Implement the first part of N4258 - allocator_traits<X>::is_always_equal. Also fixes PR#23723

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@238848 91177308-0d34-0410-b5e6-96231b3b80d8

include/memory

@@ -75,6 +75,8 @@ struct allocator_traits
           | false_type                   propagate_on_container_move_assignment;
     typedef Alloc::propagate_on_container_swap
           | false_type                   propagate_on_container_swap;
+    typedef Alloc::is_always_equal
+          | is_empty                     is_always_equal;
 
     template <class T> using rebind_alloc  = Alloc::rebind<U>::other | Alloc<T, Args...>;
     template <class T> using rebind_traits = allocator_traits<rebind_alloc<T>>;
@@ -1144,6 +1146,29 @@ struct __propagate_on_container_swap<_Alloc, true>
     typedef typename _Alloc::propagate_on_container_swap type;
 };
 
+template <class _Tp>
+struct __has_is_always_equal
+{
+private:
+    struct __two {char __lx; char __lxx;};
+    template <class _Up> static __two __test(...);
+    template <class _Up> static char __test(typename _Up::is_always_equal* = 0);
+public:
+    static const bool value = sizeof(__test<_Tp>(0)) == 1;
+};
+
+template <class _Alloc, bool = __has_is_always_equal<_Alloc>::value>
+struct __is_always_equal
+{
+    typedef typename _VSTD::is_empty<_Alloc>::type type;
+};
+
+template <class _Alloc>
+struct __is_always_equal<_Alloc, true>
+{
+    typedef typename _Alloc::is_always_equal type;
+};
+
 template <class _Tp, class _Up, bool = __has_rebind<_Tp, _Up>::value>
 struct __has_rebind_other
 {
@@ -1423,6 +1448,8 @@ struct _LIBCPP_TYPE_VIS_ONLY allocator_traits
                      propagate_on_container_move_assignment;
     typedef typename __propagate_on_container_swap<allocator_type>::type
                      propagate_on_container_swap;
+    typedef typename __is_always_equal<allocator_type>::type
+                     is_always_equal;
 
 #ifndef _LIBCPP_HAS_NO_TEMPLATE_ALIASES
     template <class _Tp> using rebind_alloc =
@@ -1667,6 +1694,7 @@ public:
     typedef _Tp               value_type;
 
     typedef true_type propagate_on_container_move_assignment;
+    typedef true_type is_always_equal;
 
     template <class _Up> struct rebind {typedef allocator<_Up> other;};
 

include/scoped_allocator

@@ -38,6 +38,7 @@ public:
     typedef see below propagate_on_container_copy_assignment;
     typedef see below propagate_on_container_move_assignment;
     typedef see below propagate_on_container_swap;
+    typedef see below is_always_equal;
 
     template <class Tp>
         struct rebind
@@ -170,6 +171,14 @@ struct __get_poc_swap<_A0, _Allocs...>
         __get_poc_swap<_Allocs...>::value;
 };
 
+template <class _A0, class ..._Allocs>
+struct __get_poc_always_equal<_A0, _Allocs...>
+{
+    static const bool value =
+        allocator_traits<_A0>::is_always_equal::value ||
+        __get_poc_always_equal<_Allocs...>::value;
+};
+
 template <class ..._Allocs>
 class __scoped_allocator_storage;
 
@@ -397,6 +406,11 @@ public:
                 bool,
                 __get_poc_swap<outer_allocator_type, _InnerAllocs...>::value
             > propagate_on_container_swap;
+    typedef integral_constant
+            <
+                bool,
+                __get_poc_always_equal<outer_allocator_type, _InnerAllocs...>::value
+            > is_always_equal;
 
     template <class _Tp>
     struct rebind

test/std/utilities/memory/allocator.traits/allocator.traits.types/is_always_equal.pass.cpp

@@ -0,0 +1,48 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <memory>
+
+// template <class Alloc>
+// struct allocator_traits
+// {
+//   typedef Alloc::is_always_equal
+//         | is_empty                     is_always_equal;
+//     ...
+// };
+
+#include <memory>
+#include <type_traits>
+
+template <class T>
+struct A
+{
+    typedef T value_type;
+    typedef std::true_type is_always_equal;
+};
+
+template <class T>
+struct B
+{
+    typedef T value_type;
+};
+
+template <class T>
+struct C
+{
+    typedef T value_type;
+	int not_empty_;  // some random member variable
+};
+
+int main()
+{
+    static_assert((std::is_same<std::allocator_traits<A<char> >::is_always_equal, std::true_type>::value), "");
+    static_assert((std::is_same<std::allocator_traits<B<char> >::is_always_equal, std::true_type>::value), "");
+    static_assert((std::is_same<std::allocator_traits<C<char> >::is_always_equal, std::false_type>::value), "");
+}

www/cxx1z_status.html

@@ -56,7 +56,7 @@
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4089">N4089</a></td><td>LWG</td></td><td>Safe conversions in <code>unique_ptr&lt;T[]&gt;</code>.</td><td>Urbana</td><td></td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4169">N4169</a></td><td>LWG</td></td><td>A proposal to add invoke function template</td><td>Urbana</td><td></td><td></td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4190">N4190</a></td></td><td>LWG</td><td>Removing auto_ptr, random_shuffle(), And Old <functional> Stuff.</td><td>Urbana</td><td></td><td></td></tr>
-	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4258">N4258</a></td><td>LWG</td></td><td>Cleaning-up noexcept in the Library.</td><td>Urbana</td><td></td><td></td></tr>
+	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4258">N4258</a></td><td>LWG</td></td><td>Cleaning-up noexcept in the Library.</td><td>Urbana</td><td>In progress</td><td>3.7</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4259">N4259</a></td><td>CWG</td></td><td>Wording for std::uncaught_exceptions</td><td>Urbana</td><td>Complete</td><td>3.7</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4277">N4277</a></td><td>LWG</td></td><td>TriviallyCopyable <code>reference_wrapper</code>.</td><td>Urbana</td><td>Complete</td><td>3.2</td></tr>
 	<tr><td><a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4279">N4279</a></td><td>LWG</td></td><td>Improved insertion interface for unique-key maps.</td><td>Urbana</td><td></td><td></td></tr>