MethodImpl(AggressiveInlining) - 它有多激进？

Question

所以我稍微看了一下MethodImplAttribute,我遇到了MethodImplOptions.AggressiveInlining,它被描述为:

如果可能,应该内联该方法.

Oooooh,我心里想,这听起来很有趣 - 我可以假装我比编译器更聪明,强制代码只使用我的邪恶意志的力量和几个方括号,ha,ha,ha ...

因此,我启动了Visual Studio 2013,创建了一个控制台应用程序,将.NET版本设置为4.5.1并编写程序以结束所有程序(Release当然,在模式下编译它):

using System;
using System.Runtime.CompilerServices;

namespace ConsoleApplication1
{   
    public static class SoHelpful
    {
        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        public static int GetSomeValueProbablyTwelve()
        {
            return 12;
        }
        [MethodImpl(MethodImplOptions.NoInlining)]
        public static int GetSomeValueLikelyThirteen()
        {
            return 13;
        }
        public static int GetSomeValueMaybeItIsTwentyEight()
        {
            return 29;
        }
    }

    class Program
    {       
        static void Main()
        {
            int twelve = SoHelpful.GetSomeValueProbablyTwelve();
            int thirteen = SoHelpful.GetSomeValueLikelyThirteen();
            int twentyNine = SoHelpful.GetSomeValueMaybeItIsTwentyEight();
            Console.WriteLine((twelve + thirteen + twentyNine));
        }
    }
}

现在,如果我做了一个快速的ildasm,我看到了这个:

.class public abstract auto ansi sealed beforefieldinit ConsoleApplication1.SoHelpful
       extends [mscorlib]System.Object
{
  .method public hidebysig static int32  GetSomeValueProbablyTwelve() cil managed
  {
    // Code size       3 (0x3)
    .maxstack  8
    IL_0000:  ldc.i4.s   12
    IL_0002:  ret
  } // end of method SoHelpful::GetSomeValueProbablyTwelve

  .method public hidebysig static int32  GetSomeValueLikelyThirteen() cil managed noinlining
  {
    // Code size       3 (0x3)
    .maxstack  8
    IL_0000:  ldc.i4.s   13
    IL_0002:  ret
  } // end of method SoHelpful::GetSomeValueLikelyThirteen

  .method public hidebysig static int32  GetSomeValueMaybeItIsTwentyEight() cil managed
  {
    // Code size       3 (0x3)
    .maxstack  8
    IL_0000:  ldc.i4.s   29
    IL_0002:  ret
  } // end of method SoHelpful::GetSomeValueMaybeItIsTwentyEight

} // end of class ConsoleApplication1.SoHelpful

.class private auto ansi beforefieldinit ConsoleApplication1.Program
       extends [mscorlib]System.Object
{
  .method private hidebysig static void  Main() cil managed
  {
    .entrypoint
    // Code size       29 (0x1d)
    .maxstack  2
    .locals init ([0] int32 twelve,
             [1] int32 thirteen,
             [2] int32 twentyNine)
    IL_0000:  call       int32 ConsoleApplication1.SoHelpful::GetSomeValueProbablyTwelve()
    IL_0005:  stloc.0
    IL_0006:  call       int32 ConsoleApplication1.SoHelpful::GetSomeValueLikelyThirteen()
    IL_000b:  stloc.1
    IL_000c:  call       int32 ConsoleApplication1.SoHelpful::GetSomeValueMaybeItIsTwentyEight()
    IL_0011:  stloc.2
    IL_0012:  ldloc.0
    IL_0013:  ldloc.1
    IL_0014:  add
    IL_0015:  ldloc.2
    IL_0016:  add
    IL_0017:  call       void [mscorlib]System.Console::WriteLine(int32)
    IL_001c:  ret
  } // end of method Program::Main

  .method public hidebysig specialname rtspecialname 
          instance void  .ctor() cil managed
  {
    // Code size       7 (0x7)
    .maxstack  8
    IL_0000:  ldarg.0
    IL_0001:  call       instance void [mscorlib]System.Object::.ctor()
    IL_0006:  ret
  } // end of method Program::.ctor

} // end of class ConsoleApplication1.Program

有意思,所以定义了三种方法:

.method public hidebysig static int32  GetSomeValueLikelyThirteen() cil managed noinlining
.method public hidebysig static int32  GetSomeValueProbablyTwelve() cil managed
.method public hidebysig static int32  GetSomeValueMaybeItIsTwentyEight() cil managed

因此,它看起来像我的侵略性内联属性丢失了.

我可以看到noinlining的GetSomeValueLikelyThirteen,但GetSomeValueProbablyTwelve并GetSomeValueMaybeItIsTwentyEight是相同的.

那发生了什么？我想有几种可能性:

1. C#编译器已经意识到GetSomeValueProbablyTwelve只是不能内联所以不会用我愚蠢的属性白痴麻烦JIT.
2. C#编译器已经意识到GetSomeValueMaybeItIsTwentyEight可以内联,这就是为什么它在IL中是相同的GetSomeValueProbablyTwelve(所以我的归属在很大程度上是毫无意义的,在这种情况下也是愚蠢的).
3. 有一些编译设置或我必须调整以获得要识别的属性.
4. 它根本没有实现C#.
5. 我发现了一个错误
6. 还有别的

那么,有谁知道它是什么？

Answer 1

MethodImplAttributes.AggressiveInlining编译为MethodDef元数据表的ImplFlags列中的标志(ECMA-335 PartitionII§22.26).此属性的值在分区II§23.1.11中列出,但未记录(0x0100表中不存在值).AggressiveInlining

在编译过程中,编译器会从元数据中删除属性本身.如果在方法的ImplFlags中设置了0x0100位,则反汇编程序必须实现特殊逻辑以添加属性.