为我解释maxstack指令

Question

我在调试模式下编译了一些测试代码，并用ILSpy反映了生成的程序集。这是我收到的IL：

.class private auto ansi beforefieldinit ArrayListBoxAndUnBox.Program 
extends [mscorlib]System.Object 
    { 
// Nested Types 
.class nested public auto ansi beforefieldinit Point 
    extends [mscorlib]System.Object 
{ 
    // Fields 
    .field public int32 x 
    .field public int32 y 

    // Methods 
    .method public hidebysig specialname rtspecialname 
     instance void .ctor() cil managed 
    { 
     // Method begins at RVA 0x209f 
     // 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 Point::.ctor 

} // end of class Point 


// Methods 
.method private hidebysig static 
    void Main (
     string[] args 
    ) cil managed 
{ 
    // Method begins at RVA 0x2050 
    // Code size 59 (0x3b) 
    .maxstack 2 
    .entrypoint 
    .locals init (
     [0] class [mscorlib]System.Collections.ArrayList list, 
     [1] int32 i, 
     [2] class ArrayListBoxAndUnBox.Program/Point p 
    ) 

    IL_0000: nop 
    IL_0001: newobj instance void [mscorlib]System.Collections.ArrayList::.ctor() 
    IL_0006: stloc.0 
    IL_0007: ldloc.0 
    IL_0008: ldc.i4.1 
    IL_0009: box [mscorlib]System.Int32 
    IL_000e: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object) 
    IL_0013: pop 
    IL_0014: ldloc.0 
    IL_0015: ldc.i4.0 
    IL_0016: callvirt instance object [mscorlib]System.Collections.ArrayList::get_Item(int32) 
    IL_001b: unbox.any [mscorlib]System.Int32 
    IL_0020: stloc.1 
    IL_0021: ldloc.0 
    IL_0022: newobj instance void ArrayListBoxAndUnBox.Program/Point::.ctor() 
    IL_0027: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object) 
    IL_002c: pop 
    IL_002d: ldloc.0 
    IL_002e: ldc.i4.1 
    IL_002f: callvirt instance object [mscorlib]System.Collections.ArrayList::get_Item(int32) 
    IL_0034: castclass ArrayListBoxAndUnBox.Program/Point 
    IL_0039: stloc.2 
    IL_003a: ret 
} // end of method Program::Main 

.method public hidebysig specialname rtspecialname 
    instance void .ctor() cil managed 
{ 
    // Method begins at RVA 0x2097 
    // 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 ArrayListBoxAndUnBox.Program 

我看到.maxstack被设置为两个，但是当我通过手工代码我有时会计算堆栈上3个元素。为什么？我是一个糟糕的IL-stack-counter，还是这背后有意义？

在我的世界中，IL_0014上的第一个ldloc.0永远不会被删除，但也许只是我没有得到callvirt如何get_Item的作品。当我到达IL_0014时，我必须参考堆栈文件中的列表，然后在IL_0015上，当0被推入评估堆栈时，程序违反了.maxstack。

我是新手，所以肯定有些东西是不对的。也许我的计数是正确的，我对.maxstack的理解是错误的，或者也许是相反的。有人能告诉我，如果我对.maxstack的理解是错误的，那么.maxstack会在运行时显示栈上的最大元素。或者如果我的计数错误？添加是否删除对列表实例的引用？编辑： 这里是我如何计数。计数是在IL代码跑完之后：

IL_0000: 0 on stack 
IL_0001: 1 on stack (the reference to array list) 
IL_0006: 0 on stack 
IL_0007: 1 on stack (the reference to arraylist) 
IL_0008: 2 on stack (reference to arraylist and int 1) 
IL_0009: 2 on stack (refernce to arraylist and reference to object that wrap 1) 
IL_000e: 2 on stack (reference to arraylist and index to the added boxed int object) 
IL_0013: 1 on stack (reference to arraylist) 
IL_0014: 2 on stack (reference to arraylist and reference to arraylist) 
IL_0015: 3 on stack (reference to arraylist and reference to arraylist and int 0) 

我还没有计算其余的，因为我知道我得到了错误的东西。

谢谢

Answer 1

很难看到你出错的地方。堆栈深度注释左边，指令执行后：

0 IL_0000: nop 
1 IL_0001: newobj instance void [mscorlib]System.Collections.ArrayList::.ctor() 
0 IL_0006: stloc.0 
1 IL_0007: ldloc.0 
2 IL_0008: ldc.i4.1 
2 IL_0009: box [mscorlib]System.Int32 
1 IL_000e: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object) 
0 IL_0013: pop 
1 IL_0014: ldloc.0 
2 IL_0015: ldc.i4.0 
1 IL_0016: callvirt instance object [mscorlib]System.Collections.ArrayList::get_Item(int32) 
1 IL_001b: unbox.any [mscorlib]System.Int32 
0 IL_0020: stloc.1 
1 IL_0021: ldloc.0 
2 IL_0022: newobj instance void ArrayListBoxAndUnBox.Program/Point::.ctor() 
1 IL_0027: callvirt instance int32 [mscorlib]System.Collections.ArrayList::Add(object) 
0 IL_002c: pop 
1 IL_002d: ldloc.0 
2 IL_002e: ldc.i4.1 
1 IL_002f: callvirt instance object [mscorlib]System.Collections.ArrayList::get_Item(int32) 
1 IL_0034: castclass ArrayListBoxAndUnBox.Program/Point 
0 IL_0039: stloc.2 
0 IL_003a: ret 

唯一的非平凡的人是ArrayList.Add（）调用。它弹出两个堆栈值，即ArrayList对象引用和Add（）参数。并且推回一个，Add（）的返回值。

编辑后：这的确是你在哪里错了。