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From: Marc Glisse <marc.glisse@inria.fr>
To: Joseph Myers <joseph@codesourcery.com>
Cc: FX <fxcoudert@gmail.com>, Jakub Jelinek <jakub@redhat.com>,
	 gcc@gcc.gnu.org, FX via Fortran <fortran@gcc.gnu.org>
Subject: Re: Floating-point comparisons in the middle-end
Date: Thu, 1 Sep 2022 17:57:21 +0200 (CEST)	[thread overview]
Message-ID: <e6060be6-2521-d581-309e-85aab3d79748@inria.fr> (raw)
In-Reply-To: <alpine.DEB.2.22.394.2209011520170.550568@digraph.polyomino.org.uk>

On Thu, 1 Sep 2022, Joseph Myers wrote:

> On Thu, 1 Sep 2022, FX via Gcc wrote:
>
>> A tentative patch is attached, it seems to work well on simple examples,
>> but for test coverage the hard part is going to be that the comparisons
>> seem to be optimised away very easily into their non-signaling versions.
>> Basically, if I do:
>
> Presumably that can be reproduced without depending on the new built-in
> function?  In which case it's an existing bug somewhere in the optimizers.

  (simplify
   (cmp @0 REAL_CST@1)
[...]
    (if (REAL_VALUE_ISNAN (TREE_REAL_CST (@1))
         && !tree_expr_signaling_nan_p (@1)
         && !tree_expr_maybe_signaling_nan_p (@0))
     { constant_boolean_node (cmp == NE_EXPR, type); })

only tries to preserve a comparison with sNaN, but not with qNaN. There 
are probably other issues since various gcc devs used to have a different 
opinion on the meaning of -ftrapping-math.


-- 
Marc Glisse

  reply	other threads:[~2022-09-01 15:57 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-01  8:04 FX
2022-09-01  8:19 ` Jakub Jelinek
2022-09-01  9:04   ` FX
2022-09-01  9:23     ` Jakub Jelinek
2022-09-01 10:06       ` FX
2022-09-01 15:21         ` Joseph Myers
2022-09-01 15:57           ` Marc Glisse [this message]
2022-09-01 16:22             ` Joseph Myers
2022-09-01 16:24           ` FX
2022-09-01 16:44             ` Joseph Myers
2022-09-01 18:15               ` FX
2022-09-01 14:32   ` Segher Boessenkool
2022-09-01 15:19 ` Joseph Myers
2022-09-01 18:38   ` FX
2022-09-01 19:13     ` Joseph Myers
2022-09-01 18:47   ` FX
2022-09-01 19:16     ` Joseph Myers

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