llvm · philnik777 · Jun 4, 2024
@@ -356,7 +356,7 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_modules``                                      ``202207L``
     ---------------------------------------------------------- -----------------
-    ``__cpp_lib_move_only_function``                           *unimplemented*
+    ``__cpp_lib_move_only_function``                           ``202110L``
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_optional``                                     ``202110L``
     ---------------------------------------------------------- -----------------
@@ -530,4 +530,3 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_variant``                                      ``202306L``
     ========================================================== =================
-
@@ -48,6 +48,7 @@ Implemented Papers
 - P2835R7: Expose ``std::atomic_ref``'s object address (`Github <https://llvm.org/PR118377>`__)
 - P2944R3: Comparisons for ``reference_wrapper`` (`Github <https://llvm.org/PR105424>`__)
 - P3168R2: Give ``std::optional`` Range Support (`Github <https://llvm.org/PR105430>`__)
+- P0288R9 - ``move_only_function`` (`Github <https://llvm.org/PR105157>`__)
 
 Improvements and New Features
 -----------------------------

@@ -23,7 +23,7 @@
 "`P2136R3 <https://wg21.link/P2136R3>`__","invoke_r","2021-06 (Virtual)","|Complete|","17","`#105155 <https://github.com/llvm/llvm-project/issues/105155>`__",""
 "`P2166R1 <https://wg21.link/P2166R1>`__","A Proposal to Prohibit std::basic_string and std::basic_string_view construction from nullptr","2021-06 (Virtual)","|Complete|","13","`#105156 <https://github.com/llvm/llvm-project/issues/105156>`__",""
 "","","","","","",""
-"`P0288R9 <https://wg21.link/P0288R9>`__","``any_invocable``","2021-10 (Virtual)","","","`#105157 <https://github.com/llvm/llvm-project/issues/105157>`__",""
+"`P0288R9 <https://wg21.link/P0288R9>`__","``move_only_function``","2021-10 (Virtual)","|Complete|","22","`#105157 <https://github.com/llvm/llvm-project/issues/105157>`__",""
 "`P0798R8 <https://wg21.link/P0798R8>`__","Monadic operations for ``std::optional``","2021-10 (Virtual)","|Complete|","14","`#105158 <https://github.com/llvm/llvm-project/issues/105158>`__",""
 "`P0849R8 <https://wg21.link/P0849R8>`__","``auto(x)``: ``DECAY_COPY`` in the language","2021-10 (Virtual)","|Complete|","14","`#105159 <https://github.com/llvm/llvm-project/issues/105159>`__",""
 "`P1072R10 <https://wg21.link/P1072R10>`__","``basic_string::resize_and_overwrite``","2021-10 (Virtual)","|Complete|","14","`#105160 <https://github.com/llvm/llvm-project/issues/105160>`__",""

@@ -427,6 +427,9 @@ set(files
   __functional/is_transparent.h
   __functional/mem_fn.h
   __functional/mem_fun_ref.h
+  __functional/move_only_function.h
+  __functional/move_only_function_common.h
+  __functional/move_only_function_impl.h
   __functional/not_fn.h
   __functional/operations.h
   __functional/perfect_forward.h

@@ -83,6 +83,7 @@
 #  define _LIBCPP_ABI_USE_WRAP_ITER_IN_STD_ARRAY
 #  define _LIBCPP_ABI_USE_WRAP_ITER_IN_STD_STRING_VIEW
 #  define _LIBCPP_ABI_VARIANT_INDEX_TYPE_OPTIMIZATION
+#  define _LIBCPP_ABI_SMALL_BUFFER_TRIVIAL_ABI
 
 #elif _LIBCPP_ABI_VERSION == 1
 #  if !(defined(_LIBCPP_OBJECT_FORMAT_COFF) || defined(_LIBCPP_OBJECT_FORMAT_XCOFF))

@@ -0,0 +1,97 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FUNCTIONAL_MOVE_ONLY_FUNCTION_H
+#define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 23 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
+
+// move_only_function design:
+//
+// move_only_function has a small buffer with a size of `3 * sizeof(void*)` bytes. This buffer can only be used when the
+// object that should be stored is trivially relocatable (currently only when it is trivially move constructible and
+// trivially destructible). There is also a bool in the lower bits of the vptr stored which is set when the contained
+// object is not trivially destructible.
+//
+// trivially relocatable: It would also be possible to store nothrow_move_constructible types, but that would mean
+// that move_only_function itself would not be trivially relocatable anymore. The decision to keep move_only_function
+// trivially relocatable was made because we expect move_only_function to be mostly used to store a functor. To only
+// forward functors there is C++26's std::function_ref.
+//
+// buffer size: We did a survey of six implementations from various vendors. Three of them had a buffer size of 24 bytes
+// on 64 bit systems. This also allows storing a std::string or std::vector inside the small buffer (once the compiler
+// has full support of trivially_relocatable annotations).
+//
+// trivially-destructible bit: This allows us to keep the overall binary size smaller because we don't have to store
+// a pointer to a noop function inside the vtable. It also avoids loading the vtable during destruction, potentially
+// resulting in fewer cache misses. The downside is that calling the function now also requires setting the lower bits
+// of the pointer to zero, but this is a very fast operation on modern CPUs.
+//
+// interaction with copyable_function: When converting a copyable_function into a move_only_function we want to avoid
+// wrapping the copyable_function inside the move_only_function to avoid a double indirection. Instead, we copy the
+// small buffer and use copyable_function's vtable.
+
+// NOLINTBEGIN(readability-duplicate-include)
+#  define _LIBCPP_IN_MOVE_ONLY_FUNCTION_H
+
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &
+#  include <__functional/move_only_function_impl.h>
+
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_NOEXCEPT true
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_CV const
+#  define _LIBCPP_MOVE_ONLY_FUNCTION_REF &&
+#  include <__functional/move_only_function_impl.h>
+
+#  undef _LIBCPP_IN_MOVE_ONLY_FUNCTION_H
+// NOLINTEND(readability-duplicate-include)
+
+#endif // _LIBCPP_STD_VER >= 23 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
+
+#endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_H
@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H
+#define _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H
+
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class...>
+class move_only_function;
+
+template <class>
+inline constexpr bool __is_move_only_function_v = false;
+
+template <class... _Args>
+inline constexpr bool __is_move_only_function_v<move_only_function<_Args...>> = true;
+
+template <class _BufferT, class _ReturnT, class... _ArgTypes>
+struct _MoveOnlyFunctionVTable {
+  using _CallFunc = _ReturnT(_BufferT&, _ArgTypes...);
+  using _DestroyFunc = void(_BufferT&) noexcept;
+
+  _CallFunc* __call_;
+  _DestroyFunc* __destroy_;
+};
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___FUNCTIONAL_MOVE_ONLY_FUNCTION_COMMON_H