Re: [PATCH] more loop.c fixes for -fprofile-loop-arrays

[Jan Hubicka <jh at suse dot cz>]

> On Wed, May 15, 2002 at 05:27:50PM -0700, Richard Henderson wrote:
> > On Wed, May 15, 2002 at 02:46:38PM -0700, Janis Johnson wrote:
> > >    -  For conditional code, skip the prefetch if PREFETCH_CONDITIONAL
> > >       is zero (this was originally intended), but preserve the current
> > >       behavior by defining PREFETCH_CONDITIONAL to one if it has not
> > >       already been defined.
> > 
> > Is there some benefit to preserving the old behaviour?
> 
> On large benchmarks (SPEC int) it doesn't make much difference on ia64.
> On small artificial benchmarks written just to check out this behavior,
> prefetching even for accesses that are seldom executed helps on ia64.
> For this and the other symbols controlling which heuristics are used
> I'd like to do more experimenting so that the defines in loop.c are good
> for the common case, and they can be overridden for each target (and
> documented, of course).

While developing the patch I didn't make much testing about tunning the
heuristics, unfortunately.  It is quite well possible, that the old behaviour
is losing at 386 as well.  My approach has been to be conservative at start and
try tunning later, unforutnately I didn't get into the second stage quite yet.

Definitly there are two (if my memory serves well) benchmarks in specs that
lose due to -fprefetch-loop-arrays.  It may be interesting to investigate the
purposes.  I hope to do so next month, after finals.

Honza
> 
> > 
> > > -	  index += size;
> > > +	  /* index += size; */
> > 
> > Remove code; do not commit it out.
> 
> Oops, that wasn't supposed to be there.
> > 
> > Otherwise ok.
> > 
> > 
> > r~