From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-482214-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 9549 invoked by alias); 30 Mar 2015 07:24:30 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 9485 invoked by uid 48); 30 Mar 2015 07:24:23 -0000
From: "kariya_mitsuru at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/65398] [5 Regression] [C++11] GCC rejects constexpr variable definitions with valid initialization
Date: Mon, 30 Mar 2015 08:18:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 5.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: kariya_mitsuru at hotmail dot com
X-Bugzilla-Status: REOPENED
X-Bugzilla-Priority: P1
X-Bugzilla-Assigned-To: mpolacek at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 5.0
X-Bugzilla-Flags:
X-Bugzilla-Changed-Fields:
Message-ID: <bug-65398-4-FyyFng8bft@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-65398-4@http.gcc.gnu.org/bugzilla/>
References: <bug-65398-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
X-SW-Source: 2015-03/txt/msg03358.txt.bz2

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.)