Hi,
The current compare_three_way implementation makes provision for constant
evaluation contexts (avoiding reinterpret_cast etc.), but the approach fails
with Clang; when it compares two const volatile void pointers: "comparison
between unequal pointers to void has unspecified result". I include a fix and
test.
Could someone commit the attached patch for me?
Thanks,
Paul
Please consider the environment and think before you print.
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diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 07cc83d98f4..638f00716c8 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2021-08-20 Paul Keir <paul.k...@uws.ac.uk>
+
+ * libsupc++/compare: Avoid constexpr pointer comparison failure
+ in std::compare_three_way with Clang.
+ * testsuite/18_support/comparisons/pointers/constexpr.cc:
+ New test.
+
2021-08-19 Jonathan Wakely <jwak...@redhat.com>
* doc/xml/manual/status_cxx2020.xml: Move row earlier in table.
diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index 5aee89e3a6e..4081a3f2315 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -553,10 +553,10 @@ namespace std
{
if constexpr (__detail::__3way_builtin_ptr_cmp<_Tp, _Up>)
{
+ if (__builtin_is_constant_evaluated())
+ return static_cast<_Tp&&>(__t) <=> static_cast<_Up&&>(__u);
auto __pt = static_cast<const volatile void*>(__t);
auto __pu = static_cast<const volatile void*>(__u);
- if (__builtin_is_constant_evaluated())
- return __pt <=> __pu;
auto __it = reinterpret_cast<__UINTPTR_TYPE__>(__pt);
auto __iu = reinterpret_cast<__UINTPTR_TYPE__>(__pu);
return __it <=> __iu;
diff --git a/libstdc++-v3/testsuite/18_support/comparisons/pointers/constexpr.cc b/libstdc++-v3/testsuite/18_support/comparisons/pointers/constexpr.cc
new file mode 100644
index 00000000000..8e1dc2ed6d1
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/comparisons/pointers/constexpr.cc
@@ -0,0 +1,43 @@
+// Copyright (C) 2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3. If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <functional>
+
+constexpr bool check01()
+{
+ int arr[2];
+ bool b1 = &arr[0] < &arr[1];
+ bool b2 = std::less{}(&arr[0], &arr[1]);
+ bool b3 = std::compare_three_way{}(&arr[0],&arr[1]) < 0;
+ return b1 && b2 && b3;
+}
+
+constexpr bool check02()
+{
+ int *p = new int[2];
+ bool b1 = &p[0] < &p[1];
+ bool b2 = std::less{}(&p[0], &p[1]);
+ bool b3 = std::compare_three_way{}(&p[0],&p[1]) < 0;
+ delete [] p;
+ return b1 && b2 && b3;
+}
+
+static_assert(check01());
+static_assert(check02());
