[PATCH] PR78052 Define std::allocator::{construct,destroy}

[Jonathan Wakely]

This let's std::allocator<void> be used in situations like:

std::allocate_shared<int>(std::allocator<void>(), 1);

where a "proto-allocator" is required. The other members such as
allocate() and max_size() don't make sense for void, but construct and
destroy don't depend on value_type.

        PR libstdc++/78052
        * include/bits/allocator.h (allocator<void>::construct)
        (allocator<void>::destroy): Define.
        * testsuite/20_util/allocator/void.cc: New test.

Tested x86_64-linux, committed to trunk. Also applying to gcc-5 and
gcc-6 branches, because this used to work before I put in the
allocator_traits<allocator<T>> partial specialization.



commit afbafc298dbed75375d0610e7e642e5cbf38d922
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu Oct 20 03:40:21 2016 +0100

    PR78052 Define std::allocator<void>::{construct,destroy}
    
        PR libstdc++/78052
        * include/bits/allocator.h (allocator<void>::construct)
        (allocator<void>::destroy): Define.
        * testsuite/20_util/allocator/void.cc: New test.

diff --git a/libstdc++-v3/include/bits/allocator.h 
b/libstdc++-v3/include/bits/allocator.h
index 8e78165..9fb5842 100644
--- a/libstdc++-v3/include/bits/allocator.h
+++ b/libstdc++-v3/include/bits/allocator.h
@@ -84,6 +84,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef true_type propagate_on_container_move_assignment;
 
       typedef true_type is_always_equal;
+
+      template<typename _Up, typename... _Args>
+        void
+        construct(_Up* __p, _Args&&... __args)
+       { ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }
+
+      template<typename _Up>
+        void
+        destroy(_Up* __p) { __p->~_Up(); }
 #endif
     };
 
diff --git a/libstdc++-v3/testsuite/20_util/allocator/void.cc 
b/libstdc++-v3/testsuite/20_util/allocator/void.cc
new file mode 100644
index 0000000..0e47fef
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/allocator/void.cc
@@ -0,0 +1,40 @@
+// Copyright (C) 2016 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-do run { target c++11 } }
+
+#include <memory>
+#include <testsuite_hooks.h>
+
+template class std::allocator<void>;
+
+void
+test01()
+{
+  int i;
+  using alloc_type = std::allocator<void>;
+  alloc_type a;
+  std::allocator_traits<alloc_type>::construct(a, &i, 42);
+  VERIFY( i == 42 );
+  std::allocator_traits<alloc_type>::destroy(a, &i);
+}
+
+int
+main()
+{
+  test01();
+}