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Re: [PATCH] -fftz-math: assume that denorms _must_ be flushed to zero optimizations
- From: Joseph Myers <joseph at codesourcery dot com>
- To: Pekka Jääskeläinen <pekka at parmance dot com>
- Cc: Richard Biener <richard dot guenther at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>, Henry Linjamäki <henry dot linjamaki at parmance dot com>, Martin Jambor <mjambor at suse dot cz>
- Date: Mon, 14 Aug 2017 12:30:23 +0000
- Subject: Re: [PATCH] -fftz-math: assume that denorms _must_ be flushed to zero optimizations
- Authentication-results: sourceware.org; auth=none
- References: <CAJk11WCfMLenz=hume0aTTpkpJ6GM0bB3xsFL+dSvnA9zVPs+Q@mail.gmail.com> <CAFiYyc07+kScuyPZSe6oeVA4PROiLg4bb=zz95BaV_oXeGjtVw@mail.gmail.com> <CAJk11WDZMdj_fUsBQTsXShZEA4eTb86cGRs4O3zgxq7uWrA1GQ@mail.gmail.com>
On Mon, 14 Aug 2017, Pekka Jääskeläinen wrote:
> Both the inputs and outputs must be flushed to zero in the HSAIL’s
> ‘ftz’ semantics.
Presumably this means that constant folding needs to know about those
semantics, both for operations with a subnormal floating-point argument
(whether or not the output is floating point, or floating point in the
same format), and those with such a result?
Can assignments copy subnormals without converting them to zero? Should
comparisons flush input subnormals to zero before comparing? Should
conversions e.g. from float to double convert a float subnormal input to
zero?
--
Joseph S. Myers
joseph@codesourcery.com