From: Roger Sayle <roger@eyesopen.com>
To: Jan Hubicka <hubicka@ucw.cz>
Cc: gcc@gcc.gnu.org
Subject: Re: x87 float truncation/accuracy (gcc vs. icc/msvc)
Date: Thu, 18 Mar 2004 19:18:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.44.0403181051460.21203-100000@www.eyesopen.com> (raw)
In-Reply-To: <20040318183718.GC25385@atrey.karlin.mff.cuni.cz>
On Thu, 18 Mar 2004, Jan Hubicka wrote:
> You can just cut&paste the extendsfdf implementation. Basically it
> immitate move pattern for x87 but do proper conversions for SSE.
> I was very tempted to do this for a while (and sent patch back in 98
> or so) but there appeared to be consensus that the truncations are
> very important, but it does not seem to be the practice.
If you can find the original posting and/or refresh this patch against
mainline, I'll be happy to review it for you, provided any change in
current functionality is guarded by flag_unsafe_math_optimizations.
> If you want to get really good about elliminating the truncations, you
> will need to play the games with combiner patterns containing truncates,
> silimarly as we do for extensions but this is tricky (you will face
> pattern explosion).
Indeed. This was my major concern about modelling truncation like
extension. i386.md already contains a large number of patterns intended
purely to provide "*ext" variants of floating point operations. I
wasn't sure if these were required by the i386 backend's extend?f?f2
implementation.
Thanks for your help,
Roger
--
next prev parent reply other threads:[~2004-03-18 19:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-03-18 17:49 Roger Sayle
2004-03-18 18:40 ` Jan Hubicka
2004-03-18 19:18 ` Roger Sayle [this message]
2004-03-20 22:07 ` Jan Hubicka
2004-03-19 11:30 ` Thomas Kunert
2004-03-19 12:28 ` Jakub Jelinek
2004-03-21 2:04 ` Robert Dewar
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