libstdc++: Destroy allocators in re-inserted container nodes [PR114401]

The allocator objects in container node handles were not being destroyed
after the node was re-inserted into a container. They are stored in a
union and so need to be explicitly destroyed when the node becomes
empty. The containers were zeroing the node handle's pointer, which
makes it empty, causing the handle's destructor to think there's nothing
to clean up.

Add a new member function to the node handle which destroys the
allocator and zeros the pointer. Change the containers to call that
instead of just changing the pointer manually.

We can also remove the _M_empty member of the union which is not
necessary.

libstdc++-v3/ChangeLog:

	PR libstdc++/114401
	* include/bits/hashtable.h (_Hashtable::_M_reinsert_node): Call
	release() on node handle instead of just zeroing its pointer.
	(_Hashtable::_M_reinsert_node_multi): Likewise.
	(_Hashtable::_M_merge_unique): Likewise.
	(_Hashtable::_M_merge_multi): Likewise.
	* include/bits/node_handle.h (_Node_handle_common::release()):
	New member function.
	(_Node_handle_common::_Optional_alloc::_M_empty): Remove
	unnecessary union member.
	(_Node_handle_common): Declare _Hashtable as a friend.
	* include/bits/stl_tree.h (_Rb_tree::_M_reinsert_node_unique):
	Call release() on node handle instead of just zeroing its
	pointer.
	(_Rb_tree::_M_reinsert_node_equal): Likewise.
	(_Rb_tree::_M_reinsert_node_hint_unique): Likewise.
	(_Rb_tree::_M_reinsert_node_hint_equal): Likewise.
	* testsuite/23_containers/multiset/modifiers/114401.cc: New test.
	* testsuite/23_containers/set/modifiers/114401.cc: New test.
	* testsuite/23_containers/unordered_multiset/modifiers/114401.cc: New test.
	* testsuite/23_containers/unordered_set/modifiers/114401.cc: New test.

(cherry picked from commit c2e28df90a1640cebadef6c6c8ab5ea964071bb1)

diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index dd3e655866ac34ba9721d5b65ee0f49d2d33b1da..1b5d0a7f42f4edcae765c91ea151e8d6ae48a8c2 100644 (file)
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -996,7 +996,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       // DR 1189.
       // reserve, if present, comes from _Rehash_base.
 
-#if __cplusplus > 201402L
+#if __cplusplus > 201404L
       /// Re-insert an extracted node into a container with unique keys.
       insert_return_type
       _M_reinsert_node(node_type&& __nh)
@@ -1021,7 +1021,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
              {
                __ret.position
                  = _M_insert_unique_node(__bkt, __code, __nh._M_ptr);
-               __nh._M_ptr = nullptr;
+               __nh.release();
                __ret.inserted = true;
              }
          }
@@ -1041,7 +1041,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        auto __code = this->_M_hash_code(__k);
        auto __ret
          = _M_insert_multi_node(__hint._M_cur, __code, __nh._M_ptr);
-       __nh._M_ptr = nullptr;
+       __nh.release();
        return __ret;
       }
 
@@ -1123,7 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                {
                  auto __nh = __src.extract(__pos);
                  _M_insert_unique_node(__bkt, __code, __nh._M_ptr, __n_elt);
-                 __nh._M_ptr = nullptr;
+                 __nh.release();
                  __n_elt = 1;
                }
              else if (__n_elt != 1)
@@ -1150,7 +1150,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
                = _M_src_hash_code(__src.hash_function(), __k, *__pos._M_cur);
              auto __nh = __src.extract(__pos);
              __hint = _M_insert_multi_node(__hint, __code, __nh._M_ptr)._M_cur;
-             __nh._M_ptr = nullptr;
+             __nh.release();
            }
        }
 #endif // C++17

diff --git a/libstdc++-v3/include/bits/node_handle.h b/libstdc++-v3/include/bits/node_handle.h
index 8904a5ac4963eb107ba90b79c090531ae1dae4f9..79afa547ec41b65bc46ef0551fb8addbc29a3270 100644 (file)
--- a/libstdc++-v3/include/bits/node_handle.h
+++ b/libstdc++-v3/include/bits/node_handle.h
@@ -168,6 +168,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        _M_ptr = nullptr;
       }
 
+      // Destroys the allocator. Does not deallocate or destroy the node.
+      // Precondition: !empty()
+      // Postcondition: empty()
+      void
+      release() noexcept
+      {
+       _M_alloc.release();
+       _M_ptr = nullptr;
+      }
+
     protected:
       typename _AllocTraits::pointer _M_ptr;
 
@@ -219,9 +229,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          return __tmp;
        }
 
-       struct _Empty { };
-
-       [[__no_unique_address__]] _Empty     _M_empty;
        [[__no_unique_address__]] _NodeAlloc _M_alloc;
       };
 
@@ -231,6 +238,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
               typename _Compare, typename _ValueAlloc>
        friend class _Rb_tree;
 
+      template<typename _Key2, typename _Value2, typename _ValueAlloc,
+              typename _ExtractKey, typename _Equal,
+              typename _Hash, typename _RangeHash, typename _Unused,
+              typename _RehashPolicy, typename _Traits>
+       friend class _Hashtable;
+
       /// @endcond
     };
 

diff --git a/libstdc++-v3/include/bits/stl_tree.h b/libstdc++-v3/include/bits/stl_tree.h
index f870f3dfa5387a5ad0434d43a0cc7b855f2f647d..c3ecbeb13796601f752c8f87814fb8eab42f26ed 100644 (file)
--- a/libstdc++-v3/include/bits/stl_tree.h
+++ b/libstdc++-v3/include/bits/stl_tree.h
@@ -1435,7 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _M_move_assign(_Rb_tree&, false_type);
 #endif
 
-#if __cplusplus > 201402L
+#if __cplusplus > 201404L
     public:
       /// Re-insert an extracted node.
       insert_return_type
@@ -1453,7 +1453,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
              {
                __ret.position
                  = _M_insert_node(__res.first, __res.second, __nh._M_ptr);
-               __nh._M_ptr = nullptr;
+               __nh.release();
                __ret.inserted = true;
              }
            else
@@ -1481,7 +1481,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
              __ret = _M_insert_node(__res.first, __res.second, __nh._M_ptr);
            else
              __ret = _M_insert_equal_lower_node(__nh._M_ptr);
-           __nh._M_ptr = nullptr;
+           __nh.release();
          }
        return __ret;
       }
@@ -1500,7 +1500,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            if (__res.second)
              {
                __ret = _M_insert_node(__res.first, __res.second, __nh._M_ptr);
-               __nh._M_ptr = nullptr;
+               __nh.release();
              }
            else
              __ret = iterator(__res.first);
@@ -1523,7 +1523,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
              __ret = _M_insert_node(__res.first, __res.second, __nh._M_ptr);
            else
              __ret = _M_insert_equal_lower_node(__nh._M_ptr);
-           __nh._M_ptr = nullptr;
+           __nh.release();
          }
        return __ret;
       }

diff --git a/libstdc++-v3/testsuite/23_containers/multiset/modifiers/114401.cc b/libstdc++-v3/testsuite/23_containers/multiset/modifiers/114401.cc
new file mode 100644 (file)
index 0000000..630e18e
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/multiset/modifiers/114401.cc
@@ -0,0 +1,125 @@
+// { dg-do run { target c++17 } }
+
+// PR libstdc++/114401 allocator destructor omitted when reinserting node_handle
+
+#include <set>
+#include <memory>
+#include <testsuite_hooks.h>
+
+template<typename T>
+struct Alloc
+{
+  using value_type = T;
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+
+  Alloc(int identity) : id(std::make_shared<int>(identity)) { }
+
+  template<typename U>
+    Alloc(const Alloc<U> a) : id(a.id) { }
+
+  T* allocate(std::size_t n) { return std::allocator<T>().allocate(n); }
+  void deallocate(T* p, std::size_t n) { std::allocator<T>().deallocate(p, n); }
+
+  template<typename U>
+    friend bool
+    operator==(const Alloc& a, const Alloc<U>& a2)
+    { return a.id == a2.id; }
+
+  template<typename U>
+    friend bool
+    operator!=(const Alloc& a, const Alloc<U>& a2)
+    { return !(a == a2); }
+
+  std::shared_ptr<int> id;
+};
+
+using test_type = std::multiset<int, std::less<int>, Alloc<int>>;
+
+void
+test_node_ops()
+{
+  test_type s1({1,3,5}, Alloc<int>(1));
+  test_type s2({2,4,6,8}, Alloc<int>(2));
+  VERIFY( s1.get_allocator() != s2.get_allocator() );
+
+  auto node_a = s1.extract(1);
+  VERIFY( ! node_a.empty() );
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+
+  node_a = std::move(node_a); // self-move
+  VERIFY( node_a.empty() );
+
+  swap(node_a, node_a); // self-swap
+  VERIFY( node_a.empty() );
+
+  auto node_b = s2.extract(2);
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  node_a = std::move(node_b); // empty = !empty
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(!empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  node_a = s1.extract(3); // !empty = !empty
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+  node_b = s2.extract(0); // empty = empty
+  VERIFY( node_b.empty() );
+  node_b = s2.extract(6); // empty = !empty
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(!empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.get_allocator() == s1.get_allocator() );
+
+  node_a = {};
+  node_b = std::move(node_a); // !empty = empty
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+}
+
+void
+test_alloc_lifetime()
+{
+  Alloc<int> a(1);
+  test_type s({1,2,3}, a);
+  VERIFY( a.id.use_count() == 2 ); // a and the copy in s
+
+  s.insert(s.extract(1));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(s.begin(), s.extract(2));
+  VERIFY( a.id.use_count() == 2 );
+
+  auto node = s.extract(1);
+  VERIFY( a.id.use_count() == 3 );
+  node = s.extract(0);
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(std::move(node));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type(s));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type({4,5,6}, a));
+  VERIFY( a.id.use_count() == 2 );
+}
+
+int main()
+{
+  test_node_ops();
+  test_alloc_lifetime();
+}

diff --git a/libstdc++-v3/testsuite/23_containers/set/modifiers/114401.cc b/libstdc++-v3/testsuite/23_containers/set/modifiers/114401.cc
new file mode 100644 (file)
index 0000000..f0a06a8
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/set/modifiers/114401.cc
@@ -0,0 +1,125 @@
+// { dg-do run { target c++17 } }
+
+// PR libstdc++/114401 allocator destructor omitted when reinserting node_handle
+
+#include <set>
+#include <memory>
+#include <testsuite_hooks.h>
+
+template<typename T>
+struct Alloc
+{
+  using value_type = T;
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+
+  Alloc(int identity) : id(std::make_shared<int>(identity)) { }
+
+  template<typename U>
+    Alloc(const Alloc<U> a) : id(a.id) { }
+
+  T* allocate(std::size_t n) { return std::allocator<T>().allocate(n); }
+  void deallocate(T* p, std::size_t n) { std::allocator<T>().deallocate(p, n); }
+
+  template<typename U>
+    friend bool
+    operator==(const Alloc& a, const Alloc<U>& a2)
+    { return a.id == a2.id; }
+
+  template<typename U>
+    friend bool
+    operator!=(const Alloc& a, const Alloc<U>& a2)
+    { return !(a == a2); }
+
+  std::shared_ptr<int> id;
+};
+
+using test_type = std::set<int, std::less<int>, Alloc<int>>;
+
+void
+test_node_ops()
+{
+  test_type s1({1,3,5}, Alloc<int>(1));
+  test_type s2({2,4,6,8}, Alloc<int>(2));
+  VERIFY( s1.get_allocator() != s2.get_allocator() );
+
+  auto node_a = s1.extract(1);
+  VERIFY( ! node_a.empty() );
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+
+  node_a = std::move(node_a); // self-move
+  VERIFY( node_a.empty() );
+
+  swap(node_a, node_a); // self-swap
+  VERIFY( node_a.empty() );
+
+  auto node_b = s2.extract(2);
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  node_a = std::move(node_b); // empty = !empty
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(!empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  node_a = s1.extract(3); // !empty = !empty
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+  node_b = s2.extract(0); // empty = empty
+  VERIFY( node_b.empty() );
+  node_b = s2.extract(6); // empty = !empty
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(!empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.get_allocator() == s1.get_allocator() );
+
+  node_a = {};
+  node_b = std::move(node_a); // !empty = empty
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+}
+
+void
+test_alloc_lifetime()
+{
+  Alloc<int> a(1);
+  test_type s({1,2,3}, a);
+  VERIFY( a.id.use_count() == 2 ); // a and the copy in s
+
+  s.insert(s.extract(1));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(s.begin(), s.extract(2));
+  VERIFY( a.id.use_count() == 2 );
+
+  auto node = s.extract(1);
+  VERIFY( a.id.use_count() == 3 );
+  node = s.extract(0);
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(std::move(node));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type(s));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type({4,5,6}, a));
+  VERIFY( a.id.use_count() == 2 );
+}
+
+int main()
+{
+  test_node_ops();
+  test_alloc_lifetime();
+}

diff --git a/libstdc++-v3/testsuite/23_containers/unordered_multiset/modifiers/114401.cc b/libstdc++-v3/testsuite/23_containers/unordered_multiset/modifiers/114401.cc
new file mode 100644 (file)
index 0000000..0a6ea77
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/unordered_multiset/modifiers/114401.cc
@@ -0,0 +1,126 @@
+// { dg-do run { target c++17 } }
+
+// PR libstdc++/114401 allocator destructor omitted when reinserting node_handle
+
+#include <unordered_set>
+#include <memory>
+#include <testsuite_hooks.h>
+
+template<typename T>
+struct Alloc
+{
+  using value_type = T;
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+
+  Alloc(int identity) : id(std::make_shared<int>(identity)) { }
+
+  template<typename U>
+    Alloc(const Alloc<U> a) : id(a.id) { }
+
+  T* allocate(std::size_t n) { return std::allocator<T>().allocate(n); }
+  void deallocate(T* p, std::size_t n) { std::allocator<T>().deallocate(p, n); }
+
+  template<typename U>
+    friend bool
+    operator==(const Alloc& a, const Alloc<U>& a2)
+    { return a.id == a2.id; }
+
+  template<typename U>
+    friend bool
+    operator!=(const Alloc& a, const Alloc<U>& a2)
+    { return !(a == a2); }
+
+  std::shared_ptr<int> id;
+};
+
+using test_type
+  = std::unordered_multiset<int, std::hash<int>, std::equal_to<int>, Alloc<int>>;
+
+void
+test_node_ops()
+{
+  test_type s1({1,3,5}, 3, Alloc<int>(1));
+  test_type s2({2,4,6,8}, 4, Alloc<int>(2));
+  VERIFY( s1.get_allocator() != s2.get_allocator() );
+
+  auto node_a = s1.extract(1);
+  VERIFY( ! node_a.empty() );
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+
+  node_a = std::move(node_a); // self-move
+  VERIFY( node_a.empty() );
+
+  swap(node_a, node_a); // self-swap
+  VERIFY( node_a.empty() );
+
+  auto node_b = s2.extract(2);
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  node_a = std::move(node_b); // empty = !empty
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(!empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  node_a = s1.extract(3); // !empty = !empty
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+  node_b = s2.extract(0); // empty = empty
+  VERIFY( node_b.empty() );
+  node_b = s2.extract(6); // empty = !empty
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(!empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.get_allocator() == s1.get_allocator() );
+
+  node_a = {};
+  node_b = std::move(node_a); // !empty = empty
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+}
+
+void
+test_alloc_lifetime()
+{
+  Alloc<int> a(1);
+  test_type s({1,2,3}, 3, a);
+  VERIFY( a.id.use_count() == 2 ); // a and the copy in s
+
+  s.insert(s.extract(1));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(s.begin(), s.extract(2));
+  VERIFY( a.id.use_count() == 2 );
+
+  auto node = s.extract(1);
+  VERIFY( a.id.use_count() == 3 );
+  node = s.extract(0);
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(std::move(node));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type(s));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type({4,5,6}, 3, a));
+  VERIFY( a.id.use_count() == 2 );
+}
+
+int main()
+{
+  test_node_ops();
+  test_alloc_lifetime();
+}

diff --git a/libstdc++-v3/testsuite/23_containers/unordered_set/modifiers/114401.cc b/libstdc++-v3/testsuite/23_containers/unordered_set/modifiers/114401.cc
new file mode 100644 (file)
index 0000000..3ae2f2d
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/unordered_set/modifiers/114401.cc
@@ -0,0 +1,126 @@
+// { dg-do run { target c++17 } }
+
+// PR libstdc++/114401 allocator destructor omitted when reinserting node_handle
+
+#include <unordered_set>
+#include <memory>
+#include <testsuite_hooks.h>
+
+template<typename T>
+struct Alloc
+{
+  using value_type = T;
+  using propagate_on_container_copy_assignment = std::true_type;
+  using propagate_on_container_move_assignment = std::true_type;
+  using propagate_on_container_swap = std::true_type;
+
+  Alloc(int identity) : id(std::make_shared<int>(identity)) { }
+
+  template<typename U>
+    Alloc(const Alloc<U> a) : id(a.id) { }
+
+  T* allocate(std::size_t n) { return std::allocator<T>().allocate(n); }
+  void deallocate(T* p, std::size_t n) { std::allocator<T>().deallocate(p, n); }
+
+  template<typename U>
+    friend bool
+    operator==(const Alloc& a, const Alloc<U>& a2)
+    { return a.id == a2.id; }
+
+  template<typename U>
+    friend bool
+    operator!=(const Alloc& a, const Alloc<U>& a2)
+    { return !(a == a2); }
+
+  std::shared_ptr<int> id;
+};
+
+using test_type
+  = std::unordered_set<int, std::hash<int>, std::equal_to<int>, Alloc<int>>;
+
+void
+test_node_ops()
+{
+  test_type s1({1,3,5}, 3, Alloc<int>(1));
+  test_type s2({2,4,6,8}, 4, Alloc<int>(2));
+  VERIFY( s1.get_allocator() != s2.get_allocator() );
+
+  auto node_a = s1.extract(1);
+  VERIFY( ! node_a.empty() );
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+
+  node_a = std::move(node_a); // self-move
+  VERIFY( node_a.empty() );
+
+  swap(node_a, node_a); // self-swap
+  VERIFY( node_a.empty() );
+
+  auto node_b = s2.extract(2);
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  node_a = std::move(node_b); // empty = !empty
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(!empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.empty() );
+
+  node_a = s1.extract(3); // !empty = !empty
+  VERIFY( node_a.get_allocator() == s1.get_allocator() );
+  node_b = s2.extract(0); // empty = empty
+  VERIFY( node_b.empty() );
+  node_b = s2.extract(6); // empty = !empty
+  VERIFY( node_b.get_allocator() == s2.get_allocator() );
+
+  swap(node_a, node_b); // swap(!empty, !empty)
+  VERIFY( node_a.get_allocator() == s2.get_allocator() );
+  VERIFY( node_b.get_allocator() == s1.get_allocator() );
+
+  node_a = {};
+  node_b = std::move(node_a); // !empty = empty
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+
+  swap(node_a, node_b); // swap(empty, empty)
+  VERIFY( node_a.empty() );
+  VERIFY( node_b.empty() );
+}
+
+void
+test_alloc_lifetime()
+{
+  Alloc<int> a(1);
+  test_type s({1,2,3}, 3, a);
+  VERIFY( a.id.use_count() == 2 ); // a and the copy in s
+
+  s.insert(s.extract(1));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(s.begin(), s.extract(2));
+  VERIFY( a.id.use_count() == 2 );
+
+  auto node = s.extract(1);
+  VERIFY( a.id.use_count() == 3 );
+  node = s.extract(0);
+  VERIFY( a.id.use_count() == 2 );
+
+  s.insert(std::move(node));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type(s));
+  VERIFY( a.id.use_count() == 2 );
+
+  s.merge(test_type({4,5,6}, 3, a));
+  VERIFY( a.id.use_count() == 2 );
+}
+
+int main()
+{
+  test_node_ops();
+  test_alloc_lifetime();
+}