[libcxx-commits] [libcxx] [lldb] [libcxx] adds a size-based representation for `vector`'s unstable ABI (PR #155330)

[Louis Dionne via libcxx-commits]

================
@@ -0,0 +1,545 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___VECTOR_LAYOUT_H
+#define _LIBCPP___VECTOR_LAYOUT_H
+
+#include <__assert>
+#include <__config>
+#include <__debug_utils/sanitizers.h>
+#include <__memory/allocator_traits.h>
+#include <__memory/compressed_pair.h>
+#include <__memory/pointer_traits.h>
+#include <__memory/swap_allocator.h>
+#include <__memory/uninitialized_algorithms.h>
+#include <__split_buffer>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__utility/exchange.h>
+#include <__utility/move.h>
+#include <__utility/swap.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+/// Defines `std::vector`'s storage layout and any operations that are affected by a change in the
+/// layout.
+///
+/// `std::vector` can be represented in a variety of ways. Each representation strongly influences
+/// the codegen when calling vector operations, which can significantly impact runtime performance
+/// and memory utilisation. libc++ provides two alternative layouts for `std::vector`, although only
+/// one can be active for an enitre binary:
----------------
ldionne wrote:

```suggestion
/// one can be active for an entire binary:
```

https://github.com/llvm/llvm-project/pull/155330