Revert "[libc++] LWG3870: Remove voidify (llvm#110355)"

This reverts commit 78f9a8b.

Author: Michael137

libcxx/docs/Status/Cxx23Issues.csv

@@ -296,7 +296,7 @@
 "`LWG3862 <https://wg21.link/LWG3862>`__","``basic_const_iterator``'s ``common_type`` specialization is underconstrained","2023-02 (Issaquah)","","",""
 "`LWG3865 <https://wg21.link/LWG3865>`__","Sorting a range of ``pairs``","2023-02 (Issaquah)","|Complete|","17.0",""
 "`LWG3869 <https://wg21.link/LWG3869>`__","Deprecate ``std::errc`` constants related to UNIX STREAMS","2023-02 (Issaquah)","|Complete|","19.0",""
-"`LWG3870 <https://wg21.link/LWG3870>`__","Remove ``voidify``","2023-02 (Issaquah)","|Complete|","20.0",""
+"`LWG3870 <https://wg21.link/LWG3870>`__","Remove ``voidify``","2023-02 (Issaquah)","","",""
 "`LWG3871 <https://wg21.link/LWG3871>`__","Adjust note about ``terminate``","2023-02 (Issaquah)","","",""
 "`LWG3872 <https://wg21.link/LWG3872>`__","``basic_const_iterator`` should have custom ``iter_move``","2023-02 (Issaquah)","","",""
 "`LWG3875 <https://wg21.link/LWG3875>`__","``std::ranges::repeat_view<T, IntegerClass>::iterator`` may be ill-formed","2023-02 (Issaquah)","|Complete|","17.0",""

libcxx/include/CMakeLists.txt

@@ -560,6 +560,7 @@ set(files
   __memory/unique_temporary_buffer.h
   __memory/uses_allocator.h
   __memory/uses_allocator_construction.h
+  __memory/voidify.h
   __memory_resource/memory_resource.h
   __memory_resource/monotonic_buffer_resource.h
   __memory_resource/polymorphic_allocator.h

libcxx/include/__memory/construct_at.h

@@ -14,6 +14,7 @@
 #include <__config>
 #include <__iterator/access.h>
 #include <__memory/addressof.h>
+#include <__memory/voidify.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_array.h>
 #include <__utility/declval.h>
@@ -37,7 +38,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 template <class _Tp, class... _Args, class = decltype(::new(std::declval<void*>()) _Tp(std::declval<_Args>()...))>
 _LIBCPP_HIDE_FROM_ABI constexpr _Tp* construct_at(_Tp* __location, _Args&&... __args) {
   _LIBCPP_ASSERT_NON_NULL(__location != nullptr, "null pointer given to construct_at");
-  return ::new (static_cast<void*>(__location)) _Tp(std::forward<_Args>(__args)...);
+  return ::new (std::__voidify(*__location)) _Tp(std::forward<_Args>(__args)...);
 }
 
 #endif
@@ -48,7 +49,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* __construct_at(_Tp* __l
   return std::construct_at(__location, std::forward<_Args>(__args)...);
 #else
   return _LIBCPP_ASSERT_NON_NULL(__location != nullptr, "null pointer given to construct_at"),
-         ::new (static_cast<void*>(__location)) _Tp(std::forward<_Args>(__args)...);
+         ::new (std::__voidify(*__location)) _Tp(std::forward<_Args>(__args)...);
 #endif
 }
 

libcxx/include/__memory/shared_ptr.h

@@ -248,35 +248,33 @@ struct __for_overwrite_tag {};
 
 template <class _Tp, class _Alloc>
 struct __shared_ptr_emplace : __shared_weak_count {
-  using __value_type = __remove_cv_t<_Tp>;
-
   template <class... _Args,
             class _Allocator                                                                         = _Alloc,
             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
     static_assert(
         sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
-    ::new (static_cast<void*>(__get_elem())) __value_type;
+    ::new ((void*)__get_elem()) _Tp;
   }
 
   template <class... _Args,
             class _Allocator                                                                          = _Alloc,
             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
-    using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __value_type>::type;
+    using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __remove_cv_t<_Tp> >::type;
     _TpAlloc __tmp(*__get_alloc());
     allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
   }
 
   _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
 
-  _LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
+  _LIBCPP_HIDE_FROM_ABI _Tp* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 
 private:
   template <class _Allocator                                                                         = _Alloc,
             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
-    __get_elem()->~__value_type();
+    __get_elem()->~_Tp();
   }
 
   template <class _Allocator                                                                          = _Alloc,
@@ -302,7 +300,7 @@ struct __shared_ptr_emplace : __shared_weak_count {
   // through `std::allocate_shared` and `std::make_shared`.
   struct _Storage {
     struct _Data {
-      _LIBCPP_COMPRESSED_PAIR(_Alloc, __alloc_, __value_type, __elem_);
+      _LIBCPP_COMPRESSED_PAIR(_Alloc, __alloc_, _Tp, __elem_);
     };
 
     _ALIGNAS_TYPE(_Data) char __buffer_[sizeof(_Data)];
@@ -314,7 +312,7 @@ struct __shared_ptr_emplace : __shared_weak_count {
       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__alloc_);
     }
 
-    _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI __value_type* __get_elem() _NOEXCEPT {
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _Tp* __get_elem() _NOEXCEPT {
       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__elem_);
     }
   };

libcxx/include/__memory/uninitialized_algorithms.h

@@ -21,6 +21,7 @@
 #include <__memory/allocator_traits.h>
 #include <__memory/construct_at.h>
 #include <__memory/pointer_traits.h>
+#include <__memory/voidify.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/extent.h>
 #include <__type_traits/is_array.h>
@@ -63,7 +64,7 @@ inline _LIBCPP_HIDE_FROM_ABI pair<_InputIterator, _ForwardIterator> __uninitiali
   try {
 #endif
     for (; __ifirst != __ilast && !__stop_copying(__idx); ++__ifirst, (void)++__idx)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(*__ifirst);
+      ::new (std::__voidify(*__idx)) _ValueType(*__ifirst);
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__ofirst, __idx);
@@ -93,7 +94,7 @@ __uninitialized_copy_n(_InputIterator __ifirst, _Size __n, _ForwardIterator __of
   try {
 #endif
     for (; __n > 0 && !__stop_copying(__idx); ++__ifirst, (void)++__idx, (void)--__n)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(*__ifirst);
+      ::new (std::__voidify(*__idx)) _ValueType(*__ifirst);
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__ofirst, __idx);
@@ -123,7 +124,7 @@ __uninitialized_fill(_ForwardIterator __first, _Sentinel __last, const _Tp& __x)
   try {
 #endif
     for (; __idx != __last; ++__idx)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(__x);
+      ::new (std::__voidify(*__idx)) _ValueType(__x);
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -151,7 +152,7 @@ __uninitialized_fill_n(_ForwardIterator __first, _Size __n, const _Tp& __x) {
   try {
 #endif
     for (; __n > 0; ++__idx, (void)--__n)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(__x);
+      ::new (std::__voidify(*__idx)) _ValueType(__x);
 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -181,7 +182,7 @@ __uninitialized_default_construct(_ForwardIterator __first, _Sentinel __last) {
   try {
 #  endif
     for (; __idx != __last; ++__idx)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType;
+      ::new (std::__voidify(*__idx)) _ValueType;
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -207,7 +208,7 @@ inline _LIBCPP_HIDE_FROM_ABI _ForwardIterator __uninitialized_default_construct_
   try {
 #  endif
     for (; __n > 0; ++__idx, (void)--__n)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType;
+      ::new (std::__voidify(*__idx)) _ValueType;
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -234,7 +235,7 @@ __uninitialized_value_construct(_ForwardIterator __first, _Sentinel __last) {
   try {
 #  endif
     for (; __idx != __last; ++__idx)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType();
+      ::new (std::__voidify(*__idx)) _ValueType();
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -260,7 +261,7 @@ inline _LIBCPP_HIDE_FROM_ABI _ForwardIterator __uninitialized_value_construct_n(
   try {
 #  endif
     for (; __n > 0; ++__idx, (void)--__n)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType();
+      ::new (std::__voidify(*__idx)) _ValueType();
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__first, __idx);
@@ -296,7 +297,7 @@ inline _LIBCPP_HIDE_FROM_ABI pair<_InputIterator, _ForwardIterator> __uninitiali
   try {
 #  endif
     for (; __ifirst != __ilast && !__stop_moving(__idx); ++__idx, (void)++__ifirst) {
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(__iter_move(__ifirst));
+      ::new (std::__voidify(*__idx)) _ValueType(__iter_move(__ifirst));
     }
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
@@ -334,7 +335,7 @@ inline _LIBCPP_HIDE_FROM_ABI pair<_InputIterator, _ForwardIterator> __uninitiali
   try {
 #  endif
     for (; __n > 0 && !__stop_moving(__idx); ++__idx, (void)++__ifirst, --__n)
-      ::new (static_cast<void*>(std::addressof(*__idx))) _ValueType(__iter_move(__ifirst));
+      ::new (std::__voidify(*__idx)) _ValueType(__iter_move(__ifirst));
 #  ifndef _LIBCPP_HAS_NO_EXCEPTIONS
   } catch (...) {
     std::__destroy(__ofirst, __idx);

libcxx/include/__memory/voidify.h

@@ -0,0 +1,30 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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___MEMORY_VOIDIFY_H
+#define _LIBCPP___MEMORY_VOIDIFY_H
+
+#include <__config>
+#include <__memory/addressof.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <typename _Tp>
+_LIBCPP_ALWAYS_INLINE _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void* __voidify(_Tp& __from) {
+  // Cast away cv-qualifiers to allow modifying elements of a range through const iterators.
+  return const_cast<void*>(static_cast<const volatile void*>(std::addressof(__from)));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___MEMORY_VOIDIFY_H