告诉 gcc 专门展开一个循环 [英] Tell gcc to specifically unroll a loop

问题描述

如何告诉 GCC 展开特定循环?我使用了 CUDA SDK，其中可以使用 #pragma unroll 手动展开循环.gcc 有类似的功能吗?我用谷歌搜索了一下，但没有找到任何东西.

How can I tell GCC to unroll a particular loop? I have used the CUDA SDK where loops can be unrolled manually using #pragma unroll. Is there a similar feature for gcc? I googled a bit but could not find anything.

推荐答案

GCC 为您提供了几种不同的处理方式:

GCC gives you a few different ways of handling this:

• 使用#pragma 指令，例如#pragma GCC optimize ("string"...)，如GCC 文档.请注意，编译指示对其余函数进行了全局优化.如果您巧妙地使用了 #pragma push_options 和 pop_options 宏，您可能可以仅围绕这样的一个函数来定义它:

• Use #pragma directives, like #pragma GCC optimize ("string"...), as seen in the GCC docs. Note that the pragma makes the optimizations global for the remaining functions. If you used #pragma push_options and pop_options macros cleverly, you could probably define this around just one function like so:

#pragma GCC push_options
#pragma GCC optimize ("unroll-loops")

//add 5 to each element of the int array.
void add5(int a[20]) {
    int i = 19;
    for(; i > 0; i--) {
        a[i] += 5;
    }
}

#pragma GCC pop_options

使用 GCC 的属性语法注释单个函数:检查 GCC函数属性 docs 有关该主题的更详细的论文.一个例子:

Annotate individual functions with GCC's attribute syntax: check the GCC function attribute docs for a more detailed dissertation on the subject. An example:

//add 5 to each element of the int array.
__attribute__((optimize("unroll-loops")))
void add5(int a[20]) {
    int i = 19;
    for(; i > 0; i--) {
        a[i] += 5;
    }
}

注意:我不确定 GCC 在展开反向迭代循环方面有多好(我这样做是为了让 Markdown 能够很好地处理我的代码).不过，这些示例应该可以很好地编译.

Note: I'm not sure how good GCC is at unrolling reverse-iterated loops (I did it to get Markdown to play nice with my code). The examples should compile fine, though.

这篇关于告诉 gcc 专门展开一个循环的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！