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Date: Fri, 26 Mar 2004 12:17:00 -0000
From: "jv244 at cam dot ac dot uk" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Message-ID: <20040326121739.14741.jv244@cam.ac.uk>
Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug optimization/14741] New: missing transformations lead to poorly optimized code
X-Bugzilla-Reason: CC
X-SW-Source: 2004-03/txt/msg03103.txt.bz2
List-Id: <gcc-bugs.sourceware.org>

I think this testcase is worth a PR so that it might be solved one day.

as shown and discussed in :
http://gcc.gnu.org/ml/gcc/2004-03/msg01457.html
and related messages gfortran is about 10 times slower than ifc (or xlf) on the
code  below, and no compiler options seem to be able to change this (this seems
not tree-ssa specific).

INTEGER, PARAMETER :: N=1024
REAL*8 :: A(N,N), B(N,N), C(N,N)
REAL*8 :: t1,t2
A=0.1D0
B=0.1D0
C=0.0D0
CALL cpu_time(t1)
CALL mult(A,B,C,N)
CALL cpu_time(t2)
write(6,*) t2-t1,C(1,1)
END

SUBROUTINE mult(A,B,C,N)
REAL*8 :: A(N,N), B(N,N), C(N,N)
INTEGER :: I,J,K,N
DO J=1,N
DO I=1,N
DO K=1,N
  C(I,J)=C(I,J)+A(I,K)*B(K,J)
ENDDO
ENDDO
ENDDO
END

-- 
           Summary: missing transformations lead to poorly optimized code
           Product: gcc
           Version: tree-ssa
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jv244 at cam dot ac dot uk
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14741