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Re: [rfc] subreg lowering pass / Overcoming double-set difficulties for CC re-use
- From: Hans-Peter Nilsson <hp at bitrange dot com>
- To: Rask Ingemann Lambertsen <rask at sygehus dot dk>
- Cc: Björn Haase <bjoern dot m dot haase at web dot de>, gcc-patches at gcc dot gnu dot org
- Date: Mon, 16 Oct 2006 15:24:34 -0400 (EDT)
- Subject: Re: [rfc] subreg lowering pass / Overcoming double-set difficulties for CC re-use
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On Mon, 16 Oct 2006, Rask Ingemann Lambertsen wrote:
> On Wed, Aug 30, 2006 at 08:28:32PM -0400, Hans-Peter Nilsson wrote:
> > On Sun, 2 Jul 2006, [utf-8] BjÃ¶rn Haase wrote:
> > > Ian Lance Taylor wrote on Montag, 19. Juni 2006 20:29 :
> > > > Obviously the MD file would have to be modified to add the double-SET
> > > > instructions. Maybe most of the CC0 machine descriptions already have
> > > > those operations--I haven't checked.
> > No, that's part of the pattern explosion you'll see when
> > adjusting the post-cc0 port to get the cc0 performance. :(
> I don't quite understand why this would cause an explosion in the
> patterns. We're talking about three times the number of patterns for insns
> which modify the condition codes as a byproduct, aren't we?
For a typical cc0 machine, almost all patterns do...
> > Further details TBD. (I think I've mentioned this idea loosely
> > before, probably on IRC.) FWIW, I'm definitely not going to
> > code up this until I've changed over the CRIS port (done, but
> > with horrible pattern explosion and code size and performance
> > regressions; the latter solvable bug fixes to general gcc
> > parts). It seems it's surely needed.
> I'm curious. I'd like to see a few examples.
If what I gave wasn't illuminating enough, that'll have to