Intel Compiler vs. GCC

test.cpp

#include <iostream>
#include <random>

struct myrand {
  uint32_t operator()() {
    static uint32_t y = 2463534242;
    y = y ^ (y << 13); y = y ^ (y >> 17);
    return y = y ^ (y << 5);
  }
  uint32_t max(){
    return std::mt19937::max();
  }
  uint32_t min(){
    return 0;
  }
};

double run(void) {
  myrand mt;
  double r = 0.0;
  std::uniform_real_distribution<> ud(-1.0, 1.0);
  for (int j = 0; j <10000; j++) {
    for (int i = 0; i < 10000; i++) {
      if (i%2) r += ud(mt);
    }
  }
  return r;
}

int main(){
  std::cout << run() << std::endl;
}

Environment

• CPU: Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
• OS: SUSE Linux Enterprise Server 11 (x86_64)
• g++ (GCC) 5.4.0
• icpc (ICC) 18.0.5 20180823

$ g++ -O3 -march=native -Wall -Wextra -std=c++11  test.cpp -o gcc.out
$ icpc -O3 -xHOST -Wall -Wextra -std=c++11  test.cpp -o icpc.out
$ time ./gcc.out
-5872.91
./gcc.out  0.26s user 0.00s system 98% cpu 0.259 total

$ time ./icpc.out
-5872.91
./icpc.out  4.52s user 0.00s system 99% cpu 4.526 total

The Intel compiler is 17.5x slower than GCC.