On Fri, Jun 15, 2007 at 11:33:52PM -0400, Vladimir N. Makarov wrote: > H. J. Lu wrote: > > >On Fri, Jun 15, 2007 at 06:21:53PM -0700, Ian Lance Taylor wrote: > > > > > >>This is hardly a new thought, but I believe that for the i386 gcc is > >>handicapped by reload. No matter how smart we are before reload, it > >>just take one poor decision by reload in an inner loop and we've lost > >>all the gains. Reload has enormous complexities which are mostly > >>irrelevant for the i386. And I think that the idea of doing register > >>allocation separately from spill code generation does not make sense > >>on the i386. > >> > >> > >> > > > >Why don't we turn on vectorizer at -O3 or even -O2, depending on > >ISA? I added -ftree-vectorize to BOOT_CFLAGS on x86-64. According to > >-ftree-vectorizer-verbose=1, there are 82 loops vectorized in > >gcc source. There are no regressions. There are not much changes > >in bootstrap time as well as "make check" time. > > > > > > > A mount ago I did some measurements of the effect of the vectorizer for > Core2 in 64-bit mode. Unfortunately, I saw small improvement (as I > remember less than 1% for SPECInt2000).
Vectorizer works only when there are vector instructions available which vectorizer can take advantage of. Adding -mssse3 should make vectorizer to work a little bit better. SSE4 will improve vectorizer even more. > > Vectorizer is a big a project and may be we will see more improvements > in future. They promissed implement SLP two years ago and now I see it > happens. It would be nice to see it not only in loops. There are quite a few known simple cases which vectorizer fails to vectorize. Also, not all x86 vector instructions are supported by vectorizer. H.J.
