Passing primitive type by reference C++

Question

I have found many people saying that passing a primitive value, such as an int, by value, is faster than passing by reference.

However, I wrote the code below, and passing by value, and it averages 2 second run time.

#include <iostream>
#include <chrono>

using namespace std;
using namespace chrono;

int func(unsigned long long x) {
  ++x;
  return x;
}

int main()
{
  for (int b = 0; b < 5; b++) {
    
    unsigned long long x = 0;
  
    auto start = high_resolution_clock::now();
    for (long long j = 0; j < 500000; j++) {
      for (long long i = 0; i < 180000000; i++) {
        x = func(x);
      }
    }
  
    auto stop = high_resolution_clock::now();
    auto elapsed = std::chrono::high_resolution_clock::now() - start;
  
    long long microseconds = std::chrono::duration_cast<std::chrono::microseconds>(elapsed).count();
    cout << x <<" iterations took " << microseconds << " microseconds\n";
  }
}

Then when I pass by reference, it averages less than 1 microsecond.

#include <iostream>
#include <chrono>

using namespace std;
using namespace chrono;

void func(unsigned long long& x) {
  ++x;
}

int main()
{
  for (int b = 0; b < 5; b++) {
    
    unsigned long long x = 0;
  
    auto start = high_resolution_clock::now();
    for (long long j = 0; j < 500000; j++) {
      for (long long i = 0; i < 180000000; i++) {
        func(x);
      }
    }
  
    auto stop = high_resolution_clock::now();
    auto elapsed = std::chrono::high_resolution_clock::now() - start;
  
    long long microseconds = std::chrono::duration_cast<std::chrono::microseconds>(elapsed).count();
    cout << x <<" Took " << microseconds << " microseconds\n";
  }
}

I would like an explanation to why this happens please.

Disclaimer: I am fairly new to C++