From: "Keith Packard" <keithp@keithp.com>
To: Brian Inglis <Brian.Inglis@SystematicSw.ab.ca>, newlib@sourceware.org
Subject: Re: [PATCH 0/3] ARM with only 32-bit floats do not have fast 64-bit FMA
Date: Mon, 07 Sep 2020 15:23:42 -0700 [thread overview]
Message-ID: <87h7s9445t.fsf@keithp.com> (raw)
In-Reply-To: <92283f3b-46a4-6ba2-1d07-a48c2db236cb@SystematicSw.ab.ca>
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Brian Inglis <Brian.Inglis@SystematicSw.ab.ca> writes:
> Can't the "super-smart" compiler use that information to work around your
> careful approach by conditionally skipping the FMA and conditionally return just
> z, or even unconditionally return z, as C makes no guarantees?
> And couldn't the "super-smart" instruction scheduler do similar at the hardware
> level?
I don't think that would be in conformance with the C specification
which says that arithmetic follows IEC 60559 that defines the various
exceptions and results. Now, if you enable -ffast-math, all bets are off...
--
-keith
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next prev parent reply other threads:[~2020-09-07 22:23 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-07 14:09 Eric Bresie
2020-09-07 17:16 ` Keith Packard
2020-09-07 20:16 ` Brian Inglis
2020-09-07 22:23 ` Keith Packard [this message]
-- strict thread matches above, loose matches on Subject: below --
2020-08-08 22:34 Keith Packard
2020-08-10 9:30 ` Corinna Vinschen
2020-08-10 14:43 ` Szabolcs Nagy
2020-08-10 15:19 ` Keith Packard
2020-08-10 19:06 ` Corinna Vinschen
2020-09-01 16:32 ` Sebastian Huber
2020-09-01 17:21 ` Sebastian Huber
2020-09-01 18:04 ` Sebastian Huber
2020-09-01 19:28 ` Keith Packard
2020-09-01 21:16 ` Joseph Myers
2020-09-01 23:06 ` Keith Packard
2020-09-02 4:41 ` Sebastian Huber
2020-09-02 5:25 ` Keith Packard
2020-09-02 5:35 ` Keith Packard
2020-09-02 17:12 ` Joseph Myers
2020-09-02 17:59 ` Sebastian Huber
2020-09-02 20:39 ` Keith Packard
2020-09-01 19:50 ` Keith Packard
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