Changing constexpr member using fail method

Question

I am trying to change the value of an object member constexprusing a method, but I do not understand why it does not work in this particular case:

#include <iostream>

struct test
{
    int m_counter = 0;

    constexpr test()
    {
        m_counter++;
        m_counter++;
        increment();
        increment();
        increment();
    }

    constexpr void increment()
    {
        m_counter++;   
    }

    constexpr int value() const
    {
        return m_counter;
    }
};

template<int value>
constexpr void check()
{
    std::cout << value << std::endl;
}

// constexpr test t; // value = 3, why ?

int main()
{
    constexpr test t; // value = 5, ok
    check<t.value()>();
}

I do not understand why the value is 3 when I create an object in the global scope. msvc and clang display 5 in both cases, but not gcc. Who is wrong?

Answer 1

, g++, g++ 5.1 g++ 7.0. , , . , , increment(), , :

constexpr test()
{
    m_counter++; // executed
    m_counter++; // executed
    increment(); // executed
    increment(); // NOT executed
    increment(); // NOT executed
}

// [...] will print 3

constexpr test()
{
    m_counter++; // executed
    m_counter++; // executed
    increment(); // executed
}

// [...] will print 3

constexpr test()
{
    m_counter++; // executed
    m_counter++; // executed
}

// [...] will print 2

constexpr test()
{
    m_counter++; // executed
    m_counter++; // executed
    increment(); // executed
    increment(); // NOT executed
    increment(); // NOT executed
    increment(); // NOT executed
    increment(); // NOT executed
    increment(); // NOT executed
}

// [...] will print 3

, increment() . increment() . m_counter++ .

constexpr test()
{
    m_counter++; // executed 
    m_counter++; // executed
    increment(); // executed
    increment(); // NOT executed
    m_counter++; // executed
    m_counter++; // executed
    increment(); // NOT executed
    increment(); // NOT executed
}

// [...] will print 5

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