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Re: [RFA: 3.2] MMIX: Fix gcc.c-torture/execute/ieee/mzero2.c
- From: Fergus Henderson <fjh at cs dot mu dot OZ dot AU>
- To: Roger Sayle <roger at eyesopen dot com>
- Cc: Hans-Peter Nilsson <hp at bitrange dot com>, gcc-patches at gcc dot gnu dot org, Mark Mitchell <mark at codesourcery dot com>
- Date: Fri, 20 Sep 2002 14:20:55 +1000
- Subject: Re: [RFA: 3.2] MMIX: Fix gcc.c-torture/execute/ieee/mzero2.c
- References: <Pine.LNX.4.33.0209192108540.9345-100000@www.eyesopen.com>
On 19-Sep-2002, Roger Sayle <roger@eyesopen.com> wrote:
>
> > Question: Given that "-1.00 * pzero" can signal when using
> > multiplication, but a negation is allowed not to, is it really
> > correct to now translate it to a negation?
>
> This transformation is disabled by -fsignaling-nans. Neither GCC
> nor the C standard honor signaling NaNs by default, so I think
> its reasonable to apply this optimization unless told not to.
> ... I doubt there are enough performance critical uses of GCC's
> "-fsignaling-nans" to warrant new target macros for neg and abs :>
Note that the standards committee responsible for the IEEE floating
point standard is currently considering removing support for signaling
NaNs from the next revision of the standard.
--
Fergus Henderson <fjh@cs.mu.oz.au> | "I have always known that the pursuit
The University of Melbourne | of excellence is a lethal habit"
WWW: <http://www.cs.mu.oz.au/~fjh> | -- the last words of T. S. Garp.