C编码性能或code尺寸的做法 - 远远超出了一个编译器 [英] C coding practices for performance or code size - beyond what a compiler does

问题描述

我在寻找，看看有什么可以程序员用C做的，可以确定的性能和/或生成的目标文件的大小。

I'm looking to see what can a programmer do in C, that can determine the performance and/or the size of the generated object file.

有关例如，结果
1.简单的声明的get / set函数为内联可以提高性能（在更大的足迹成本）结果
2.对于没有使用循环变量的值本身回路，计数下降到零，而不是向上计数到一定值
等等。

For e.g,
1. Declaring simple get/set functions as inline may increase performance (at the cost of a larger footprint)
2. For loops that do not use the value of the loop variable itself, count down to zero instead of counting up to a certain value etc.

它看起来像编译器现在已经进展到简单的技巧（如上面两个点）不会在所有需要的水平。在编译过程中适当的选项反正做的工作。哎呀，我也看到了帖子这里的编译器手柄如何递归 - 这是非常有趣！那么，什么是我们离开在C水平怎么做呢？ ：）

It looks like compilers now have advanced to a level where "simple" tricks (like the two points above) are not required at all. Appropriate options during compilation do the job anyway. Heck, I also saw posts here on how compilers handle recursion - that was very interesting! So what are we left to do at a C level then? :)

我的具体环境是：GCC 4.3.3再针对ARM架构（V4）。但在其他编译器的反应/处理器也欢迎和将在被嚼。

My specific environment is: GCC 4.3.3 re-targeted for ARM architecture (v4). But responses on other compilers/processors are also welcome and will be munched upon.

PS：我的这种做法有悖于code首先!,然后基准和的最后的优化的做法

PS: This approach of mine goes against the usual "code first!, then benchmark, and finally optimize" approach.

修改：就像恰巧，我发现了一个类似的帖子张贴问题后：的我们应该仍然可以优化＆QUOT;在小＆QUOT;？

Edit: Just like it so happens, I found a similar post after posting the question: Should we still be optimizing "in the small"?

推荐答案

有一件事我能想到的，编译器可能不会优化是缓存友好性：如果你遍历一个二维数组行优先的顺序，也就是说，要确保在整个列索引你的内循环运行，以避免高速缓存抖动。其运行在错误的索引内循环会导致巨大的性能损失。

One thing I can think of that a compiler probably won't optimize is "cache-friendliness": If you're iterating over a two-dimensional array in row-major order, say, make sure your inner loop runs across the column index to avoid cache thrashing. Having the inner loop run over the wrong index can cause a huge performance hit.

这适用于所有的编程语言，但如果你在C语言进行编程，性能可能是你的关键，所以这是特别重要。

This applies to all programming languages, but if you're programming in C, performance is probably critical to you, so it's especially relevant.

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