From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 10168 invoked by alias); 16 Jun 2014 22:28:17 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 10122 invoked by uid 48); 16 Jun 2014 22:28:13 -0000 From: "redi at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/56785] std::tuple of two elements does not apply empty base class optimization when one of its elements is a std::tuple with two elements Date: Mon, 16 Jun 2014 22:28:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Version: 4.7.2 X-Bugzilla-Keywords: X-Bugzilla-Severity: enhancement X-Bugzilla-Who: redi at gcc dot gnu.org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: 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: 2014-06/txt/msg01406.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56785 --- Comment #4 from Jonathan Wakely --- The cause is that every N-tuple hierarchy ends with an empty _Tuple_impl base, so when there are several of those in the same hierarchy they need to have separate addresses. It should be possible to fix by eliminating that terminal objet in the inheritance hierarchy. The obvious way duplicates a chunk of code, I think it should be possible to do it in a nicer way, which I'm experimenting with.