)
Shell脚本名叫step
#!/bin/bashif [[ $# -ne 1 ]]; then exit; firun() { C="g++ $1 main.cpp"; echo $C; $C; a.out; }case $1 in '0') run '' ;; '1') run '-fprofile-generate=.' ;; '2') run '-fprofile-use=.' ;; # -march=native不是默认选项，需显式指定，其作用是根据当前编译机器 # 的CPU自动启用支持的指令集优化。 '3') run '-O3 -march=native' ;; esac
main.cpp
#include <chrono> // C++11时间库 #include <random> #include <iostream> using namespace std;auto now = chrono::high_resolution_clock::now;// 模拟热点分支（PGO优化重点） int process (int x) {if (x > 100) // 该条件90%概率成立（模拟热点分支）return x * 2;return x + 1; }int main () {random_device rd;auto seed = rd();mt19937 gen(seed);//生成伯努利分布随机布尔值，90% truebernoulli_distribution dist(0.9);auto start = now();int sum = 0;for (int i = 0; i < 1'000'000; ++i)sum += process(dist(gen) ? 150 : 50);// F U C K !cout << chrono::duration<double>(now() - start).count() << "s\n";exit(sum); }
运行 (Intel N100)
~/pgo$ step 0 g++ main.cpp 0.0532354s ~/pgo$ step 1 g++ -fprofile-generate=. main.cpp 0.060655s ~/pgo$ step 2 g++ -fprofile-use=. main.cpp 0.0532936s ~/pgo$ step 3 g++ -O3 -march=native main.cpp 0.00564738s
colinsblog说：I experimented with some existing C++ 14 applications I’ve written. One, a flat-file to Parquet format converter, improved by only about five percent over an executable built with blanket -O3 optimization levels. Another, the “DCP” I’ve discussed before, improved by around thirty percent faster compared with the same program built with -O3. These tests were done with GCC 5.4, not exactly the newest. I’ll attempt to do similar tests with GCC 7 and 9.
我用的是gcc version 12.2.0 (Debian 12.2.0-14)
AI说：PGO是一种编译器优化技术，通过分析程序实际运行数据（如函数调用频率、分支路径等）生成配置文件，指导编译器对热点代码进行精准优化。其核心流程包括：插桩编译→数据采集→二次优化编译。PGO能显著提升性能，例如减少分支预测错误、优化代码布局以提高缓存命中率，在Chrome等应用中实现10%-20%的性能提升。该技术适用于计算密集型场景，需配合代表性数据收集以发挥最大效果。
AI好啊，讲PGO的中文网页基本上没有代码，而AI能编演示程序，写Makefile，虽然把-fprofile-generate和use的参数当成了文件名，导致use时说找不到文件。
补丁：step 1前得先rm *.gcda.
改成15'000'000后，0.799088s, 0.906551s, 0.800046s, 0.0843707s