Avoid copies in std::scoped_allocator_adaptor piecewise construction

	* include/std/scoped_allocator (scoped_allocator_adaptor): Forward
	piecewise construction arguments as tuples of references, to avoid
	copies (related to LWG 2511).
	* testsuite/20_util/scoped_allocator/construct_pair.cc: New test.

From-SVN: r241169

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index a87971f9fe89a82abde3a4987b88d65e259d0d08..7a3fdaf29f157ac7ddd0356a347a9f2a68b44dbe 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,10 @@
+2016-10-14  Jonathan Wakely  <jwakely@redhat.com>
+
+       * include/std/scoped_allocator (scoped_allocator_adaptor): Forward
+       piecewise construction arguments as tuples of references, to avoid
+       copies (related to LWG 2511).
+       * testsuite/20_util/scoped_allocator/construct_pair.cc: New test.
+
 2016-10-14  Paolo Carlini  <paolo.carlini@oracle.com>
 
        * testsuite/26_numerics/accumulate/1.cc: Remove 'test' variables.

diff --git a/libstdc++-v3/include/std/scoped_allocator b/libstdc++-v3/include/std/scoped_allocator
index 39762fe444d4f8c46b2db5f1da493b5b29e5e6c6..dcb97df63b39c77d6cf2da457b71493fe8aa3b96 100644 (file)
--- a/libstdc++-v3/include/std/scoped_allocator
+++ b/libstdc++-v3/include/std/scoped_allocator
@@ -369,10 +369,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            = __use_alloc<_T1, inner_allocator_type, _Args1...>(__inner);
          auto __y_use_tag
            = __use_alloc<_T2, inner_allocator_type, _Args2...>(__inner);
+         typename _Build_index_tuple<sizeof...(_Args1)>::__type __x_indices;
+         typename _Build_index_tuple<sizeof...(_Args2)>::__type __y_indices;
          typedef __outermost_alloc_traits<scoped_allocator_adaptor> _O_traits;
          _O_traits::construct(__outermost(*this), __p, piecewise_construct,
-                              _M_construct_p(__x_use_tag, __x),
-                              _M_construct_p(__y_use_tag, __y));
+                              _M_construct_p(__x_use_tag, __x_indices, __x),
+                              _M_construct_p(__y_use_tag, __y_indices, __y));
        }
 
       template<typename _T1, typename _T2>
@@ -428,26 +430,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                  const scoped_allocator_adaptor<_OutA2, _InA...>& __b) noexcept;
 
     private:
-      template<typename _Tuple>
-       _Tuple&&
-       _M_construct_p(__uses_alloc0, _Tuple& __t)
+      template<typename _Ind, typename... _Args>
+       tuple<_Args&&...>
+       _M_construct_p(__uses_alloc0, _Ind, tuple<_Args...>& __t)
        { return std::move(__t); }
 
-      template<typename... _Args>
-       std::tuple<allocator_arg_t, inner_allocator_type&, _Args...>
-       _M_construct_p(__uses_alloc1_, std::tuple<_Args...>& __t)
+      template<size_t... _Ind, typename... _Args>
+       tuple<allocator_arg_t, inner_allocator_type&, _Args&&...>
+       _M_construct_p(__uses_alloc1_, _Index_tuple<_Ind...>,
+                      tuple<_Args...>& __t)
        {
-         typedef std::tuple<allocator_arg_t, inner_allocator_type&> _Tuple;
-         return std::tuple_cat(_Tuple(allocator_arg, inner_allocator()),
-                               std::move(__t));
+         return { allocator_arg, inner_allocator(),
+             std::get<_Ind>(std::move(__t))...
+         };
        }
 
-      template<typename... _Args>
-       std::tuple<_Args..., inner_allocator_type&>
-       _M_construct_p(__uses_alloc2_, std::tuple<_Args...>& __t)
+      template<size_t... _Ind, typename... _Args>
+       tuple<_Args&&..., inner_allocator_type&>
+       _M_construct_p(__uses_alloc2_, _Index_tuple<_Ind...>,
+                      tuple<_Args...>& __t)
        {
-         typedef std::tuple<inner_allocator_type&> _Tuple;
-         return std::tuple_cat(std::move(__t), _Tuple(inner_allocator()));
+         return { std::get<_Ind>(std::move(__t))..., inner_allocator() };
        }
     };
 

diff --git a/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc b/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc
new file mode 100644 (file)
index 0000000..2996412
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/scoped_allocator/construct_pair.cc
@@ -0,0 +1,81 @@
+// 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 <utility>
+#include <tuple>
+#include <scoped_allocator>
+
+struct do_not_copy {
+  do_not_copy() = default;
+  do_not_copy(const do_not_copy&) { throw 1; }
+};
+
+void
+test01()
+{
+  struct X {
+    X(do_not_copy&&) { }
+  };
+
+  using pair = std::pair<X, int>;
+  std::scoped_allocator_adaptor<std::allocator<pair>> a;
+  auto ptr = a.allocate(1);
+  a.construct(ptr, std::piecewise_construct,
+      std::tuple<do_not_copy>{}, std::make_tuple(1));
+  a.deallocate(ptr, 1);
+}
+
+void
+test02()
+{
+  struct X {
+    using allocator_type = std::allocator<int>;
+    X(do_not_copy&&, const allocator_type&) { }
+  };
+
+  using pair = std::pair<X, int>;
+  std::scoped_allocator_adaptor<std::allocator<pair>> a;
+  auto ptr = a.allocate(1);
+  a.construct(ptr, std::piecewise_construct,
+      std::tuple<do_not_copy>{}, std::make_tuple(1));
+  a.deallocate(ptr, 1);
+}
+
+void
+test03()
+{
+  struct X {
+    using allocator_type = std::allocator<int>;
+    X(std::allocator_arg_t, const allocator_type&, do_not_copy&&) { }
+  };
+
+  using pair = std::pair<X, int>;
+  std::scoped_allocator_adaptor<std::allocator<pair>> a;
+  auto ptr = a.allocate(1);
+  a.construct(ptr, std::piecewise_construct,
+      std::tuple<do_not_copy>{}, std::make_tuple(1));
+  a.deallocate(ptr, 1);
+}
+
+int main()
+{
+  test01();
+  test02();
+  test03();
+}