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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107608] [13 Regression] Failure on fold-overflow-1.c and pr95115.c
Date: Fri, 27 Jan 2023 11:30:26 +0000 [thread overview]
Message-ID: <bug-107608-4-2lzrOaK7C0@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-107608-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107608
--- Comment #50 from rguenther at suse dot de <rguenther at suse dot de> ---
On Fri, 27 Jan 2023, jakub at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107608
>
> --- Comment #49 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
> (In reply to rguenther@suse.de from comment #47)
> > > Glibc already changed the code from Inf/Inf to (x - x) / (x - x) where x
>
> (x - x) / (x - x) is 0 / 0, not Inf / Inf.
> Anyway, for frange potential in GCC 14, I'd hope we do figure out that
> x - x has [0, 0] range (never -0.0 even, unless -frounding-math where it could
> be -0.0 when rounding to -Inf) provided x is known to be finite -
> all of Inf - Inf, (-Inf) - (-Inf) and NaN - NaN are NaN.
> And frange already has an infrastructure for that, foperator_minus::rv_fold is
> passed relation_kind between op1 and op2, so if it is VREL_EQ and we can check
> that Inf or NaN isn't possible in the range, we should yield [0, 0].
> Or for -ffast-math do it always and yield [-0., 0] as Inf/NaN aren't expected
> but signed zeros are present but are insignificant.
> Shall we file a PR for that?
>
> > > is not a constant, but I'm wandering if the compiler will attempt to
> > > optimize out (x - x) / (x - x) later... Is it possible to provide a
> > > "__builtin_feraiseexcept" so we'd be able to use it instead of the nasty
> > > (x - x) / (x - x) to raise the exception?
> >
> > Not trivially. I'd suggest glibc uses a volatile use, like for example
> >
> > tem = Inf/Inf;
> > __asm__ volatile ("" : : "g" (tem));
>
> In this case I guess that is at least right now fine (and glibc I think even
> has a macro for that, some math_*). The thing is that the result is NaN and we
> don't treat NaN as singleton (because there are many representations of NaN).
> Similarly the workaround for fold-overflow-1.c added in this PR will not treat
> for now
> operations from finite operands yielding singleton Inf or -Inf as singleton.
> But if it is something else, say finite + finite and the expectation is that
> inexact is raised, then the above wouldn't help, because we'd just turn it into
> "g" (constant)
> in the asm.
For inexact yes, but we do refrain from constant folding when that loses
exceptions (in some cases at least), not just when it produces a NaN.
prev parent reply other threads:[~2023-01-27 11:30 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-10 9:47 [Bug tree-optimization/107608] New: [13 Regression] Failure on fold-overflow-1.c jakub at gcc dot gnu.org
2022-11-10 9:49 ` [Bug tree-optimization/107608] " jakub at gcc dot gnu.org
2022-11-10 13:47 ` rguenth at gcc dot gnu.org
2022-11-10 18:13 ` pinskia at gcc dot gnu.org
2022-11-11 7:18 ` pinskia at gcc dot gnu.org
2022-11-13 6:30 ` [Bug tree-optimization/107608] [13 Regression] Failure on fold-overflow-1.c and pr95115.c xry111 at gcc dot gnu.org
2022-11-28 10:06 ` rguenth at gcc dot gnu.org
2022-12-05 13:22 ` aldyh at gcc dot gnu.org
2022-12-05 15:14 ` rguenth at gcc dot gnu.org
2022-12-05 16:30 ` aldyh at gcc dot gnu.org
2022-12-16 13:20 ` jakub at gcc dot gnu.org
2022-12-16 13:32 ` rguenth at gcc dot gnu.org
2023-01-09 15:18 ` aldyh at gcc dot gnu.org
2023-01-10 8:56 ` rguenth at gcc dot gnu.org
2023-01-10 8:58 ` rguenth at gcc dot gnu.org
2023-01-10 10:20 ` aldyh at gcc dot gnu.org
2023-01-10 10:25 ` aldyh at gcc dot gnu.org
2023-01-10 11:00 ` rguenth at gcc dot gnu.org
2023-01-10 11:09 ` jakub at gcc dot gnu.org
2023-01-10 12:08 ` rguenther at suse dot de
2023-01-10 14:14 ` jakub at gcc dot gnu.org
2023-01-10 14:25 ` amacleod at redhat dot com
2023-01-10 14:33 ` aldyh at gcc dot gnu.org
2023-01-10 14:39 ` jakub at gcc dot gnu.org
2023-01-10 14:40 ` aldyh at gcc dot gnu.org
2023-01-10 14:42 ` jakub at gcc dot gnu.org
2023-01-12 11:42 ` aldyh at gcc dot gnu.org
2023-01-12 12:03 ` jakub at gcc dot gnu.org
2023-01-12 12:26 ` xry111 at gcc dot gnu.org
2023-01-13 13:19 ` aldyh at gcc dot gnu.org
2023-01-13 13:25 ` aldyh at gcc dot gnu.org
2023-01-15 15:43 ` cvs-commit at gcc dot gnu.org
2023-01-16 21:38 ` romain.geissler at amadeus dot com
2023-01-16 21:46 ` jakub at gcc dot gnu.org
2023-01-16 21:55 ` romain.geissler at amadeus dot com
2023-01-16 21:58 ` fw at gcc dot gnu.org
2023-01-18 12:26 ` aldyh at gcc dot gnu.org
2023-01-18 12:54 ` jakub at gcc dot gnu.org
2023-01-18 12:56 ` aldyh at gcc dot gnu.org
2023-01-18 13:00 ` rguenth at gcc dot gnu.org
2023-01-18 13:03 ` rguenth at gcc dot gnu.org
2023-01-18 13:05 ` rguenth at gcc dot gnu.org
2023-01-19 1:15 ` xry111 at gcc dot gnu.org
2023-01-19 7:17 ` rguenther at suse dot de
2023-01-26 14:29 ` xry111 at gcc dot gnu.org
2023-01-27 7:35 ` rguenth at gcc dot gnu.org
2023-01-27 7:59 ` xry111 at gcc dot gnu.org
2023-01-27 9:53 ` rguenther at suse dot de
2023-01-27 10:02 ` xry111 at gcc dot gnu.org
2023-01-27 10:13 ` jakub at gcc dot gnu.org
2023-01-27 11:30 ` rguenther at suse dot de [this message]
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