This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: Bootstrap times on mainline are getting worse
- From: Tim Prince <tprince at computer dot org>
- To: Geert Bosch <bosch at gnat dot com>
- Cc: Zack Weinberg <zack at codesourcery dot com>, <gcc at gcc dot gnu dot org>
- Date: Sat, 19 Oct 2002 12:10:58 -0700
- Subject: Re: Bootstrap times on mainline are getting worse
- References: <AB43B2F6-E394-11D6-84EB-00039344BF4A@gnat.com>
- Reply-to: tprince at computer dot org
On Saturday 19 October 2002 11:57, Geert Bosch wrote:
> Roger wrote:
> > Also be carefull about changing these RTX costs to unsigned char.
> > Pentium4 already has integer division costs at around 120, and
> > improvements in superscalar issue vs memory latency could easily
> > push values above 256 on x86 within only a year or so. Just look
> > at the curves for i386, i486, pentium, pentiumpro, pentium4....
>
> I don't see how it can hurt to max out the cost at some point.
> If we select an instruction with a cost higher than 100, it must
> mean there is little alternative but to use that instruction.
>
> -Geert
I understand there are examples where the high costs assessed for P4 shift
and multiply produce slower code, since long add sequences may exceed trace
cache capacity in practical contexts. Processor variants are coming along
with P4 instruction set compatibility, with smaller latencies. I usually
modify the costs arbitrarily to come closer to the Intel P4 Optimization
Guide recommended instruction sequence choice trade points.
--
Tim Prince