From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30394 invoked by alias); 21 Oct 2013 02:14:39 -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 30356 invoked by uid 48); 21 Oct 2013 02:14:33 -0000 From: "glisse at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/58806] New attribute for functions that access memory only through their arguments Date: Mon, 21 Oct 2013 02:14:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 4.9.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: enhancement X-Bugzilla-Who: glisse 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: 2013-10/txt/msg01430.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58806 --- Comment #1 from Marc Glisse --- struct A { int i; double d; }; void g(double*); void f(){ A a; a.i=1; g(&a.d); if(a.i != 1) __builtin_abort(); } Here, I guess g is allowed to take its argument, cast it to char*, subtract offsetof(struct A, d), cast to A* and go modify ->i of that? It would be convenient to have a way to promise that g does no such thing, but that looks like a different type of promise than the one in comment #0. The example is derived from the use of a temporary object of a reference-counted type, where ideally all uses of the counter should disappear and the code be equivalent to: double d; g(&d);