[libc++][WIP] Implement relocation primitives

Author: ldionne

libcxx/include/CMakeLists.txt

@@ -552,18 +552,21 @@ set(files
   __memory/destroy.h
   __memory/destruct_n.h
   __memory/inout_ptr.h
+  __memory/is_trivially_allocator_relocatable.h
   __memory/noexcept_move_assign_container.h
   __memory/out_ptr.h
   __memory/pointer_traits.h
   __memory/ranges_construct_at.h
   __memory/ranges_uninitialized_algorithms.h
   __memory/raw_storage_iterator.h
+  __memory/relocate_at.h
   __memory/shared_count.h
   __memory/shared_ptr.h
   __memory/swap_allocator.h
   __memory/temp_value.h
   __memory/temporary_buffer.h
   __memory/uninitialized_algorithms.h
+  __memory/uninitialized_relocate.h
   __memory/unique_ptr.h
   __memory/unique_temporary_buffer.h
   __memory/uses_allocator.h

libcxx/include/__memory/is_trivially_allocator_relocatable.h

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_IS_TRIVIALLY_ALLOCATOR_RELOCATABLE_H
+#define _LIBCPP___MEMORY_IS_TRIVIALLY_ALLOCATOR_RELOCATABLE_H
+
+#include <__config>
+#include <__memory/allocator_traits.h>
+#include <__type_traits/conjunction.h>
+#include <__type_traits/disjunction.h>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/is_trivially_relocatable.h>
+#include <__type_traits/negation.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// A type is trivially allocator relocatable if the allocator's move construction and destruction
+// don't do anything beyond calling the type's move constructor and destructor, and if the type
+// itself is trivially relocatable.
+
+template <class _Alloc, class _Type>
+struct __allocator_has_trivial_move_construct : _Not<__has_construct<_Alloc, _Type*, _Type&&> > {};
+
+template <class _Type>
+struct __allocator_has_trivial_move_construct<allocator<_Type>, _Type> : true_type {};
+
+template <class _Alloc, class _Tp>
+struct __allocator_has_trivial_destroy : _Not<__has_destroy<_Alloc, _Tp*> > {};
+
+template <class _Tp, class _Up>
+struct __allocator_has_trivial_destroy<allocator<_Tp>, _Up> : true_type {};
+
+template <class _Alloc, class _Tp>
+struct __is_trivially_allocator_relocatable
+    : integral_constant<bool,
+                        __allocator_has_trivial_move_construct<_Alloc, _Tp>::value &&
+                            __allocator_has_trivial_destroy<_Alloc, _Tp>::value &&
+                            __libcpp_is_trivially_relocatable<_Tp>::value> {};
+
+template <class _Alloc, class _Tp>
+struct __is_nothrow_allocator_relocatable
+    : _Or<_And<__allocator_has_trivial_move_construct<_Alloc, _Tp>, is_nothrow_move_constructible<_Tp>>,
+          __is_trivially_allocator_relocatable<_Alloc, _Tp>> {};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___MEMORY_IS_TRIVIALLY_ALLOCATOR_RELOCATABLE_H

libcxx/include/__memory/relocate_at.h

@@ -0,0 +1,88 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_RELOCATE_AT_H
+#define _LIBCPP___MEMORY_RELOCATE_AT_H
+
+#include <__memory/allocator_traits.h>
+#include <__memory/construct_at.h>
+#include <__memory/is_trivially_allocator_relocatable.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_constant_evaluated.h>
+#include <__type_traits/is_trivially_relocatable.h>
+#include <__utility/move.h>
+#include <__utility/scope_guard.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+struct __destroy_object {
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 void operator()() const { std::__destroy_at(__obj_); }
+  _Tp* __obj_;
+};
+
+template <class _Alloc, class _Tp>
+struct __allocator_destroy_object {
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 void operator()() const { allocator_traits<_Alloc>::destroy(__alloc_, __obj_); }
+  _Alloc& __alloc_;
+  _Tp* __obj_;
+};
+
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp* __libcpp_builtin_trivially_relocate_at(_Tp* __source, _Tp* __dest) _NOEXCEPT {
+  static_assert(__libcpp_is_trivially_relocatable<_Tp>::value, "");
+  // Casting to void* to suppress clang complaining that this is technically UB.
+  __builtin_memcpy(static_cast<void*>(__dest), __source, sizeof(_Tp));
+  return __dest;
+}
+
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp* __libcpp_builtin_trivially_relocate_at(_Tp* __first, Tp* __last, _Tp* __dest) _NOEXCEPT {
+  static_assert(__libcpp_is_trivially_relocatable<_Tp>::value, "");
+  // Casting to void* to suppress clang complaining that this is technically UB.
+  __builtin_memmove(static_cast<void*>(__dest), __first, (__last - __first) * sizeof(_Tp));
+  return __dest;
+}
+
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* __relocate_at(_Tp* __source, _Tp* __dest) {
+  if constexpr (__libcpp_is_trivially_relocatable<_Tp>::value) {
+    if (!__libcpp_is_constant_evaluated()) {
+      return std::__libcpp_builtin_trivially_relocate_at(__source, __dest);
+    }
+  }
+  auto __guard = std::__make_scope_guard(__destroy_object<_Tp>{__source});
+  return std::__construct_at(__dest, std::move(*__source));
+}
+
+template <class _Alloc, class _Tp>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp*
+__allocator_relocate_at(_Alloc& __alloc, _Tp* __source, _Tp* __dest) {
+  if constexpr (__allocator_has_trivial_move_construct<_Alloc, _Tp>::value &&
+                __allocator_has_trivial_destroy<_Alloc, _Tp>::value) {
+    (void)__alloc; // ignore the allocator
+    return std::__relocate_at(__source, __dest);
+  } else {
+    auto __guard = std::__make_scope_guard(__allocator_destroy_object<_Alloc, _Tp>{__alloc, __source});
+    allocator_traits<_Alloc>::construct(__alloc, __dest, std::move(*__source));
+    return __dest;
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___MEMORY_RELOCATE_AT_H

libcxx/include/__memory/uninitialized_algorithms.h

@@ -21,6 +21,7 @@
 #include <__memory/destroy.h>
 #include <__memory/allocator_traits.h>
 #include <__memory/construct_at.h>
+#include <__memory/is_trivially_allocator_relocatable.h>
 #include <__memory/pointer_traits.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/extent.h>
@@ -584,19 +585,7 @@ __uninitialized_allocator_copy(_Alloc& __alloc, _Iter1 __first1, _Sent1 __last1,
   return std::__rewrap_iter(__first2, __result);
 }
 
-template <class _Alloc, class _Type>
-struct __allocator_has_trivial_move_construct : _Not<__has_construct<_Alloc, _Type*, _Type&&> > {};
-
-template <class _Type>
-struct __allocator_has_trivial_move_construct<allocator<_Type>, _Type> : true_type {};
-
-template <class _Alloc, class _Tp>
-struct __allocator_has_trivial_destroy : _Not<__has_destroy<_Alloc, _Tp*> > {};
-
-template <class _Tp, class _Up>
-struct __allocator_has_trivial_destroy<allocator<_Tp>, _Up> : true_type {};
-
-// __uninitialized_allocator_relocate relocates the objects in [__first, __last) into __result.
+// __uninitialized_allocator_relocate_for_vector relocates the objects in [__first, __last) into __result.
 // Relocation means that the objects in [__first, __last) are placed into __result as-if by move-construct and destroy,
 // except that the move constructor and destructor may never be called if they are known to be equivalent to a memcpy.
 //
@@ -609,15 +598,13 @@ struct __allocator_has_trivial_destroy<allocator<_Tp>, _Up> : true_type {};
 // - is_copy_constructible<_ValueType>
 // - __libcpp_is_trivially_relocatable<_ValueType>
 template <class _Alloc, class _ContiguousIterator>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void __uninitialized_allocator_relocate(
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void __uninitialized_allocator_relocate_for_vector(
     _Alloc& __alloc, _ContiguousIterator __first, _ContiguousIterator __last, _ContiguousIterator __result) {
   static_assert(__libcpp_is_contiguous_iterator<_ContiguousIterator>::value, "");
   using _ValueType = typename iterator_traits<_ContiguousIterator>::value_type;
   static_assert(__is_cpp17_move_insertable<_Alloc>::value,
                 "The specified type does not meet the requirements of Cpp17MoveInsertable");
-  if (__libcpp_is_constant_evaluated() || !__libcpp_is_trivially_relocatable<_ValueType>::value ||
-      !__allocator_has_trivial_move_construct<_Alloc, _ValueType>::value ||
-      !__allocator_has_trivial_destroy<_Alloc, _ValueType>::value) {
+  if (__libcpp_is_constant_evaluated() || !__is_trivially_allocator_relocatable<_Alloc, _ValueType>::value) {
     auto __destruct_first = __result;
     auto __guard          = std::__make_exception_guard(
         _AllocatorDestroyRangeReverse<_Alloc, _ContiguousIterator>(__alloc, __destruct_first, __result));