有没有一种方法可以在Mac上启用本地clang ++的优化？ [英] is there a way to enable optimization for local clang++ on mac?

问题描述

此问题源自帖子。

似乎在线编译器在优化时会放弃此功能。

it seems that the online compiler discard this function while optimizing.

void functiona()
{
    long long number = 0;
    // long long problemSize = 100000000000;
    long long problemSize = 10;

    for( long long i = 0; i < problemSize; ++i )
    {
       for(long long j = 0; j < problemSize; j++)
       {
           for(long long k = 0; k < problemSize; k++)
           {
               for(long long l = 0; l < problemSize; l++)
               {
                   for(long long l = 0; l < problemSize; l++)
                   {
                       number++;
                       number--;
                   }
               }
            }
        }
    }
}

在本地Mac上编译这段代码
$ b

compiling this piece of code on my local mac

clang++ -std=c++11 -stdlib=libc++ benchmark.cpp

./a.out
409

似乎没有优化。

此帖子和文档提供了一些有关clang优化的信息。

this post and doc provide some info about clang optimization.

是否可以启用clang ++优化，这样本地输出就接近在线输出。

is there a way to enable optimization for clang++, so that the local output is close to online one.

推荐答案

clang ++ 与 clang 基本上具有相同的开关，在您自己找到的链接中有完整介绍。最明显的最大优化方法是 -Ofast ，但是鉴于这种优化的简单性和明显性，基本上任何水平的优化都可能触发该优化， -O3 ， -02 ， -Os ，甚至 -O1 。确切行为会因编译器版本而异，因此您可以尝试确定消除版本循环所需的最低级别。

clang++ takes basically the same switches as clang, which are fully covered in the links you found on your own. The obvious one for maximum optimization would be -Ofast, but given how simple and obvious this optimization is, basically any level of optimization is likely to trigger it, -O3, -02, -Os, even -O1. The exact behavior will vary by compiler version, so you can experiment to determine the minimal level needed to eliminate the loop on your version.

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