From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 28042 invoked by alias); 30 Oct 2002 22:16:09 -0000 Mailing-List: contact gcc-prs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-prs-owner@gcc.gnu.org Received: (qmail 27988 invoked by uid 71); 30 Oct 2002 22:16:06 -0000 Date: Wed, 30 Oct 2002 14:16:00 -0000 Message-ID: <20021030221606.27987.qmail@sources.redhat.com> To: nobody@gcc.gnu.org Cc: gcc-prs@gcc.gnu.org, From: Michael Matz Subject: Re: optimization/6162: gcc 3.0.4: certain i386 asm reloader ice Reply-To: Michael Matz X-SW-Source: 2002-10/txt/msg01272.txt.bz2 List-Id: The following reply was made to PR optimization/6162; it has been noted by GNATS. From: Michael Matz To: Nathanael Nerode , Kevin Ryde Cc: , , , Subject: Re: optimization/6162: gcc 3.0.4: certain i386 asm reloader ice Date: Wed, 30 Oct 2002 23:09:20 +0100 (CET) Hi, On Wed, 30 Oct 2002, Nathanael Nerode wrote: > I know this is a regression, but: > * it's a subtle and difficult bug in reload, which may take a long time > and a lot of work to find Well, to find it is quite easy. reload is inherently incapable of handling more than one commutative operand, but there are two of them in the asm. If you are unlucky both of them would need to be swapped to make the insn valid, and this is what breaks reload, as it only can swap the last pair. I don't know why this constraint isn't documented, but anyway, that's the reason. To fix this indeed would be quite involved, as we would need to handle then all permutations of swappings (of which there are 4 with two pairs). Well, _I_ would fix this bug by documenting that behaviour. Note, that also, if we get rid of reload, the functionality will likely not change in that respect. > * reload is intended to go away for 3.4 On Thu, 31 Oct 2002, Kevin Ryde wrote: > The second (simpler) example I posted does it without that. > > > I don't think it's reasonable to hold up 3.2.1 or 3.3 for this bug. > > As far as I can tell you have to be pretty lucky, or unlucky, to > actually strike it. I've only had it two (or maybe three) times, and > not on finished code. Simply don't use more than one commutative pair, and you are safe (except if you really hit a bug of course ;-) ) Ciao, Michael.