“rep ret”是什么意思？(What does `rep ret` mean?)

 我在Visual Studio 2008上测试了一些代码，并注意到了security_cookie 。 我可以理解它的意义，但我不明白这个指令的目的是什么。 
 
    rep ret /* REP to avoid AMD branch prediction penalty */
 
 当然，我可以理解评论:)但是，这个前缀exaclty与ret上下文是什么关系？如果ecx是！= 0，会发生什么？ 显然， ecx的循环计数在调试时会被忽略，这是可以预料的。 
 
 我发现这里的代码在这里（由编译器注入以保证安全性）： 
 
void __declspec(naked) __fastcall __security_check_cookie(UINT_PTR cookie)
{
    /* x86 version written in asm to preserve all regs */
    __asm {
        cmp ecx, __security_cookie
        jne failure
        rep ret /* REP to avoid AMD branch prediction penalty */
failure:
        jmp __report_gsfailure
    }
}

I was testing some code on Visual Studio 2008 and noticed security_cookie. I can understand the point of it, but I don't understand what the purpose of this instruction is.
 
    rep ret /* REP to avoid AMD branch prediction penalty */
 
Of course I can understand the comment :) but what is this prefix exaclty doing in context with the ret and what happens if ecx is != 0? Apparently the loop count from ecx is ignored when I debug it, which is to be expected.
 
The code where I found this was here (injected by the compiler for security):
 
void __declspec(naked) __fastcall __security_check_cookie(UINT_PTR cookie)
{
    /* x86 version written in asm to preserve all regs */
    __asm {
        cmp ecx, __security_cookie
        jne failure
        rep ret /* REP to avoid AMD branch prediction penalty */
failure:
        jmp __report_gsfailure
    }
}

原文：https://stackoverflow.com/questions/20526361