Prevent __uses_alloc from holding dangling references

	* include/bits/uses_allocator.h (__use_alloc(const _Alloc&&)): Add
	deleted overload to prevent dangling references to rvalues.
	* include/experimental/memory_resource
	(polymorphic_allocator::construct): Do not call __use_alloc with
	rvalue arguments.

From-SVN: r250019

libstdc++-v3/ChangeLog

+2017-07-06  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/uses_allocator.h (__use_alloc(const _Alloc&&)): Add
+	deleted overload to prevent dangling references to rvalues.
+	* include/experimental/memory_resource
+	(polymorphic_allocator::construct): Do not call __use_alloc with
+	rvalue arguments.
+
 2017-06-27  Tim Shen  <timshen@google.com>
 
 	PR libstdc++/80187

libstdc++-v3/include/bits/uses_allocator.h

@@ -109,6 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __ret._M_a = std::__addressof(__a);
       return __ret;
     }
+
+  template<typename _Tp, typename _Alloc, typename... _Args>
+    void
+    __use_alloc(const _Alloc&&) = delete;
+
 #if __cplusplus > 201402L
   template <typename _Tp, typename _Alloc>
     inline constexpr bool uses_allocator_v =

libstdc++-v3/include/experimental/memory_resource

@@ -168,8 +168,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template <typename _Tp1, typename... _Args> //used here
 	void construct(_Tp1* __p, _Args&&... __args)
 	{
-	  auto __use_tag = __use_alloc<_Tp1, memory_resource*,
-	       _Args...>(this->resource());
+	  memory_resource* const __resource = this->resource();
+	  auto __use_tag
+	    = __use_alloc<_Tp1, memory_resource*, _Args...>(__resource);
 	  _M_construct(__use_tag, __p, std::forward<_Args>(__args)...);
 	}
 
@@ -180,10 +181,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 		       tuple<_Args1...> __x,
 		       tuple<_Args2...> __y)
 	{
+	  memory_resource* const __resource = this->resource();
 	  auto __x_use_tag =
-	    __use_alloc<_Tp1, memory_resource*, _Args1...>(this->resource());
+	    __use_alloc<_Tp1, memory_resource*, _Args1...>(__resource);
 	  auto __y_use_tag =
-	    __use_alloc<_Tp2, memory_resource*, _Args2...>(this->resource());
+	    __use_alloc<_Tp2, memory_resource*, _Args2...>(__resource);
 
 	  ::new(__p) std::pair<_Tp1, _Tp2>(piecewise_construct,
 					   _M_construct_p(__x_use_tag, __x),