This patch fixes the oversight.
Tested on x86-64 Linux.
Pushed.
On Wed, Nov 9, 2022 at 12:05 AM Aldy Hernandez <al...@redhat.com> wrote:
>
> Sigh, one more thing.
>
> There are further possibilities for a NAN result, even if the operands
> are !NAN and the result from frange_arithmetic is free of NANs.
> Adding different signed infinities.
>
> For example, [-INF,+INF] + [-INF,+INF] has the possibility of adding
> -INF and +INF, which is a NAN. Since we end up calling frange
> arithmetic on the lower bounds and then on the upper bounds, we miss
> this, and mistakenly think we're free of NANs.
>
> I have a patch in testing, but FYI, in case anyone notices this before
> I get around to it tomorrow.
>
> Aldy
>
> On Tue, Nov 8, 2022 at 3:11 PM Jakub Jelinek <ja...@redhat.com> wrote:
> >
> > On Tue, Nov 08, 2022 at 03:06:53PM +0100, Aldy Hernandez wrote:
> > > +// If either operand is a NAN, set R to the combination of both NANs
> > > +// signwise and return TRUE.
> >
> > This comment doesn't describe what it does now.
> > If either operand is a NAN, set R to NAN with unspecified sign bit and
> > return
> > TRUE.
> > ?
> >
> > Other than this LGTM.
> >
> > Jakub
> >
From 68b0615be2aaff3a8ce91ba7cd0f69ebbd93702c Mon Sep 17 00:00:00 2001
From: Aldy Hernandez <al...@redhat.com>
Date: Tue, 8 Nov 2022 23:42:04 +0100
Subject: [PATCH] [range-op-float] Set NAN possibility for INF + (-INF) and
vice versa.
Some combinations of operations can yield a NAN even if no operands
have the possiblity of a NAN. For example, [-INF] + [+INF] = NAN and
vice versa.
For [-INF,+INF] + [-INF,+INF], frange_arithmetic will not return a
NAN, and since the operands have no possibility of a NAN, we will
mistakenly assume the result cannot have a NAN. This fixes the
oversight.
gcc/ChangeLog:
* range-op-float.cc (foperator_plus::fold_range): Set NAN for
addition of different signed infinities.
(range_op_float_tests): New test.
---
gcc/range-op-float.cc | 26 +++++++++++++++++++++++++-
1 file changed, 25 insertions(+), 1 deletion(-)
diff --git a/gcc/range-op-float.cc b/gcc/range-op-float.cc
index 3bc6cc8849d..8282c912fc4 100644
--- a/gcc/range-op-float.cc
+++ b/gcc/range-op-float.cc
@@ -1863,7 +1863,21 @@ foperator_plus::fold_range (frange &r, tree type,
r.set (type, lb, ub);
- if (lb_nan || ub_nan)
+ // Some combinations can yield a NAN even if no operands have the
+ // possibility of a NAN.
+ bool maybe_nan;
+ // [-INF] + [+INF] = NAN
+ if (real_isinf (&op1.lower_bound (), true)
+ && real_isinf (&op2.upper_bound (), false))
+ maybe_nan = true;
+ // [+INF] + [-INF] = NAN
+ else if (real_isinf (&op1.upper_bound (), false)
+ && real_isinf (&op2.lower_bound (), true))
+ maybe_nan = true;
+ else
+ maybe_nan = false;
+
+ if (lb_nan || ub_nan || maybe_nan)
// Keep the default NAN (with a varying sign) set by the setter.
;
else if (!op1.maybe_isnan () && !op2.maybe_isnan ())
@@ -1960,6 +1974,16 @@ range_op_float_tests ()
r1 = frange_float ("-1", "-0");
r1.update_nan (false);
ASSERT_EQ (r, r1);
+
+ // [-INF,+INF] + [-INF,+INF] could be a NAN.
+ range_op_handler plus (PLUS_EXPR, float_type_node);
+ r0.set_varying (float_type_node);
+ r1.set_varying (float_type_node);
+ r0.clear_nan ();
+ r1.clear_nan ();
+ plus.fold_range (r, float_type_node, r0, r1);
+ if (HONOR_NANS (float_type_node))
+ ASSERT_TRUE (r.maybe_isnan ());
}
} // namespace selftest
--
2.38.1
