[libcxx-commits] [libcxx] [libc++] Replace `__compressed_pair` with `[[no_unique_address]]` (PR #76756)
Louis Dionne via libcxx-commits
libcxx-commits at lists.llvm.org
Thu Jan 25 09:23:51 PST 2024
================
@@ -11,161 +11,79 @@
#define _LIBCPP___MEMORY_COMPRESSED_PAIR_H
#include <__config>
-#include <__fwd/get.h>
-#include <__fwd/tuple.h>
-#include <__tuple/tuple_indices.h>
-#include <__type_traits/decay.h>
-#include <__type_traits/dependent_type.h>
-#include <__type_traits/enable_if.h>
-#include <__type_traits/is_default_constructible.h>
+#include <__type_traits/datasizeof.h>
#include <__type_traits/is_empty.h>
#include <__type_traits/is_final.h>
-#include <__type_traits/is_same.h>
-#include <__type_traits/is_swappable.h>
-#include <__utility/forward.h>
-#include <__utility/move.h>
-#include <__utility/piecewise_construct.h>
-#include <cstddef>
+#include <__type_traits/is_object.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
-
_LIBCPP_BEGIN_NAMESPACE_STD
-// Tag used to default initialize one or both of the pair's elements.
-struct __default_init_tag {};
-struct __value_init_tag {};
-
-template <class _Tp, int _Idx, bool _CanBeEmptyBase = is_empty<_Tp>::value && !__libcpp_is_final<_Tp>::value>
-struct __compressed_pair_elem {
- using _ParamT = _Tp;
- using reference = _Tp&;
- using const_reference = const _Tp&;
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_() {}
-
- template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, __decay_t<_Up> >::value> >
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(_Up&& __u)
- : __value_(std::forward<_Up>(__u)) {}
-
-#ifndef _LIBCPP_CXX03_LANG
- template <class... _Args, size_t... _Indices>
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit __compressed_pair_elem(
- piecewise_construct_t, tuple<_Args...> __args, __tuple_indices<_Indices...>)
- : __value_(std::forward<_Args>(std::get<_Indices>(__args))...) {}
-#endif
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference __get() _NOEXCEPT { return __value_; }
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return __value_; }
-
-private:
- _Tp __value_;
-};
-
-template <class _Tp, int _Idx>
-struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
- using _ParamT = _Tp;
- using reference = _Tp&;
- using const_reference = const _Tp&;
- using __value_type = _Tp;
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem() = default;
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_type() {}
-
- template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, __decay_t<_Up> >::value> >
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(_Up&& __u)
- : __value_type(std::forward<_Up>(__u)) {}
-
-#ifndef _LIBCPP_CXX03_LANG
- template <class... _Args, size_t... _Indices>
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17
- __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args, __tuple_indices<_Indices...>)
- : __value_type(std::forward<_Args>(std::get<_Indices>(__args))...) {}
-#endif
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference __get() _NOEXCEPT { return *this; }
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return *this; }
-};
-
-template <class _T1, class _T2>
-class __compressed_pair : private __compressed_pair_elem<_T1, 0>, private __compressed_pair_elem<_T2, 1> {
-public:
- // NOTE: This static assert should never fire because __compressed_pair
- // is *almost never* used in a scenario where it's possible for T1 == T2.
- // (The exception is std::function where it is possible that the function
- // object and the allocator have the same type).
- static_assert(
- (!is_same<_T1, _T2>::value),
- "__compressed_pair cannot be instantiated when T1 and T2 are the same type; "
- "The current implementation is NOT ABI-compatible with the previous implementation for this configuration");
-
- using _Base1 _LIBCPP_NODEBUG = __compressed_pair_elem<_T1, 0>;
- using _Base2 _LIBCPP_NODEBUG = __compressed_pair_elem<_T2, 1>;
-
- template <bool _Dummy = true,
- class = __enable_if_t< __dependent_type<is_default_constructible<_T1>, _Dummy>::value &&
- __dependent_type<is_default_constructible<_T2>, _Dummy>::value > >
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair()
- : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
-
- template <class _U1, class _U2>
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair(_U1&& __t1, _U2&& __t2)
- : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
-
-#ifndef _LIBCPP_CXX03_LANG
- template <class... _Args1, class... _Args2>
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 explicit __compressed_pair(
- piecewise_construct_t __pc, tuple<_Args1...> __first_args, tuple<_Args2...> __second_args)
- : _Base1(__pc, std::move(__first_args), typename __make_tuple_indices<sizeof...(_Args1)>::type()),
- _Base2(__pc, std::move(__second_args), typename __make_tuple_indices<sizeof...(_Args2)>::type()) {}
-#endif
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 typename _Base1::reference first() _NOEXCEPT {
- return static_cast<_Base1&>(*this).__get();
- }
+#ifndef _LIBCPP_ABI_NO_COMPRESSED_PAIR_PADDING
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR typename _Base1::const_reference first() const _NOEXCEPT {
- return static_cast<_Base1 const&>(*this).__get();
- }
+// ================================================================================================================== //
+// The utilites here are for staying ABI compatible with the legacy `__compressed_pair`. They should not be used //
+// for new data structures. Use `_LIBCPP_NO_UNIQUE_ADDRESS` for new data structures instead. //
+// ================================================================================================================== //
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 typename _Base2::reference second() _NOEXCEPT {
- return static_cast<_Base2&>(*this).__get();
- }
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR typename _Base2::const_reference second() const _NOEXCEPT {
- return static_cast<_Base2 const&>(*this).__get();
- }
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static _Base1* __get_first_base(__compressed_pair* __pair) _NOEXCEPT {
- return static_cast<_Base1*>(__pair);
- }
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static _Base2* __get_second_base(__compressed_pair* __pair) _NOEXCEPT {
- return static_cast<_Base2*>(__pair);
- }
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void swap(__compressed_pair& __x)
- _NOEXCEPT_(__is_nothrow_swappable<_T1>::value&& __is_nothrow_swappable<_T2>::value) {
- using std::swap;
- swap(first(), __x.first());
- swap(second(), __x.second());
- }
+// The first member is aligned to the alignment of the second member to force padding in front of the compressed pair
+// in case there are members before it.
+//
+// For example:
+// (assuming x86-64 linux)
+// class SomeClass {
+// uint32_t member1;
+// _LIBCPP_COMPRESSED_PAIR(uint32_t, member2, uint64_t, member3);
+// }
+//
+// The layout with __compressed_pair is:
+// member1 - offset: 0, size: 4
+// padding - offset: 4, size: 4
+// member2 - offset: 8, size: 4
+// padding - offset: 12, size: 4
+// member3 - offset: 16, size: 8
+//
+// If the [[gnu::aligned]] wasn't there, the layout would instead be:
+// member1 - offset: 0, size: 4
+// member2 - offset: 4, size: 4
+// member3 - offset: 8, size: 8
+
+template <class _ToPad>
+class __compressed_pair_padding {
+ char __padding_[(!is_object<_ToPad>::value || (is_empty<_ToPad>::value && !__libcpp_is_final<_ToPad>::value))
+ ? 0
+ : sizeof(_ToPad) - __libcpp_datasizeof<_ToPad>::value];
};
-template <class _T1, class _T2>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
-swap(__compressed_pair<_T1, _T2>& __x, __compressed_pair<_T1, _T2>& __y)
- _NOEXCEPT_(__is_nothrow_swappable<_T1>::value&& __is_nothrow_swappable<_T2>::value) {
- __x.swap(__y);
-}
+# define _LIBCPP_COMPRESSED_PAIR(T1, Name1, T2, Name2) \
+ [[__gnu__::__aligned__(_LIBCPP_ALIGNOF(T2))]] _LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
+ _LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T1> Name1##_padding_; \
+ _LIBCPP_NO_UNIQUE_ADDRESS T2 Name2; \
+ _LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T2> Name2##_padding_
+
+# define _LIBCPP_COMPRESSED_TRIPLE(T1, Name1, T2, Name2, T3, Name3) \
+ [[using __gnu__: __aligned__(_LIBCPP_ALIGNOF(T2)), \
+ __aligned__(_LIBCPP_ALIGNOF(T3))]] _LIBCPP_NO_UNIQUE_ADDRESS T1 Name1; \
+ _LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T1> Name1##padding_; \
+ _LIBCPP_NO_UNIQUE_ADDRESS T2 Name2; \
+ _LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T2> Name2##padding_; \
+ _LIBCPP_NO_UNIQUE_ADDRESS T3 Name3; \
+ _LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T3> Name3##padding_
----------------
ldionne wrote:
```suggestion
# define _LIBCPP_COMPRESSED_TRIPLE(T1, Initializer1, T2, Initializer2, T3, Initializer3) \
[[using __gnu__: __aligned__(_LIBCPP_ALIGNOF(T2)), \
__aligned__(_LIBCPP_ALIGNOF(T3))]] _LIBCPP_NO_UNIQUE_ADDRESS T1 Initializer1; \
_LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T1> _LIBCPP_CONCAT(__padding1_, __LINE__); \
_LIBCPP_NO_UNIQUE_ADDRESS T2 Initializer2; \
_LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T2> _LIBCPP_CONCAT(__padding2_, __LINE__); \
_LIBCPP_NO_UNIQUE_ADDRESS T3 Initializer3; \
_LIBCPP_NO_UNIQUE_ADDRESS __compressed_pair_padding<T3> _LIBCPP_CONCAT(__padding3_, __LINE__)
```
This way, you can do `_LIBCPP_COMPRESSED_TRIPLE(T, foo = 3, ...)` to have member initializers.
https://github.com/llvm/llvm-project/pull/76756
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