X-POP3-Rcpt: mlehmann AT universe DOT sgh-net DOT de
24 Jan 1998 23:50:49 +0100 (CET)
From: Ronald Wahl <Ronald DOT Wahl AT Informatik DOT TU-Chemnitz DOT DE>
X-Sender: rwa AT goliath DOT csn DOT tu-chemnitz DOT de
To: Holger Burbach <holly AT cthulhu DOT rhein-neckar DOT de>
cc: Jack Duan <jduan AT sprintmail DOT com>, Brian Makin <makinb AT ctc DOT com>,
        beastium-list AT Desk DOT nl
Subject: Re: PGCC optimizing AMD K6?
In-Reply-To: <Pine.LNX.3.96.980121222144.998A-100000@uggae.rhein-neckar.de>
Message-ID: <Pine.LNX.3.96.980124232801.6485A-100000@goliath.csn.tu-chemnitz.de>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: Marc Lehmann <pcg AT goof DOT com>
Status: RO
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Content-Length: 1566
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On Wed, 21 Jan 1998, Holger Burbach wrote:

> On Wed, 21 Jan 1998, Ronald Wahl wrote:
> 
> > No test w/o -funroll-loops? I've had discovered that it will result in
> > slower code. Maybe this has changed with pgcc/egcs-980115 but it would be
> > nice to see the results.
> 
> Okay, here they are!
> [...]

Thanx...

Since pgcc-980122 is out, can you verify that -ffast-math
(w/o funroll-loops) slows down some integer benches? The neural net bench
still doesn't return if -funroll-loops or -funroll-all-loops is used. Has
anybody checked if this is a problem of egcs or only pgcc? Maybe we should
report this problem on the egcs-list...
But anyway it's nice to see that -funroll-loops is a big win...

ron

PS: If you send benches it would be nice to see how -ffast-math influences
    the results. At the moment it's not generally a win and seem to slow
    down integer code (how this?).

PPS (for Marc): Since I've seen many fxch instructions in the assembly
                output of nbench I have to note that these will not
                improve performance like on a pentium. If it's possible
                we should remove these. Minimizing the number of fpu
                instructions should be one of the goals on a K6 since
                most of these have a latency of 2 cycles and need two
                cycles to execute.

-- 
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 \ WWW: http://www.tu-chemnitz.de/~row             \
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