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Re: [PATCH] Don't fold nextafter/nexttoward if -ftrapping-math or -fmath-errno if they produce denormal results (PR c/86420)
- From: Marc Glisse <marc dot glisse at inria dot fr>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Richard Biener <rguenther at suse dot de>, gcc-patches at gcc dot gnu dot org
- Date: Sat, 7 Jul 2018 11:55:17 +0200 (CEST)
- Subject: Re: [PATCH] Don't fold nextafter/nexttoward if -ftrapping-math or -fmath-errno if they produce denormal results (PR c/86420)
- References: <20180707080605.GP7166@tucnak>
- Reply-to: gcc-patches at gcc dot gnu dot org
On Sat, 7 Jul 2018, Jakub Jelinek wrote:
2018-07-07 Jakub Jelinek <jakub@redhat.com>
PR c/86420
* real.c (real_nextafter): Return true if result is denormal.
I have a question on the side: would it be hard / useful, in cases where
nextafter may set errno or some exception flag, to fold the result to a
constant while keeping the function call (ignoring the value it returns)?
To clarify, I mean replace
_2 = nextafter(DBL_DENORM_MIN, 0);
with
nextafter(DBL_DENORM_MIN, 0);
_2 = 0;
I think we already do that for some other calls, although I can't remember
where. The point would be that we have the value of _2 and can keep
folding its uses.
--
Marc Glisse