返回内部if块或写if / else块之间是否存在性能差异？ [英] Is there a performance difference between returning inside if block, or writing if/else block?

问题描述

我正在通过我的项目来重构一些代码，并意识到我写了这样的东西：

I was going through my project to refactor some code and realized I had written something like this:

if(errorCode > 0)
{
   DisplayError(errorCode);
   return;
}

// Continue to do stuff otherwise.

您可能已经猜到，该函数的返回类型为void。当我开始研究这个问题时，我思考是否将它放入if / else块之间是否有任何真正的区别：

As you may have guessed, the function has a return type of void. As I started to look this over, I pondered whether there was any real difference between putting this inside an if/else block instead:

if(errorCode > 0)
{
   DisplayError(errorCode);
}
else
{
   // Do other stuff
}

else块将一直持续到函数结束，因此控制流程基本相同。这里是否存在性能差异，或者应该使用的约定，或者这两者是否完全相同？

The else block will continue until the end of the function, so the flow of control is essentially the same. Is there a performance difference here, or a convention that should be used, or are these two really exactly the same?

推荐答案

两种情况下生成的代码完全相同。

The generated code in both cases is completely identical.

（在第一个示例中，您缺少代码周围的括号，但我只是假设这是一个错误而你实际上是询问使用返回和否则之间的差异。）

(You are missing brackets around the code in the first example, but I will just assume that it's a typo and you are actually asking about the difference betwen using return and else.)

如果你看一下这两种方法生成的代码：

If you look at the generated code for these two methods:

public static void Test1(int errorCode) {
  if (errorCode > 0) {
    Console.WriteLine(errorCode);
    return;
  }
  Console.WriteLine("ok");
}

public static void Test2(int errorCode) {
  if (errorCode > 0) {
    Console.WriteLine(errorCode);
  } else {
    Console.WriteLine("ok");
  }
}

它将如下所示：

            if (errorCode > 0) {
011A00DA  in          al,dx  
011A00DB  push        eax  
011A00DC  mov         dword ptr [ebp-4],ecx  
011A00DF  cmp         dword ptr ds:[10F3178h],0  
011A00E6  je          011A00ED  
011A00E8  call        7470C310  
011A00ED  cmp         dword ptr [ebp-4],0  
011A00F1  jle         011A0100  
                Console.WriteLine(errorCode);
011A00F3  mov         ecx,dword ptr [ebp-4]  
011A00F6  call        73C5A920  
                return;
011A00FB  nop  
011A00FC  mov         esp,ebp  
011A00FE  pop         ebp  
011A00FF  ret  
            }
            Console.WriteLine("ok");
011A0100  mov         ecx,dword ptr ds:[3E92190h]  
011A0106  call        7359023C  
        }
011A010B  nop  
011A010C  mov         esp,ebp  
011A010E  pop         ebp  
011A010F  ret

和：

            if (errorCode > 0) {
011A0122  in          al,dx  
011A0123  push        eax  
011A0124  mov         dword ptr [ebp-4],ecx  
011A0127  cmp         dword ptr ds:[10F3178h],0  
011A012E  je          011A0135  
011A0130  call        7470C310  
011A0135  cmp         dword ptr [ebp-4],0  
011A0139  jle         011A0148  
                Console.WriteLine(errorCode);
011A013B  mov         ecx,dword ptr [ebp-4]  
011A013E  call        73C5A920  
011A0143  nop  
011A0144  mov         esp,ebp  
011A0146  pop         ebp  
011A0147  ret  
            } else {
                Console.WriteLine("ok");
011A0148  mov         ecx,dword ptr ds:[3E92190h]  
011A014E  call        7359023C  
            }
        }
011A0153  nop  
011A0154  mov         esp,ebp  
011A0156  pop         ebp  
011A0157  ret

生成的代码完全相同，一直到最后指示。

The generated code is completely identical, down to the last instruction.

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