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

[Louis Dionne via lldb-commits]

================
@@ -184,242 +458,232 @@ public:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void 
swap(__split_buffer& __x)
       _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;
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool __invariants() 
const {
+    if (__data() == nullptr) {
+      if (begin() != nullptr)
+        return false;
+
+      if (!empty())
+        return false;
+
+      if (capacity() != 0)
+        return false;
+
+      return true;
+    } else {
+      if (begin() < __data())
+        return false;
+
+      if (capacity() < size())
+        return false;
+
+      if (end() < begin())
+        return false;
+
+      return true;
+    }
+  }
 
 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_);
+    __get_allocator() = std::move(__c.__get_allocator());
   }
 
   _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_->__set_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;
-}
-
-//  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);
+template <class _Tp, class _Allocator, template <class, class, class> class 
_Layout>
+_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator, 
_Layout>::__construct_at_end(size_type __n) {
+  _ConstructTransaction __tx(this, end(), __n);
   for (; __tx.__pos_ != __tx.__end_; ++__tx.__pos_) {
-    __alloc_traits::construct(__alloc_, std::__to_address(__tx.__pos_));
+    __alloc_traits::construct(__get_allocator(), 
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:

Why not say `end()` here?

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

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