[Bug c++/65398] [5 Regression] [C++11] GCC rejects constexpr variable definitions with valid initialization

["kariya_mitsuru at hotmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65398

--- Comment #6 from Mitsuru Kariya <kariya_mitsuru at hotmail dot com> ---
I also found a strange behavior like below.

============================== sample code ==============================
#include <iostream>

constexpr char s1[] = "s1";
constexpr char s2[] = "s2";

bool f(const char* p1, const char* p2) { return p1 == p2; }

constexpr auto eq1 =   &s1[sizeof(s1)] == &s2[0];
          auto eq2 = f(&s1[sizeof(s1)],   &s2[0]);

int main()
{
    std::cout << static_cast<const void*>(&s1[sizeof(s1)]) << std::endl;
    std::cout << static_cast<const void*>(&s2[0]) << std::endl;
    std::cout << std::boolalpha << eq1 << ", " << eq2 << std::endl;
}
============================== sample code ==============================
============================== output ==============================
0x400bb8
0x400bb8
false, true
============================== output ==============================
cf. http://melpon.org/wandbox/permlink/Iu0rFFMgeYqT98fo


I think that it should either

1) cause a compilation error at the definition of the eq1 if the result of
"&s1[sizeof(s1)] == &s2[0]" is "unspecified".

or

2) output "true, true" because both the "&s1[sizeof(s1)]" and "&s2[0]"
represent the same address.

but I am not sure which behavior is appropriate.

(I cannot find an explicit description by which comparison between one past the
end pointer and another object's pointer is "unspecified behavior", in the C++
standard.)