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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/109154] [13 regression] jump threading
 de-optimizes nested floating point comparisons
Date: Mon, 27 Mar 2023 09:30:19 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109154

--- Comment #12 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #11)
> _1 shoud be [-Inf, nextafter (0.0, -Inf)], not [-Inf, -0.0]

Well, that is a consequence of the decision to always flush denormals to ze=
ro
in
frange::flush_denormals_to_zero, because some CPUs do it always and others =
do
it when asked for (e.g. x86 if linked with -ffast-math).
Unless we revert that decision and flush denormals to zero only selectively
(say on alpha in non-ieee mode (the default), or if fast math (which exact
suboption?) etc.

(In reply to Aldy Hernandez from comment #10)
> BTW, I don't think it helps at all here, but casting from l_10 to a float,
> we know _1 can't be either -0.0 or +-INF or +-NAN.  We could add a range-=
op
> entry for NOP_EXPR / CONVERT_EXPR to expose this fact.  Well, at the very
> least that it can't be a NAN...in the current representation for frange's.

We definitely should add range-ops for conversions from integral to floating
point and from floating to integral and their reverses.  But until we have =
more
than one range, if the integral value is VARYING, for 32-bit signed int the
range would be
[-0x1.p+31, 0x1.p+31] so nothing specific around zero.  With 3+ ranges we c=
ould
make it
[-0x1.p+31, -1.][0., 0.][1., 0x1.p+31] if we think normal values around zero
are important special cases.
Not sure how that would help in this case.

The reduced testcase is invalid because it uses uninitialized l.=