[Lldb-commits] [lldb] [WIP][lldb][test] Add a layout simulator test for std::unique_ptr (PR #98330)

[Pavel Labath via lldb-commits]

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@@ -0,0 +1,89 @@
+#ifndef STD_LLDB_COMPRESSED_PAIR_H
+#define STD_LLDB_COMPRESSED_PAIR_H
+
+#include <__memory/compressed_pair.h>
+#include <type_traits>
+
+namespace std {
+namespace __lldb {
+
+#if COMPRESSED_PAIR_REV == 0 // Post-c88580c layout
+struct __value_init_tag {};
+struct __default_init_tag {};
+
+template <class _Tp, int _Idx,
+          bool _CanBeEmptyBase =
+              std::is_empty<_Tp>::value && !std::is_final<_Tp>::value>
+struct __compressed_pair_elem {
+  explicit __compressed_pair_elem(__default_init_tag) {}
+  explicit __compressed_pair_elem(__value_init_tag) : __value_() {}
+
+  explicit __compressed_pair_elem(_Tp __t) : __value_(__t) {}
+
+  _Tp &__get() { return __value_; }
+
+private:
+  _Tp __value_;
+};
+
+template <class _Tp, int _Idx>
+struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
+  explicit __compressed_pair_elem(_Tp __t) : _Tp(__t) {}
+  explicit __compressed_pair_elem(__default_init_tag) {}
+  explicit __compressed_pair_elem(__value_init_tag) : _Tp() {}
+
+  _Tp &__get() { return *this; }
+};
+
+template <class _T1, class _T2>
+class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
+                          private __compressed_pair_elem<_T2, 1> {
+public:
+  using _Base1 = __compressed_pair_elem<_T1, 0>;
+  using _Base2 = __compressed_pair_elem<_T2, 1>;
+
+  explicit __compressed_pair(_T1 __t1, _T2 __t2) : _Base1(__t1), _Base2(__t2) {}
+  explicit __compressed_pair()
+      : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
+
+  template <class _U1, class _U2>
+  explicit __compressed_pair(_U1 &&__t1, _U2 &&__t2)
+      : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
+
+  _T1 &first() { return static_cast<_Base1 &>(*this).__get(); }
+};
+#elif COMPRESSED_PAIR_REV == 1
+#define _LLDB_COMPRESSED_PAIR(T1, Initializer1, T2, Initializer2)              \
+  [[__gnu__::__aligned__(alignof(T2))]] [[no_unique_address]] T1 Initializer1; \
+  [[no_unique_address]] __compressed_pair_padding<T1> _LIBCPP_CONCAT3(         \
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labath wrote:

Where are  __compressed_pair_padding and _LIBCPP_CONCAT3  defined? in libc++? I don't think we want to depend on it for several reasons:
- it makes the test non-hermetic
- it means the test will not run without libc++
- libc++ folks might now like us reaching into their private headers like that

https://github.com/llvm/llvm-project/pull/98330