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Re: floor on i386

To: Brad Lucier <lucier at math dot purdue dot edu>
Subject: Re: floor on i386
From: Jan Hubicka <jh at suse dot cz>
Date: Tue, 25 Sep 2001 17:00:25 +0200
Cc: Jan Hubicka <jh at suse dot cz>, Alexandre Oliva <aoliva at redhat dot com>, Joe Buck <jbuck at synopsys dot COM>, Chris Lattner <sabre at nondot dot org>, gcc at gcc dot gnu dot org
References: <20010925154659.B13734@atrey.karlin.mff.cuni.cz> <200109251447.f8PEl2E05637@banach.math.purdue.edu>

> > Major problem still remains in reload.
> > If we don't want to get exact IEEE by setting proper precisity before each
> > mathematic operation (as SH4 does IMO), we will run into problems with spills ,
> > since these can be put in place control word is set to some wrong value
> > resutlting in wrong rounding before storing.
> 
> If spills spilled the extended precision value, which is needed
> anyway for proper IEEE conformance, this wouldn't be an issue.

Yes, but it is big performance problem when done, at least for AMD CPUs, where
XFmode spills cost a lot more than DF/or SFmode, so it should not be enabled unconditionally.
(I was trying to implement this idea in the past and it appears to be quite dificult to do
too :( )

Honza
> 
> Brad

Follow-Ups:
- Re: floor on i386
  - From: Tim Prince

References:
- Re: floor on i386
  - From: Jan Hubicka
- Re: floor on i386
  - From: Brad Lucier

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