[libc++] Add the C++17 <memory_resource> header (mono-patch)

This patch is the rebase and squash of three earlier patches.
It supersedes all three of them.

- D47111: experimental monotonic_buffer_resource.
- D47358: experimental pool resources.
- D47360: Copy std::experimental::pmr to std::pmr.

The significant difference between this patch and the-sum-of-those-three
is that this patch does not add `std::experimental::pmr::monotonic_buffer_resource`
and so on. This patch simply adds the C++17 standard facilities, and
leaves the `std::experimental` namespace entirely alone.

Differential Revision: https://reviews.llvm.org/D89057

libcxx/docs/FeatureTestMacroTable.rst

@@ -126,7 +126,7 @@ Status
     ------------------------------------------------- -----------------
     ``__cpp_lib_math_special_functions``              *unimplemented*
     ------------------------------------------------- -----------------
-    ``__cpp_lib_memory_resource``                     *unimplemented*
+    ``__cpp_lib_memory_resource``                     ``201603L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_node_extract``                        ``201606L``
     ------------------------------------------------- -----------------

libcxx/docs/ReleaseNotes.rst

@@ -48,6 +48,7 @@ Improvements and New Features
 - Declarations of ``std::c8rtomb()`` and ``std::mbrtoc8()`` from P0482R6 are
   now provided when implementations in the global namespace are provided by
   the C library.
+- Implemented ``<memory_resource>`` header from C++17
 
 Deprecations and Removals
 -------------------------

libcxx/include/CMakeLists.txt

@@ -414,6 +414,12 @@ set(files
   __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
+  __memory_resource/pool_options.h
+  __memory_resource/synchronized_pool_resource.h
+  __memory_resource/unsynchronized_pool_resource.h
   __mutex_base
   __node_handle
   __numeric/accumulate.h
@@ -776,6 +782,7 @@ set(files
   map
   math.h
   memory
+  memory_resource
   mutex
   new
   numbers

libcxx/include/__memory_resource/memory_resource.h

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_RESOURCE_MEMORY_RESOURCE_H
+#define _LIBCPP___MEMORY_RESOURCE_MEMORY_RESOURCE_H
+
+#include <__config>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace pmr {
+
+// [mem.res.class]
+
+_LIBCPP_DIAGNOSTIC_PUSH
+_LIBCPP_CLANG_DIAGNOSTIC_IGNORED("-Wweak-vtables") // TODO: move destructor into the dylib
+class _LIBCPP_TYPE_VIS memory_resource {
+  static const size_t __max_align = alignof(max_align_t);
+
+public:
+  virtual ~memory_resource() = default;
+
+  _LIBCPP_HIDE_FROM_ABI void* allocate(size_t __bytes, size_t __align = __max_align) {
+    return do_allocate(__bytes, __align);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI void deallocate(void* __p, size_t __bytes, size_t __align = __max_align) {
+    do_deallocate(__p, __bytes, __align);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI bool is_equal(const memory_resource& __other) const noexcept { return do_is_equal(__other); }
+
+private:
+  virtual void* do_allocate(size_t, size_t)                       = 0;
+  virtual void do_deallocate(void*, size_t, size_t)               = 0;
+  virtual bool do_is_equal(memory_resource const&) const noexcept = 0;
+};
+_LIBCPP_DIAGNOSTIC_POP
+
+// [mem.res.eq]
+
+inline _LIBCPP_HIDE_FROM_ABI bool operator==(const memory_resource& __lhs, const memory_resource& __rhs) noexcept {
+  return &__lhs == &__rhs || __lhs.is_equal(__rhs);
+}
+
+inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const memory_resource& __lhs, const memory_resource& __rhs) noexcept {
+  return !(__lhs == __rhs);
+}
+
+// [mem.res.global]
+
+_LIBCPP_FUNC_VIS memory_resource* get_default_resource() noexcept;
+
+_LIBCPP_FUNC_VIS memory_resource* set_default_resource(memory_resource*) noexcept;
+
+_LIBCPP_FUNC_VIS memory_resource* new_delete_resource() noexcept;
+
+_LIBCPP_FUNC_VIS memory_resource* null_memory_resource() noexcept;
+
+} // namespace pmr
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 14
+
+#endif // _LIBCPP___MEMORY_RESOURCE_MEMORY_RESOURCE_H

libcxx/include/__memory_resource/monotonic_buffer_resource.h

@@ -0,0 +1,119 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
+#define _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H
+
+#include <__config>
+#include <__memory/addressof.h>
+#include <__memory_resource/memory_resource.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER > 14
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace pmr {
+
+// [mem.res.monotonic.buffer]
+
+class _LIBCPP_TYPE_VIS monotonic_buffer_resource : public memory_resource {
+  static const size_t __default_buffer_capacity  = 1024;
+  static const size_t __default_buffer_alignment = 16;
+
+  struct __chunk_footer {
+    __chunk_footer* __next_;
+    char* __start_;
+    char* __cur_;
+    size_t __align_;
+    size_t __allocation_size() { return (reinterpret_cast<char*>(this) - __start_) + sizeof(*this); }
+    void* __try_allocate_from_chunk(size_t, size_t);
+  };
+
+  struct __initial_descriptor {
+    char* __start_;
+    char* __cur_;
+    union {
+      char* __end_;
+      size_t __size_;
+    };
+    void* __try_allocate_from_chunk(size_t, size_t);
+  };
+
+public:
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource()
+      : monotonic_buffer_resource(nullptr, __default_buffer_capacity, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(size_t __initial_size)
+      : monotonic_buffer_resource(nullptr, __initial_size, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size)
+      : monotonic_buffer_resource(__buffer, __buffer_size, get_default_resource()) {}
+
+  _LIBCPP_HIDE_FROM_ABI explicit monotonic_buffer_resource(memory_resource* __upstream)
+      : monotonic_buffer_resource(nullptr, __default_buffer_capacity, __upstream) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(size_t __initial_size, memory_resource* __upstream)
+      : monotonic_buffer_resource(nullptr, __initial_size, __upstream) {}
+
+  _LIBCPP_HIDE_FROM_ABI monotonic_buffer_resource(void* __buffer, size_t __buffer_size, memory_resource* __upstream)
+      : __res_(__upstream) {
+    __initial_.__start_ = static_cast<char*>(__buffer);
+    if (__buffer != nullptr) {
+      __initial_.__cur_ = static_cast<char*>(__buffer);
+      __initial_.__end_ = static_cast<char*>(__buffer) + __buffer_size;
+    } else {
+      __initial_.__cur_  = nullptr;
+      __initial_.__size_ = __buffer_size;
+    }
+    __chunks_ = nullptr;
+  }
+
+  monotonic_buffer_resource(const monotonic_buffer_resource&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI ~monotonic_buffer_resource() override { release(); }
+
+  monotonic_buffer_resource& operator=(const monotonic_buffer_resource&) = delete;
+
+  _LIBCPP_HIDE_FROM_ABI void release() {
+    __initial_.__cur_ = __initial_.__start_;
+    while (__chunks_ != nullptr) {
+      __chunk_footer* __next = __chunks_->__next_;
+      __res_->deallocate(__chunks_->__start_, __chunks_->__allocation_size(), __chunks_->__align_);
+      __chunks_ = __next;
+    }
+  }
+
+  _LIBCPP_HIDE_FROM_ABI memory_resource* upstream_resource() const { return __res_; }
+
+protected:
+  void* do_allocate(size_t __bytes, size_t __alignment) override; // key function
+
+  _LIBCPP_HIDE_FROM_ABI void do_deallocate(void*, size_t, size_t) override {}
+
+  _LIBCPP_HIDE_FROM_ABI bool do_is_equal(const memory_resource& __other) const _NOEXCEPT override {
+    return this == std::addressof(__other);
+  }
+
+private:
+  __initial_descriptor __initial_;
+  __chunk_footer* __chunks_;
+  memory_resource* __res_;
+};
+
+} // namespace pmr
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER > 14
+
+#endif // _LIBCPP___MEMORY_RESOURCE_MONOTONIC_BUFFER_RESOURCE_H