[patch] enabling vectorization by default at -O3

[H.J. Lu]

On Thu, Sep 06, 2007 at 09:23:31AM -0400, Daniel Berlin wrote:
> On 9/6/07, H.J. Lu <hjl@lucon.org> wrote:
> > On Thu, Sep 06, 2007 at 01:49:52PM +0200, Uros Bizjak wrote:
> > > >
> > > > * Hmm, why is --ffast-math slower? And with vectorization that much
> >
> > Also see
> >
> > http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32183
> >
> > With -O2 --ffast-math, we turn a faster loop:
> >
> >       float sf;
> >       ...
> >       sf = 500 * sf;
> >       for (i = 0; i < ceplen; i++)
> >         sum[i] *= sf;
> >
> > into a slower loop:
> >
> >       for (i = 0; i < ceplen; i++)
> >         sum[i] = (sum[i]* 500)*sf;
> >
> > > > slower? I recheck induct (V.F, NV.F) and I could reproduce the timings.
> > > >
> > >
> > > > that is indeed interesting (I'd be happy to look at a testcase)
> > >
> > > This is PR 32084, http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32084
> > >
> 
> I still don't remember why we have reassoc2.  I'm in favor of removing
> it unless someone can show it's producing performance improvements :)

I got

Here are SPEC CPU 2006 -O2 -ffast-math differences between revision
125281 without the second reassoc and revision 125281 on Intel64:

                          (r125281 w/o reassoc2 - r125281)/r125281
400.perlbench                    0.492611%
401.bzip2                        0.613497%
403.gcc                          0%
429.mcf                          0%
445.gobmk                        0%
456.hmmer                        -0.787402%
458.sjeng                        1.14286%
462.libquantum                   0%
464.h264ref                      0%
471.omnetpp                      -0.869565%
473.astar                        0%
483.xalancbmk                    0.105374%
Est. SPECint(R)_base2006                 0%

410.bwaves                       1.8018%
416.gamess                       -1.14286%
433.milc                         -0.840336%
434.zeusmp                       0.657895%
435.gromacs                      -1.73348%
436.cactusADM                    -0.952381%
437.leslie3d                     -0.21692%
444.namd                         0%
447.dealII                       -2.33463%
450.soplex                       0%
453.povray                       0%
454.calculix                     -26.3852%
459.GemsFDTD                     0%
465.tonto                        0.704225%
470.lbm                          0%
481.wrf                          8.9613%
482.sphinx3                      0%
Est. SPECfp(R)_base2006                  -1.51515%

That is without reassoc2, SPEC CPU 2006 FP with -O2 -ffast-math
is down by about 1.5% on Core 2 Duo.


H.J.