C# MSIL:为什么数组初始值设定项使用dup
我最近在学习MSIL,对阵列有一些困惑: 以下2种方法:C# MSIL:为什么数组初始值设定项使用dup,c#,cil,C#,Cil,我最近在学习MSIL,对阵列有一些困惑: 以下2种方法: private static void FormatTest3() { string s = string.Format("{0}{1}{2}", 1, 2,3); } private static void FormatTest4() { string s = string.Format("{0}{1}{2}{3}", 1, 2,3,4); /* equal to object[] obj =
private static void FormatTest3()
{
string s = string.Format("{0}{1}{2}", 1, 2,3);
}
private static void FormatTest4()
{
string s = string.Format("{0}{1}{2}{3}", 1, 2,3,4);
/*
equal to
object[] obj = new object[4];
obj[0] = 1;
obj[1] = 2;
obj[2] = 3;
obj[3] = 4;
string text = string.Format("{0}{1}{2}{3}", obj);
*/
}
以下是IL:
.class private auto ansi '<Module>'
{
} // end of class <Module>
.class private auto ansi beforefieldinit Program
extends [System.Private.CoreLib]System.Object
{
// Methods
.method private hidebysig static
void FormatTest3 () cil managed
{
// Method begins at RVA 0x2050
// Code size 31 (0x1f)
.maxstack 4
.locals init (
[0] string
)
IL_0000: nop
IL_0001: ldstr "{0}{1}{2}"
IL_0006: ldc.i4.1
IL_0007: box [System.Private.CoreLib]System.Int32
IL_000c: ldc.i4.2
IL_000d: box [System.Private.CoreLib]System.Int32
IL_0012: ldc.i4.3
IL_0013: box [System.Private.CoreLib]System.Int32
IL_0018: call string [System.Private.CoreLib]System.String::Format(string, object, object, object)
IL_001d: stloc.0
IL_001e: ret
} // end of method Program::FormatTest3
.method private hidebysig static
void FormatTest4 () cil managed
{
// Method begins at RVA 0x207c
// Code size 55 (0x37)
.maxstack 5
.locals init (
[0] string
)
IL_0000: nop
IL_0001: ldstr "{0}{1}{2}{3}"
IL_0006: ldc.i4.4
IL_0007: newarr [System.Private.CoreLib]System.Object
IL_000c: dup
IL_000d: ldc.i4.0
IL_000e: ldc.i4.1
IL_000f: box [System.Private.CoreLib]System.Int32
IL_0014: stelem.ref
IL_0015: dup
IL_0016: ldc.i4.1
IL_0017: ldc.i4.2
IL_0018: box [System.Private.CoreLib]System.Int32
IL_001d: stelem.ref
IL_001e: dup
IL_001f: ldc.i4.2
IL_0020: ldc.i4.3
IL_0021: box [System.Private.CoreLib]System.Int32
IL_0026: stelem.ref
IL_0027: dup
IL_0028: ldc.i4.3
IL_0029: ldc.i4.4
IL_002a: box [System.Private.CoreLib]System.Int32
IL_002f: stelem.ref
IL_0030: call string [System.Private.CoreLib]System.String::Format(string, object[])
IL_0035: stloc.0
IL_0036: ret
} // end of method Program::FormatTest4
.method public hidebysig specialname rtspecialname
instance void .ctor () cil managed
{
// Method begins at RVA 0x20bf
// Code size 8 (0x8)
.maxstack 8
IL_0000: ldarg.0
IL_0001: call instance void [System.Private.CoreLib]System.Object::.ctor()
IL_0006: nop
IL_0007: ret
} // end of method Program::.ctor
} // end of class Program
.class私有自动ansi“”
{
}//下课
.class专用自动ansi BEFOREFILDInit程序
扩展[System.Private.CoreLib]System.Object
{
//方法
.method私有隐藏静态
void FormatTest3()cil托管
{
//方法从RVA 0x2050开始
//代码大小31(0x1f)
.maxstack 4
.init(
[0]字符串
)
IL_0000:没有
IL_0001:ldstr“{0}{1}{2}”
IL_0006:ldc.i4.1
IL_0007:box[System.Private.CoreLib]System.Int32
IL_000c:ldc.i4.2
IL_000d:box[System.Private.CoreLib]System.Int32
IL_0012:ldc.i4.3
IL_0013:box[System.Private.CoreLib]System.Int32
IL_0018:调用字符串[System.Private.CoreLib]System.string::Format(字符串,对象,对象)
IL_001d:stloc.0
IL_001e:ret
}//方法结束程序::FormatTest3
.method私有隐藏静态
void FormatTest4()cil托管
{
//方法从RVA 0x207c开始
//代码大小55(0x37)
.maxstack 5
.init(
[0]字符串
)
IL_0000:没有
IL_0001:ldstr“{0}{1}{2}{3}”
IL_0006:ldc.i4.4
IL_0007:newarr[System.Private.CoreLib]System.Object
IL_000c:dup
IL_000d:ldc.i4.0
IL_000e:ldc.i4.1
IL_000f:box[System.Private.CoreLib]System.Int32
IL_0014:stelem.ref
IL_0015:dup
IL_0016:ldc.i4.1
IL_0017:ldc.i4.2
IL_0018:box[System.Private.CoreLib]System.Int32
IL_001d:stelem.ref
IL_001e:dup
IL_001f:ldc.i4.2
IL_0020:ldc.i4.3
IL_0021:box[System.Private.CoreLib]System.Int32
IL_0026:stelem.ref
IL_0027:dup
IL_0028:ldc.i4.3
IL_0029:ldc.i4.4
IL_002a:box[System.Private.CoreLib]System.Int32
IL_002f:stelem.ref
IL_0030:调用字符串[System.Private.CoreLib]System.string::Format(字符串,对象[])
IL_0035:stloc.0
IL_0036:ret
}//方法结束程序::FormatTest4
.method公共隐藏显示特殊名称rtspecialname
实例void.ctor()cil托管
{
//方法从RVA 0x20bf开始
//代码大小8(0x8)
.maxstack 8
IL_0000:ldarg.0
IL_0001:调用实例void[System.Private.CoreLib]System.Object::.ctor()
IL_0006:没有
IL_0007:ret
}//方法程序结束::.ctor
}//课程结束
我的问题是:
params
array参数,从而节省分配(虽然可能仍然需要装箱,但这比数组便宜)。理论上,0、1、2和3个参数的重载不需要存在,因为采用params对象[]
的方法也可以处理所有这些参数。只是更贵dup
复制堆栈上的当前项stelem.ref
从堆栈中获取三项:数组、索引和该数组索引的值,并将该值存储在数组中的索引处。这意味着以后数组引用不再在堆栈上。因此,dup
。我们希望将该数组引用保留在堆栈顶部,因为我们需要将其传递给被调用的方法,所以我们创建一个数组,复制它,推送索引和第一项,使用stelem.ref
将该项存储在数组中,并且仍然保留该数组引用,否则该数组引用将消失
有其他方法可以做到这一点。如果从反编译的C#中复制代码,则最终会得到不同的IL,其中数组引用每次都从局部变量中获取:
IL_0036: ldc.i4.4
IL_0037: newarr [System.Private.CoreLib]System.Object
IL_003c: stloc.1
IL_003d: ldloc.1
IL_003e: ldc.i4.0
IL_003f: ldc.i4.1
IL_0040: box [System.Private.CoreLib]System.Int32
IL_0045: stelem.ref
IL_0046: ldloc.1
IL_0047: ldc.i4.1
IL_0048: ldc.i4.2
IL_0049: box [System.Private.CoreLib]System.Int32
IL_004e: stelem.ref
我相信这比dup的效率要低,但也许JIT并不在乎这两种方式。真正的反编译C#代码实际上是这样的:
string text = string.Format("{0}{1}{2}{3}", new object[] { 1, 2, 3, 4 });
这将导致与相同的IL
string text = string.Format("{0}{1}{2}{3}", 1, 2, 3, 4);
params
array参数,从而节省分配(虽然可能仍然需要装箱,但这比数组便宜)。理论上,0、1、2和3个参数的重载不需要存在,因为采用params对象[]
的方法也可以处理所有这些参数。只是更贵dup
复制堆栈上的当前项stelem.ref
从堆栈中获取三项:数组、索引和该数组索引的值,并将该值存储在数组中的索引处。这意味着以后数组引用不再在堆栈上。因此,dup
。我们希望将该数组引用保留在堆栈顶部,因为我们需要将其传递给被调用的方法,所以我们创建一个数组,复制它,推送索引和第一项,使用stelem.ref
将该项存储在数组中,并且仍然保留该数组引用,否则该数组引用将消失
有其他方法可以做到这一点。如果从反编译的C#中复制代码,则最终会得到不同的IL,其中数组引用每次都从局部变量中获取:
IL_0036: ldc.i4.4
IL_0037: newarr [System.Private.CoreLib]System.Object
IL_003c: stloc.1
IL_003d: ldloc.1
IL_003e: ldc.i4.0
IL_003f: ldc.i4.1
IL_0040: box [System.Private.CoreLib]System.Int32
IL_0045: stelem.ref
IL_0046: ldloc.1
IL_0047: ldc.i4.1
IL_0048: ldc.i4.2
IL_0049: box [System.Private.CoreLib]System.Int32
IL_004e: stelem.ref
我相信这比dup的效率要低,但也许JIT并不在乎这两种方式。真正的反编译C#代码实际上是这样的:
string text = string.Format("{0}{1}{2}{3}", new object[] { 1, 2, 3, 4 });
这将导致与相同的IL
string text = string.Format("{0}{1}{2}{3}", 1, 2, 3, 4);