MSIL：多余的分支 [英] MSIL : Superfluous branch

问题描述

考虑以下C＃代码段：

static string input = null;
static string output = null;

static void Main(string[] args)
{
     input = "input";
     output = CallMe(input);
}

public static string CallMe(string input)
{
     output = "output";
     return output;
}

使用Reflector显示进行拆卸：

Dissassembling using Reflector shows:

.method private hidebysig static void Main(string[] args) cil managed
    {
        .entrypoint
        .maxstack 8
        L_0000: nop 
        L_0001: ldstr "input"
        L_0006: stsfld string Reflector_Test.Program::input
        L_000b: ldsfld string Reflector_Test.Program::input
        L_0010: call string Reflector_Test.Program::CallMe(string)
        L_0015: stsfld string Reflector_Test.Program::output
        L_001a: ret 
    }

 .method public hidebysig static string CallMe(string input) cil managed
    {
        .maxstack 1
        .locals init (
            [0] string CS$1$0000)
        L_0000: nop 
        L_0001: ldstr "output"
        L_0006: stsfld string Reflector_Test.Program::output
        L_000b: ldsfld string Reflector_Test.Program::output
        L_0010: stloc.0 
        L_0011: br.s L_0013
        L_0013: ldloc.0 
        L_0014: ret 
    }

令我困惑的部分是：

L_0010: stloc.0 
L_0011: br.s L_0013
L_0013: ldloc.0 

它存储该项目，分支到下一行（无论如何将执行该行），然后再次加载。

It stores the item, branches to the next line (which would have been executed anyway) and then loads it again.

是否有此原因？

推荐答案

这仅在Debug中发生，而在Release中不发生。我怀疑它可以在调试期间提供帮助。也许它可以让您查清语句中的断点并查看返回值。

This only happens in Debug, not in Release. I suspect its to assist during debugging. It perhaps allows you to chuck breakpoints mid statement and see the return value.

请注意，发行版的IL更为简洁：

Note the release version has much more concise IL:

.method private hidebysig static void Main(string[] args) cil managed
{
    .maxstack 8
    L_0000: ldstr "input"
    L_0005: stsfld string Reflector_Test.Program::input
    L_000a: ldsfld string Reflector_Test.Program::input
    L_000f: call string Reflector_Test.Program::CallMe(string)
    L_0014: stsfld string Reflector_Test.Program::output
    L_0019: ret 
}




.method public hidebysig static string CallMe(string input) cil managed
{
    .maxstack 8
    L_0000: ldstr "output"
    L_0005: stsfld string Reflector_Test.Program::output
    L_000a: ldsfld string Reflector_Test.Program::output
    L_000f: ret 
}

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