


  1. Speculation of the optimization in newer versions of .net that were being released
  2. Building application as a x64bit application to achieve the optimization
  3. Switching from a debug build to a release build in Visual Studio to achieve the optimization
  4. No optimization at all and that the microsoft community had claimed that they wouldn't do tail recursive optimization for "security issues" (didn't really understand this one)
  5. It happens by random

因此C＃4.0（Visual Studio 2013/2015）如何确保尾递归优化if

So as of C# 4.0 (Visual Studio 2013/2015) how does one ensure the tail recursive optimization if one can ensure it at all?

答

有可以支持尾调用优化的不同级别。 JIT真正负责许多优化发生。 C＃编译器本身甚至不做方法内联，这是JIT编译器的责任。 C＃编译器可以使用 Tailcall IL操作码指定一个调用作为尾调用，但我相信没有版本的C＃编译器这样做。 JIT编译器允许在看到合适的时候进行尾调用优化。特别是，我相信只有64位的JIT这样做。本博文介绍了一些方案其中JIT64不能使用尾调用优化。我确定标准可能会改变，因为他们正在改写JIT编译器，代号为RyuJIT。

There are different levels at which the tail call optimization can be supported. The JIT is really responsible for a lot of the optimizations that happen. The C# compiler itself doesn't even do method inlining, that is the JIT compiler's responsibility. The C# compiler could use the Tailcall IL opcode designating a call as a tail call, however I believe no version of C# compiler does this. The JIT compiler is permitted to make tail call optimizations whenever it see fit. In particular, I believe only the 64-bit JIT does this. This blog post outlines a number of scenarios in which JIT64 cannot use tail call optimization. I'm sure the criteria may be subject to change since they are working on a rewrite of the JIT compiler, codenamed RyuJIT.

如果你想要一个简单的程序示例可以使用TCO尝试：

If you want a short example of program that can use TCO try this:

class Program
{
    static void Main(string[] args)
    {
        Test(1);
    }

    private static void Test(int i)
    {
        Console.WriteLine(i);
        Test(i + 1);
    }
}

设置项目以构建Release / x64 w / o喜欢32位），并在没有连接调试器的情况下启动。程序将永远运行。如果我不做所有这些事情，那么我在20947附近得到一个stackoverflow异常。

Set the project to build Release/x64 (or AnyCPU w/o prefer 32-bit) and start without the debugger attached. The program will run forever. If I do not do all of those things, then I get a stackoverflow exception around 20947.

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