将内嵌GCC的一个函数，指针？ [英] Will GCC inline a function that takes a pointer?

问题描述

我有对数据块进行操作的函数（比方说，一个 INT ），我想传递一个参考valule改到位。因此，我具备的功能：无效myFunction的为（int *的东西）{...} 。当我使用它，我这样称呼它： myFunction的（安培; ANINT）。

I have a function which operates on piece of data (let's say, an int), and I want to change it in place by passing a reference to the valule. As such, I have the function: void myFunction(int *thing) { ... }. When I use it I call it thus: myFunction(&anInt).

由于我的函数往往（但来自许多不同的地方）叫我关心它的性能。我已经重构它变成一个功能的原因是可测试性和code重用。

As my function is called frequently (but from many different places) I am concerned about its performance. The reason I have refactored it into a function is testability and code reuse.

编译器将能够优化功能，它内联直接在我的 ANINT 变量进行操作？

Will the compiler be able to optimize the function, inlining it to operate directly on my anInt variable?

我希望您能在它的要求精神，这个问题（即我不是prematurely担心的优化，我很好奇的答案）。同样，我不想把它做成一个宏。

I hope you'll take this question in the spirit in which it's asked (i.e. I'm not prematurely worrying about optimisation, I'm curious about the answer). Similarly, I don't want to make it into a macro.

推荐答案

GCC是相当聪明的。考虑这个code片段：

GCC is quite smart. Consider this code fragment:

#include <stdio.h>

void __inline__ inc(int *val)
{
    ++ *val;
}

int main()
{
    int val;

    scanf("%d", &val);

    inc(&val);

    printf("%d\n", val);

    return 0;
}

在之后的gcc -S -O3 test.c以你会得到以下相关ASM：

After a gcc -S -O3 test.c you'll get the following relevant asm:

...
call    __isoc99_scanf
movl    12(%rsp), %esi
movl    $.LC1, %edi
xorl    %eax, %eax
addl    $1, %esi
movl    %esi, 12(%rsp)
call    printf
...

正如你所看到的，有没有必要成为一个ASM专家看INC（）调用已被转换为增量指令。

As you can see, there's no need to be an asm expert to see the inc() call has been converted to an increment instruction.

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