[libcxx-commits] [libcxx] [lldb] [libcxx] adds size-based `__split_buffer` representation to unstable ABI (PR #139632)

[Louis Dionne via libcxx-commits]

================
@@ -185,66 +382,52 @@ public:
       _NOEXCEPT_(!__alloc_traits::propagate_on_container_swap::value || __is_nothrow_swappable_v<__alloc_rr>);
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool __invariants() const;
-
 private:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__split_buffer& __c, true_type)
       _NOEXCEPT_(is_nothrow_move_assignable<allocator_type>::value) {
-    __alloc_ = std::move(__c.__alloc_);
+    __data_.__alloc_ = std::move(__c.__data_.__alloc_);
   }
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__split_buffer&, false_type) _NOEXCEPT {}
 
   struct _ConstructTransaction {
     _LIBCPP_CONSTEXPR_SINCE_CXX20
-    _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(pointer* __p, size_type __n) _NOEXCEPT
-        : __pos_(*__p),
-          __end_(*__p + __n),
-          __dest_(__p) {}
+    _LIBCPP_HIDE_FROM_ABI explicit _ConstructTransaction(__split_buffer* __parent, pointer __p, size_type __n) _NOEXCEPT
+    : __pos_(__p),
+      __end_(__p + __n),
+      __parent_(__parent) {}
 
-    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI ~_ConstructTransaction() { *__dest_ = __pos_; }
+    _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI ~_ConstructTransaction() {
+      __parent_->__data_.__update_sentinel(__pos_);
+    }
 
     pointer __pos_;
     const pointer __end_;
 
   private:
-    pointer* __dest_;
+    __split_buffer* __parent_;
   };
 };
 
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __split_buffer<_Tp, _Allocator>::__invariants() const {
-  if (__first_ == nullptr) {
-    if (__begin_ != nullptr)
-      return false;
-    if (__end_ != nullptr)
-      return false;
-    if (__cap_ != nullptr)
-      return false;
-  } else {
-    if (__begin_ < __first_)
-      return false;
-    if (__end_ < __begin_)
-      return false;
-    if (__cap_ < __end_)
-      return false;
-  }
-  return true;
+  return __data_.__invariants();
 }
 
-//  Default constructs __n objects starting at __end_
+//  Default constructs __n objects starting at `__begin_ + size()`
 //  throws if construction throws
 //  Precondition:  __n > 0
 //  Precondition:  size() + __n <= capacity()
 //  Postcondition:  size() == size() + __n
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::__construct_at_end(size_type __n) {
-  _ConstructTransaction __tx(std::addressof(this->__end_), __n);
+  _ConstructTransaction __tx(this, __data_.end(), __n);
   for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
-    __alloc_traits::construct(__alloc_, std::__to_address(__tx.__pos_));
+    __alloc_traits::construct(__data_.__alloc_, std::__to_address(__tx.__pos_));
   }
 }
 
-//  Copy constructs __n objects starting at __end_ from __x
+//  Copy constructs __n objects starting at `__begin_ + size()` from __x
----------------
ldionne wrote:

```suggestion
//  Copy constructs __n objects starting at `end()` from __x
```

https://github.com/llvm/llvm-project/pull/139632