[libc++] Remove get_temporary_buffer/return_temporary_buffer

libcxx/docs/ReleaseNotes/20.rst

@@ -47,6 +47,9 @@ Improvements and New Features
 - The ``lexicographical_compare`` and ``ranges::lexicographical_compare`` algorithms have been optimized for trivially
   equality comparable types, resulting in a performance improvement of up to 40x.
 
+- The ``_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER`` macro has been added to make ``std::get_temporary_buffer`` and
+  ``std::return_temporary_buffer`` available.
+
 
 Deprecations and Removals
 -------------------------

libcxx/docs/Status/Cxx20.rst

@@ -42,7 +42,7 @@ Paper Status
    .. [#note-P0645] P0645: The implementation was complete since Clang 14,
       except the feature-test macro was not set until Clang 19.
    .. [#note-P0966] P0966: It was previously erroneously marked as complete in version 8.0. See `bug 45368 <https://llvm.org/PR45368>`__.
-   .. [#note-P0619] P0619: Only sections D.8, D.9, D.10 and D.13 are implemented. Sections D.4, D.7, D.11, and D.12 remain undone.
+   .. [#note-P0619] P0619: Only sections D.8, D.9, D.10, D.12, and D.13 are implemented. Sections D.4, D.7, and D.11 remain undone.
    .. [#note-P0883.1] P0883: shared_ptr and floating-point changes weren't applied as they themselves aren't implemented yet.
    .. [#note-P0883.2] P0883: ``ATOMIC_FLAG_INIT`` was marked deprecated in version 14.0, but was undeprecated with the implementation of LWG3659 in version 15.0.
    .. [#note-P0660] P0660: The paper is implemented but the features are experimental and can be enabled via ``-fexperimental-library``.

libcxx/docs/UserDocumentation.rst

@@ -179,6 +179,9 @@ C++20 Specific Configuration Macros
 **_LIBCPP_ENABLE_CXX20_REMOVED_RAW_STORAGE_ITERATOR**:
   This macro is used to re-enable `raw_storage_iterator`.
 
+**_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER**:
+  This macro is used to re-enable `get_temporary_buffer` and `return_temporary_buffer`.
+
 **_LIBCPP_ENABLE_CXX20_REMOVED_TYPE_TRAITS**:
   This macro is used to re-enable `is_literal_type`, `is_literal_type_v`,
   `result_of` and `result_of_t`.

libcxx/include/CMakeLists.txt

@@ -541,6 +541,7 @@ set(files
   __memory/ranges_construct_at.h
   __memory/ranges_uninitialized_algorithms.h
   __memory/raw_storage_iterator.h
+  __memory/scoped_temporary_buffer.h
   __memory/shared_ptr.h
   __memory/swap_allocator.h
   __memory/temp_value.h

libcxx/include/__algorithm/inplace_merge.h

@@ -24,7 +24,7 @@
 #include <__iterator/iterator_traits.h>
 #include <__iterator/reverse_iterator.h>
 #include <__memory/destruct_n.h>
-#include <__memory/temporary_buffer.h>
+#include <__memory/scoped_temporary_buffer.h>
 #include <__memory/unique_ptr.h>
 #include <__utility/pair.h>
 #include <new>
@@ -211,13 +211,17 @@ _LIBCPP_HIDE_FROM_ABI void __inplace_merge(
   difference_type __len1     = _IterOps<_AlgPolicy>::distance(__first, __middle);
   difference_type __len2     = _IterOps<_AlgPolicy>::distance(__middle, __last);
   difference_type __buf_size = std::min(__len1, __len2);
-  // TODO: Remove the use of std::get_temporary_buffer
-  _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-  pair<value_type*, ptrdiff_t> __buf = std::get_temporary_buffer<value_type>(__buf_size);
-  _LIBCPP_SUPPRESS_DEPRECATED_POP
-  unique_ptr<value_type, __return_temporary_buffer> __h(__buf.first);
+  __scoped_temporary_buffer<value_type> __scoped_buf(__buf_size);
+  __temporary_allocation_result<value_type> __buf_state = __scoped_buf.__get();
   return std::__inplace_merge<_AlgPolicy>(
-      std::move(__first), std::move(__middle), std::move(__last), __comp, __len1, __len2, __buf.first, __buf.second);
+      std::move(__first),
+      std::move(__middle),
+      std::move(__last),
+      __comp,
+      __len1,
+      __len2,
+      __buf_state.__ptr,
+      __buf_state.__count);
 }
 
 template <class _BidirectionalIterator, class _Compare>

libcxx/include/__algorithm/stable_partition.h

@@ -16,7 +16,7 @@
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
 #include <__memory/destruct_n.h>
-#include <__memory/temporary_buffer.h>
+#include <__memory/scoped_temporary_buffer.h>
 #include <__memory/unique_ptr.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
@@ -132,14 +132,13 @@ __stable_partition_impl(_ForwardIterator __first, _ForwardIterator __last, _Pred
   // We now have a reduced range [__first, __last)
   // *__first is known to be false
   difference_type __len = _IterOps<_AlgPolicy>::distance(__first, __last);
+  __scoped_temporary_buffer<value_type> __scoped_buf;
   pair<value_type*, ptrdiff_t> __p(0, 0);
-  unique_ptr<value_type, __return_temporary_buffer> __h;
   if (__len >= __alloc_limit) {
-    // TODO: Remove the use of std::get_temporary_buffer
-    _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-    __p = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
-    __h.reset(__p.first);
+    __scoped_buf.__try_allocate(__len);
+    __temporary_allocation_result<value_type> __buf_state = __scoped_buf.__get();
+    __p.first                                             = __buf_state.__ptr;
+    __p.second                                            = __buf_state.__count;
   }
   return std::__stable_partition_impl<_AlgPolicy, _Predicate&>(
       std::move(__first), std::move(__last), __pred, __len, __p, forward_iterator_tag());
@@ -272,14 +271,13 @@ _LIBCPP_HIDE_FROM_ABI _BidirectionalIterator __stable_partition_impl(
   // *__last is known to be true
   // __len >= 2
   difference_type __len = _IterOps<_AlgPolicy>::distance(__first, __last) + 1;
+  __scoped_temporary_buffer<value_type> __scoped_buf;
   pair<value_type*, ptrdiff_t> __p(0, 0);
-  unique_ptr<value_type, __return_temporary_buffer> __h;
   if (__len >= __alloc_limit) {
-    // TODO: Remove the use of std::get_temporary_buffer
-    _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-    __p = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
-    __h.reset(__p.first);
+    __scoped_buf.__try_allocate(__len);
+    __temporary_allocation_result<value_type> __buf_state = __scoped_buf.__get();
+    __p.first                                             = __buf_state.__ptr;
+    __p.second                                            = __buf_state.__count;
   }
   return std::__stable_partition_impl<_AlgPolicy, _Predicate&>(
       std::move(__first), std::move(__last), __pred, __len, __p, bidirectional_iterator_tag());

libcxx/include/__algorithm/stable_sort.h

@@ -18,7 +18,7 @@
 #include <__debug_utils/strict_weak_ordering_check.h>
 #include <__iterator/iterator_traits.h>
 #include <__memory/destruct_n.h>
-#include <__memory/temporary_buffer.h>
+#include <__memory/scoped_temporary_buffer.h>
 #include <__memory/unique_ptr.h>
 #include <__type_traits/is_trivially_assignable.h>
 #include <__utility/move.h>
@@ -241,14 +241,13 @@ __stable_sort_impl(_RandomAccessIterator __first, _RandomAccessIterator __last,
   using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
 
   difference_type __len = __last - __first;
+  __scoped_temporary_buffer<value_type> __scoped_buf;
   pair<value_type*, ptrdiff_t> __buf(0, 0);
-  unique_ptr<value_type, __return_temporary_buffer> __h;
   if (__len > static_cast<difference_type>(__stable_sort_switch<value_type>::value)) {
-    // TODO: Remove the use of std::get_temporary_buffer
-    _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-    __buf = std::get_temporary_buffer<value_type>(__len);
-    _LIBCPP_SUPPRESS_DEPRECATED_POP
-    __h.reset(__buf.first);
+    __scoped_buf.__try_allocate(__len);
+    __temporary_allocation_result<value_type> __buf_state = __scoped_buf.__get();
+    __buf.first                                           = __buf_state.__ptr;
+    __buf.second                                          = __buf_state.__count;
   }
 
   std::__stable_sort<_AlgPolicy, __comp_ref_type<_Compare> >(__first, __last, __comp, __len, __buf.first, __buf.second);

libcxx/include/__memory/scoped_temporary_buffer.h

@@ -0,0 +1,122 @@
+// -*- 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_SCOPED_TEMPORARY_BUFFER_H
+#define _LIBCPP___MEMORY_SCOPED_TEMPORARY_BUFFER_H
+
+#include <__config>
+#include <__memory/allocator.h>
+#include <__type_traits/is_constant_evaluated.h>
+#include <cstddef>
+#include <new>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Tp>
+struct __temporary_allocation_result {
+  _Tp* __ptr;
+  ptrdiff_t __count;
+};
+
+template <class _Tp>
+class __scoped_temporary_buffer {
+public:
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __scoped_temporary_buffer() _NOEXCEPT
+      : __ptr_(NULL),
+        __count_(0) {}
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 explicit __scoped_temporary_buffer(ptrdiff_t __count) _NOEXCEPT
+      : __ptr_(NULL),
+        __count_(0) {
+    __try_allocate(__count);
+  }
+
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+  // pre: __buf_ptr points to the beginning of a previously allocated scoped temporary buffer or is null
+  // notes: __count_ is ignored in non-constant evaluation
+  _LIBCPP_HIDE_FROM_ABI explicit __scoped_temporary_buffer(_Tp* __buf_ptr) _NOEXCEPT : __ptr_(__buf_ptr), __count_(0) {}
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 ~__scoped_temporary_buffer() _NOEXCEPT {
+    if (__libcpp_is_constant_evaluated()) {
+      allocator<_Tp>().deallocate(__ptr_, __count_);
+    }
+
+    std::__libcpp_deallocate_unsized((void*)__ptr_, _LIBCPP_ALIGNOF(_Tp));
+  }
+
+  __scoped_temporary_buffer(const __scoped_temporary_buffer&)            = delete;
+  __scoped_temporary_buffer& operator=(const __scoped_temporary_buffer&) = delete;
+
+  // pre: __ptr_ == nullptr && __count_ == 0
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __try_allocate(ptrdiff_t __count) _NOEXCEPT {
+    if (__libcpp_is_constant_evaluated()) {
+      __ptr_   = allocator<_Tp>().allocate(__count);
+      __count_ = __count;
+      return;
+    }
+
+    const ptrdiff_t __max_count =
+        (~ptrdiff_t(0) ^ ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1))) / sizeof(_Tp);
+    if (__count > __max_count)
+      __count = __max_count;
+    while (__count > 0) {
+#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
+      if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
+        align_val_t __al = align_val_t(_LIBCPP_ALIGNOF(_Tp));
+        __ptr_           = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), __al, nothrow));
+      } else {
+        __ptr_ = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), nothrow));
+      }
+#else
+      if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
+        // Since aligned operator new is unavailable, constructs an empty buffer rather than one with invalid alignment.
+        return;
+      }
+
+      __ptr_ = static_cast<_Tp*>(::operator new(__count * sizeof(_Tp), nothrow));
+#endif
+
+      if (__ptr_) {
+        __count_ = __count;
+        break;
+      }
+      __count_ /= 2;
+    }
+  }
+
+  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 __temporary_allocation_result<_Tp>
+  __get() const _NOEXCEPT {
+    __temporary_allocation_result<_Tp> __result = {__ptr_, __count_};
+    return __result;
+  }
+
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+  _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI __temporary_allocation_result<_Tp> __release_to_raw() _NOEXCEPT {
+    __temporary_allocation_result<_Tp> __result = {__ptr_, __count_};
+
+    __ptr_   = NULL;
+    __count_ = 0;
+
+    return __result;
+  }
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
+private:
+  _Tp* __ptr_;
+  ptrdiff_t __count_;
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___MEMORY_SCOPED_TEMPORARY_BUFFER_H

libcxx/include/__memory/temporary_buffer.h

@@ -11,6 +11,7 @@
 #define _LIBCPP___MEMORY_TEMPORARY_BUFFER_H
 
 #include <__config>
+#include <__memory/scoped_temporary_buffer.h>
 #include <__utility/pair.h>
 #include <cstddef>
 #include <new>
@@ -19,57 +20,26 @@
 #  pragma GCC system_header
 #endif
 
+#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Tp>
 _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
 get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
-  pair<_Tp*, ptrdiff_t> __r(0, 0);
-  const ptrdiff_t __m =
-      (~ptrdiff_t(0) ^ ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1))) / sizeof(_Tp);
-  if (__n > __m)
-    __n = __m;
-  while (__n > 0) {
-#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
-    if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
-      align_val_t __al = align_val_t(_LIBCPP_ALIGNOF(_Tp));
-      __r.first        = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), __al, nothrow));
-    } else {
-      __r.first = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), nothrow));
-    }
-#else
-    if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp))) {
-      // Since aligned operator new is unavailable, return an empty
-      // buffer rather than one with invalid alignment.
-      return __r;
-    }
-
-    __r.first = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), nothrow));
-#endif
-
-    if (__r.first) {
-      __r.second = __n;
-      break;
-    }
-    __n /= 2;
-  }
-  return __r;
+  __scoped_temporary_buffer<_Tp> __scoped_buf(__n);
+  __temporary_allocation_result<_Tp> __result = __scoped_buf.__release_to_raw();
+  return pair<_Tp*, ptrdiff_t>(__result.__ptr, __result.__count);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 void return_temporary_buffer(_Tp* __p) _NOEXCEPT {
-  std::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
+  __scoped_temporary_buffer<_Tp> __scoped_buf(__p);
+  (void)__scoped_buf;
 }
 
-struct __return_temporary_buffer {
-  _LIBCPP_SUPPRESS_DEPRECATED_PUSH
-  template <class _Tp>
-  _LIBCPP_HIDE_FROM_ABI void operator()(_Tp* __p) const {
-    std::return_temporary_buffer(__p);
-  }
-  _LIBCPP_SUPPRESS_DEPRECATED_POP
-};
-
 _LIBCPP_END_NAMESPACE_STD
 
+#endif // _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER)
+
 #endif // _LIBCPP___MEMORY_TEMPORARY_BUFFER_H

libcxx/include/memory

@@ -182,8 +182,8 @@ public:
     raw_storage_iterator  operator++(int);
 };
 
-template <class T> pair<T*,ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept;
-template <class T> void               return_temporary_buffer(T* p) noexcept;
+template <class T> pair<T*,ptrdiff_t> get_temporary_buffer(ptrdiff_t n) noexcept; // deprecated in C++17, removed in C++20
+template <class T> void               return_temporary_buffer(T* p) noexcept;     // deprecated in C++17, removed in C++20
 
 template <class T> T* addressof(T& r) noexcept;
 template <class T> T* addressof(const T&& r) noexcept = delete;

libcxx/include/module.modulemap

@@ -1532,6 +1532,10 @@ module std_private_memory_ranges_uninitialized_algorithms [system] {
   export std_private_algorithm_in_out_result
 }
 module std_private_memory_raw_storage_iterator            [system] { header "__memory/raw_storage_iterator.h" }
+module std_private_memory_scoped_temporary_buffer         [system] {
+  header "__memory/scoped_temporary_buffer.h"
+  export std_private_type_traits_is_constant_evaluated
+}
 module std_private_memory_shared_ptr                      [system] {
   header "__memory/shared_ptr.h"
   export std_private_memory_uninitialized_algorithms

libcxx/include/syncstream

@@ -358,7 +358,7 @@ private:
   // TODO Use a more generic buffer.
   // That buffer should be light with almost no additional headers. Then
   // it can be use here, the __retarget_buffer, and place that use
-  // the now deprecated get_temporary_buffer
+  // the now removed get_temporary_buffer
 
   basic_string<_CharT, _Traits, _Allocator> __str_;
   bool __emit_on_sync_{false};

libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp

@@ -10,6 +10,7 @@
 
 // check that <memory> functions are marked [[nodiscard]]
 
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
 // ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
 
 // clang-format off