From: Alexander Monakov <amonakov@ispras.ru>
To: Florian Weimer <fweimer@redhat.com>
Cc: Richard Biener <richard.guenther@gmail.com>, gcc@gcc.gnu.org
Subject: Re: Concerns regarding the -ffp-contract=fast default
Date: Mon, 18 Sep 2023 14:12:29 +0300 (MSK) [thread overview]
Message-ID: <ba5e062a-51eb-26d9-f802-aba9867c07a0@ispras.ru> (raw)
In-Reply-To: <877condc69.fsf@oldenburg.str.redhat.com>
On Mon, 18 Sep 2023, Florian Weimer via Gcc wrote:
> x - x is different because replacing it with 0 doesn't seem to be a
> valid contraction because it's incorrect for NaNs. x + x - x seems to
> be different in this regard, but in our implementation, there might be a
> quirk about sNaNs and qNaNs.
Sorry, do you mean contracting 'x + x - x' to 'x'? That is not allowed
due to different result and lack of FP exception for infinities.
Contracting 'x + x - x' to fma(x, 2, -x) would be fine.
Alexander
next prev parent reply other threads:[~2023-09-18 11:12 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-14 16:48 Florian Weimer
2023-09-14 17:09 ` Alexander Monakov
2023-09-18 7:50 ` Alexander Monakov
2023-09-18 8:06 ` Richard Biener
2023-09-18 10:10 ` Florian Weimer
2023-09-18 10:37 ` Richard Biener
2023-09-18 11:37 ` Florian Weimer
2023-09-18 11:12 ` Alexander Monakov [this message]
2023-09-18 11:34 ` Florian Weimer
2023-09-18 11:55 ` Alexander Monakov
2023-09-18 16:41 ` Florian Weimer
2023-09-18 17:31 ` Alexander Monakov
2023-09-18 17:39 ` Joseph Myers
2023-09-18 11:26 ` Martin Uecker
2023-09-18 11:32 ` Jakub Jelinek
2023-09-18 11:43 ` Alexander Monakov
2023-09-18 12:13 ` Martin Uecker
2023-09-18 15:38 ` Alexander Monakov
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