[PATCH][_GLIBCXX_DEBUG] Enhance __gnu_debug::vector iterator invalidation

François Dumont frs.dumont@gmail.com
Mon Jun 8 05:06:47 GMT 2026


Hi

I've totally reworked this patch.

     libstdc++: [_GLIBCXX_DEBUG] Enhance __gnu_debug::vector iterator 
invalidation

     Rework the way std::__debug::vector's iterators are being 
invalidated. Use a guard
     approach which on destructor invalidates iterators based on the 
state of the container.

     Moreover update invalidation policy in following vector methods:
     - operator=(initializer_list)
     - assign(Iterator, Iterator)
     - assign(size_t, const _Tp&)
     - assign(initializer_list)

     Current behavior to invalidate all iterators unconditionally is 
preserved only if
     _GLIBCXX_DEBUG_PEDANTIC is defined. Otherwise if a reallocation 
occurs all iterators
     are invaliidated else only iterators after the new container size 
are invalidated.

     libstdc++-v3/ChangeLog:

             * include/debug/assertions.h [_GLIBCXX_DEBUG_STD_C]: New macro.
             * include/debug/vector (_Safe_vector<_Tp, _Allocator>): 
Update template parameter.
             (_Safe_vector::_M_seq): Remove const qualification.
             (_Safe_vector::_M_requires_reallocation): Remove.
             (_Safe_vector::_Guard): New.
             (vector::_ResizeInvalidationPolicy): New.
[_GLIBCXX_DEBUG_PEDANTIC](vector::_PedanticInvalidationPolicy): New.
             (vector::_InsertInvalidationPolicy): New.
             (vector::_ReallocInvalidationPolicy): New.
             (vector): Adapt methods to use new guard type.
             * testsuite/23_containers/vector/capacity/shrink_to_fit.cc: 
Adapt check, size shall
             be lower-or-equal to capacity, not strictly lower.
             * 
testsuite/23_containers/vector/cons/destructible_debug_neg.cc: Adapt 
error line
             number.
             * testsuite/23_containers/vector/debug/initializer_list.cc: 
New test case.
             * 
testsuite/23_containers/vector/debug/initializer_list_pedantic.cc: New 
test case.

Tested under Linux x86_64 w/o _GLIBCXX_DEBUG, w/o 
_GLIBCXX_DEBUG_PEDANTIC in C++98, C++11, C++23.

Note that in _GLIBCXX_DEBUG_PEDANTIC there is still a problem with this 
test:

23_containers/vector/modifiers/push_back/strong_guarantee.cc

But it goes beyond this patch so left as-is.

Ok to commit ?

François


On 5/31/26 22:17, François Dumont wrote:
>
>
> On 5/28/26 13:46, Jonathan Wakely wrote:
>> On Thu, 21 May 2026 at 22:20 +0200, François Dumont wrote:
>>> Hi
>>>
>>> Following your remark Jonathan regarding how iterators are 
>>> invalidated in vector I reviewed the std::__debug::vector 
>>> implementation.
>>
>> Can you remind me where I said that? I remember discussing it for
>> inplace_vector::assign (2025-11-03 in the thread about
>> __debug::inplace_vector).
>>
>> I don't remember the comment you're referring to, so I don't know what
>> I said :-)
>
> In this message:
>
> https://gcc.gnu.org/pipermail/libstdc++/2025-November/064301.html
>
> You said:
>
> Is it too aggressive to invalidate all iterators?
>
> I know the generic Sequence requirements say that assign(i, j)
> invalidates all iterators, but I think maybe that's a defect.
>
> As std::vector is also a Sequence I thought you were talking about 
> both inplace_vector and vector.
>
> Maybe I over interpreted it but I also think that when you are 
> assigning a vector to some new content the iterators do not have to be 
> invalidated.
>
> Reading this email again I think I'll have to consider the problem of 
> the end iterator, in a future patch...
>
>>> I'll do something similar on std::__debug::inplace_vector.
>>>
>>>     libstdc++: [_GLIBCXX_DEBUG] Enhance __gnu_debug::vector iterator 
>>> invalidation
>>>
>>>     Rework the way std::__debug::vector's iterators are being 
>>> invalidated. Use a guard
>>>     approach which on destructor invalidates iterators based on the 
>>> state of the container.
>>>
>>>     Moreover update invalidation policy in following vector methods:
>>>     - operator=(initializer_list)
>>>     - assign(Iterator, Iterator)
>>>     - assign(size_t, const _Tp&)
>>>     - assign(initializer_list)
>>>
>>>     Current behavior to invalidate all iterators unconditionally is 
>>> preserved only if
>>>     _GLIBCXX_DEBUG_PEDANTIC is defined. Otherwise if a reallocation 
>>> occurs all iterators
>>>     are invaliidated else only iterators after the new container 
>>> size are invalidated.
>>>
>>>     libstdc++-v3/ChangeLog:
>>>
>>>             * include/debug/assertions.h [_GLIBCXX_DEBUG_STD_C]: New 
>>> macro.
>>>             * include/debug/vector (_Safe_vector<_Tp, _Allocator>): 
>>> Update template parameter.
>>>             (_Safe_vector::_M_requires_reallocation): Remove.
>>>             (_SafeVectorGuard): New.
>>> [_GLIBCXX_DEBUG_PEDANTIC](_SafeVectorPedanticGuard): New.
>>>             (_SafeVectorInsertGuard): New.
>>>             (vector): Adapt methods to use new guard type.
>>>             * 
>>> testsuite/23_containers/vector/cons/destructible_debug_neg.cc: Adapt 
>>> error line
>>>             number.
>>>             * 
>>> testsuite/23_containers/vector/debug/initializer_list.cc: New test 
>>> case.
>>>             * 
>>> testsuite/23_containers/vector/debug/initializer_list_pedantic.cc: 
>>> New test case.
>>>
>>> Partially tested on x86_64 w/o _GLIBCXX_DEBUG mode.
>>>
>>> Ok to commit once tests completed ?
>>>
>>> https://forge.sourceware.org/gcc/gcc-TEST/pulls/159
>>>
>>> François
>>>
>>>
>>
>>> diff --git a/libstdc++-v3/include/debug/assertions.h 
>>> b/libstdc++-v3/include/debug/assertions.h
>>> index c4993dc8596..768a7f05228 100644
>>> --- a/libstdc++-v3/include/debug/assertions.h
>>> +++ b/libstdc++-v3/include/debug/assertions.h
>>> @@ -31,6 +31,12 @@
>>>
>>> #include <bits/c++config.h>
>>>
>>> +#ifdef _GLIBCXX_DEBUG
>>> +# define _GLIBCXX_DEBUG_STD_C ::std::_GLIBCXX_STD_C
>>> +#else
>>> +# define _GLIBCXX_DEBUG_STD_C ::std
>>> +#endif
>>> +
>>> #ifndef _GLIBCXX_DEBUG
>>> // Verify that [_First, _Last) forms a non-empty iterator range.
>>> # define __glibcxx_requires_non_empty_range(_First,_Last)    \
>>> diff --git a/libstdc++-v3/include/debug/vector 
>>> b/libstdc++-v3/include/debug/vector
>>> index 61e5ff78a7a..1e1a971036e 100644
>>> --- a/libstdc++-v3/include/debug/vector
>>> +++ b/libstdc++-v3/include/debug/vector
>>> @@ -51,11 +51,12 @@ namespace __gnu_debug
>>>    * detecting code which relies on non-portable implementation 
>>> details of
>>>    * the libstdc++ reallocation policy.
>>>    */
>>> -  template<typename _SafeSequence,
>>> -       typename _BaseSequence>
>>> +  template<class _Tp, typename _Allocator>
>>>     class _Safe_vector
>>>     {
>>> -      typedef typename _BaseSequence::size_type size_type;
>>> +      typedef std::__debug::vector<_Tp, _Allocator> _SafeSequence;
>>> +      typedef _GLIBCXX_DEBUG_STD_C::vector<_Tp, _Allocator> 
>>> _StdVector;
>>> +      typedef typename _StdVector::size_type size_type;
>>>
>>>       _GLIBCXX20_CONSTEXPR
>>>       const _SafeSequence&
>>> @@ -103,10 +104,6 @@ namespace __gnu_debug
>>>
>>>       size_type _M_guaranteed_capacity;
>>>
>>> -      bool
>>> -      _M_requires_reallocation(size_type __elements) const 
>>> _GLIBCXX_NOEXCEPT
>>> -      { return __elements > _M_seq().capacity(); }
>>> -
>>>       _GLIBCXX20_CONSTEXPR
>>>       void
>>>       _M_update_guaranteed_capacity() _GLIBCXX_NOEXCEPT
>>> @@ -115,6 +112,66 @@ namespace __gnu_debug
>>>       _M_guaranteed_capacity = _M_seq().size();
>>>       }
>>>     };
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    class _SafeVectorGuard
>>> +    {
>>> +      typedef std::__debug::vector<_Tp, _Allocator> _SafeVector;
>>> +      typedef _GLIBCXX_DEBUG_STD_C::vector<_Tp, _Allocator> 
>>> _StdVector;
>>> +      typedef typename _StdVector::size_type size_type;
>>> +
>>> +      _SafeVector& _M_vect;
>>> +      size_type _M_capacity, _M_size;
>>> +
>>> +    public:
>>> +      bool _M_active;
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      _SafeVectorGuard(_SafeVector& __vector);
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      ~_SafeVectorGuard();
>>> +    };
>>> +
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +  template<class _Tp, typename _Allocator>
>>> +    class _SafeVectorPedanticGuard
>>> +    {
>>> +      typedef std::__debug::vector<_Tp, _Allocator> _SafeVector;
>>> +      _SafeVector& _M_vect;
>>> +
>>> +    public:
>>> +      bool _M_active;
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      _SafeVectorPedanticGuard(_SafeVector& __vector);
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      ~_SafeVectorPedanticGuard();
>>> +    };
>>> +#endif
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    class _SafeVectorInsertGuard
>>> +    {
>>> +      typedef std::__debug::vector<_Tp, _Allocator> _SafeVector;
>>> +      typedef _GLIBCXX_DEBUG_STD_C::vector<_Tp, _Allocator> 
>>> _StdVector;
>>> +      typedef typename _StdVector::size_type size_type;
>>> +      typedef typename _StdVector::difference_type difference_type;
>>> +
>>> +      _SafeVector& _M_vect;
>>> +      size_type _M_capacity;
>>> +      difference_type _M_offset;
>>> +
>>> +    public:
>>> +      bool _M_active;
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      _SafeVectorInsertGuard(_SafeVector& __vector, difference_type 
>>> __offset);
>>> +
>>> +      _GLIBCXX20_CONSTEXPR
>>> +      ~_SafeVectorInsertGuard();
>>> +    };
>>> }
>>
>> All the guard types above need comments explaining what they do. When
>> should you use each one? How are they different from each other?
>>
>> How do we deviate from the standard when not in pedantic mode?
>>
>> I'm unclear what they actually do, and how that corresponds to the
>> standard.
>>
>> _SafeVectorGuard invalidates all iterators if the size increased to
>> greater than capacity. That's used by resize and emplace_back and
>> push_back, right? And if the size was reduced, invalidate iterators to
>> the erased elements. This must not be used for reserve, because it
>> would not invalidate all iterators on reallocation, because the size
>> would not change.
>>
>> _SafeVectorPedanticGuard invalidates all iterators unconditionally,
>> which is what the standard says to do for assign.
>>
>> _SafeVectorInsertGuard seems to be almost the same as _SafeVectorGuard
>> but using an arbitrary position for the "invalidates all after pos"
>> instead of only invalidating at the end.
>
> Yes, I wonder if I could use only 1 implementation for both but I 
> think it would make this implementation more complicated to get it right.
>
> Ideally we should have a 4th implementation just invalidating all 
> iterators in case of reallocation. I preferred to use _SafeVectorGuard 
> (_ResizeGuard) in this case, which is fine to use when size if always 
> increased like in push_back or emplace_back.
>
>>
>> Would it be more clear to have _ResizeGuard, _AssignGuard (which
>> changes behaviour for pedantic vs non-pedantic), and _InsertGuard?
>>
> I've adopted those names.
>
> And doing so I changed the type of guard used in assign_range and 
> insert_range.
>
>>>
>>> namespace std _GLIBCXX_VISIBILITY(default)
>>> @@ -128,14 +185,33 @@ namespace __debug
>>>     : public __gnu_debug::_Safe_container<
>>>     vector<_Tp, _Allocator>, _Allocator, __gnu_debug::_Safe_sequence>,
>>>       public _GLIBCXX_STD_C::vector<_Tp, _Allocator>,
>>> -      public __gnu_debug::_Safe_vector<
>>> -    vector<_Tp, _Allocator>,
>>> -    _GLIBCXX_STD_C::vector<_Tp, _Allocator> >
>>> +      public __gnu_debug::_Safe_vector<_Tp, _Allocator>
>>>     {
>>>       typedef _GLIBCXX_STD_C::vector<_Tp, _Allocator>        _Base;
>>>       typedef __gnu_debug::_Safe_container<
>>>     vector, _Allocator, __gnu_debug::_Safe_sequence> _Safe;
>>> -      typedef __gnu_debug::_Safe_vector<vector, _Base>        
>>> _Safe_vector;
>>> +      typedef __gnu_debug::_Safe_vector<_Tp, _Allocator>    
>>> _Safe_vector;
>>> +
>>> +      typedef __gnu_debug::_SafeVectorGuard<_Tp, _Allocator> _Guard;
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +      typedef __gnu_debug::_SafeVectorPedanticGuard<_Tp, _Allocator>
>>> +    _MaybePedanticGuard;
>>> +#else
>>> +      typedef _Guard _MaybePedanticGuard;
>>
>> This name seems focused on the detail of how we decide which type to
>> use, not what it actually does. And _SafeVectorGuard is also "maybe
>> pedantic" because its destructor changes behaviour for pedantic mode.
>>
>> Would _AssignGuard be a better name? That reflects where it's actually
>> used.
>
> Yes, looks better. Only _ResizeGuard looks a little bit surprising in 
> push_back/emplace_back/append_Range.
>
> Maybe I should define _ReallocGuard for those methods, even it would 
> just be another alias of _SafeVectorGuard.
>
>>
>>> +#endif
>>> +      typedef __gnu_debug::_SafeVectorInsertGuard<_Tp, _Allocator>
>>> +    _InsertGuard;
>>> +
>>> +      template<typename _Tp2, typename _Alloc2>
>>> +    friend class ::__gnu_debug::_SafeVectorGuard;
>>> +
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +      template<typename _Tp2, typename _Alloc2>
>>> +    friend class ::__gnu_debug::_SafeVectorPedanticGuard;
>>> +#endif
>>> +
>>> +      template<typename _Tp2, typename _Alloc2>
>>> +    friend class ::__gnu_debug::_SafeVectorInsertGuard;
>>>
>>>       typedef typename _Base::iterator _Base_iterator;
>>>       typedef typename _Base::const_iterator _Base_const_iterator;
>>> @@ -276,12 +352,9 @@ namespace __debug
>>>       vector&
>>>       operator=(initializer_list<value_type> __l)
>>>       {
>>> +    _MaybePedanticGuard __guard(*this);
>>>     _Base::operator=(__l);
>>> -    if (!std::__is_constant_evaluated())
>>> -      {
>>> -        this->_M_invalidate_all();
>>> -        this->_M_update_guaranteed_capacity();
>>> -      }
>>> +    __guard._M_active = true;
>>>     return *this;
>>>       }
>>> #endif
>>> @@ -303,26 +376,23 @@ namespace __debug
>>>       typename __gnu_debug::_Distance_traits<_InputIterator>::__type 
>>> __dist;
>>>       __glibcxx_check_valid_range2(__first, __last, __dist);
>>>
>>> +      _MaybePedanticGuard __guard(*this);
>>>       if (__dist.second >= __gnu_debug::__dp_sign)
>>>         _Base::assign(__gnu_debug::__unsafe(__first),
>>>               __gnu_debug::__unsafe(__last));
>>>       else
>>>         _Base::assign(__first, __last);
>>>
>>> -      this->_M_invalidate_all();
>>> -      this->_M_update_guaranteed_capacity();
>>> +      __guard._M_active = true;
>>>     }
>>>
>>>       _GLIBCXX20_CONSTEXPR
>>>       void
>>>       assign(size_type __n, const _Tp& __u)
>>>       {
>>> +    _MaybePedanticGuard __guard(*this);
>>>     _Base::assign(__n, __u);
>>> -    if (!std::__is_constant_evaluated())
>>> -      {
>>> -        this->_M_invalidate_all();
>>> -        this->_M_update_guaranteed_capacity();
>>> -      }
>>> +    __guard._M_active = true;
>>>       }
>>>
>>> #if __cplusplus >= 201103L
>>> @@ -330,12 +400,9 @@ namespace __debug
>>>       void
>>>       assign(initializer_list<value_type> __l)
>>>       {
>>> +    _MaybePedanticGuard __guard(*this);
>>>     _Base::assign(__l);
>>> -    if (!std::__is_constant_evaluated())
>>> -      {
>>> -        this->_M_invalidate_all();
>>> -        this->_M_update_guaranteed_capacity();
>>> -      }
>>> +    __guard._M_active = true;
>>>       }
>>> #endif
>>>
>>> @@ -428,13 +495,9 @@ namespace __debug
>>>     if (std::__is_constant_evaluated())
>>>       return _Base::resize(__sz);
>>>
>>> -    bool __realloc = this->_M_requires_reallocation(__sz);
>>> -    if (__sz < this->size())
>>> -      this->_M_invalidate_after_nth(__sz);
>>> +    _Guard __guard(*this);
>>>     _Base::resize(__sz);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    this->_M_update_guaranteed_capacity();
>>> +    __guard._M_active = true;
>>>       }
>>>
>>>       _GLIBCXX20_CONSTEXPR
>>> @@ -444,25 +507,17 @@ namespace __debug
>>>     if (std::__is_constant_evaluated())
>>>       return _Base::resize(__sz, __c);
>>>
>>> -    bool __realloc = this->_M_requires_reallocation(__sz);
>>> -    if (__sz < this->size())
>>> -      this->_M_invalidate_after_nth(__sz);
>>> +    _Guard __guard(*this);
>>>     _Base::resize(__sz, __c);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    this->_M_update_guaranteed_capacity();
>>> +    __guard._M_active = true;
>>>       }
>>> #else
>>>       void
>>>       resize(size_type __sz, _Tp __c = _Tp())
>>>       {
>>> -    bool __realloc = this->_M_requires_reallocation(__sz);
>>> -    if (__sz < this->size())
>>> -      this->_M_invalidate_after_nth(__sz);
>>> +    _Guard __guard(*this);
>>>     _Base::resize(__sz, __c);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    this->_M_update_guaranteed_capacity();
>>> +    __guard._M_active = true;
>>>       }
>>> #endif
>>>
>>> @@ -506,7 +561,7 @@ namespace __debug
>>>     if (std::__is_constant_evaluated())
>>>       return _Base::reserve(__n);
>>>
>>> -    bool __realloc = this->_M_requires_reallocation(__n);
>>> +    bool __realloc = __n > capacity();
>>>     _Base::reserve(__n);
>>>     if (__n > this->_M_guaranteed_capacity)
>>>       this->_M_guaranteed_capacity = __n;
>>> @@ -583,11 +638,9 @@ namespace __debug
>>>     if (std::__is_constant_evaluated())
>>>       return _Base::push_back(__x);
>>>
>>> -    bool __realloc = this->_M_requires_reallocation(this->size() + 1);
>>> +    _Guard __guard(*this);
>>>     _Base::push_back(__x);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    this->_M_update_guaranteed_capacity();
>>> +    __guard._M_active = true;
>>>       }
>>>
>>> #if __cplusplus >= 201103L
>>> @@ -610,11 +663,9 @@ namespace __debug
>>>       if (std::__is_constant_evaluated())
>>>         return _Base::emplace_back(std::forward<_Args>(__args)...);
>>>
>>> -      bool __realloc = this->_M_requires_reallocation(this->size() 
>>> + 1);
>>> +      _Guard __guard(*this);
>>>       _Base::emplace_back(std::forward<_Args>(__args)...);
>>> -      if (__realloc)
>>> -        this->_M_invalidate_all();
>>> -      this->_M_update_guaranteed_capacity();
>>> +      __guard._M_active = true;
>>> #if __cplusplus > 201402L
>>>       return back();
>>> #endif
>>> @@ -645,15 +696,14 @@ namespace __debug
>>>                 this);
>>>
>>>       __glibcxx_check_insert(__position);
>>> -      bool __realloc = this->_M_requires_reallocation(this->size() 
>>> + 1);
>>> +      _Base_iterator __res;
>>> +      {
>>>         difference_type __offset = __position.base() - _Base::cbegin();
>>> -      _Base_iterator __res = _Base::emplace(__position.base(),
>>> +        _InsertGuard __guard(*this, __offset);
>>> +        __res = _Base::emplace(__position.base(),
>>> std::forward<_Args>(__args)...);
>>> -      if (__realloc)
>>> -        this->_M_invalidate_all();
>>> -      else
>>> -        this->_M_invalidate_after_nth(__offset);
>>> -      this->_M_update_guaranteed_capacity();
>>> +        __guard._M_active = true;
>>> +      }
>>>       return { __res, this };
>>>     }
>>> #endif
>>> @@ -670,14 +720,13 @@ namespace __debug
>>>       return iterator(_Base::insert(__position.base(), __x), this);
>>>
>>>     __glibcxx_check_insert(__position);
>>> -    bool __realloc = this->_M_requires_reallocation(this->size() + 1);
>>> +    _Base_iterator __res;
>>> +    {
>>>       difference_type __offset = __position.base() - _Base::begin();
>>> -    _Base_iterator __res = _Base::insert(__position.base(), __x);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    else
>>> -      this->_M_invalidate_after_nth(__offset);
>>> -    this->_M_update_guaranteed_capacity();
>>> +      _InsertGuard __guard(*this, __offset);
>>> +      __res = _Base::insert(__position.base(), __x);
>>> +      __guard._M_active = true;
>>> +    }
>>>     return iterator(__res, this);
>>>       }
>>>
>>> @@ -704,14 +753,13 @@ namespace __debug
>>>       return iterator(_Base::insert(__position.base(), __n, __x), 
>>> this);
>>>
>>>     __glibcxx_check_insert(__position);
>>> -    bool __realloc = this->_M_requires_reallocation(this->size() + 
>>> __n);
>>> +    _Base_iterator __res;
>>> +    {
>>>       difference_type __offset = __position.base() - _Base::cbegin();
>>> -    _Base_iterator __res = _Base::insert(__position.base(), __n, __x);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    else
>>> -      this->_M_invalidate_after_nth(__offset);
>>> -    this->_M_update_guaranteed_capacity();
>>> +      _InsertGuard __guard(*this, __offset);
>>> +      __res = _Base::insert(__position.base(), __n, __x);
>>> +      __guard._M_active = true;
>>> +    }
>>>     return { __res, this };
>>>       }
>>> #else
>>> @@ -719,14 +767,10 @@ namespace __debug
>>>       insert(iterator __position, size_type __n, const _Tp& __x)
>>>       {
>>>     __glibcxx_check_insert(__position);
>>> -    bool __realloc = this->_M_requires_reallocation(this->size() + 
>>> __n);
>>>     difference_type __offset = __position.base() - _Base::begin();
>>> +    _InsertGuard __guard(*this, __offset);
>>>     _Base::insert(__position.base(), __n, __x);
>>> -    if (__realloc)
>>> -      this->_M_invalidate_all();
>>> -    else
>>> -      this->_M_invalidate_after_nth(__offset);
>>> -    this->_M_update_guaranteed_capacity();
>>> +    __guard._M_active = true;
>>>       }
>>> #endif
>>>
>>> @@ -746,12 +790,10 @@ namespace __debug
>>>       typename __gnu_debug::_Distance_traits<_InputIterator>::__type 
>>> __dist;
>>>       __glibcxx_check_insert_range(__position, __first, __last, 
>>> __dist);
>>>
>>> -      /* Hard to guess if invalidation will occur, because __last
>>> -         - __first can't be calculated in all cases, so we just
>>> -         punt here by checking if it did occur. */
>>> -      _Base_iterator __old_begin = _M_base().begin();
>>> -      difference_type __offset = __position.base() - _Base::cbegin();
>>>       _Base_iterator __res;
>>> +      {
>>> +        difference_type __offset = __position.base() - 
>>> _Base::cbegin();
>>> +        _InsertGuard __guard(*this, __offset);
>>>         if (__dist.second >= __gnu_debug::__dp_sign)
>>>           __res = _Base::insert(__position.base(),
>>>                     __gnu_debug::__unsafe(__first),
>>> @@ -759,11 +801,8 @@ namespace __debug
>>>         else
>>>           __res = _Base::insert(__position.base(), __first, __last);
>>>
>>> -      if (_M_base().begin() != __old_begin)
>>> -        this->_M_invalidate_all();
>>> -      else
>>> -        this->_M_invalidate_after_nth(__offset);
>>> -      this->_M_update_guaranteed_capacity();
>>> +        __guard._M_active = true;
>>> +      }
>>>       return { __res, this };
>>>     }
>>> #else
>>> @@ -775,22 +814,15 @@ namespace __debug
>>>       typename __gnu_debug::_Distance_traits<_InputIterator>::__type 
>>> __dist;
>>>       __glibcxx_check_insert_range(__position, __first, __last, 
>>> __dist);
>>>
>>> -      /* Hard to guess if invalidation will occur, because __last
>>> -         - __first can't be calculated in all cases, so we just
>>> -         punt here by checking if it did occur. */
>>> -      _Base_iterator __old_begin = _M_base().begin();
>>>       difference_type __offset = __position.base() - _Base::begin();
>>> +      _InsertGuard __guard(*this, __offset);
>>>       if (__dist.second >= __gnu_debug::__dp_sign)
>>>         _Base::insert(__position.base(), 
>>> __gnu_debug::__unsafe(__first),
>>>                          __gnu_debug::__unsafe(__last));
>>>       else
>>>         _Base::insert(__position.base(), __first, __last);
>>>
>>> -      if (_M_base().begin() != __old_begin)
>>> -        this->_M_invalidate_all();
>>> -      else
>>> -        this->_M_invalidate_after_nth(__offset);
>>> -      this->_M_update_guaranteed_capacity();
>>> +      __guard._M_active = true;
>>>     }
>>> #endif
>>>
>>> @@ -876,30 +908,20 @@ namespace __debug
>>>     constexpr void
>>>     assign_range(_Rg&& __rg)
>>>     {
>>> -      auto __old_capacity = _Base::capacity();
>>> -      auto __old_size = _Base::size();
>>> +      _Guard __guard(*this);
>>>       _Base::assign_range(__rg);
>>> -      if (!std::__is_constant_evaluated())
>>> -        {
>>> -          if (_Base::capacity() != __old_capacity)
>>> -        this->_M_invalidate_all();
>>> -          else if (_Base::size() < __old_size)
>>> -        this->_M_invalidate_after_nth(_Base::size());
>>> -          this->_M_update_guaranteed_capacity();
>>> -        }
>>> +      __guard._M_active = true;
>>>     }
>>>
>>>       template<__detail::__container_compatible_range<_Tp> _Rg>
>>>     constexpr iterator
>>>     insert_range(const_iterator __pos, _Rg&& __rg)
>>>     {
>>> -      auto __old_capacity = _Base::capacity();
>>> -      auto __res = _Base::insert_range(__pos.base(), __rg);
>>> -      if (!std::__is_constant_evaluated())
>>> +      _Base_iterator __res;
>>>       {
>>> -          if (_Base::capacity() != __old_capacity)
>>> -        this->_M_invalidate_all();
>>> -          this->_M_update_guaranteed_capacity();
>>> +        _Guard __guard(*this);
>>> +        __res = _Base::insert_range(__pos.base(), __rg);
>>> +        __guard._M_active = true;
>>>       }
>>>       return iterator(__res, this);
>>>     }
>>> @@ -908,14 +930,9 @@ namespace __debug
>>>     constexpr void
>>>     append_range(_Rg&& __rg)
>>>     {
>>> -      auto __old_capacity = _Base::capacity();
>>> +      _Guard __guard(*this);
>>>       _Base::append_range(__rg);
>>> -      if (!std::__is_constant_evaluated())
>>> -        {
>>> -          if (_Base::capacity() != __old_capacity)
>>> -        this->_M_invalidate_all();
>>> -          this->_M_update_guaranteed_capacity();
>>> -        }
>>> +      __guard._M_active = true;
>>>     }
>>> #endif
>>>
>>> @@ -1057,6 +1074,84 @@ _GLIBCXX_END_NAMESPACE_VERSION
>>>
>>> namespace __gnu_debug
>>> {
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorGuard<_Tp, _Allocator>::_SafeVectorGuard(
>>> + std::__debug::vector<_Tp, _Allocator>& __vector)
>>> +    : _M_vect(__vector)
>>> +    , _M_capacity(__vector.capacity())
>>> +    , _M_size(__vector.size())
>>> +    , _M_active(false)
>>> +    { }
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorGuard<_Tp, _Allocator>::~_SafeVectorGuard()
>>> +    {
>>> +      if (!std::__is_constant_evaluated() && _M_active)
>>> +    {
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +      if (_M_vect.size() > _M_capacity)
>>> +#else
>>> +      if (_M_vect.capacity() != _M_capacity)
>>> +#endif
>>
>> I don't understand this condition. What difference does it make, and
>> why do we want it?
>>
>> For resize and emplace_back/push_back the two conditions are
>> equivalent, right? _M_vect.capacity() would not change (i.e.
>> reallocation would not occur) unless v.size() == v.capacity(),
>> and in that case v.size() would become greater than capacity.
>>
>> When are these different?
>
> When _GLIBCXX_DEBUG_PEDANTIC _M_vect.capacity() returns a 'guaranteed 
> capacity' and not the actual underlying vector capacity.
>
> This guaranteed capacity can change on emplace_back/push_back. The 
> problem is that it is updated later in the guard destructor, on the 
> call to _M_update_guaranteed_capacity().
>
> Thinking about it to reply I realized that I should not preserve 
> original code order and just update guaranteed capacity first so that 
> I only need (_M_vect.capacity() != _M_capacity) check.
>
>>
>>> +        _M_vect._M_invalidate_all();
>>> +      else if (_M_vect.size() < _M_size)
>>> +        _M_vect._M_invalidate_after_nth(_M_vect.size());
>>> +
>>> +      _M_vect._M_update_guaranteed_capacity();
>>> +    }
>>> +    }
>>> +
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorPedanticGuard<_Tp, 
>>> _Allocator>::_SafeVectorPedanticGuard(
>>> + std::__debug::vector<_Tp, _Allocator>& __vector)
>>> +    : _M_vect(__vector), _M_active(false)
>>> +    { }
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorPedanticGuard<_Tp, 
>>> _Allocator>::~_SafeVectorPedanticGuard()
>>> +    {
>>> +      if (!std::__is_constant_evaluated() && _M_active)
>>> +    {
>>> +      _M_vect._M_invalidate_all();
>>> +      _M_vect._M_update_guaranteed_capacity();
>>> +    }
>>> +    }
>>> +#endif
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorInsertGuard<_Tp, _Allocator>::_SafeVectorInsertGuard(
>>> + std::__debug::vector<_Tp, _Allocator>& __vector, difference_type 
>>> __offset)
>>> +    : _M_vect(__vector)
>>> +    , _M_capacity(__vector.capacity())
>>> +    , _M_offset(__offset)
>>> +    , _M_active(false)
>>> +    { }
>>> +
>>> +  template<class _Tp, typename _Allocator>
>>> +    _GLIBCXX20_CONSTEXPR
>>> +    _SafeVectorInsertGuard<_Tp, _Allocator>::~_SafeVectorInsertGuard()
>>> +    {
>>> +      if (!std::__is_constant_evaluated() && _M_active)
>>> +    {
>>> +#ifdef _GLIBCXX_DEBUG_PEDANTIC
>>> +      if (_M_vect.size() > _M_capacity)
>>> +#else
>>> +      if (_M_vect.capacity() != _M_capacity)
>>> +#endif
>>
>> Same question here.
>>
>>> +        _M_vect._M_invalidate_all();
>>> +      else
>>> +        _M_vect._M_invalidate_after_nth(_M_offset);
>>> +
>>> +      _M_vect._M_update_guaranteed_capacity();
>>> +    }
>>> +    }
>>> +
>>>   template<typename _Tp, typename _Alloc>
>>>     struct _Is_contiguous_sequence<std::__debug::vector<_Tp, _Alloc> >
>>>     : std::__true_type
>>> diff --git 
>>> a/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc 
>>> b/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc 
>>>
>>> index 2c9abcdbb91..0a29c0432e6 100644
>>> --- 
>>> a/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc
>>> +++ 
>>> b/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc
>>> @@ -47,4 +47,4 @@ test02()
>>> // { dg-error "PrivateDtor.* is private" "" { target *-*-* } 0 }
>>>
>>> // In Debug Mode the "required from here" errors come from 
>>> <debug/vector>
>>> -// { dg-error "required from here" "" { target *-*-* } 182 }
>>> +// { dg-error "required from here" "" { target *-*-* } 258 }
>>> diff --git 
>>> a/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc 
>>> b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc
>>> new file mode 100644
>>> index 00000000000..318f6b98de9
>>> --- /dev/null
>>> +++ 
>>> b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc
>>> @@ -0,0 +1,26 @@
>>> +// { dg-do compile { target c++11 } }
>>> +
>>> +#include <debug/vector>
>>> +#include <testsuite_hooks.h>
>>> +
>>> +void
>>> +test01()
>>> +{
>>> +  __gnu_debug::vector<int> v = { 0, 1, 2, 3, 4, 5 };
>>> +
>>> +  auto it1 = v.begin() + 1;
>>> +  auto it4 = v.begin() + 4;
>>> +
>>> +  VERIFY( !it1._M_singular() );
>>> +  VERIFY( !it4._M_singular() );
>>> +
>>> +  v = { 10, 11, 12, 13 };
>>> +
>>> +  VERIFY( !it1._M_singular() );
>>> +  VERIFY( it4._M_singular() );
>>> +}
>>> +
>>> +int main()
>>> +{
>>> +  test01();
>>> +}
>>> diff --git 
>>> a/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc 
>>> b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc 
>>>
>>> new file mode 100644
>>> index 00000000000..c8b3af25bd1
>>> --- /dev/null
>>> +++ 
>>> b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc
>>> @@ -0,0 +1,27 @@
>>> +// { dg-do compile { target c++11 } }
>>> +// { dg-options "-D_GLIBCXX_DEBUG_PEDANTIC" }
>>> +
>>> +#include <debug/vector>
>>> +#include <testsuite_hooks.h>
>>> +
>>> +void
>>> +test01()
>>> +{
>>> +  __gnu_debug::vector<int> v = { 0, 1, 2, 3, 4, 5 };
>>> +
>>> +  auto it1 = v.begin() + 1;
>>> +  auto it4 = v.begin() + 4;
>>> +
>>> +  VERIFY( !it1._M_singular() );
>>> +  VERIFY( !it4._M_singular() );
>>> +
>>> +  v = { 10, 11, 12, 13 };
>>> +
>>> +  VERIFY( it1._M_singular() );
>>> +  VERIFY( it4._M_singular() );
>>> +}
>>> +
>>> +int main()
>>> +{
>>> +  test01();
>>> +}
>>
> Here is the new patch.
>
> Tested under Linux x86_64 w/o _GLIBCXX_DEBUG mode.
>
> Ok to commit ?
>
> François
>
>
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diff --git a/libstdc++-v3/include/debug/assertions.h b/libstdc++-v3/include/debug/assertions.h
index c4993dc8596..768a7f05228 100644
--- a/libstdc++-v3/include/debug/assertions.h
+++ b/libstdc++-v3/include/debug/assertions.h
@@ -31,6 +31,12 @@
 
 #include <bits/c++config.h>
 
+#ifdef _GLIBCXX_DEBUG
+# define _GLIBCXX_DEBUG_STD_C ::std::_GLIBCXX_STD_C
+#else
+# define _GLIBCXX_DEBUG_STD_C ::std
+#endif
+
 #ifndef _GLIBCXX_DEBUG
 // Verify that [_First, _Last) forms a non-empty iterator range.
 # define __glibcxx_requires_non_empty_range(_First,_Last)	\
diff --git a/libstdc++-v3/include/debug/vector b/libstdc++-v3/include/debug/vector
index 56645d1e92c..e624b955c7d 100644
--- a/libstdc++-v3/include/debug/vector
+++ b/libstdc++-v3/include/debug/vector
@@ -51,15 +51,17 @@ namespace __gnu_debug
    * detecting code which relies on non-portable implementation details of
    * the libstdc++ reallocation policy.
    */
-  template<typename _SafeSequence,
-	   typename _BaseSequence>
+  template<typename _Tp, typename _Allocator>
     class _Safe_vector
     {
-      typedef typename _BaseSequence::size_type size_type;
+      typedef std::__debug::vector<_Tp, _Allocator> _SafeSequence;
+      typedef _GLIBCXX_DEBUG_STD_C::vector<_Tp, _Allocator> _StdVector;
+      typedef typename _StdVector::size_type size_type;
+      typedef typename _StdVector::difference_type difference_type;
 
       _GLIBCXX20_CONSTEXPR
-      const _SafeSequence&
-      _M_seq() const { return *static_cast<const _SafeSequence*>(this); }
+      _SafeSequence&
+      _M_seq() { return *static_cast<_SafeSequence*>(this); }
 
     protected:
       _GLIBCXX20_CONSTEXPR
@@ -103,10 +105,6 @@ namespace __gnu_debug
 
       size_type _M_guaranteed_capacity;
 
-      bool
-      _M_requires_reallocation(size_type __elements) const _GLIBCXX_NOEXCEPT
-      { return __elements > _M_seq().capacity(); }
-
       _GLIBCXX20_CONSTEXPR
       void
       _M_update_guaranteed_capacity() _GLIBCXX_NOEXCEPT
@@ -114,6 +112,31 @@ namespace __gnu_debug
 	if (_M_seq().size() > _M_guaranteed_capacity)
 	  _M_guaranteed_capacity = _M_seq().size();
       }
+
+      template<typename _InvalidationPolicy>
+	struct _Guard
+	{
+	  bool _M_active;
+
+	  _GLIBCXX20_CONSTEXPR
+	  _Guard(_Safe_vector& __vector, difference_type __offset = 0)
+	  : _M_active(false), _M_vector(__vector)
+	  , _M_invalidation_policy(__vector._M_seq(), __offset) { }
+
+	  _GLIBCXX20_CONSTEXPR
+	  ~_Guard()
+	  {
+	    if (!std::__is_constant_evaluated() && _M_active)
+	      {
+		_M_vector._M_update_guaranteed_capacity();
+		_M_invalidation_policy(_M_vector._M_seq());
+	      }
+	  }
+
+	private:
+	  _Safe_vector& _M_vector;
+	  _InvalidationPolicy _M_invalidation_policy;
+	};
     };
 }
 
@@ -128,14 +151,97 @@ namespace __debug
     : public __gnu_debug::_Safe_container<
 	vector<_Tp, _Allocator>, _Allocator, __gnu_debug::_Safe_sequence>,
       public _GLIBCXX_STD_C::vector<_Tp, _Allocator>,
-      public __gnu_debug::_Safe_vector<
-	vector<_Tp, _Allocator>,
-	_GLIBCXX_STD_C::vector<_Tp, _Allocator> >
+      public __gnu_debug::_Safe_vector<_Tp, _Allocator>
     {
       typedef _GLIBCXX_STD_C::vector<_Tp, _Allocator>		_Base;
       typedef __gnu_debug::_Safe_container<
 	vector, _Allocator, __gnu_debug::_Safe_sequence>	_Safe;
-      typedef __gnu_debug::_Safe_vector<vector, _Base>		_Safe_vector;
+      typedef __gnu_debug::_Safe_vector<_Tp, _Allocator>	_Safe_vector;
+
+    public:
+      typedef typename _Base::size_type			size_type;
+      typedef typename _Base::difference_type		difference_type;
+
+    private:
+      struct _ResizeInvalidationPolicy
+      {
+	size_type _M_capacity, _M_size;
+
+	_GLIBCXX20_CONSTEXPR
+	_ResizeInvalidationPolicy(const vector& __vector, difference_type)
+	: _M_capacity(__vector.capacity()), _M_size(__vector.size()) { }
+
+	void
+	operator()(vector& __vector) const _GLIBCXX_NOEXCEPT
+	{
+	  if (__vector.capacity() != _M_capacity)
+	    __vector._M_invalidate_all();
+	  else if (__vector.size() < _M_size)
+	    __vector._M_invalidate_after_nth(__vector.size());
+	}
+      };
+
+#ifdef _GLIBCXX_DEBUG_PEDANTIC
+      struct _PedanticInvalidationPolicy
+      {
+	_GLIBCXX20_CONSTEXPR
+	_PedanticInvalidationPolicy(const vector&, difference_type) { }
+
+	void
+	operator()(vector& __vector) const _GLIBCXX_NOEXCEPT
+	{ __vector._M_invalidate_all(); }
+      };
+#endif
+
+      struct _InsertInvalidationPolicy
+      {
+	size_type _M_capacity;
+	difference_type _M_offset;
+
+	_GLIBCXX20_CONSTEXPR
+	_InsertInvalidationPolicy(const vector& __vector,
+				  difference_type __offset)
+	: _M_capacity(__vector.capacity()), _M_offset(__offset) { }
+
+	void
+	operator()(vector& __vector) const _GLIBCXX_NOEXCEPT
+	{
+	  if (__vector.capacity() != _M_capacity)
+	    __vector._M_invalidate_all();
+	  else
+	    __vector._M_invalidate_after_nth(_M_offset);
+	}
+      };
+
+      struct _ReallocInvalidationPolicy
+      {
+	size_type _M_capacity;
+
+	_GLIBCXX20_CONSTEXPR
+	_ReallocInvalidationPolicy(const vector& __vector, difference_type)
+	: _M_capacity(__vector.capacity()) { }
+
+	void
+	operator()(vector& __vector) const _GLIBCXX_NOEXCEPT
+	{
+	  if (__vector.capacity() != _M_capacity)
+	    __vector._M_invalidate_all();
+	}
+      };
+
+      typedef typename _Safe_vector::
+	template _Guard<_ResizeInvalidationPolicy> _ResizeGuard;
+#ifdef _GLIBCXX_DEBUG_PEDANTIC
+      typedef typename _Safe_vector::
+	template _Guard<_PedanticInvalidationPolicy> _AssignGuard;
+#else
+      typedef _ResizeGuard _AssignGuard;
+#endif
+      typedef typename _Safe_vector::
+	template _Guard<_InsertInvalidationPolicy> _InsertGuard;
+
+      typedef typename _Safe_vector::
+	template _Guard<_ReallocInvalidationPolicy> _ReallocGuard;
 
       typedef typename _Base::iterator		_Base_iterator;
       typedef typename _Base::const_iterator	_Base_const_iterator;
@@ -163,9 +269,6 @@ namespace __debug
       typedef __gnu_debug::_Safe_iterator<
 	_Base_const_iterator, vector>			const_iterator;
 
-      typedef typename _Base::size_type			size_type;
-      typedef typename _Base::difference_type		difference_type;
-
       typedef _Tp					value_type;
       typedef _Allocator				allocator_type;
       typedef typename _Base::pointer			pointer;
@@ -276,12 +379,9 @@ namespace __debug
       vector&
       operator=(initializer_list<value_type> __l)
       {
+	_AssignGuard __guard(*this);
 	_Base::operator=(__l);
-	if (!std::__is_constant_evaluated())
-	  {
-	    this->_M_invalidate_all();
-	    this->_M_update_guaranteed_capacity();
-	  }
+	__guard._M_active = true;
 	return *this;
       }
 #endif
@@ -303,26 +403,23 @@ namespace __debug
 	  typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
 	  __glibcxx_check_valid_range2(__first, __last, __dist);
 
+	  _AssignGuard __guard(*this);
 	  if (__dist.second >= __gnu_debug::__dp_sign)
 	    _Base::assign(__gnu_debug::__unsafe(__first),
 			  __gnu_debug::__unsafe(__last));
 	  else
 	    _Base::assign(__first, __last);
 
-	  this->_M_invalidate_all();
-	  this->_M_update_guaranteed_capacity();
+	  __guard._M_active = true;
 	}
 
       _GLIBCXX20_CONSTEXPR
       void
       assign(size_type __n, const _Tp& __u)
       {
+	_AssignGuard __guard(*this);
 	_Base::assign(__n, __u);
-	if (!std::__is_constant_evaluated())
-	  {
-	    this->_M_invalidate_all();
-	    this->_M_update_guaranteed_capacity();
-	  }
+	__guard._M_active = true;
       }
 
 #if __cplusplus >= 201103L
@@ -330,12 +427,9 @@ namespace __debug
       void
       assign(initializer_list<value_type> __l)
       {
+	_AssignGuard __guard(*this);
 	_Base::assign(__l);
-	if (!std::__is_constant_evaluated())
-	  {
-	    this->_M_invalidate_all();
-	    this->_M_update_guaranteed_capacity();
-	  }
+	__guard._M_active = true;
       }
 #endif
 
@@ -428,13 +522,9 @@ namespace __debug
 	if (std::__is_constant_evaluated())
 	  return _Base::resize(__sz);
 
-	bool __realloc = this->_M_requires_reallocation(__sz);
-	if (__sz < this->size())
-	  this->_M_invalidate_after_nth(__sz);
+	_ResizeGuard __guard(*this);
 	_Base::resize(__sz);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	this->_M_update_guaranteed_capacity();
+	__guard._M_active = true;
       }
 
       _GLIBCXX20_CONSTEXPR
@@ -444,25 +534,17 @@ namespace __debug
 	if (std::__is_constant_evaluated())
 	  return _Base::resize(__sz, __c);
 
-	bool __realloc = this->_M_requires_reallocation(__sz);
-	if (__sz < this->size())
-	  this->_M_invalidate_after_nth(__sz);
+	_ResizeGuard __guard(*this);
 	_Base::resize(__sz, __c);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	this->_M_update_guaranteed_capacity();
+	__guard._M_active = true;
       }
 #else
       void
       resize(size_type __sz, _Tp __c = _Tp())
       {
-	bool __realloc = this->_M_requires_reallocation(__sz);
-	if (__sz < this->size())
-	  this->_M_invalidate_after_nth(__sz);
+	_ResizeGuard __guard(*this);
 	_Base::resize(__sz, __c);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	this->_M_update_guaranteed_capacity();
+	__guard._M_active = true;
       }
 #endif
 
@@ -506,7 +588,7 @@ namespace __debug
 	if (std::__is_constant_evaluated())
 	  return _Base::reserve(__n);
 
-	bool __realloc = this->_M_requires_reallocation(__n);
+	bool __realloc = __n > capacity();
 	_Base::reserve(__n);
 	if (__n > this->_M_guaranteed_capacity)
 	  this->_M_guaranteed_capacity = __n;
@@ -583,11 +665,9 @@ namespace __debug
 	if (std::__is_constant_evaluated())
 	  return _Base::push_back(__x);
 
-	bool __realloc = this->_M_requires_reallocation(this->size() + 1);
+	_ReallocGuard __guard(*this);
 	_Base::push_back(__x);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	this->_M_update_guaranteed_capacity();
+	__guard._M_active = true;
       }
 
 #if __cplusplus >= 201103L
@@ -610,11 +690,9 @@ namespace __debug
 	  if (std::__is_constant_evaluated())
 	    return _Base::emplace_back(std::forward<_Args>(__args)...);
 
-	  bool __realloc = this->_M_requires_reallocation(this->size() + 1);
+	  _ReallocGuard __guard(*this);
 	  _Base::emplace_back(std::forward<_Args>(__args)...);
-	  if (__realloc)
-	    this->_M_invalidate_all();
-	  this->_M_update_guaranteed_capacity();
+	  __guard._M_active = true;
 #if __cplusplus > 201402L
 	  return back();
 #endif
@@ -645,15 +723,14 @@ namespace __debug
 			    this);
 
 	  __glibcxx_check_insert(__position);
-	  bool __realloc = this->_M_requires_reallocation(this->size() + 1);
-	  difference_type __offset = __position.base() - _Base::cbegin();
-	  _Base_iterator __res = _Base::emplace(__position.base(),
-						std::forward<_Args>(__args)...);
-	  if (__realloc)
-	    this->_M_invalidate_all();
-	  else
-	    this->_M_invalidate_after_nth(__offset);
-	  this->_M_update_guaranteed_capacity();
+	  _Base_iterator __res;
+	  {
+	    difference_type __offset = __position.base() - _Base::cbegin();
+	    _InsertGuard __guard(*this, __offset);
+	    __res = _Base::emplace(__position.base(),
+				   std::forward<_Args>(__args)...);
+	    __guard._M_active = true;
+	  }
 	  return { __res, this };
 	}
 #endif
@@ -670,14 +747,13 @@ namespace __debug
 	  return iterator(_Base::insert(__position.base(), __x), this);
 
 	__glibcxx_check_insert(__position);
-	bool __realloc = this->_M_requires_reallocation(this->size() + 1);
-	difference_type __offset = __position.base() - _Base::begin();
-	_Base_iterator __res = _Base::insert(__position.base(), __x);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	else
-	  this->_M_invalidate_after_nth(__offset);
-	this->_M_update_guaranteed_capacity();
+	_Base_iterator __res;
+	{
+	  difference_type __offset = __position.base() - _Base::begin();
+	  _InsertGuard __guard(*this, __offset);
+	  __res = _Base::insert(__position.base(), __x);
+	  __guard._M_active = true;
+	}
 	return iterator(__res, this);
       }
 
@@ -704,14 +780,13 @@ namespace __debug
 	  return iterator(_Base::insert(__position.base(), __n, __x), this);
 
 	__glibcxx_check_insert(__position);
-	bool __realloc = this->_M_requires_reallocation(this->size() + __n);
-	difference_type __offset = __position.base() - _Base::cbegin();
-	_Base_iterator __res = _Base::insert(__position.base(), __n, __x);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	else
-	  this->_M_invalidate_after_nth(__offset);
-	this->_M_update_guaranteed_capacity();
+	_Base_iterator __res;
+	{
+	  difference_type __offset = __position.base() - _Base::cbegin();
+	  _InsertGuard __guard(*this, __offset);
+	  __res = _Base::insert(__position.base(), __n, __x);
+	  __guard._M_active = true;
+	}
 	return { __res, this };
       }
 #else
@@ -719,14 +794,10 @@ namespace __debug
       insert(iterator __position, size_type __n, const _Tp& __x)
       {
 	__glibcxx_check_insert(__position);
-	bool __realloc = this->_M_requires_reallocation(this->size() + __n);
 	difference_type __offset = __position.base() - _Base::begin();
+	_InsertGuard __guard(*this, __offset);
 	_Base::insert(__position.base(), __n, __x);
-	if (__realloc)
-	  this->_M_invalidate_all();
-	else
-	  this->_M_invalidate_after_nth(__offset);
-	this->_M_update_guaranteed_capacity();
+	__guard._M_active = true;
       }
 #endif
 
@@ -746,24 +817,19 @@ namespace __debug
 	  typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
 	  __glibcxx_check_insert_range(__position, __first, __last, __dist);
 
-	  /* Hard to guess if invalidation will occur, because __last
-	     - __first can't be calculated in all cases, so we just
-	     punt here by checking if it did occur. */
-	  _Base_iterator __old_begin = _M_base().begin();
-	  difference_type __offset = __position.base() - _Base::cbegin();
 	  _Base_iterator __res;
-	  if (__dist.second >= __gnu_debug::__dp_sign)
-	    __res = _Base::insert(__position.base(),
-				  __gnu_debug::__unsafe(__first),
-				  __gnu_debug::__unsafe(__last));
-	  else
-	    __res = _Base::insert(__position.base(), __first, __last);
-
-	  if (_M_base().begin() != __old_begin)
-	    this->_M_invalidate_all();
-	  else
-	    this->_M_invalidate_after_nth(__offset);
-	  this->_M_update_guaranteed_capacity();
+	  {
+	    difference_type __offset = __position.base() - _Base::cbegin();
+	    _InsertGuard __guard(*this, __offset);
+	    if (__dist.second >= __gnu_debug::__dp_sign)
+	      __res = _Base::insert(__position.base(),
+				    __gnu_debug::__unsafe(__first),
+				    __gnu_debug::__unsafe(__last));
+	    else
+	      __res = _Base::insert(__position.base(), __first, __last);
+
+	    __guard._M_active = true;
+	  }
 	  return { __res, this };
 	}
 #else
@@ -775,22 +841,15 @@ namespace __debug
 	  typename __gnu_debug::_Distance_traits<_InputIterator>::__type __dist;
 	  __glibcxx_check_insert_range(__position, __first, __last, __dist);
 
-	  /* Hard to guess if invalidation will occur, because __last
-	     - __first can't be calculated in all cases, so we just
-	     punt here by checking if it did occur. */
-	  _Base_iterator __old_begin = _M_base().begin();
 	  difference_type __offset = __position.base() - _Base::begin();
+	  _InsertGuard __guard(*this, __offset);
 	  if (__dist.second >= __gnu_debug::__dp_sign)
 	    _Base::insert(__position.base(), __gnu_debug::__unsafe(__first),
 					     __gnu_debug::__unsafe(__last));
 	  else
 	    _Base::insert(__position.base(), __first, __last);
 
-	  if (_M_base().begin() != __old_begin)
-	    this->_M_invalidate_all();
-	  else
-	    this->_M_invalidate_after_nth(__offset);
-	  this->_M_update_guaranteed_capacity();
+	  __guard._M_active = true;
 	}
 #endif
 
@@ -876,31 +935,22 @@ namespace __debug
 	constexpr void
 	assign_range(_Rg&& __rg)
 	{
-	  auto __old_capacity = _Base::capacity();
-	  auto __old_size = _Base::size();
+	  _AssignGuard __guard(*this);
 	  _Base::assign_range(__rg);
-	  if (!std::__is_constant_evaluated())
-	    {
-	      if (_Base::capacity() != __old_capacity)
-		this->_M_invalidate_all();
-	      else if (_Base::size() < __old_size)
-		this->_M_invalidate_after_nth(_Base::size());
-	      this->_M_update_guaranteed_capacity();
-	    }
+	  __guard._M_active = true;
 	}
 
       template<__detail::__container_compatible_range<_Tp> _Rg>
 	constexpr iterator
 	insert_range(const_iterator __pos, _Rg&& __rg)
 	{
-	  auto __old_capacity = _Base::capacity();
-	  auto __res = _Base::insert_range(__pos.base(), __rg);
-	  if (!std::__is_constant_evaluated())
-	    {
-	      if (_Base::capacity() != __old_capacity)
-		this->_M_invalidate_all();
-	      this->_M_update_guaranteed_capacity();
-	    }
+	  _Base_iterator __res;
+	  {
+	    difference_type __offset = __pos.base() - _Base::cbegin();
+	    _InsertGuard __guard(*this, __offset);
+	    __res = _Base::insert_range(__pos.base(), __rg);
+	    __guard._M_active = true;
+	  }
 	  return iterator(__res, this);
 	}
 
@@ -908,14 +958,9 @@ namespace __debug
 	constexpr void
 	append_range(_Rg&& __rg)
 	{
-	  auto __old_capacity = _Base::capacity();
+	  _ReallocGuard __guard(*this);
 	  _Base::append_range(__rg);
-	  if (!std::__is_constant_evaluated())
-	    {
-	      if (_Base::capacity() != __old_capacity)
-		this->_M_invalidate_all();
-	      this->_M_update_guaranteed_capacity();
-	    }
+	  __guard._M_active = true;
 	}
 #endif
 
diff --git a/libstdc++-v3/testsuite/23_containers/vector/capacity/shrink_to_fit.cc b/libstdc++-v3/testsuite/23_containers/vector/capacity/shrink_to_fit.cc
index d4aa4d89b56..6ca1ac8822a 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/capacity/shrink_to_fit.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/capacity/shrink_to_fit.cc
@@ -28,7 +28,7 @@ void test01()
   std::vector<int> v(100);
   v.push_back(1);
   v.push_back(1);
-  VERIFY( v.size() < v.capacity() );
+  VERIFY( v.size() <= v.capacity() );
   v.shrink_to_fit();
 #ifdef __glibcxx_allocate_at_least
   unsigned limit = __STDCPP_DEFAULT_NEW_ALIGNMENT__ / sizeof(int);
diff --git a/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc b/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc
index 2c9abcdbb91..9f6eab0f919 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/cons/destructible_debug_neg.cc
@@ -47,4 +47,4 @@ test02()
 // { dg-error "PrivateDtor.* is private" "" { target *-*-* } 0 }
 
 // In Debug Mode the "required from here" errors come from <debug/vector>
-// { dg-error "required from here" "" { target *-*-* } 182 }
+// { dg-error "required from here" "" { target *-*-* } 285 }
diff --git a/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc
new file mode 100644
index 00000000000..318f6b98de9
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list.cc
@@ -0,0 +1,26 @@
+// { dg-do compile { target c++11 } }
+
+#include <debug/vector>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  __gnu_debug::vector<int> v = { 0, 1, 2, 3, 4, 5 };
+
+  auto it1 = v.begin() + 1;
+  auto it4 = v.begin() + 4;
+
+  VERIFY( !it1._M_singular() );
+  VERIFY( !it4._M_singular() );
+
+  v = { 10, 11, 12, 13 };
+
+  VERIFY( !it1._M_singular() );
+  VERIFY( it4._M_singular() );
+}
+
+int main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc
new file mode 100644
index 00000000000..c8b3af25bd1
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/vector/debug/initializer_list_pedantic.cc
@@ -0,0 +1,27 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-D_GLIBCXX_DEBUG_PEDANTIC" }
+
+#include <debug/vector>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  __gnu_debug::vector<int> v = { 0, 1, 2, 3, 4, 5 };
+
+  auto it1 = v.begin() + 1;
+  auto it4 = v.begin() + 4;
+
+  VERIFY( !it1._M_singular() );
+  VERIFY( !it4._M_singular() );
+
+  v = { 10, 11, 12, 13 };
+
+  VERIFY( it1._M_singular() );
+  VERIFY( it4._M_singular() );
+}
+
+int main()
+{
+  test01();
+}


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