在c＃中转到语句影响性能

Question

在GOTO代码中是否存在c#语句的性能影响，而不是使用loop或多个单独的用户定义的functions。

我不确定但是GOTO语句可能会出现内存跳转并且会影响性​​能。

Answer 1

不，它没有。

如果不知道替代方案是什么，很难回答“它会影响性能”，但我会编制一个样本：

using System;
public class C {
    public void M() {
        var x = 7;
        switch(x) // START SWITCH
        {
            case 1:
                Console.WriteLine("Hello");
                break;
            case 2:
                Console.WriteLine("World");
                break;
            default:
                Console.WriteLine("Uh...");
                break;
        }
        // END SWITCH
        // START GOTO
        if (x == 1)
        {
            goto Hello;
        }
        else if (x == 2)
        {
            goto World;
        }
        Console.WriteLine("Uh...");
        goto End;
    Hello:
        Console.WriteLine("Hello");
        goto End;
    World:
        Console.WriteLine("World");
    End:
        // END GOTO
        Console.WriteLine("Done");
    }
}

在发布模式下使用C＃进行编译（使用sharplab.io默认值为2.9.0）会生成以下IL（即Java民谣的字节码）：

.class private auto ansi '<Module>'
{
} // end of class <Module>

.class public auto ansi beforefieldinit C
    extends [mscorlib]System.Object
{
    // Methods
    .method public hidebysig 
        instance void M () cil managed 
    {
        // Method begins at RVA 0x2050
        // Code size 99 (0x63)
        .maxstack 2
        .locals init (
            [0] int32
        )

        IL_0000: ldc.i4.7
        IL_0001: stloc.0
        // START SWITCH
        IL_0002: ldloc.0
        IL_0003: ldc.i4.1
        IL_0004: beq.s IL_000c

        IL_0006: ldloc.0
        IL_0007: ldc.i4.2
        IL_0008: beq.s IL_0018

        IL_000a: br.s IL_0024

        IL_000c: ldstr "Hello"
        IL_0011: call void [mscorlib]System.Console::WriteLine(string)
        IL_0016: br.s IL_002e

        IL_0018: ldstr "World"
        IL_001d: call void [mscorlib]System.Console::WriteLine(string)
        IL_0022: br.s IL_002e

        IL_0024: ldstr "Uh..."
        IL_0029: call void [mscorlib]System.Console::WriteLine(string)
        // END SWITCH
        // START GOTO
        IL_002e: ldloc.0
        IL_002f: ldc.i4.1
        IL_0030: beq.s IL_0042

        IL_0032: ldloc.0
        IL_0033: ldc.i4.2
        IL_0034: beq.s IL_004e

        IL_0036: ldstr "Uh..."
        IL_003b: call void [mscorlib]System.Console::WriteLine(string)
        IL_0040: br.s IL_0058

        IL_0042: ldstr "Hello"
        IL_0047: call void [mscorlib]System.Console::WriteLine(string)
        IL_004c: br.s IL_0058

        IL_004e: ldstr "World"
        IL_0053: call void [mscorlib]System.Console::WriteLine(string)
        // END GOTO
        IL_0058: ldstr "Done"
        IL_005d: call void [mscorlib]System.Console::WriteLine(string)
        IL_0062: ret
    } // end of method C::M

    .method public hidebysig specialname rtspecialname 
        instance void .ctor () cil managed 
    {
        // Method begins at RVA 0x20bf
        // 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 C::.ctor

} // end of class C

开关形式有3个beq和1个br.s，goto形式有2个beq和2个br.s，除此之外它们是相同的。 br.s的成本可能小于或等于beq的成本，因此goto方法的成本不高于切换方法的成本。

最后，使用goto是个坏主意。如果你想争论这个事实，请在另一个问题上这样做：What is wrong with using goto?