Returning a C string in a constexpr function: why no warning from the compiler?

Consider the following code:

constexpr auto f()
{
    auto str = "Hello World!";
    return str;
}

int main(int argc, char* argv[])
{
    static constexpr auto str = f();
    std::cout << str << std::endl;
    return 0;
}

Is that normal that my compiler does not display any warning? Is it defined behavior? Do I have the guarantee that the program will display "Hello World!"? I would expect the "Hello World!" not to live beyond the scope of the function...