GCC -O2 与 -march / -ftree-vectorize

发布于 2024-10-17 07:18:16 字数 747 浏览 5 评论 0原文

我正在针对一个在两个图像（ 2000Hx3000W 和 6800Hx8500W ）上执行索贝尔内核卷积的程序尝试几个编译器开关。有一些我无法解释的观察结果，以下是数据 - 编译器标志和以秒为单位的时间（请关注最后一列，因为它表示较大图像的 Y 轴卷积）：

O2-march=barcelona                  0.1483326   0.833264    1.6018882   28.6711242
O2-ftree-vectorize                  0.1462104   0.847973    1.506708    26.628592
O2                                  0.1468406   0.8368156   1.5999718   20.61377564
O2-ftree-vectorize-march=barcelona  0.1441898   0.827366    1.4687354   15.2572644

我期望 -O2- March=barcelona 稍微好一些，考虑到我运行的机器是 AMD barcelona。关于为什么 -O2 比 -O2 -march 有什么想法吗？

关于 -ftree-vectorize，它应该能够并行运行指令，因为我的循环是无依赖性的。但是，-O2-ftree-vectorize-march=barcelona 是其中最好的，单独来看，时间上存在合理的差异。

如果我能理解这种行为那就太好了。

问候，
萨彦

原文

I am trying out several compiler switches against a program that performs sobel kernel convolution on two images( 2000Hx3000W and 6800Hx8500W ). There are some observations that I am not able to interprete, following are the data - compiler flags and time taken in secs (please focus on the last column, as it signifies convolution on Y axis for the larger image):

O2-march=barcelona                  0.1483326   0.833264    1.6018882   28.6711242
O2-ftree-vectorize                  0.1462104   0.847973    1.506708    26.628592
O2                                  0.1468406   0.8368156   1.5999718   20.61377564
O2-ftree-vectorize-march=barcelona  0.1441898   0.827366    1.4687354   15.2572644

I expected -O2-march=barcelona to be moderately better, considering the machine I am running on is AMD barcelona. Any ideas as to why -O2 is better than -O2 -march?

About -ftree-vectorize, it should be able to run instructions in parallel since my loop is dependence free. But then, -O2-ftree-vectorize-march=barcelona is the best of the lot, when individually there are reasonable differences in timing.

It would be great if I could understand this behavior.

Regards,
Sayan

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