https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109386
--- Comment #4 from CVS Commits ---
The master branch has been updated by Jakub Jelinek :
https://gcc.gnu.org/g:ce243c9eefc2728cb8743ebbcb84c3e08236f06a
commit r13-7002-gce243c9eefc2728cb8743ebbcb84c3e08236f06a
Author: Jakub Jelinek
Date: Tue Apr 4 16:13:06 2023 +0200
range-op-float: Fix reverse ops of comparisons [PR109386]
I've missed one of my recent range-op-float.cc changes (likely the
r13-6967 one) caused
FAIL: libphobos.phobos/std/math/algebraic.d execution test
FAIL: libphobos.phobos_shared/std/math/algebraic.d execution test
regressions, distilled into a C testcase below.
In the testcase, we have
!(u >= v)
condition where both u and v are results of fabs*, which guards
t1 = u u<= __FLT_MAX__;
and
t2 = v u<= __FLT_MAX__;
comparisons. From false u >= v where u and v have [0.0, +Inf] NAN
ranges we (incorrectly deduce that one of them is [nextafterf (0.0, 1.0),
+Inf] NAN
and the other is [0.0, nextafterf (+Inf, 0.0)] NAN and from that deduce
that
one of the comparisons is always true, because UNLE_EXPR with the maximum
representable number are false only if the value is +Inf and our ranges
tell
that is not possible.
The bug is that the u >= v comparison determines a sensible range only when
it is true - we then know neither operand can be NAN and it behaves
correctly. But when the comparison is false, our current code gives
sensible answers only if the other op can't be NAN. If it can be NAN,
whenever it is NAN, the comparison is always false regardless of the other
value, so the other value needs to be VARYING.
Now, foperator_unordered_lt::op1_range etc. had code to deal with that
for op?.known_nan (), but as the testcase shows, it is enough if it may be
a
NAN at runtime to make it VARYING.
So, the following patch replaces for all those BRS_FALSE cases of the
normal
non-equality comparisons if (opOTHER.known_isnan ()) r.set_varying (type);
to do it also if maybe_isnan ().
For the unordered or ... comparisons, it is similar for BRS_TRUE. Those
comparisons are true whenever either operand is NAN, or if neither is NAN,
the corresponding normal comparison. So, if those comparisons are true
and other operand might be a NAN, we can't tell (VARYING), if it is false,
currently handling is correct.
2023-04-04 Jakub Jelinek
PR tree-optimization/109386
* range-op-float.cc (foperator_lt::op1_range,
foperator_lt::op2_range,
foperator_le::op1_range, foperator_le::op2_range,
foperator_gt::op1_range, foperator_gt::op2_range,
foperator_ge::op1_range, foperator_ge::op2_range): Make r varying
for
BRS_FALSE case even if the other op is maybe_isnan, not just
known_isnan.
(foperator_unordered_lt::op1_range,
foperator_unordered_lt::op2_range,
foperator_unordered_le::op1_range,
foperator_unordered_le::op2_range,
foperator_unordered_gt::op1_range,
foperator_unordered_gt::op2_range,
foperator_unordered_ge::op1_range,
foperator_unordered_ge::op2_range):
Make r varying for BRS_TRUE case even if the other op is
maybe_isnan,
not just known_isnan.
* gcc.c-torture/execute/ieee/pr109386.c: New test.
