profile.cpp

#include <iostream>
#include <chrono>

struct Color {
    float a, b, c, d;
};

volatile float sink = 0.0f;

#if defined(_MSC_VER)
#define NOINLINE __declspec(noinline)
#else
#define NOINLINE __attribute__((noinline))
#endif

void pass_by_value(Color col) {
    sink = col.a + col.b + col.c + col.d;
}

NOINLINE void pass_by_const_ref(const Color &col) {
    sink = col.a + col.b + col.c + col.d;
}

int main() {
    const int iterations = 100000000;
    Color col { 1.0f, 2.0f, 3.0f, 4.0f };

    auto start = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < iterations; ++i) {
        pass_by_value(col);
    }
    auto end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> elapsed_value = end - start;
    std::cout << "Time pass_by_value: " << elapsed_value.count() << " s\n";

    start = std::chrono::high_resolution_clock::now();
    for (int i = 0; i < iterations; ++i) {
        pass_by_const_ref(col);
    }
    end = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double> elapsed_const_ref = end - start;
    std::cout << "Time pass_by_const_ref: " << elapsed_const_ref.count() << " s\n";

    return 0;
}

g++ -O2 -std=c++11 profile.cpp -o profile