[PATCH] libstdc++: Adjust how __gnu_debug::vector detects invalidation

[Jonathan Wakely]

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.

 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