From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-patches-return-321414-listarch-gcc-patches=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 31603 invoked by alias); 21 Jun 2012 15:54:15 -0000
Received: (qmail 31589 invoked by uid 22791); 21 Jun 2012 15:54:13 -0000
X-SWARE-Spam-Status: No, hits=-6.0 required=5.0	tests=AWL,BAYES_00,KHOP_RCVD_UNTRUST,KHOP_THREADED,RCVD_IN_DNSWL_HI,RCVD_IN_HOSTKARMA_W,T_RP_MATCHES_RCVD
X-Spam-Check-By: sourceware.org
Received: from cantor2.suse.de (HELO mx2.suse.de) (195.135.220.15)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 21 Jun 2012 15:54:00 +0000
Received: from relay2.suse.de (unknown [195.135.220.254])	(using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits))	(No client certificate requested)	by mx2.suse.de (Postfix) with ESMTP id DB2A19FB23;	Thu, 21 Jun 2012 17:53:59 +0200 (CEST)
Date: Thu, 21 Jun 2012 16:41:00 -0000
From: Michael Matz <matz@suse.de>
To: Richard Guenther <richard.guenther@gmail.com>
Cc: Xinliang David Li <davidxl@google.com>,	Jason Merrill <jason@redhat.com>,	GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: New option to turn off stack reuse for temporaries
In-Reply-To: <CAFiYyc2_genu4SOJ963YqforcuopxXDWYXUeC6=66V-2pYEPXw@mail.gmail.com>
Message-ID: <alpine.LNX.2.00.1206211750190.6758@wotan.suse.de>
References: <CAAkRFZK_27tveOTLioz-YwfF_4w4qtTJkRFjno7r8risRVQsnQ@mail.gmail.com> <4FE26AFC.3000703@redhat.com> <CAAkRFZL_WkRtxRD4_U=_KzfPGtnmf=QxJSN_E=KfROKwTALjHQ@mail.gmail.com> <CAFiYyc2_genu4SOJ963YqforcuopxXDWYXUeC6=66V-2pYEPXw@mail.gmail.com>
User-Agent: Alpine 2.00 (LNX 1167 2008-08-23)
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; CHARSET=US-ASCII
Content-ID: <alpine.LNX.2.00.1206211752291.6758@wotan.suse.de>
X-IsSubscribed: yes
Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-patches.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-patches/>
List-Post: <mailto:gcc-patches@gcc.gnu.org>
List-Help: <mailto:gcc-patches-help@gcc.gnu.org>
Sender: gcc-patches-owner@gcc.gnu.org
X-SW-Source: 2012-06/txt/msg01419.txt.bz2

Hi,

On Thu, 21 Jun 2012, Richard Guenther wrote:

> The flag is not restricted to the C++ compiler and applies to all 
> automatic variables.

The use of that flag in the gimplifier (->in_cleanup_expr) makes it 
actually c++ specific.

> Also even with this flag there is no guarantee we cannot figure out 
> lifetime in other ways, for example if the temporary gets promoted to a 
> register. Also with this patch you remove code motion barriers which 
> might cause other issues.
> 
> A more "proper" place to fix this is when we actually do the stack 
> reuse, in cfgexpand.

That is true, though.  It would then also enable debugging help for 
pointers to things that go out-of-scope.


Ciao,
Michael.