On Tue, Mar 25, 2025 at 12:26 PM Jonathan Wakely <jwak...@redhat.com> wrote:
> The new C++23 member functions assign_range, insert_range and
> append_range were checking whether the begin() iterator changed after
> calling the base class member. That works, but is technically undefined
> when the original iterator has been invalidated by a change in capacity.
>
> We can just check the capacity directly, because reallocation only
> occurs if a change in capacity is required.
>
> N.B. we can't use data() either because std::vector<bool> doesn't have
> it.
>
> libstdc++-v3/ChangeLog:
>
> * include/debug/vector (vector::assign_range): Use change in
> capacity to detect reallocation.
> (vector::insert_range, vector::append_range): Likewise. Remove
> unused variables.
> ---
>
> Tested x86_64-linux.
>
LGTM.
>
> libstdc++-v3/include/debug/vector | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/libstdc++-v3/include/debug/vector
> b/libstdc++-v3/include/debug/vector
> index 022ebe8c664..b49766c18a7 100644
> --- a/libstdc++-v3/include/debug/vector
> +++ b/libstdc++-v3/include/debug/vector
> @@ -876,12 +876,12 @@ namespace __debug
> constexpr void
> assign_range(_Rg&& __rg)
> {
> - auto __old_begin = _Base::begin();
> + auto __old_capacity = _Base::capacity();
> auto __old_size = _Base::size();
> _Base::assign_range(__rg);
> if (!std::__is_constant_evaluated())
> {
> - if (_Base::begin() != __old_begin)
> + if (_Base::capacity() != __old_capacity)
> this->_M_invalidate_all();
> else if (_Base::size() < __old_size)
> this->_M_invalidate_after_nth(_Base::size());
> @@ -893,12 +893,11 @@ namespace __debug
> constexpr iterator
> insert_range(const_iterator __pos, _Rg&& __rg)
> {
> - auto __old_begin = _Base::begin();
> - auto __old_size = _Base::size();
> + auto __old_capacity = _Base::capacity();
> auto __res = _Base::insert_range(__pos.base(), __rg);
> if (!std::__is_constant_evaluated())
> {
> - if (_Base::begin() != __old_begin)
> + if (_Base::capacity() != __old_capacity)
> this->_M_invalidate_all();
> this->_M_update_guaranteed_capacity();
> }
> @@ -909,12 +908,11 @@ namespace __debug
> constexpr void
> append_range(_Rg&& __rg)
> {
> - auto __old_begin = _Base::begin();
> - auto __old_size = _Base::size();
> + auto __old_capacity = _Base::capacity();
> _Base::append_range(__rg);
> if (!std::__is_constant_evaluated())
> {
> - if (_Base::begin() != __old_begin)
> + if (_Base::capacity() != __old_capacity)
> this->_M_invalidate_all();
> this->_M_update_guaranteed_capacity();
> }
> --
> 2.49.0
>
>
