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From: Segher Boessenkool <segher@koffie.nl>
To: David Edelsohn <dje@watson.ibm.com>,
	Zack Weinberg <zack@codesourcery.com>,
	Richard Kenner <kenner@vlsi1.ultra.nyu.edu>,
	gcc-patches@gcc.gnu.org
Subject: Re: rs6000 fused multiply-add patch [+ patchlet]
Date: Mon, 06 Jan 2003 04:07:00 -0000	[thread overview]
Message-ID: <3E19010F.D399E5C2@koffie.nl> (raw)
In-Reply-To: <3E18FFA3.37F681F7@koffie.nl>

Segher Boessenkool wrote:
> 
> David Edelsohn wrote:
> >
> >         I don't think that anyone is objecting to the concept and the
> > benefit.  If I understand correctly, the patch violates the semantics of
> > the combiner algorithm which requires a declining cost calculated as the
> > number of instructions.  Allowing combinations that do not decrease the
> > cost would make the algorithm non-deterministic and possibly not converge,
> > right?
> 
> Only if the "canonicalizations" don't actually canonicalize... but yes, in
> that (hypothetical) case that could happen.  Some documentation might be
> needed to that extend if this patch ever gets accepted.

I should add that this would require two simplifications that do exactly the
opposite transform, and would maybe already recurse -- in a subroutine of combine.


Segher

  reply	other threads:[~2003-01-06  4:07 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2002-12-31  3:59 Richard Kenner
2003-01-05 23:24 ` Zack Weinberg
2003-01-06  2:26   ` David Edelsohn
2003-01-06  4:02     ` Segher Boessenkool
2003-01-06  4:07       ` Segher Boessenkool [this message]
2003-01-06 23:21     ` Geoff Keating
2003-01-09 22:41       ` Segher Boessenkool
  -- strict thread matches above, loose matches on Subject: below --
2003-01-10  2:15 Richard Kenner
2003-01-12  1:38 ` Segher Boessenkool
2003-01-06 22:09 Richard Kenner
2003-01-02  1:39 Richard Kenner
2003-01-04  1:59 ` Segher Boessenkool
2002-12-30  4:58 Richard Kenner
2002-12-30 20:17 ` Segher Boessenkool
2002-12-30 20:51   ` David Edelsohn
2003-01-02  0:52     ` Segher Boessenkool
2003-01-02  1:44       ` Geoff Keating
2003-01-04  1:59         ` Segher Boessenkool
2002-12-29  5:13 Richard Kenner
2002-12-29 19:25 ` Segher Boessenkool
2002-12-03 17:29 rs6000 fused multiply-add patch David Edelsohn
2002-12-04 19:41 ` Segher Boessenkool
2002-12-05 14:04   ` Geoff Keating
2002-12-20 21:08     ` rs6000 fused multiply-add patch [+ patchlet] Segher Boessenkool
2002-12-20 21:38       ` Geoff Keating
2002-12-20 22:21         ` Segher Boessenkool
2002-12-20 22:28           ` David Edelsohn
2002-12-21 21:55           ` Geoff Keating
2002-12-28 22:08           ` Segher Boessenkool

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