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Re: [rfc] subreg lowering pass / Overcoming double-set difficulties for CC re-use
- From: Rask Ingemann Lambertsen <rask at sygehus dot dk>
- To: Hans-Peter Nilsson <hp at bitrange dot com>
- 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 16:50:55 +0200
- Subject: Re: [rfc] subreg lowering pass / Overcoming double-set difficulties for CC re-use
- References: <Pine.LNX.4.44.0605280835280.26534-100000@www.eyesopen.com> <200606182228.11327.bjoern.m.haase@web.de> <m3psh5yp5v.fsf@keats.corp.google.com> <200607021713.20971.bjoern.m.haase@web.de> <Pine.BSF.4.58.0608301855120.15007@dair.pair.com>
On Wed, Aug 30, 2006 at 08:28:32PM -0400, Hans-Peter Nilsson wrote:
> On Sun, 2 Jul 2006, [utf-8] Björn 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?
> 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.
--
Rask Ingemann Lambertsen