[PATCH] Remove lambdas from _Rb_tree

François Dumont frs.dumont@gmail.com
Thu Nov 19 13:20:09 GMT 2020 

On 19/11/20 12:31 pm, Jonathan Wakely wrote:
> On 19/11/20 07:46 +0100, François Dumont via Libstdc++ wrote:
>> On 18/11/20 12:50 am, Jonathan Wakely wrote:
>>> On 17/11/20 21:51 +0100, François Dumont via Libstdc++ wrote:
>>>> This is a change that has been done to _Hashtable and that I forgot 
>>>> to propose for _Rb_tree.
>>>>
>>>> The _GLIBCXX_XREF macro can be easily removed of course.
>>>>
>>>>     libstdc++: _Rb_tree code cleanup, remove lambdas.
>>>>
>>>>     Use an additional template parameter on the clone 
>>>> method to propagate if the values must be
>>>>     copy or move rather than lambdas.
>>>>
>>>>     libstdc++-v3/ChangeLog:
>>>>
>>>>             * include/bits/move.h 
>>>> (_GLIBCXX_XREF): New.
>>>>             * 
>>>> include/bits/stl_tree.h: Adapt to use latter.
>>>>            
>>>> (_Rb_tree<>::_S_fwd_value_for): New.
>>>>            
>>>> (_Rb_tree<>::_M_clone_node): Add _Tree template parameter.
>>>>             Use _S_fwd_value_for.
>>>>            
>>>> (_Rb_tree<>::_M_cbegin): New.
>>>>            (_Rb_tree<>::_M_begin): 
>>>> Use latter.
>>>>            (_Rb_tree<>::_M_copy): 
>>>> Add _Tree template parameter.
>>>>            
>>>> (_Rb_tree<>::_M_move_data): Use rvalue reference for _Rb_tree 
>>>> parameter.
>>>>            
>>>> (_Rb_tree<>::_M_move_assign): Likewise.
>>>>
>>>> Tested under Linux x86_64.
>>>>
>>>> Ok to commit ?
>>>
>>> GCC is in stage 3 now, so this should have been posted last week
>>> really.
>>
>> Ok, no problem, it can wait.
>>
>> Still, following your advises here is what I come up with, much 
>> simpler indeed.
>
> Yes, this simpler patch looks promising even though it's stage 3.
>
>> I just run a few tests for the moment but so far so good.
>>
>> Thanks
>>
>>>
>>>
>>>> diff --git a/libstdc++-v3/include/bits/move.h 
>>>> b/libstdc++-v3/include/bits/move.h
>>>> index 5a4dbdc823c..e0d68ca9108 100644
>>>> --- a/libstdc++-v3/include/bits/move.h
>>>> +++ b/libstdc++-v3/include/bits/move.h
>>>> @@ -158,9 +158,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>
>>>>   /// @} group utilities
>>>>
>>>> +#define _GLIBCXX_XREF(_Tp) _Tp&&
>>>
>>> I think this does improve the code that uses this. But the correct
>>> name for this is forwarding reference, so I think FWDREF would be
>>> better than XREF. XREF doesn't tell me anything about what it's for.
>>>
>>>> #define _GLIBCXX_MOVE(__val) std::move(__val)
>>>> #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
>>>> #else
>>>> +#define _GLIBCXX_XREF(_Tp) const _Tp&
>>>> #define _GLIBCXX_MOVE(__val) (__val)
>>>> #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
>>>> #endif
>>>> diff --git a/libstdc++-v3/include/bits/stl_tree.h 
>>>> b/libstdc++-v3/include/bits/stl_tree.h
>>>> index ec141ea01c7..128c7e2c892 100644
>>>> --- a/libstdc++-v3/include/bits/stl_tree.h
>>>> +++ b/libstdc++-v3/include/bits/stl_tree.h
>>>> @@ -478,11 +478,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>
>>>>     template<typename _Arg>
>>>>       _Link_type
>>>> -#if __cplusplus < 201103L
>>>> -      operator()(const _Arg& __arg)
>>>> -#else
>>>> -      operator()(_Arg&& __arg)
>>>> -#endif
>>>> +      operator()(_GLIBCXX_XREF(_Arg) __arg)
>>>>       {
>>>>         _Link_type __node = 
>>>> static_cast<_Link_type>(_M_extract());
>>>>         if (__node)
>>>> @@ -544,11 +540,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>
>>>>     template<typename _Arg>
>>>>       _Link_type
>>>> -#if __cplusplus < 201103L
>>>> -      operator()(const _Arg& __arg) const
>>>> -#else
>>>> -      operator()(_Arg&& __arg) const
>>>> -#endif
>>>> +      operator()(_GLIBCXX_XREF(_Arg) __arg) const
>>>>       { return _M_t._M_create_node(_GLIBCXX_FORWARD(_Arg, 
>>>> __arg)); }
>>>>
>>>>       private:
>>>> @@ -655,11 +647,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>     _M_put_node(__p);
>>>>       }
>>>>
>>>> -      template<typename _NodeGen>
>>>> +#if __cplusplus >= 201103L
>>>> +      template<typename _Tree>
>>>> +    static constexpr
>>>> +    typename conditional<std::is_lvalue_reference<_Tree>::value,
>>>> +                 const value_type&, 
>>>> value_type&&>::type
>>>> +    _S_fwd_value_for(value_type& __val) noexcept
>>>> +    { return std::move(__val); }
>>>> +#else
>>>> +      template<typename _Tree>
>>>> +    static const value_type&
>>>> +    _S_fwd_value_for(value_type& __val)
>>>> +    { return __val; }
>>>> +#endif
>>>> +
>>>> +      template<typename _Tree, typename _NodeGen>
>>>>     _Link_type
>>>> -    _M_clone_node(_Const_Link_type __x, _NodeGen& __node_gen)
>>>> +    _M_clone_node(_GLIBCXX_XREF(_Tree),
>>>
>>> Since the _Tree type is only used to decide whether to copy or move,
>>> could it just be a bool instead?
>>>
>>>       template<bool _Move, typename _NodeGen>
>>>      _Link_type
>>>     _M_clone_node(_Link_type __x, _NodeGen& __node_gen)
>>>
>>> Then it would be called as _M_clone_node<_Move>(__x, __node_gen)
>>> instead of _M_clone_node(_GLIBCXX_FORWARD(_Tree, __t), __x, 
>>> __node_gen).
>>> That seems easier to read.
>>>
>>>> +              _Link_type __x, _NodeGen& __node_gen)
>>>>     {
>>>> -      _Link_type __tmp = __node_gen(*__x->_M_valptr());
>>>> +      _Link_type __tmp
>>>> +        = 
>>>> __node_gen(_S_fwd_value_for<_Tree>(*__x->_M_valptr()));
>>>
>>> Is _S_fwd_value_for necessary? This would work:
>>>
>>> #if __cplusplus >= 201103L
>>>           using _Vp = typename 
>>> conditional<is_lvalue_reference<_Tree>::value,
>>>                                           
>>> const value_type&,
>>> value_type&&>::type;
>>> #else
>>>           typedef const value_type& _Vp;
>>> #endif
>>>           _Link_type __tmp
>>>             = __node_gen(_GLIBCXX_FORWARD(_Vp, 
>>> *__x->_M_valptr()));
>>>
>>> Or with the suggestion above, the typedef would be:
>>>
>>>           using _Vp = typename conditional<_Move, 
>>> value_type&&,
>>>                                           
>>> const value_type&>::type;
>>>
>>>
>>>>       __tmp->_M_color = __x->_M_color;
>>>>       __tmp->_M_left = 0;
>>>>       __tmp->_M_right = 0;
>>>> @@ -748,9 +756,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>       { return this->_M_impl._M_header._M_right; }
>>>>
>>>>       _Link_type
>>>> -      _M_begin() _GLIBCXX_NOEXCEPT
>>>> +      _M_cbegin() const _GLIBCXX_NOEXCEPT
>>>
>>> It's confusing that this is called cbegin but returns a non-const
>>> link. The standard cbegin() functions return a const_iterator. I would
>>> expect this to return a _Const_Link_type, based on the name.
>>>
>>>
>>>>       { return 
>>>> static_cast<_Link_type>(this->_M_impl._M_header._M_parent); }
>>>>
>>>> +      _Link_type
>>>> +      _M_begin() _GLIBCXX_NOEXCEPT
>>>> +      { return _M_cbegin(); }
>>>> +
>>>>       _Const_Link_type
>>>>       _M_begin() const _GLIBCXX_NOEXCEPT
>>>>       {
>>>> @@ -889,15 +901,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>       _M_insert_equal_lower(const value_type& __x);
>>>> #endif
>>>>
>>>> -      template<typename _NodeGen>
>>>> +      template<typename _Tree, typename _NodeGen>
>>>>     _Link_type
>>>> -    _M_copy(_Const_Link_type __x, _Base_ptr __p, _NodeGen&);
>>>> +    _M_copy(_GLIBCXX_XREF(_Tree), _Link_type, _Base_ptr, 
>>>> _NodeGen&);
>>>
>>> This could use 'bool _Move' instead of 'typename _Tree'.
>>>
>>>> -      template<typename _NodeGen>
>>>> +      template<typename _Tree, typename _NodeGen>
>>>>     _Link_type
>>>> -    _M_copy(const _Rb_tree& __x, _NodeGen& __gen)
>>>> +    _M_copy(_GLIBCXX_XREF(_Tree) __x, _NodeGen& __gen)
>>>
>>> This one gets called from _M_copy(const _Rb_tree&) with const _Rb_tree
>>> argument, so I think using the XREF macro (or FWDREF) does make sense
>>> here.
>>>
>>>>     {
>>>> -      _Link_type __root = _M_copy(__x._M_begin(), _M_end(), 
>>>> __gen);
>>>> +      _Link_type __root = _M_copy(_GLIBCXX_FORWARD(_Tree, __x),
>>>> +                      __x._M_cbegin(), 
>>>> _M_end(), __gen);
>>>
>>> This would have to be:
>>>
>>> #if __cplusplus >= 201103L
>>>           constexpr bool __move = !is_reference<_Tree>::value;
>>> #else
>>>           const bool __move = false;
>>> #endif
>>>           _Link_type __root = 
>>> _M_copy<__move>(__x._M_cbegin(), _M_end(), __gen);
>>>
>>> Would doing it this way make sense?
>>>
>>>
>>>>       _M_leftmost() = _S_minimum(__root);
>>>>       _M_rightmost() = _S_maximum(__root);
>>>>       _M_impl._M_node_count = __x._M_impl._M_node_count;
>>>> @@ -1426,22 +1439,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>     private:
>>>>       // Move elements from container with equal allocator.
>>>>       void
>>>> -      _M_move_data(_Rb_tree& __x, true_type)
>>>> +      _M_move_data(_Rb_tree&& __x, true_type)
>>>>       { _M_impl._M_move_data(__x._M_impl); }
>>>>
>>>>       // Move elements from container with possibly non-equal 
>>>> allocator,
>>>>       // which might result in a copy not a move.
>>>>       void
>>>> -      _M_move_data(_Rb_tree&, false_type);
>>>> +      _M_move_data(_Rb_tree&&, false_type);
>>>>
>>>>       // Move assignment from container with equal allocator.
>>>>       void
>>>> -      _M_move_assign(_Rb_tree&, true_type);
>>>> +      _M_move_assign(_Rb_tree&&, true_type);
>>>>
>>>>       // Move assignment from container with possibly 
>>>> non-equal allocator,
>>>>       // which might result in a copy not a move.
>>>>       void
>>>> -      _M_move_assign(_Rb_tree&, false_type);
>>>> +      _M_move_assign(_Rb_tree&&, false_type);
>>>
>>> These changes don't seem necessary. While they might be preferable if
>>> we were writing this from scratch, changing them now means that
>>> binaries built with more than one version of GCC will be larger.
>>> Objects built with older versions of GCC will have instantiations of
>>> the old versions and objects built with newer versions will have
>>> instantiations of the new versions. The increase in executable size
>>> (and icache pressure) doesn't seem worthwhile.
>>>
>>> The other changes (to remove the lambdas) also have this consequence,
>>> but the benefits of simplifying the code do seem worthwhile. Just
>>> changing _Rb_tree& to _Rb_tree&& (and having to use std::move to call
>>> those functions) doesn't simplify anything. The functions already have
>>> "move" in the name, so it's pretty obvious they perform moves.
>>>
>>>
>>>
>>>
>>>> @@ -1859,29 +1864,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>>
>>>>   template<typename _Key, typename _Val, typename _KoV,
>>>>        typename _Compare, typename _Alloc>
>>>> -    template<typename _NodeGen>
>>>> +    template<typename _Tree, typename _NodeGen>
>>>>       typename _Rb_tree<_Key, _Val, _KoV, _Compare, 
>>>> _Alloc>::_Link_type
>>>>       _Rb_tree<_Key, _Val, _KoV, _Compare, _Alloc>::
>>>> -      _M_copy(_Const_Link_type __x, _Base_ptr __p, _NodeGen& 
>>>> __node_gen)
>>>> +      _M_copy(_GLIBCXX_XREF(_Tree) __t,
>>>
>>> The __t parameter is only needed below to be forwarded, so its type
>>> can be checked later on. Using bool _Move instead would work fine, and
>>> avoid having to pass an extra parameter on the stack which never gets
>>> used (only its type).
>>>
>>>> +          _Link_type __x, _Base_ptr __p, _NodeGen& 
>>>> __node_gen)
>>>>       {
>>>>     // Structural copy. __x and __p must be non-null.
>>>> -    _Link_type __top = _M_clone_node(__x, __node_gen);
>>>> +    _Link_type __top = _M_clone_node(_GLIBCXX_FORWARD(_Tree, __t),
>>>> +                     __x, __node_gen);
>>>>     __top->_M_parent = __p;
>>>>
>>>>     __try
>>>>       {
>>>>         if (__x->_M_right)
>>>> -          __top->_M_right = _M_copy(_S_right(__x), __top, 
>>>> __node_gen);
>>>> +          __top->_M_right = 
>>>> _M_copy(_GLIBCXX_FORWARD(_Tree, __t),
>>>> +                    _S_right(__x), __top, 
>>>> __node_gen);
>>>>         __p = __top;
>>>>         __x = _S_left(__x);
>>>>
>>>>         while (__x != 0)
>>>>           {
>>>> -        _Link_type __y = _M_clone_node(__x, __node_gen);
>>>> +        _Link_type __y = 
>>>> _M_clone_node(_GLIBCXX_FORWARD(_Tree, __t),
>>>> +                           __x, 
>>>> __node_gen);
>>>>         __p->_M_left = __y;
>>>>         __y->_M_parent = __p;
>>>>         if (__x->_M_right)
>>>> -          __y->_M_right = _M_copy(_S_right(__x), __y, 
>>>> __node_gen);
>>>> +          __y->_M_right = _M_copy(_GLIBCXX_FORWARD(_Tree, 
>>>> __t),
>>>> +                      _S_right(__x), __y, 
>>>> __node_gen);
>>>>         __p = __y;
>>>>         __x = _S_left(__x);
>>>>           }
>>>
>>
>
>> diff --git a/libstdc++-v3/include/bits/move.h 
>> b/libstdc++-v3/include/bits/move.h
>> index 5a4dbdc823c..b33c22a4374 100644
>> --- a/libstdc++-v3/include/bits/move.h
>> +++ b/libstdc++-v3/include/bits/move.h
>> @@ -158,9 +158,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>>   /// @} group utilities
>>
>> +#define _GLIBCXX_FWDREF(_Tp) _Tp&&
>> #define _GLIBCXX_MOVE(__val) std::move(__val)
>> #define _GLIBCXX_FORWARD(_Tp, __val) std::forward<_Tp>(__val)
>> #else
>> +#define _GLIBCXX_FWDREF(_Tp) const _Tp&
>> #define _GLIBCXX_MOVE(__val) (__val)
>> #define _GLIBCXX_FORWARD(_Tp, __val) (__val)
>> #endif
>> diff --git a/libstdc++-v3/include/bits/stl_tree.h 
>> b/libstdc++-v3/include/bits/stl_tree.h
>> index ec141ea01c7..baa4c81a7ed 100644
>> --- a/libstdc++-v3/include/bits/stl_tree.h
>> +++ b/libstdc++-v3/include/bits/stl_tree.h
>> @@ -478,11 +478,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>>     template<typename _Arg>
>>       _Link_type
>> -#if __cplusplus < 201103L
>> -      operator()(const _Arg& __arg)
>> -#else
>> -      operator()(_Arg&& __arg)
>> -#endif
>> +      operator()(_GLIBCXX_FWDREF(_Arg) __arg)
>>       {
>>         _Link_type __node = static_cast<_Link_type>(_M_extract());
>>         if (__node)
>> @@ -544,11 +540,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>>     template<typename _Arg>
>>       _Link_type
>> -#if __cplusplus < 201103L
>> -      operator()(const _Arg& __arg) const
>> -#else
>> -      operator()(_Arg&& __arg) const
>> -#endif
>> +      operator()(_GLIBCXX_FWDREF(_Arg) __arg) const
>>       { return _M_t._M_create_node(_GLIBCXX_FORWARD(_Arg, __arg)); }
>>
>>       private:
>> @@ -655,11 +647,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>     _M_put_node(__p);
>>       }
>>
>> -      template<typename _NodeGen>
>> +      template<bool _Move, typename _NodeGen>
>>     _Link_type
>> -    _M_clone_node(_Const_Link_type __x, _NodeGen& __node_gen)
>> +    _M_clone_node(_Link_type __x, _NodeGen& __node_gen)
>>     {
>> -      _Link_type __tmp = __node_gen(*__x->_M_valptr());
>> +#if __cplusplus >= 201103L
>> +      using _Vp =
>> +        typename conditional<_Move, value_type&&, const 
>> value_type&>::type;
>> +#endif
>> +      _Link_type __tmp
>> +        = __node_gen(_GLIBCXX_FORWARD(_Vp, *__x->_M_valptr()));
>
> Oh this is nice, I forgot that _GLIBCXX_FORWARD doesn't use the first
> argument at all for C++98, so we don't need _Vp.
>
>>       __tmp->_M_color = __x->_M_color;
>>       __tmp->_M_left = 0;
>>       __tmp->_M_right = 0;
>> @@ -748,9 +745,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       { return this->_M_impl._M_header._M_right; }
>>
>>       _Link_type
>> -      _M_begin() _GLIBCXX_NOEXCEPT
>> +      _M_mbegin() const _GLIBCXX_NOEXCEPT
>
> Nice.
>
>>       { return 
>> static_cast<_Link_type>(this->_M_impl._M_header._M_parent); }
>>
>> +      _Link_type
>> +      _M_begin() _GLIBCXX_NOEXCEPT
>> +      { return _M_mbegin(); }
>> +
>>       _Const_Link_type
>>       _M_begin() const _GLIBCXX_NOEXCEPT
>>       {
>> @@ -889,15 +890,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       _M_insert_equal_lower(const value_type& __x);
>> #endif
>>
>> -      template<typename _NodeGen>
>> +      template<bool _Move, typename _NodeGen>
>>     _Link_type
>> -    _M_copy(_Const_Link_type __x, _Base_ptr __p, _NodeGen&);
>> +    _M_copy(_Link_type, _Base_ptr, _NodeGen&);
>>
>> -      template<typename _NodeGen>
>> +      template<bool _Move, typename _NodeGen>
>>     _Link_type
>>     _M_copy(const _Rb_tree& __x, _NodeGen& __gen)
>>     {
>> -      _Link_type __root = _M_copy(__x._M_begin(), _M_end(), __gen);
>> +      _Link_type __root = _M_copy<_Move>(__x._M_mbegin(), _M_end(), 
>> __gen);
>>       _M_leftmost() = _S_minimum(__root);
>>       _M_rightmost() = _S_maximum(__root);
>>       _M_impl._M_node_count = __x._M_impl._M_node_count;
>> @@ -908,7 +909,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       _M_copy(const _Rb_tree& __x)
>>       {
>>     _Alloc_node __an(*this);
>> -    return _M_copy(__x, __an);
>> +    return _M_copy<false>(__x, __an);
>>       }
>>
>>       void
>> @@ -1655,13 +1656,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       else
>>     {
>>       _Alloc_node __an(*this);
>> -      auto __lbd =
>> -        [&__an](const value_type& __cval)
>> -        {
>> -          auto& __val = const_cast<value_type&>(__cval);
>> -          return __an(std::move_if_noexcept(__val));
>> -        };
>> -      _M_root() = _M_copy(__x, __lbd);
>> +      _M_root() =
>> + _M_copy<__move_if_noexcept_cond<value_type>::value>(__x, __an);
>
> Should this be !__move_if_noexcept_cond<value_type>::value ?

Yes, this is why I was not confident about this patch for the moment. I 
knew I had to check this and at the same time check if a test is 
catching this.


>
> The condition is confusing. Maybe we should replace
> __move_if_noexcept_cond with something like:
>
>   // True if copying should be used for strong exception-safety 
> guarantee.
>   // False if the type has nothrow move, or isn't copyable.
>   template<typename _Tp>
>     using __use_copy_for_exception_safety
>       = typename __and_<__not_<is_nothrow_move_constructible<_Tp>>,
>             is_copy_constructible<_Tp>>::type;

Indeed, I find it confusing too. I'll try that.


>
>
>
>>     }
>>     }
>>
>> @@ -1693,13 +1689,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       _M_impl._M_reset();
>>       if (__x._M_root() != nullptr)
>>     {
>> -      auto __lbd =
>> -        [&__roan](const value_type& __cval)
>> -        {
>> -          auto& __val = const_cast<value_type&>(__cval);
>> -          return __roan(std::move(__val));
>> -        };
>> -      _M_root() = _M_copy(__x, __lbd);
>> +      _M_root() = _M_copy<true>(__x, __roan);
>
> I've realised the downside of my suggestion: _M_copy<true> does a move
> and _M_copy<false> does a copy. Maybe we should do:
>
>   enum _CopyType { __as_lvalue, __as_rvalue };
>
> And then _M_copy<__as_rvalue> or _M_copy<__as_lvalue>
>
> We can't use typedefs for true_type and false_type here because the
> code needs to be valid in C++98.
>
I was thinking to simply rename _Move with a clearer name like: _MoveValues.

But your proposal makes the code clearer even at call site so I'll do it.


>
>>       __x.clear();
>>     }
>>     }
>> @@ -1773,7 +1763,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>       _M_impl._M_reset();
>>       _M_impl._M_key_compare = __x._M_impl._M_key_compare;
>>       if (__x._M_root() != 0)
>> -        _M_root() = _M_copy(__x, __roan);
>> +        _M_root() = _M_copy<false>(__x, __roan);
>>     }
>>
>>       return *this;
>> @@ -1859,29 +1849,30 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>>   template<typename _Key, typename _Val, typename _KoV,
>>        typename _Compare, typename _Alloc>
>> -    template<typename _NodeGen>
>> +    template<bool _Move, typename _NodeGen>
>>       typename _Rb_tree<_Key, _Val, _KoV, _Compare, _Alloc>::_Link_type
>>       _Rb_tree<_Key, _Val, _KoV, _Compare, _Alloc>::
>> -      _M_copy(_Const_Link_type __x, _Base_ptr __p, _NodeGen& 
>> __node_gen)
>> +      _M_copy(_Link_type __x, _Base_ptr __p, _NodeGen& __node_gen)
>>       {
>>     // Structural copy. __x and __p must be non-null.
>> -    _Link_type __top = _M_clone_node(__x, __node_gen);
>> +    _Link_type __top = _M_clone_node<_Move>(__x, __node_gen);
>>     __top->_M_parent = __p;
>>
>>     __try
>>       {
>>         if (__x->_M_right)
>> -          __top->_M_right = _M_copy(_S_right(__x), __top, __node_gen);
>> +          __top->_M_right =
>> +        _M_copy<_Move>(_S_right(__x), __top, __node_gen);
>>         __p = __top;
>>         __x = _S_left(__x);
>>
>>         while (__x != 0)
>>           {
>> -        _Link_type __y = _M_clone_node(__x, __node_gen);
>> +        _Link_type __y = _M_clone_node<_Move>(__x, __node_gen);
>>         __p->_M_left = __y;
>>         __y->_M_parent = __p;
>>         if (__x->_M_right)
>> -          __y->_M_right = _M_copy(_S_right(__x), __y, __node_gen);
>> +          __y->_M_right = _M_copy<_Move>(_S_right(__x), __y, 
>> __node_gen);
>>         __p = __y;
>>         __x = _S_left(__x);
>>           }
>

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