[Bug ipa/123227] -Os miscompiles code by merging member and non-member functions with different nullability assumptions

[dave.w4 at coalgebraic dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123227

--- Comment #1 from Dave <dave.w4 at coalgebraic dot com> ---
In the sample code the Data struct is unnecessary. The following simpler
code also exhibits the problem:

enum Val { zero = 0 };

inline Val&
operator|=(Val& a, Val b)
{
    return a = static_cast<Val>(static_cast<int>(a) | static_cast<int>(b));
}

struct Link {
    Val get_vals();
    Val val;
    Link* next;
};

Val
Link::get_vals()
{
    Val v = zero;
    for (Link* l = this; l; l = l->next)
        v |= l->val;
    return v;
}

Val
get_vals(Link* l)
{
    Val v = zero;
    for (; l; l = l->next)
        v |= l->val;
    return v;
}

int
main(int, char**)
{
    return get_vals(0);
}