void bar(){}

constexpr int foo(int a)
{
    if (a <=0 )
        bar();

    return 1;
}

int main()
{
    int a1[foo(1)];  //no compile error
}

int a2[foo(-1)]; //will give a compile error, which is expected,
                 //since non-constexpr function is not allowd in constexpr context