Trad vs. Clang

main.cpp

#include <algorithm>
#include <random>
#include <cstdio>

int main(void) {
  std::mt19937 mt(1);
  int s = 0;
  for (int i = 0; i < 100; i++) {
    std::uniform_real_distribution<double> ud(0.0, 1.0);
    for(int j=0;j<10000;j++){
      if(ud(mt) < 0.5){
        s +=1;
      }
    }
  }
  printf("%d\n",s);
}

Compile.

FCCpx -Kfast main.cpp -o trad.out
FCCpx -Kfast -Nclang main.cpp -o clang.out

Run.

$ time ./trad.out
499042

real    0m0.101s
user    0m0.068s
sys     0m0.022s

$ time ./clang.out
499042

real    0m2.964s
user    0m2.938s
sys     0m0.020s