[Bug target/64377] nios2 compile error in options-save.c

["marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64377

--- Comment #16 from Martin Liška <marxin at gcc dot gnu.org> ---
Thank you for testing, there's patch I've just sent to gcc-patches ML:
https://gcc.gnu.org/ml/gcc-patches/2015-01/msg01008.html.

Martin
>From gcc-bugs-return-473178-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Wed Jan 14 11:34:14 2015
Return-Path: <gcc-bugs-return-473178-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Delivered-To: listarch-gcc-bugs@gcc.gnu.org
Received: (qmail 5149 invoked by alias); 14 Jan 2015 11:34:13 -0000
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
Delivered-To: mailing list gcc-bugs@gcc.gnu.org
Received: (qmail 4535 invoked by uid 48); 14 Jan 2015 11:34:07 -0000
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/64541] FRE pass optimization failure
Date: Wed, 14 Jan 2015 11:34:00 -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: 5.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth 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: keywords cc short_desc
Message-ID: <bug-64541-4-gkfWlAPAF1@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-64541-4@http.gcc.gnu.org/bugzilla/>
References: <bug-64541-4@http.gcc.gnu.org/bugzilla/>
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: 2015-01/txt/msg01172.txt.bz2
Content-length: 1299

https://gcc.gnu.org/bugzilla/show_bug.cgi?idd541

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
                 CC|rguenther at suse dot de           |rguenth at gcc dot gnu.org
            Summary|.fre1 pass optimization     |FRE pass optimization
                   |failure                     |failure

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
The sources are different in that 2.c dereferences *p one more time after
*q is stored to while 1.c dereferences *q for the return value.  Thus an
equivalent 2.c would be

int f (int ** p, int ** q)
{
        ++*p;
        *q = *p;
        return **q;
}

it is true that we can still optimize the original 2.c but only because
*p and *q are equivalent (but it is probably not worthwhile the compile-time
cost
handling this). That is, we have to assume that p == q and thus the store to *q
invalidates the previously load *p.

I also think we have a duplicate report for this somewhere.

Simpler testcase (which is probably that in the duplicate):

int foo (int *p, int *q)
{
  *p = 1;
  *q = 1;
  return *p;
}