From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-343467-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 3139 invoked by alias); 14 Jan 2011 20:04:38 -0000
Received: (qmail 3124 invoked by uid 22791); 14 Jan 2011 20:04:37 -0000
X-SWARE-Spam-Status: No, hits=-2.8 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 14 Jan 2011 20:04:32 +0000
From: "Joost.VandeVondele at pci dot uzh.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/47298] New: -O3 destroys beautifully vectorized code obtained at -O2
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: Joost.VandeVondele at pci dot uzh.ch
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-47298-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Date: Fri, 14 Jan 2011 20:53:00 -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
X-SW-Source: 2011-01/txt/msg01406.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47298

           Summary: -O3 destroys beautifully vectorized code obtained at
                    -O2
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: Joost.VandeVondele@pci.uzh.ch


current trunk generates really fast vectorized code for the following testcase
(a 12x12x12 matrix multiply, c=c+a*b, benchmarked with a,b,c in cache) as can
be seen from the assembly:

> cat compare.f90
   SUBROUTINE HARD_NN_12_12_12(C,A,B) 
      REAL(KIND=8), INTENT(INOUT) :: C(12,*)
      REAL(KIND=8), INTENT(IN)    :: B(12,*), A(12,*)
      INTEGER ::i,j,l
      DO j=1,12 ; DO i=1,12; DO l=1,12
         C(i,j)=C(i,j)+A(i,l)*B(l,j)
      ENDDO ; ENDDO ; ENDDO
   END SUBROUTINE HARD_NN_12_12_12

however, this only happens with:

gfortran-trunk -O2 -funroll-loops -ftree-vectorize -ffast-math -march=corei7
-msse4.2  compare.f90

while switch -O2 to -O3 causes 'bad' code.

gfortran-trunk -O3 -funroll-loops -ftree-vectorize -ffast-math -march=corei7
-msse4.2  compare.f90

with the following tester below

-O2 runs in about 4.4s
-O3 runs in about 7.0s

> cat test_compare.f90 
      REAL(KIND=8), DIMENSION(12,12) :: A,B,C
      A=0 ; B=0 ; C=0
      DO I=1,10000000
         CALL HARD_NN_12_12_12(C,12,A,12,B,12)
      ENDDO
      END