[Bug c++/66287] [C++11] A constexpr variable of "const int* const&" cannot be initialized

[kariya_mitsuru at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66287

--- Comment #1 from Mitsuru Kariya <kariya_mitsuru at hotmail dot com> ---
I found several examples that cause the similar error message.

=========== sample code 1 ===========
constexpr int copy(const int& v)
{
    return v;
}

constexpr const int& r = 42;
constexpr const int& c = copy(r);

int main() {}
=========== sample code 1 ===========
================================== output 1 ==================================
prog.cc:7:32: error: modification of '_ZGR1c1' is not a constant-expression
 constexpr const int& c = copy(r);
                                ^
================================== output 1 ==================================
cf. http://melpon.org/wandbox/permlink/fbHQBPKu1LETPmIr


=========== sample code 2 ===========
struct T {
    int i;
};

constexpr T copy(const T& v)
{
    return v;
}

constexpr const auto& r = T{42};
constexpr const auto& c = copy(r);

int main() {}
=========== sample code 2 ===========
================================== output 2 ==================================
prog.cc:11:33: error: modification of '_ZGR1c1' is not a constant-expression
 constexpr const auto& c = copy(r);
                                 ^
================================== output 2 ==================================
cf. http://melpon.org/wandbox/permlink/0KeNtSOZrybNAnxa

I think these examples should be compiled successfully, but I am not sure about
the latter case because CLANG also rejects it.