From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-411315-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 27884 invoked by alias); 7 Jan 2013 04:27:18 -0000
Received: (qmail 26733 invoked by uid 48); 7 Jan 2013 04:25:56 -0000
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/53900] [regression] Too optimistic on a alignment assert
Date: Mon, 07 Jan 2013 04:27:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia at gcc dot gnu.org
X-Bugzilla-Status: RESOLVED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-53900-4-wUqsI8Rq5g@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-53900-4@http.gcc.gnu.org/bugzilla/>
References: <bug-53900-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
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
X-SW-Source: 2013-01/txt/msg00434.txt.bz2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53900

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> 2013-01-07 04:25:38 UTC ---
>  __attribute__((aligned(16))) float array[4];

Explicitly says the array is aligned to 16 bytes which means it is undefined by
the C/C++ standard what happens if you a pointer to the struct which contains
this array.  As this pointer will always be aligned by definition of the struct
(and any other use of it is undefined), then by definition
std::ptrdiff_t(array) will always have the lower 8bits be zero.