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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107569] [13 Regression] Failure to optimize
 std::isfinite since r13-3596
Date: Thu, 10 Nov 2022 12:54:00 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107569

--- Comment #28 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Aldy Hernandez from comment #27)
> > As for signed zeros in -fsigned-zeros (default) mode, wonder if we e.g.=
 don't
> > say sqrt is nonnegative (even when sqrt (-0.0) is -0.0).
>=20
> It seems tree_call_nonnegative_warnv_p is already doing the right thing f=
or
> sqrt?
>=20
>     CASE_CFN_SQRT:
>     CASE_CFN_SQRT_FN:
>       /* sqrt(-0.0) is -0.0.  */
>       if (!HONOR_SIGNED_ZEROS (type))
> 	return true;
>       return RECURSE (arg0);

Ah, ok.  So, if we during stage3 go through all the cases and convince
ourselves it is good enough, it might be ok for signed zeros then.  Still t=
he
sign of NAN is separate question from that, and there we should set +NAN on=
ly
when we see
CASE_CFN_FABS{,_FN} or ABS_EXPR, toggle the sign of NEGATE_EXPR, inherit fr=
om
second argument for CASE_CFN_COPYSIGN{,_FN} and copy over for copies.=