From maintainers-request at octave dot org Thu Nov 11 23:40:50 2004
Subject: Re: gcc 3.4 and Octave/lapack problems
From: "Dmitri A. Sergatskov" <dmitri at unm dot edu>
To: Jskud at Jskud dot com
CC: "John W. Eaton" <jwe at bevo dot che dot wisc dot edu>, maintainers@octave.org
Date: Thu, 11 Nov 2004 22:37:43 -0700

Jskud at Jskud dot com wrote:

> 
> The problem is that -ffloat-store can really slow things down.  Dmitri
> observed a 20% slowdown in Octave using -ffloat-store everywhere.  I saw
   ^^^^^^^^^^^^^^^^^^^^^^^^

I noticed a slowdown with for loop in octave interpreter. But that of little importance
(since it is slow anyway). I do not see _any_
slowdown with functions which call some lapack or fft routines. In fact some of
the lapack routines (schur() e.g.) run faster (I guess they converge faster).
I still believe that this is a gcc bug/problem, but gcc people will not
talk to me unless I provide them a simple code sample. I have a simple code that
demonstrate the problem in lapack (see below), but that opens to interpretation that
this is a lapack problem.

Dmitri.
p.s. The following code linked with lapack shipped with FedoraCore 3 hangs for at least
few minutes:

[dima at localhost test1]$ cat xxx.f
       program xxx
       character*1 jobvl, jobvr
       integer n, ldvl, ldvr, lwork
       parameter (jobvl='N', jobvr='N')
       parameter (n = 3, ldvl = 3, ldvr = 3, lwork = 9)
       double precision a(n,n)
       double precision wr(n)
       double precision wi(n)
       double precision vl(ldvl,n)
       double precision vr(ldvr,n)
       double precision work(lwork)
       integer info, i, j
       data a /1.0d0, 4.0d0, 7.0d0,
      $        2.0d0, 5.0d0, 8.0d0,
      $        3.0d0, 6.0d0, 9.0d0/
       do i = 1, n
         print *, (a(i,j), j = 1, n)
       enddo
       call dgeev (jobvl, jobvr, n, a, lda, wr, wi, vl, ldvl, vr, ldvr,
      $ work, lwork, info)
       print *, 'dgeev info: ', info
       end
[dima at localhost test1]$ g77 xxx.f -llapack -lblas
[dima at localhost test1]$ ./a.out
   1.  2.  3.
   4.  5.  6.
   7.  8.  9.