Fix PR37694 - std::vector doesn't correctly move construct allocators.

C++2a[container.requirements.general]p8 states that when move constructing
a container, the allocator is move constructed. Vector previously copy
constructed these allocators. This patch fixes that bug.

Additionally it cleans up some unnecessary allocator conversions
when copy constructing containers. Libc++ uses
__internal_allocator_traits::select_on_copy_construction to select
the correct allocator during copy construction, but it unnecessarily
converted the resulting allocator to the user specified allocator
type and back. After this patch list and forward_list no longer
do that.

Technically we're supposed to be using allocator_traits<allocator_type>::select_on_copy_construction,
but that should seemingly be addressed as a separate patch, if at all.

llvm-svn: 334053

1 files changed, 11 insertions, 8 deletions

diff --git a/libcxx/include/forward_list b/libcxx/include/forward_list
index c98ddc00a03..571afdc925b 100644
--- a/libcxx/include/forward_list
+++ b/libcxx/include/forward_list
@@ -457,6 +457,10 @@ protected:
     typedef typename allocator_traits<__begin_node_allocator>::pointer
                                                       __begin_node_pointer;
 
+    static_assert((!is_same<allocator_type, __node_allocator>::value),
+                  "internal allocator type must differ from user-specified "
+                  "type; otherwise overload resolution breaks");
+
     __compressed_pair<__begin_node, __node_allocator> __before_begin_;
 
     _LIBCPP_INLINE_VISIBILITY
@@ -481,9 +485,11 @@ protected:
         _NOEXCEPT_(is_nothrow_default_constructible<__node_allocator>::value)
         : __before_begin_(__begin_node()) {}
     _LIBCPP_INLINE_VISIBILITY
-    __forward_list_base(const allocator_type& __a)
+    explicit __forward_list_base(const allocator_type& __a)
         : __before_begin_(__begin_node(), __node_allocator(__a)) {}
-
+    _LIBCPP_INLINE_VISIBILITY
+    explicit __forward_list_base(const __node_allocator& __a)
+        : __before_begin_(__begin_node(), __a) {}
 #ifndef _LIBCPP_CXX03_LANG
 public:
     _LIBCPP_INLINE_VISIBILITY
@@ -954,12 +960,9 @@ forward_list<_Tp, _Alloc>::forward_list(_InputIterator __f, _InputIterator __l,
 
 template <class _Tp, class _Alloc>
 forward_list<_Tp, _Alloc>::forward_list(const forward_list& __x)
-    : base(allocator_type(
-             __node_traits::select_on_container_copy_construction(__x.__alloc())
-                         )
-          )
-{
-    insert_after(cbefore_begin(), __x.begin(), __x.end());
+    : base(
+          __node_traits::select_on_container_copy_construction(__x.__alloc())) {
+  insert_after(cbefore_begin(), __x.begin(), __x.end());
 }
 
 template <class _Tp, class _Alloc>