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

[Christopher Di Bella via lldb-commits]

================
@@ -65,6 +203,170 @@ public:
   using iterator                       = pointer;
   using const_iterator                 = const_pointer;
 
+public:
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI __split_buffer_size_layout() = default;
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI explicit __split_buffer_size_layout(const allocator_type& __alloc)
+      : __alloc_(__alloc) {}
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer __data() _NOEXCEPT { return __data_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_pointer __data() const _NOEXCEPT { return __data_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer begin() _NOEXCEPT { return __begin_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_pointer begin() const _NOEXCEPT { return __begin_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer end() _NOEXCEPT { return __begin_ + __size_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer end() const _NOEXCEPT { return __begin_ + __size_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __size_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT { return __size_ == 0; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type capacity() const _NOEXCEPT { return __cap_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI allocator_type& __get_allocator() _NOEXCEPT { return __alloc_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI allocator_type const& __get_allocator() const _NOEXCEPT {
+    return __alloc_;
+  }
+
+  // Returns the sentinel object directly. Should be used in conjunction with automatic type deduction,
+  // not explicit types.
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __sentinel() const _NOEXCEPT { return __size_; }
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __raw_capacity() const _NOEXCEPT { return __cap_; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_data(pointer __new_first) _NOEXCEPT {
+    __data_ = __new_first;
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __set_valid_range(pointer __new_begin, pointer __new_end) _NOEXCEPT {
+    // Size-based __split_buffers track their size directly: we need to explicitly update the size
+    // when the front is adjusted.
+    __size_ -= __new_begin - __begin_;
+    __begin_ = __new_begin;
+    __set_sentinel(__new_end);
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __set_valid_range(pointer __new_begin, size_type __new_size) _NOEXCEPT {
+    // Size-based __split_buffers track their size directly: we need to explicitly update the size
+    // when the front is adjusted.
+    __size_ -= __new_begin - __begin_;
+    __begin_ = __new_begin;
+    __set_sentinel(__new_size);
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_sentinel(pointer __new_end) _NOEXCEPT {
+    _LIBCPP_ASSERT_INTERNAL(__data_ <= __new_end, "__new_end cannot precede __data_");
+    __size_ += __new_end - end();
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_sentinel(size_type __new_size) _NOEXCEPT {
+    __size_ = __new_size;
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_capacity(size_type __new_capacity) _NOEXCEPT {
+    __cap_ = __new_capacity;
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __set_capacity(pointer __new_capacity) _NOEXCEPT {
+    __cap_ = __new_capacity - __begin_;
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __front_spare() const _NOEXCEPT {
+    return static_cast<size_type>(__begin_ - __data_);
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI size_type __back_spare() const _NOEXCEPT {
+    // `__cap_ - __end_` tells us the total number of spares when in size-mode. We need to remove
+    // the __front_spare from the count.
+    return __cap_ - __size_ - __front_spare();
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI reference back() _NOEXCEPT { return __begin_[__size_ - 1]; }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_reference back() const _NOEXCEPT {
+    return __begin_[__size_ - 1];
+  }
+
+  template <class _Data2>
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __swap_without_allocator(_Data2& __other) _NOEXCEPT {
+    std::swap(__data_, __other.__data_);
+    std::swap(__begin_, __other.__begin_);
+    std::swap(__cap_, __other.__cap_);
+    std::swap(__size_, __other.__size_);
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void swap(__split_buffer_size_layout& __other) _NOEXCEPT {
+    __swap_without_allocator(__other);
+    std::__swap_allocator(__alloc_, __other.__alloc_);
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __reset() _NOEXCEPT {
+    __data_  = nullptr;
+    __begin_ = nullptr;
+    __size_  = 0;
+    __cap_   = 0;
+  }
+
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __copy_without_alloc(__split_buffer_size_layout const& __other)
+      _NOEXCEPT_(is_nothrow_copy_assignable<pointer>::value) {
+    __data_  = __other.__data_;
+    __begin_ = __other.__begin_;
+    __cap_   = __other.__cap_;
+    __size_  = __other.__size_;
+  }
+
+private:
+  pointer __data_   = nullptr;
+  pointer __begin_  = nullptr;
+  size_type __size_ = 0;
+  size_type __cap_  = 0;
+  _LIBCPP_NO_UNIQUE_ADDRESS allocator_type __alloc_;
+
+  template <class, class, class>
+  friend class __split_buffer_size_layout;
+};
+
+// __split_buffer allocates a contiguous chunk of memory and stores objects in the range [__begin_, __end_).
+// It has uninitialized memory in the ranges  [__data_, __begin_) and [__end_, __cap_). That allows
+// it to grow both in the front and back without having to move the data.
+
+template <class _Tp,
----------------
cjdb wrote:

Done.

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