From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-133309-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 4381 invoked by alias); 4 Mar 2005 03:42:02 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
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
Received: (qmail 4315 invoked by uid 48); 4 Mar 2005 03:41:54 -0000
Date: Fri, 04 Mar 2005 03:42:00 -0000
Message-ID: <20050304034154.4314.qmail@sourceware.org>
From: "pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
In-Reply-To: <20040817140542.17064.pbrook@gcc.gnu.org>
References: <20040817140542.17064.pbrook@gcc.gnu.org>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug tree-optimization/17064] -falias-noargument-global doesn't eliminate dead stores/loads
X-Bugzilla-Reason: CC
X-SW-Source: 2005-03/txt/msg00464.txt.bz2
List-Id: <gcc-bugs.sourceware.org>


------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-04 03:41 -------
Here is a testcase which we semi optimize on the RTL level but not at the tree level:
sum cannot alias a or b at all because of the default option for gfortran.

subroutine dot_product (sum, a, b, n)
   real*8 a(n), b(n), sum
   sum = 0
   do i = 1, n
     sum = sum + a (i) * b(i)
   end do
end

The reason why I say semi is because there is an extra fmr (PPC):
The loop looks like:
L4:
        lfd f13,0(r4)
        addi r4,r4,8
        lfd f0,0(r5)
        addi r5,r5,8
        fmadd f0,f13,f0,f12
        fmr f12,f0
        bdnz L4

If we had optimizate it at the tree level it would look like:
L4:
        lfd f13,0(r4)
        addi r4,r4,8
        lfd f0,0(r5)
        addi r5,r5,8
        fmadd f12,f13,f0,f12
        bdnz L4

Note how we don't have the extra fmr.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17064