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Re: std::vector default default and move constructors


On 16/01/2018 01:20, Jonathan Wakely wrote:
On 15/01/18 22:32 +0100, François Dumont wrote:
On 15/01/2018 13:29, Jonathan Wakely wrote:
In fact it introduces a serious regression because of this line:

-      vector(vector&& __x) noexcept
-      : _Base(std::move(__x)) { }
+      vector(vector&&) = default;

Consider what happens if we have an allocator that is not
nothrow-move-constructible, which can happen if the allocator has a
noexcept(false) move constructor, or more likely just has no move
constructor but has a noexcept(false) copy constructor:

One of the move constructors needs to be defined with a function body,
not defaulted, so that it can also be declared noexcept

Here is an updated patch with this change. Do you also want an explicit noexcept on the vector(vector&&) default declaration ? Ok to commit this vector patch ?

I was going to propose a similar patch for vector<bool> but checking Standard there is not this noexcept qualification on the move constructor.

François

diff --git a/libstdc++-v3/include/bits/stl_vector.h b/libstdc++-v3/include/bits/stl_vector.h
index acec501..a6282ec 100644
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -85,34 +85,56 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       typedef typename __gnu_cxx::__alloc_traits<_Tp_alloc_type>::pointer
        	pointer;
 
-      struct _Vector_impl
-      : public _Tp_alloc_type
+      struct _Vector_impl_data
       {
 	pointer _M_start;
 	pointer _M_finish;
 	pointer _M_end_of_storage;
 
-	_Vector_impl()
-	: _Tp_alloc_type(), _M_start(), _M_finish(), _M_end_of_storage()
-	{ }
-
-	_Vector_impl(_Tp_alloc_type const& __a) _GLIBCXX_NOEXCEPT
-	: _Tp_alloc_type(__a), _M_start(), _M_finish(), _M_end_of_storage()
+	_Vector_impl_data() _GLIBCXX_NOEXCEPT
+	: _M_start(), _M_finish(), _M_end_of_storage()
 	{ }
 
 #if __cplusplus >= 201103L
-	_Vector_impl(_Tp_alloc_type&& __a) noexcept
-	: _Tp_alloc_type(std::move(__a)),
-	  _M_start(), _M_finish(), _M_end_of_storage()
-	{ }
+	_Vector_impl_data(_Vector_impl_data&& __x) noexcept
+	: _M_start(__x._M_start), _M_finish(__x._M_finish),
+	  _M_end_of_storage(__x._M_end_of_storage)
+	{ __x._M_start = __x._M_finish = __x._M_end_of_storage = pointer(); }
 #endif
 
-	void _M_swap_data(_Vector_impl& __x) _GLIBCXX_NOEXCEPT
+	void
+	_M_swap_data(_Vector_impl_data& __x) _GLIBCXX_NOEXCEPT
 	{
 	  std::swap(_M_start, __x._M_start);
 	  std::swap(_M_finish, __x._M_finish);
 	  std::swap(_M_end_of_storage, __x._M_end_of_storage);
 	}
+      };
+
+      struct _Vector_impl
+	: public _Tp_alloc_type, public _Vector_impl_data
+      {
+	_Vector_impl() _GLIBCXX_NOEXCEPT_IF( noexcept(_Tp_alloc_type()) )
+	: _Tp_alloc_type()
+	{ }
+
+	_Vector_impl(_Tp_alloc_type const& __a) _GLIBCXX_NOEXCEPT
+	: _Tp_alloc_type(__a)
+	{ }
+
+#if __cplusplus >= 201103L
+	_Vector_impl(_Vector_impl&& __x) noexcept
+	: _Tp_alloc_type(std::move(__x)), _Vector_impl_data(std::move(__x))
+	{ }
+
+	_Vector_impl(_Tp_alloc_type&& __a) noexcept
+	  : _Tp_alloc_type(std::move(__a))
+	{ }
+
+	_Vector_impl(_Tp_alloc_type&& __a, _Vector_impl&& __rv) noexcept
+	: _Tp_alloc_type(std::move(__a)), _Vector_impl_data(std::move(__rv))
+	{ }
+#endif
 
 #if _GLIBCXX_SANITIZE_STD_ALLOCATOR && _GLIBCXX_SANITIZE_VECTOR
 	template<typename = _Tp_alloc_type>
@@ -235,38 +257,42 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       _Tp_alloc_type&
       _M_get_Tp_allocator() _GLIBCXX_NOEXCEPT
-      { return *static_cast<_Tp_alloc_type*>(&this->_M_impl); }
+      { return this->_M_impl; }
 
       const _Tp_alloc_type&
       _M_get_Tp_allocator() const _GLIBCXX_NOEXCEPT
-      { return *static_cast<const _Tp_alloc_type*>(&this->_M_impl); }
+      { return this->_M_impl; }
 
       allocator_type
       get_allocator() const _GLIBCXX_NOEXCEPT
       { return allocator_type(_M_get_Tp_allocator()); }
 
-      _Vector_base()
-      : _M_impl() { }
+#if __cplusplus >= 201103L
+      _Vector_base() = default;
+#else
+      _Vector_base() { }
+#endif
 
       _Vector_base(const allocator_type& __a) _GLIBCXX_NOEXCEPT
       : _M_impl(__a) { }
 
+#if !_GLIBCXX_INLINE_VERSION
       _Vector_base(size_t __n)
       : _M_impl()
       { _M_create_storage(__n); }
+#endif
 
       _Vector_base(size_t __n, const allocator_type& __a)
       : _M_impl(__a)
       { _M_create_storage(__n); }
 
 #if __cplusplus >= 201103L
+      _Vector_base(_Vector_base&&) = default;
+
+# if !_GLIBCXX_INLINE_VERSION
       _Vector_base(_Tp_alloc_type&& __a) noexcept
       : _M_impl(std::move(__a)) { }
 
-      _Vector_base(_Vector_base&& __x) noexcept
-      : _M_impl(std::move(__x._M_get_Tp_allocator()))
-      { this->_M_impl._M_swap_data(__x._M_impl); }
-
       _Vector_base(_Vector_base&& __x, const allocator_type& __a)
       : _M_impl(__a)
       {
@@ -278,6 +304,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	    _M_create_storage(__n);
 	  }
       }
+# endif
+
+      _Vector_base(const allocator_type& __a, _Vector_base&& __x)
+      : _M_impl(_Tp_alloc_type(__a), std::move(__x._M_impl))
+      { }
 #endif
 
       ~_Vector_base() _GLIBCXX_NOEXCEPT
@@ -304,7 +335,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  _Tr::deallocate(_M_impl, __p, __n);
       }
 
-    private:
+    protected:
       void
       _M_create_storage(size_t __n)
       {
@@ -388,11 +419,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       /**
        *  @brief  Creates a %vector with no elements.
        */
-      vector()
 #if __cplusplus >= 201103L
-      noexcept(is_nothrow_default_constructible<_Alloc>::value)
+      vector() = default;
+#else
+      vector() { }
 #endif
-      : _Base() { }
 
       /**
        *  @brief  Creates a %vector with no elements.
@@ -468,13 +499,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 #if __cplusplus >= 201103L
       /**
        *  @brief  %Vector move constructor.
-       *  @param  __x  A %vector of identical element and allocator types.
        *
-       *  The newly-created %vector contains the exact contents of @a __x.
-       *  The contents of @a __x are a valid, but unspecified %vector.
+       *  The newly-created %vector contains the exact contents of the
+       *  moved instance.
+       *  The contents of the moved instance are a valid, but unspecified
+       *  %vector.
        */
-      vector(vector&& __x) noexcept
-      : _Base(std::move(__x)) { }
+      vector(vector&&) = default;
 
       /// Copy constructor with alternative allocator
       vector(const vector& __x, const allocator_type& __a)
@@ -486,13 +517,19 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 				      _M_get_Tp_allocator());
       }
 
-      /// Move constructor with alternative allocator
-      vector(vector&& __rv, const allocator_type& __m)
-      noexcept(_Alloc_traits::_S_always_equal())
-      : _Base(std::move(__rv), __m)
+    private:
+      vector(vector&& __rv, const allocator_type& __m, true_type) noexcept
+      : _Base(__m, std::move(__rv))
+      { }
+
+      vector(vector&& __rv, const allocator_type& __m, false_type)
+      : _Base(__m)
       {
-	if (__rv.get_allocator() != __m)
+	if (__rv.get_allocator() == __m)
+	  this->_M_impl._M_swap_data(__rv._M_impl);
+	else if (!__rv.empty())
 	  {
+	    this->_M_create_storage(__rv.size());
 	    this->_M_impl._M_finish =
 	      std::__uninitialized_move_a(__rv.begin(), __rv.end(),
 					  this->_M_impl._M_start,
@@ -501,6 +538,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	  }
       }
 
+    public:
+      /// Move constructor with alternative allocator
+      vector(vector&& __rv, const allocator_type& __m)
+	noexcept(_Alloc_traits::_S_always_equal())
+      : vector(std::move(__rv), __m, typename _Alloc_traits::is_always_equal{})
+      { }
+
       /**
        *  @brief  Builds a %vector from an initializer list.
        *  @param  __l  An initializer_list.
@@ -543,7 +587,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	vector(_InputIterator __first, _InputIterator __last,
 	       const allocator_type& __a = allocator_type())
 	: _Base(__a)
-	{ _M_initialize_dispatch(__first, __last, __false_type()); }
+	{
+	  _M_range_initialize(__first, __last,
+			      std::__iterator_category(__first));
+	}
 #else
       template<typename _InputIterator>
 	vector(_InputIterator __first, _InputIterator __last,
@@ -1414,6 +1461,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 
       // Called by the range constructor to implement [23.1.1]/9
 
+#if __cplusplus < 201103L
       // _GLIBCXX_RESOLVE_LIB_DEFECTS
       // 438. Ambiguity in the "do the right thing" clause
       template<typename _Integer>
@@ -1432,10 +1480,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
 	_M_initialize_dispatch(_InputIterator __first, _InputIterator __last,
 			       __false_type)
 	{
-	  typedef typename std::iterator_traits<_InputIterator>::
-	    iterator_category _IterCategory;
-	  _M_range_initialize(__first, __last, _IterCategory());
+	  _M_range_initialize(__first, __last,
+			      std::__iterator_category(__first));
 	}
+#endif
 
       // Called by the second initialize_dispatch above
       template<typename _InputIterator>
@@ -1669,7 +1717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       // moved, either because the source's allocator will move too
       // or because the allocators are equal.
       void
-      _M_move_assign(vector&& __x, std::true_type) noexcept
+      _M_move_assign(vector&& __x, true_type) noexcept
       {
 	vector __tmp(get_allocator());
 	this->_M_impl._M_swap_data(__tmp._M_impl);
@@ -1680,10 +1728,10 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
       // Do move assignment when it might not be possible to move source
       // object's memory, resulting in a linear-time operation.
       void
-      _M_move_assign(vector&& __x, std::false_type)
+      _M_move_assign(vector&& __x, false_type)
       {
 	if (__x._M_get_Tp_allocator() == this->_M_get_Tp_allocator())
-	  _M_move_assign(std::move(__x), std::true_type());
+	  _M_move_assign(std::move(__x), true_type());
 	else
 	  {
 	    // The rvalue's allocator cannot be moved and is not equal,
diff --git a/libstdc++-v3/testsuite/23_containers/vector/allocator/default_init.cc b/libstdc++-v3/testsuite/23_containers/vector/allocator/default_init.cc
new file mode 100644
index 0000000..5981b8f
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/allocator/default_init.cc
@@ -0,0 +1,67 @@
+// Copyright (C) 2018 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-do run { target c++11 } }
+// { dg-options "-O0" }
+// { dg-xfail-run-if "PR c++/65816" { *-*-* } }
+
+#include <vector>
+#include <testsuite_hooks.h>
+#include <testsuite_allocator.h>
+
+#include <ext/aligned_buffer.h>
+
+using T = int;
+
+using __gnu_test::default_init_allocator;
+
+void test01()
+{
+  typedef default_init_allocator<T> alloc_type;
+  typedef std::vector<T, alloc_type> test_type;
+
+  __gnu_cxx::__aligned_buffer<test_type> buf;
+  __builtin_memset(buf._M_addr(), ~0, sizeof(test_type));
+
+  test_type *tmp = ::new(buf._M_addr()) test_type;
+
+  VERIFY( tmp->get_allocator().state == 0 );
+
+  tmp->~test_type();
+}
+
+void test02()
+{
+  typedef default_init_allocator<T> alloc_type;
+  typedef std::vector<T, alloc_type> test_type;
+
+  __gnu_cxx::__aligned_buffer<test_type> buf;
+  __builtin_memset(buf._M_addr(), ~0, sizeof(test_type));
+
+  test_type *tmp = ::new(buf._M_addr()) test_type();
+
+  VERIFY( tmp->get_allocator().state == 0 );
+
+  tmp->~test_type();
+}
+
+int main()
+{
+  test01();
+  test02();
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/cons/noexcept_move_construct.cc b/libstdc++-v3/testsuite/23_containers/vector/cons/noexcept_move_construct.cc
index f8f71a5..268a46c 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/cons/noexcept_move_construct.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/cons/noexcept_move_construct.cc
@@ -24,3 +24,22 @@
 typedef std::vector<int> vtype;
 
 static_assert(std::is_nothrow_move_constructible<vtype>::value, "Error");
+
+template<typename Type>
+  class NoExceptMoveConstructorAlloc : public std::allocator<Type>
+  {
+  public:
+    NoExceptMoveConstructorAlloc() = default;
+    NoExceptMoveConstructorAlloc(const NoExceptMoveConstructorAlloc&) = default;
+    NoExceptMoveConstructorAlloc(NoExceptMoveConstructorAlloc&& __x) noexcept(false)
+    : std::allocator<Type>(std::move(__x))
+    { }
+
+    template<typename _Tp1>
+      struct rebind
+      { typedef NoExceptMoveConstructorAlloc<_Tp1> other; };
+  };
+
+typedef std::vector<int, NoExceptMoveConstructorAlloc<int>> vtype2;
+
+static_assert(std::is_nothrow_move_constructible<vtype2>::value, "Error");


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