Re: Improve insert/emplace robustness to self insertion

[Jonathan Wakely <jwakely at redhat dot com>]

On 02/07/16 08:37 +0200, François Dumont wrote:
> I haven't consider in this patch your remark about using allocator to 
> build instance so don't hesitate to commit what you want and I will 
> rebase.

Here's what I've committed to trunk.

I'm getting nervous about the smart insertion trick to avoid making a
copy, I have a devious testcase in mind which will break with that
change. I'll share the testcase later today.


commit 6aa6fa55a89c34c51366ed432bd942e09f691a0b
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Mon Jul 4 14:52:54 2016 +0000

    Add tests for inserting aliased objects into std::vector
    
    2016-07-04  Fran??ois Dumont  <fdumont@gcc.gnu.org>
    
    	* testsuite/23_containers/vector/modifiers/emplace/self_emplace.cc:
    	New test.
    	* testsuite/23_containers/vector/modifiers/insert/self_insert.cc: New
    	test.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@237986 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/libstdc++-v3/testsuite/23_containers/vector/modifiers/emplace/self_emplace.cc b/libstdc++-v3/testsuite/23_containers/vector/modifiers/emplace/self_emplace.cc
new file mode 100644
index 0000000..d452b5b
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/modifiers/emplace/self_emplace.cc
@@ -0,0 +1,144 @@
+// { dg-options "-std=gnu++11" }
+
+// 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/>.
+
+#include <vector>
+#include "testsuite_hooks.h"
+
+bool test __attribute__((unused)) = true;
+
+void
+test01()
+{
+  std::vector<std::vector<int>> vv =
+    {
+      { 2, 3 },
+      { 4, 5 },
+      { 0, 1 }
+    };
+
+  // Make sure emplace will imply reallocation.
+  VERIFY( vv.capacity() == 3 );
+
+  vv.emplace(vv.begin(), vv[0]);
+
+  VERIFY( vv.size() == 4 );
+  VERIFY( vv[0].size() == 2 );
+  VERIFY( vv[0][0] == 2 );
+  VERIFY( vv[0][1] == 3 );
+}
+
+void
+test02()
+{
+  std::vector<std::vector<int>> vv =
+    {
+      { 2, 3 },
+      { 4, 5 },
+      { 0, 1 }
+    };
+
+  // Make sure emplace won't reallocate.
+  vv.reserve(4);
+  vv.emplace(vv.begin(), vv[0]);
+
+  VERIFY( vv.size() == 4 );
+  VERIFY( vv[0].size() == 2 );
+  VERIFY( vv[0][0] == 2 );
+  VERIFY( vv[0][1] == 3 );
+}
+
+struct A
+{
+  A(int i) : _i(i)
+  { }
+
+  A(const A& other) : _i(other._i)
+  {
+    VERIFY( other._i >= 0 );
+  }
+
+  A(A&& other) : _i(other._i)
+  {
+    VERIFY( other._i >= 0 );
+
+    other._i = -1;
+  }
+
+  A(std::vector<A>::iterator it) : _i(it->_i)
+  {
+    VERIFY( it->_i >= 0 );
+  }
+
+  A& operator=(const A&) = default;
+  A& operator=(A&& other)
+  {
+    VERIFY(other._i >= 0 );
+
+    _i = other._i;
+    other._i = -1;
+    return *this;
+  }
+
+  int _i;
+};
+
+void
+test03()
+{
+  std::vector<A> va =
+    {
+      { A(1) },
+      { A(2) },
+      { A(3) }
+    };
+
+  // Make sure emplace will imply reallocation.
+  VERIFY( va.capacity() == 3 );
+
+  va.emplace(va.begin(), va.begin());
+
+  VERIFY( va.size() == 4 );
+  VERIFY( va[0]._i == 1 );
+}
+
+void
+test04()
+{
+  std::vector<A> va =
+    {
+      { A(1) },
+      { A(2) },
+      { A(3) }
+    };
+
+  // Make sure emplace won't reallocate.
+  va.reserve(4);
+  va.emplace(va.begin(), va.begin());
+
+  VERIFY( va.size() == 4 );
+  VERIFY( va[0]._i == 1 );
+}
+
+int main()
+{
+  test01();
+  test02();
+  test03();
+  test04();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/self_insert.cc b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/self_insert.cc
new file mode 100644
index 0000000..9944cbb
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert/self_insert.cc
@@ -0,0 +1,70 @@
+// { dg-options "-std=gnu++11" }
+
+// 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/>.
+
+#include <vector>
+
+#include "testsuite_hooks.h"
+
+bool test __attribute__((unused)) = true;
+
+void test01()
+{
+  std::vector<std::vector<int>> vv =
+    {
+      { 2, 3 },
+      { 4, 5 },
+      { 0, 1 }
+    };
+
+  // Make sure it doesn't reallocate during insertion.
+  vv.reserve(4);
+
+  vv.insert(vv.begin(), vv[0]);
+
+  VERIFY( vv.size() == 4 );
+  VERIFY( vv[0].size() == 2 );
+  VERIFY( vv[0][0] == 2 );
+  VERIFY( vv[0][1] == 3 );
+}
+
+void test02()
+{
+  std::vector<std::vector<int>> vv =
+    {
+      { 2, 3 },
+      { 4, 5 },
+      { 0, 1 }
+    };
+
+  // Make sure we will reallocate for insertion.
+  VERIFY( vv.capacity() == 3 );
+
+  vv.insert(vv.begin(), vv[0]);
+
+  VERIFY( vv.size() == 4 );
+  VERIFY( vv[0].size() == 2 );
+  VERIFY( vv[0][0] == 2 );
+  VERIFY( vv[0][1] == 3 );
+}
+
+int main()
+{
+  test01();
+  test02();
+}

commit c1e8e16c5c977ebc08d3a76e5ae9428b693d8a8c
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Mon Jul 4 14:52:46 2016 +0000

    Fix std::vector's use of temporary objects
    
    	* include/bits/stl_vector.h (emplace(const_iterator, _Args&&...)):
    	Define inline. Forward to _M_emplace_aux.
    	(insert(const_iterator, value_type&&)): Forward to _M_insert_rval.
    	(_M_insert_rval, _M_emplace_aux): Declare new functions.
    	(_Temporary_value): New RAII type using allocator to construct/destroy.
    	(_S_insert_aux_assign): Remove.
    	(_M_insert_aux): Make non-variadic.
    	* include/bits/vector.tcc (insert(const_iterator, const value_type&)):
    	Use _Temporary_value.
    	(emplace(const_iterator, _Args&&...)): Remove definition.
    	(_M_insert_rval, _M_emplace_aux): Define.
    	(_M_insert_aux): Make non-variadic, stop using _S_insert_aux_assign.
    	(_M_fill_insert): Use _Temporary_value.
    	* testsuite/23_containers/vector/allocator/construction.cc: New test.
    	* testsuite/23_containers/vector/modifiers/insert_vs_emplace.cc:
    	Adjust expected results for emplacing an lvalue with reallocation.
    	* testsuite/23_containers/vector/check_construct_destroy.cc: Adjust
    	expected results to account for construction/destruction of temporary
    	using allocator.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@237985 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index eaafa22..8e8aa7c 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -995,7 +995,8 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        */
       template<typename... _Args>
 	iterator
-	emplace(const_iterator __position, _Args&&... __args);
+	emplace(const_iterator __position, _Args&&... __args)
+	{ return _M_emplace_aux(__position, std::forward<_Args>(__args)...); }
 
       /**
        *  @brief  Inserts given value into %vector before specified iterator.
@@ -1040,7 +1041,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        */
       iterator
       insert(const_iterator __position, value_type&& __x)
-      { return emplace(__position, std::move(__x)); }
+      { return _M_insert_rval(__position, std::move(__x)); }
 
       /**
        *  @brief  Inserts an initializer_list into the %vector.
@@ -1431,30 +1432,65 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       _M_shrink_to_fit();
 #endif
 
-      // Called by insert(p,x)
 #if __cplusplus < 201103L
+      // Called by insert(p,x)
       void
       _M_insert_aux(iterator __position, const value_type& __x);
 #else
-      template<typename... _Args>
-	static void
-	_S_insert_aux_assign(iterator __pos, _Args&&... __args)
-	{ *__pos =  _Tp(std::forward<_Args>(__args)...); }
+      // A value_type object constructed with _Alloc_traits::construct()
+      // and destroyed with _Alloc_traits::destroy().
+      struct _Temporary_value
+      {
+	template<typename... _Args>
+	  explicit
+	  _Temporary_value(vector* __vec, _Args&&... __args) : _M_this(__vec)
+	  {
+	    _Alloc_traits::construct(_M_this->_M_impl, _M_ptr(),
+				     std::forward<_Args>(__args)...);
+	  }
 
-      static void
-      _S_insert_aux_assign(iterator __pos, _Tp&& __arg)
-      { *__pos = std::move(__arg); }
+	~_Temporary_value()
+	{ _Alloc_traits::destroy(_M_this->_M_impl, _M_ptr()); }
 
-      template<typename... _Args>
+	value_type&
+	_M_val() { return *reinterpret_cast<_Tp*>(&__buf); }
+
+      private:
+	pointer
+	_M_ptr() { return pointer_traits<pointer>::pointer_to(_M_val()); }
+
+	vector* _M_this;
+	typename aligned_storage<sizeof(_Tp), alignof(_Tp)>::type __buf;
+      };
+
+      // Called by insert(p,x) and other functions when insertion needs to
+      // reallocate or move existing elements. _Arg is either _Tp& or _Tp.
+      template<typename _Arg>
 	void
-	_M_insert_aux(iterator __position, _Args&&... __args);
+	_M_insert_aux(iterator __position, _Arg&& __arg);
 
+      // Either move-construct at the end, or forward to _M_insert_aux.
+      iterator
+      _M_insert_rval(const_iterator __position, value_type&& __v);
+
+      // Called by push_back(x) and emplace_back(args) when they need to
+      // reallocate.
       template<typename... _Args>
 	void
 	_M_emplace_back_aux(_Args&&... __args);
+
+      // Try to emplace at the end, otherwise forward to _M_insert_aux.
+      template<typename... _Args>
+	iterator
+	_M_emplace_aux(const_iterator __position, _Args&&... __args);
+
+      // Emplacing an rvalue of the correct type can use _M_insert_rval.
+      iterator
+      _M_emplace_aux(const_iterator __position, value_type&& __v)
+      { return _M_insert_rval(__position, std::move(__v)); }
 #endif
 
-      // Called by the latter.
+      // Called by _M_fill_insert, _M_insert_aux etc.
       size_type
       _M_check_len(size_type __n, const char* __s) const
       {
diff --git a/libstdc++-v3/include/bits/vector.tcc b/libstdc++-v3/include/bits/vector.tcc
index 9cb5464..dd0d288 100644
--- a/libstdc++-v3/include/bits/vector.tcc
+++ b/libstdc++-v3/include/bits/vector.tcc
@@ -124,8 +124,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  const auto __pos = begin() + (__position - cbegin());
 	  if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage)
 	    {
-	      _Tp __x_copy = __x;
-	      _M_insert_aux(__pos, std::move(__x_copy));
+	      // __x could be an existing element of this vector, so make a
+	      // copy of it before _M_insert_aux moves elements around.
+	      _Temporary_value __x_copy(this, __x);
+	      _M_insert_aux(__pos, std::move(__x_copy._M_val()));
 	    }
 	  else
 	    _M_insert_aux(__pos, __x);
@@ -297,30 +299,49 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
 #if __cplusplus >= 201103L
   template<typename _Tp, typename _Alloc>
+    auto
+    vector<_Tp, _Alloc>::
+    _M_insert_rval(const_iterator __position, value_type&& __v) -> iterator
+    {
+      const auto __n = __position - cbegin();
+      if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage
+	  && __position == cend())
+	{
+	  _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
+				   std::move(__v));
+	  ++this->_M_impl._M_finish;
+	}
+      else
+	_M_insert_aux(begin() + __n, std::move(__v));
+      return iterator(this->_M_impl._M_start + __n);
+    }
+
+  template<typename _Tp, typename _Alloc>
     template<typename... _Args>
-      typename vector<_Tp, _Alloc>::iterator
+      auto
       vector<_Tp, _Alloc>::
-      emplace(const_iterator __position, _Args&&... __args)
+      _M_emplace_aux(const_iterator __position, _Args&&... __args)
+      -> iterator
       {
-	const size_type __n = __position - begin();
-	if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage
-	    && __position == end())
-	  {
-	    _Alloc_traits::construct(this->_M_impl, this->_M_impl._M_finish,
-				     std::forward<_Args>(__args)...);
-	    ++this->_M_impl._M_finish;
-	  }
+	const auto __n = __position - cbegin();
+	if (__position == cend())
+	  emplace_back(std::forward<_Args>(__args)...);
 	else
-	  _M_insert_aux(begin() + (__position - cbegin()),
-			std::forward<_Args>(__args)...);
+	  {
+	    // We need to construct a temporary because something in __args...
+	    // could alias one of the elements of the container and so we
+	    // need to use it before _M_insert_aux moves elements around.
+	    _Temporary_value __tmp(this, std::forward<_Args>(__args)...);
+	    _M_insert_aux(begin() + __n, std::move(__tmp._M_val()));
+	  }
 	return iterator(this->_M_impl._M_start + __n);
       }
 
   template<typename _Tp, typename _Alloc>
-    template<typename... _Args>
+    template<typename _Arg>
       void
       vector<_Tp, _Alloc>::
-      _M_insert_aux(iterator __position, _Args&&... __args)
+      _M_insert_aux(iterator __position, _Arg&& __arg)
 #else
   template<typename _Tp, typename _Alloc>
     void
@@ -343,7 +364,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 #if __cplusplus < 201103L
 	  *__position = __x_copy;
 #else
-	  _S_insert_aux_assign(__position, std::forward<_Args>(__args)...);
+	  *__position = std::forward<_Arg>(__arg);
 #endif
 	}
       else
@@ -355,14 +376,15 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  pointer __new_finish(__new_start);
 	  __try
 	    {
-	      // The order of the three operations is dictated by the C++0x
+	      // The order of the three operations is dictated by the C++11
 	      // case, where the moves could alter a new element belonging
 	      // to the existing vector.  This is an issue only for callers
-	      // taking the element by const lvalue ref (see 23.1/13).
+	      // taking the element by lvalue ref (see last bullet of C++11
+	      // [res.on.arguments]).
 	      _Alloc_traits::construct(this->_M_impl,
 		                       __new_start + __elems_before,
 #if __cplusplus >= 201103L
-				       std::forward<_Args>(__args)...);
+				       std::forward<_Arg>(__arg));
 #else
 	                               __x);
 #endif
@@ -455,7 +477,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  if (size_type(this->_M_impl._M_end_of_storage
 			- this->_M_impl._M_finish) >= __n)
 	    {
+#if __cplusplus < 201103L
 	      value_type __x_copy = __x;
+#else
+	      _Temporary_value __tmp(this, __x);
+	      value_type& __x_copy = __tmp._M_val();
+#endif
 	      const size_type __elems_after = end() - __position;
 	      pointer __old_finish(this->_M_impl._M_finish);
 	      if (__elems_after > __n)
diff --git a/libstdc++-v3/testsuite/23_containers/vector/allocator/construction.cc b/libstdc++-v3/testsuite/23_containers/vector/allocator/construction.cc
new file mode 100644
index 0000000..8040949
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/allocator/construction.cc
@@ -0,0 +1,105 @@
+// 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-options "-std=gnu++11" }
+// { dg-do compile }
+
+#include <vector>
+
+struct Tag { };
+
+template<typename T>
+  struct TaggingAllocator
+  {
+    using value_type = T;
+
+    TaggingAllocator() = default;
+
+    template<typename U>
+      TaggingAllocator(const TaggingAllocator<U>&) { }
+
+    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, typename... Args>
+      void
+      construct(U* p, Args&&... args)
+      { ::new((void*)p) U(Tag{}, std::forward<Args>(args)...); }
+
+    template<typename U, typename... Args>
+      void
+      destroy(U* p)
+      { p->~U(); }
+  };
+
+template<typename T, typename U>
+  bool
+  operator==(const TaggingAllocator<T>&, const TaggingAllocator<U>&)
+  { return true; }
+
+template<typename T, typename U>
+  bool
+  operator!=(const TaggingAllocator<T>&, const TaggingAllocator<U>&)
+  { return false; }
+
+struct X
+{
+  // All constructors must be passed the Tag type.
+
+  // DefaultInsertable into vector<X, TaggingAllocator<X>>,
+  X(Tag) { }
+  // CopyInsertable into vector<X, TaggingAllocator<X>>,
+  X(Tag, const X&) { }
+  // MoveInsertable into vector<X, TaggingAllocator<X>>, and
+  X(Tag, X&&) { }
+
+  // EmplaceConstructible into vector<X, TaggingAllocator<X>> from args.
+  template<typename... Args>
+    X(Tag, Args&&...) { }
+
+  // not DefaultConstructible, CopyConstructible or MoveConstructible.
+  X() = delete;
+  X(const X&) = delete;
+  X(X&&) = delete;
+
+  // CopyAssignable.
+  X& operator=(const X&) { return *this; }
+
+  // MoveAssignable.
+  X& operator=(X&&) { return *this; }
+
+private:
+  // Not Destructible.
+  ~X() { }
+
+  // Erasable from vector<X, TaggingAllocator<X>>.
+  friend class TaggingAllocator<X>;
+};
+
+template class std::vector<X, TaggingAllocator<X>>;
+
+void test01()
+{
+  std::vector<X, TaggingAllocator<X>> v;
+  v.reserve(3);
+  v.emplace_back();
+  v.emplace(v.begin());
+  v.emplace(v.begin(), 1, 2, 3);
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/check_construct_destroy.cc b/libstdc++-v3/testsuite/23_containers/vector/check_construct_destroy.cc
index cf2f7c7..b92a152 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/check_construct_destroy.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/check_construct_destroy.cc
@@ -49,9 +49,9 @@ int main()
     c.reserve(100);
     tracker_allocator_counter::reset();
     c.insert(c.begin(), arr10[0]);
-    ok = check_construct_destroy("Insert element", 1, 0) && ok;
+    ok = check_construct_destroy("Insert element", 2, 1) && ok;
   }
-  ok = check_construct_destroy("Insert element", 1, 11) && ok;
+  ok = check_construct_destroy("Insert element", 2, 12) && ok;
 
   {
     Container c(arr10, arr10 + 10);
diff --git a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert_vs_emplace.cc b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert_vs_emplace.cc
index 39a3f03..1b46124 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert_vs_emplace.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/modifiers/insert_vs_emplace.cc
@@ -223,7 +223,8 @@ test03()
 void
 test04()
 {
-  const X::special expected{ 0, 3, 1, 0, 3, 0 };
+  const X::special expected_ins{ 0, 3, 1, 0, 3, 0 };
+  const X::special expected_emp{ 0, 4, 1, 0, 4, 0 };
   X::special ins, emp;
   {
     std::vector<X> v;
@@ -253,8 +254,8 @@ test04()
     // std::cout << "----\n";
     emp = X::sp;
   }
-  VERIFY( ins == emp );
-  VERIFY( ins == expected );
+  VERIFY( ins == expected_ins );
+  VERIFY( emp == expected_emp );
 }
 
 // insert vs emplace xvalue reallocation
diff --git a/libstdc++-v3/testsuite/backward/hash_set/check_construct_destroy.cc b/libstdc++-v3/testsuite/backward/hash_set/check_construct_destroy.cc
index 5693c76..5740fe1 100644
--- a/libstdc++-v3/testsuite/backward/hash_set/check_construct_destroy.cc
+++ b/libstdc++-v3/testsuite/backward/hash_set/check_construct_destroy.cc
@@ -39,45 +39,48 @@ int main()
 
   int buckets;
 
+  // Add 1 to all counts, because the std::vector used internally by the
+  // hashtable creates and destroys a temporary object using the allocator.
+
   tracker_allocator_counter::reset();
   {
     Container c;
     buckets = c.bucket_count();
-    ok = check_construct_destroy("empty container", buckets, 0) && ok;
+    ok = check_construct_destroy("empty container", buckets+1, 1) && ok;
   }
-  ok = check_construct_destroy("empty container", buckets, buckets) && ok;
+  ok = check_construct_destroy("empty container", buckets+1, buckets+1) && ok;
 
 
   tracker_allocator_counter::reset();
   {
     Container c(arr10, arr10 + 10);
-    ok = check_construct_destroy("Construct from range", buckets+10, 0) && ok;
+    ok = check_construct_destroy("Construct from range", buckets+10+1, 1) && ok;
   }
-  ok = check_construct_destroy("Construct from range", buckets+10, buckets+10) && ok;
+  ok = check_construct_destroy("Construct from range", buckets+10+1, buckets+10+1) && ok;
 
   tracker_allocator_counter::reset();
   {
     Container c(arr10, arr10 + 10);
     c.insert(arr10a[0]);
-    ok = check_construct_destroy("Insert element", buckets+11, 0) && ok;
+    ok = check_construct_destroy("Insert element", buckets+11+1, 1) && ok;
   }
-  ok = check_construct_destroy("Insert element", buckets+11, buckets+11) && ok;
+  ok = check_construct_destroy("Insert element", buckets+11+1, buckets+11+1) && ok;
 
   tracker_allocator_counter::reset();
   {
     Container c(arr10, arr10 + 10);
     c.insert(arr10a, arr10a+3);
-    ok = check_construct_destroy("Insert short range", buckets+13, 0) && ok;
+    ok = check_construct_destroy("Insert short range", buckets+13+1, 1) && ok;
   }
-  ok = check_construct_destroy("Insert short range", buckets+13, buckets+13) && ok;
+  ok = check_construct_destroy("Insert short range", buckets+13+1, buckets+13+1) && ok;
 
   tracker_allocator_counter::reset();
   {
     Container c(arr10, arr10 + 10);
     c.insert(arr10a, arr10a+10);
-    ok = check_construct_destroy("Insert long range", buckets+20, 0) && ok;
+    ok = check_construct_destroy("Insert long range", buckets+20+1, 1) && ok;
   }
-  ok = check_construct_destroy("Insert long range", buckets+20, buckets+20) && ok;
+  ok = check_construct_destroy("Insert long range", buckets+20+1, buckets+20+1) && ok;
 
   return ok ? 0 : 1;
 }