Emit基础学习-选择分支

2009-07-13 09:51 Kevin-wang 阅读(389) 评论(0) 编辑收藏举报

C#代码

int sum = 0;
if (num1 > 0)
{
sum = num1 + 100;
}

IL代码

    .maxstack 2
    .locals init (
        [0] int32 num,
        [1] bool flag)
    L_0000: ldc.i4.0
    L_0001: stloc.0
    L_0002: ldc.i4.0
    L_0003: stloc.1
    L_0004: ldarg.0
    L_0005: ldc.i4.0
    L_0006: cgt
    L_0008: ldc.i4.0
    L_0009: ceq
    L_000b: stloc.1
    L_000c: ldloc.1
    L_000d: brtrue.s L_0017
    L_000f: ldarg.0
    L_0010: ldc.i4 100
    L_0015: add
    L_0016: stloc.0
    L_0017: ret

Emit代码

_Method = _TypeBuilder.DefineMethod("Dotest4",
MethodAttributes.Public |MethodAttributes.Static,
null,new Type[] { typeof(int) });
_MethodIL = _Method.GetILGenerator();
l1 = _MethodIL.DefineLabel();
// l2 = _MethodIL.DefineLabel();
//int _Sum=0;
LocalBuilder _v1 = _MethodIL.DeclareLocal(typeof(int));
_MethodIL.Emit(OpCodes.Ldc_I4_0);
_MethodIL.Emit(OpCodes.Stloc_0);

LocalBuilder _v2 = _MethodIL.DeclareLocal(typeof(bool));
_MethodIL.Emit(OpCodes.Ldc_I4_0);
_MethodIL.Emit(OpCodes.Stloc_1);

_MethodIL.Emit(OpCodes.Ldarg_0);
_MethodIL.Emit(OpCodes.Ldc_I4_0);
_MethodIL.Emit(OpCodes.Cgt);

_MethodIL.Emit(OpCodes.Ldc_I4_0);
_MethodIL.Emit(OpCodes.Ceq);

_MethodIL.Emit(OpCodes.Stloc_1);

_MethodIL.Emit(OpCodes.Ldloc_1);

_MethodIL.Emit(OpCodes.Brtrue_S, l1);
//_sum=pNum+100;
_MethodIL.Emit(OpCodes.Ldarg_0);
_MethodIL.Emit(OpCodes.Ldc_I4, 100);
_MethodIL.Emit(OpCodes.Add);
_MethodIL.Emit(OpCodes.Stloc_0);

_MethodIL.MarkLabel(l1);
_MethodIL.Emit(OpCodes.Ret);

C#代码—条件表达式
使用Emit生成IL后反射的C#代码

return ((num1 > 100) ? -1 : 0);

手工编写的代码

return ((num > 100) ? -1 : 0);

IL代码
使用Emit生成的IL代码

.maxstack 3
L_0000: ldarg.0
L_0001: ldc.i4.s 100
L_0003: nop
L_0004: nop
L_0005: nop
L_0006: bgt.s L_000b
L_0008: ldc.i4.0
L_0009: br.s L_000c
L_000b: ldc.i4.m1
L_000c: ret

手工编写的代生成的IL代码

    .maxstack 2
    .locals init (
        [0] int32 CS$1$0000)
    L_0000: nop
    L_0001: ldarg.0
    L_0002: ldc.i4.s 100
    L_0004: bgt.s L_0009
    L_0006: ldc.i4.0
    L_0007: br.s L_000a
    L_0009: ldc.i4.m1
    L_000a: stloc.0
    L_000b: br.s L_000d
    L_000d: ldloc.0
    L_000e: ret

Emit代码

_Method = _TypeBuilder.DefineMethod("Dotest1",MethodAttributes.Public | MethodAttributes.Static,
typeof(int), new Type[] { typeof(int) });

_MethodIL = _Method.GetILGenerator();
failed = _MethodIL.DefineLabel();
endOfMthd = _MethodIL.DefineLabel();

//生成代码
//if (num1 > 100)
//将索引为 0 的参数加载到计算堆栈上。
_MethodIL.Emit(OpCodes.Ldarg_0);
//将提供的 int8 值作为 int32 推送到计算堆栈上
_MethodIL.Emit(OpCodes.Ldc_I4_S, 100);
//如果第一个值大于第二个值，则将控制转移到目标指令
_MethodIL.Emit(OpCodes.Bgt_S, failed);

_MethodIL.Emit(OpCodes.Ldc_I4_0);
_MethodIL.Emit(OpCodes.Br_S, endOfMthd);

_MethodIL.MarkLabel(failed);
_MethodIL.Emit(OpCodes.Ldc_I4_M1);

_MethodIL.MarkLabel(endOfMthd);

_MethodIL.Emit(OpCodes.Ret);

Switch分支

C#代码

switch (num1)
{
    case 4:
        return 30;

    case 7:
        return 0x1f;

    case 8:
        return 0x1d;
}
return 0x1c;

生成的IL代码

.method public static int32 Dotest5(int32) cil managed
{
    .maxstack 7
    .locals init (
        [0] int32 num,
        [1] int32 num2,
        [2] int32 num3)
    L_0000: nop
    L_0001: ldc.i4.0
    L_0002: stloc.0
    L_0003: ldarg.0
    L_0004: stloc.2
    L_0005: ldloc.2
    L_0006: ldc.i4.4
    L_0007: beq.s L_0013
    L_0009: ldloc.2
    L_000a: ldc.i4.7
    L_000b: beq.s L_001b
    L_000d: ldloc.2
    L_000e: ldc.i4.8
    L_000f: beq.s L_0023
    L_0011: br.s L_002b
    L_0013: ldc.i4.s 30
    L_0015: nop
    L_0016: nop
    L_0017: nop
    L_0018: stloc.0
    L_0019: br.s L_0033
    L_001b: ldc.i4.s 0x1f
    L_001d: nop
    L_001e: nop
    L_001f: nop
    L_0020: stloc.0
    L_0021: br.s L_0033
    L_0023: ldc.i4.s 0x1d
    L_0025: nop
    L_0026: nop
    L_0027: nop
    L_0028: stloc.0
    L_0029: br.s L_0033
    L_002b: ldc.i4.s 0x1c
    L_002d: nop
    L_002e: nop
    L_002f: nop
    L_0030: stloc.0
    L_0031: br.s L_0033
    L_0033: ldloc.0
    L_0034: ret
}

Emit生成代码

  _Method = _TypeBuilder.DefineMethod("Dotest5",
  MethodAttributes.Public | MethodAttributes.Static,
  typeof(int), new Type[] { typeof(int) });

  _MethodIL = _Method.GetILGenerator();

  Label[] _Lbls = new Label[3];
  //默认(switch语句的default节点)
  Label _defaultLabel = _MethodIL.DefineLabel();
  //endswitch
  Label _endswitch = _MethodIL.DefineLabel();
  Label _endswitch2 = _MethodIL.DefineLabel();

  for (int i = 0; i < _Lbls.Length; i++)
  {
      _Lbls[i] = _MethodIL.DefineLabel();
  }
  //声明变量
  //int result=0;
  LocalBuilder _result = _MethodIL.DeclareLocal(typeof(int));
  LocalBuilder _num1 = _MethodIL.DeclareLocal(typeof(int));
  LocalBuilder _num2 = _MethodIL.DeclareLocal(typeof(int));
  _MethodIL.Emit(OpCodes.Nop);

  _MethodIL.Emit(OpCodes.Ldc_I4_0);
  _MethodIL.Emit(OpCodes.Stloc_0);

  _MethodIL.Emit(OpCodes.Ldarg_0);
  _MethodIL.Emit(OpCodes.Stloc_2);

  //_MethodIL.Emit(OpCodes.Switch, _Lbls);
  //            L_0005: ldloc.2
  //L_0006: ldc.i4.4
  //L_0007: beq.s L_000f  //如果两个值相等，则将控制转移到目标指令。
  _MethodIL.Emit(OpCodes.Ldloc_2);
  _MethodIL.Emit(OpCodes.Ldc_I4_4);
  _MethodIL.Emit(OpCodes.Beq_S, _Lbls[0]);

  _MethodIL.Emit(OpCodes.Ldloc_2);
  _MethodIL.Emit(OpCodes.Ldc_I4_7);
  _MethodIL.Emit(OpCodes.Beq_S, _Lbls[1]);

  _MethodIL.Emit(OpCodes.Ldloc_2);
  _MethodIL.Emit(OpCodes.Ldc_I4_8);
  _MethodIL.Emit(OpCodes.Beq_S, _Lbls[2]);

  _MethodIL.Emit(OpCodes.Br_S, _defaultLabel);

  _MethodIL.MarkLabel(_Lbls[0]);
  _MethodIL.Emit(OpCodes.Ldc_I4_S, 30);
  _MethodIL.Emit(OpCodes.Stloc_0);
  _MethodIL.Emit(OpCodes.Br_S, _endswitch);

  _MethodIL.MarkLabel(_Lbls[1]);
  _MethodIL.Emit(OpCodes.Ldc_I4_S, 31);
  _MethodIL.Emit(OpCodes.Stloc_0);
  _MethodIL.Emit(OpCodes.Br_S, _endswitch);

  _MethodIL.MarkLabel(_Lbls[2]);
  _MethodIL.Emit(OpCodes.Ldc_I4_S, 29);
  _MethodIL.Emit(OpCodes.Stloc_0);
  _MethodIL.Emit(OpCodes.Br_S, _endswitch);

  _MethodIL.MarkLabel(_defaultLabel);
  _MethodIL.Emit(OpCodes.Ldc_I4_S, 28);
  _MethodIL.Emit(OpCodes.Stloc_0);
  _MethodIL.Emit(OpCodes.Br_S, _endswitch);

  _MethodIL.MarkLabel(_endswitch);

  _MethodIL.Emit(OpCodes.Ldloc_0);

  _MethodIL.Emit(OpCodes.Ret);

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Emit基础学习-选择分支

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