GCC Optimization Example

example.cpp

#include <chrono>
#include <iostream>

int test() {
    long long number = 0;
    for (long long i = 0; i != 2000000000; ++i) {
        number += 3;
    }
	std::cout << number << "\n";
    return 3;
}

template <typename T>

float getExecutionTime(T f) {
    auto getTime1 = std::chrono::high_resolution_clock::now();
    f();
    auto getTime2 = std::chrono::high_resolution_clock::now();
    std::chrono::duration<double, std::milli> fpms = getTime2 - getTime1;
    return fpms.count();
}


int main() {
    std::cout << getExecutionTime(test) << "ms";
} 

run.bat

g++ example.cpp -o l0.exe
g++ example.cpp -o l1.exe -O
g++ example.cpp -o l2.exe -O2
g++ example.cpp -o l3.exe -O3
l0
l1
l2
l3
pause

~Makefile

all: l0 l1 l2 l3

clean: 
	rm -f l0 l1 l2 l3
run:
	./l0
	./l1
	./l2
	./l3

l0: example.cpp
	g++ -o l0 example.cpp -w

l1: example.cpp
	g++ -o l1 example.cpp -O -w

l2: example.cpp
	g++ -o l2 example.cpp -O2 -w

l3: example.cpp
	g++ -o l3 example.cpp -O3 -w