[PATCH] Constexpr in std::pointer_traits (P1006R1)

[Jonathan Wakely]

        * include/bits/ptr_traits.h [C++20] (pointer_traits<T*>::pointer_to):
        Add constexpr.
        * testsuite/20_util/pointer_traits/pointer_to_constexpr.cc: New test.

Tested powerpc64le-linux, committed to trunk.



commit 8125740feaa7aa66589d0922992b9bf1065e1699
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Wed Mar 6 10:45:02 2019 +0000

    Constexpr in std::pointer_traits (P1006R1)
    
            * include/bits/ptr_traits.h [C++20] 
(pointer_traits<T*>::pointer_to):
            Add constexpr.
            * testsuite/20_util/pointer_traits/pointer_to_constexpr.cc: New 
test.

diff --git a/libstdc++-v3/include/bits/ptr_traits.h 
b/libstdc++-v3/include/bits/ptr_traits.h
index 76355863852..c90a35080f1 100644
--- a/libstdc++-v3/include/bits/ptr_traits.h
+++ b/libstdc++-v3/include/bits/ptr_traits.h
@@ -137,7 +137,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        *  @param  __r  A reference to an object of type @c element_type
        *  @return @c addressof(__r)
       */
-      static pointer
+      static _GLIBCXX20_CONSTEXPR pointer
       pointer_to(__make_not_void<element_type>& __r) noexcept
       { return std::addressof(__r); }
     };
diff --git 
a/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc 
b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc
new file mode 100644
index 00000000000..ed4f2157adc
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/pointer_traits/pointer_to_constexpr.cc
@@ -0,0 +1,27 @@
+// Copyright (C) 2019 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 <memory>
+
+int i = 0;
+static_assert( std::pointer_traits<int*>::pointer_to(i) == &i );
+
+struct X { } x;
+static_assert( std::pointer_traits<X*>::pointer_to(x) == &x );