[libc++] <experimental/simd> Add swap functions of simd reference (#86478)

libcxx/docs/Status/ParallelismProjects.csv

@@ -16,6 +16,7 @@ Section,Description,Dependencies,Assignee,Complete
 | `[parallel.simd.whereexpr] <https://wg21.link/N4808>`_, "Where expression class templates", None, Yin Zhang, |In Progress|
 | `[parallel.simd.reference] <https://wg21.link/N4808>`_, "`Element references operator value_type() <https://github.com/llvm/llvm-project/pull/68960>`_", None, Yin Zhang, |Complete|
 | `[parallel.simd.reference] <https://wg21.link/N4808>`_, "`Element references operator= <https://github.com/llvm/llvm-project/pull/70020>`_", None, Yin Zhang, |Complete|
+| `[parallel.simd.reference] <https://wg21.link/N4808>`_, "`Element references swap functions <https://github.com/llvm/llvm-project/pull/86478>`_", None, Yin Zhang, |Complete|
 | `[parallel.simd.class] <https://wg21.link/N4808>`_, "`Class template simd declaration and alias <https://reviews.llvm.org/D144362>`_", [parallel.simd.abi], Yin Zhang, |Complete|
 | `[parallel.simd.class] <https://wg21.link/N4808>`_, "`simd<>::size() <https://reviews.llvm.org/D144363>`_", [parallel.simd.traits] simd_size[_v], Yin Zhang, |Complete|
 | `[parallel.simd.class] <https://wg21.link/N4808>`_, "`simd default constructor <https://github.com/llvm/llvm-project/pull/70424>`_", None, Yin Zhang, |Complete|

libcxx/include/experimental/__simd/reference.h

@@ -13,10 +13,14 @@
 #include <__type_traits/is_assignable.h>
 #include <__type_traits/is_same.h>
 #include <__utility/forward.h>
+#include <__utility/move.h>
 #include <cstddef>
 #include <experimental/__config>
 #include <experimental/__simd/utility.h>
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 #if _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
 
 _LIBCPP_BEGIN_NAMESPACE_EXPERIMENTAL
@@ -55,10 +59,47 @@ public:
     __set(static_cast<value_type>(std::forward<_Up>(__v)));
     return {__s_, __idx_};
   }
+
+  // Note: This approach might not fully align with the specification,
+  // which might be a wording defect. (https://wg21.link/N4808 section 9.6.3)
+  template <class _Tp1, class _Storage1, class _Vp1>
+  friend void
+  swap(__simd_reference<_Tp1, _Storage1, _Vp1>&& __a, __simd_reference<_Tp1, _Storage1, _Vp1>&& __b) noexcept;
+
+  template <class _Tp1, class _Storage1, class _Vp1>
+  friend void swap(_Vp1& __a, __simd_reference<_Tp1, _Storage1, _Vp1>&& __b) noexcept;
+
+  template <class _Tp1, class _Storage1, class _Vp1>
+  friend void swap(__simd_reference<_Tp1, _Storage1, _Vp1>&& __a, _Vp1& __b) noexcept;
 };
 
+template <class _Tp, class _Storage, class _Vp>
+_LIBCPP_HIDE_FROM_ABI void
+swap(__simd_reference<_Tp, _Storage, _Vp>&& __a, __simd_reference<_Tp, _Storage, _Vp>&& __b) noexcept {
+  _Vp __tmp(std::move(__a));
+  std::move(__a) = std::move(__b);
+  std::move(__b) = std::move(__tmp);
+}
+
+template <class _Tp, class _Storage, class _Vp>
+_LIBCPP_HIDE_FROM_ABI void swap(_Vp& __a, __simd_reference<_Tp, _Storage, _Vp>&& __b) noexcept {
+  _Vp __tmp(std::move(__a));
+  __a            = std::move(__b);
+  std::move(__b) = std::move(__tmp);
+}
+
+template <class _Tp, class _Storage, class _Vp>
+_LIBCPP_HIDE_FROM_ABI void swap(__simd_reference<_Tp, _Storage, _Vp>&& __a, _Vp& __b) noexcept {
+  _Vp __tmp(std::move(__a));
+  std::move(__a) = std::move(__b);
+  __b            = std::move(__tmp);
+}
+
 } // namespace parallelism_v2
 _LIBCPP_END_NAMESPACE_EXPERIMENTAL
 
 #endif // _LIBCPP_STD_VER >= 17 && defined(_LIBCPP_ENABLE_EXPERIMENTAL)
+
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP_EXPERIMENTAL___SIMD_REFERENCE_H

libcxx/include/experimental/simd

@@ -78,6 +78,7 @@ inline namespace parallelism_v2 {
 #include <experimental/__config>
 #include <experimental/__simd/aligned_tag.h>
 #include <experimental/__simd/declaration.h>
+#include <experimental/__simd/reference.h>
 #include <experimental/__simd/scalar.h>
 #include <experimental/__simd/simd.h>
 #include <experimental/__simd/simd_mask.h>

libcxx/test/std/experimental/simd/simd.reference/reference_swap.pass.cpp

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+
+// <experimental/simd>
+//
+// Note: To ensure the swap functions can be called directly in the std::experimental namespace,
+// the implementation approach might not fully align with the specification.
+//
+// [simd.reference]
+// friend void swap(reference&& a, reference&& b) noexcept;
+// friend void swap(value_type& a, reference&& b) noexcept;
+// friend void swap(reference&& a, value_type& b) noexcept;
+
+#include "../test_utils.h"
+#include <experimental/simd>
+
+namespace ex = std::experimental::parallelism_v2;
+
+template <class T, std::size_t>
+struct CheckSimdRefSwap {
+  template <class SimdAbi>
+  void operator()() {
+    ex::simd<T, SimdAbi> origin_simd_1(1);
+    ex::simd<T, SimdAbi> origin_simd_2(2);
+    T value = 3;
+
+    static_assert(noexcept(ex::swap(std::move(origin_simd_1[0]), std::move(origin_simd_2[0]))));
+    ex::swap(std::move(origin_simd_1[0]), std::move(origin_simd_2[0]));
+    assert((origin_simd_1[0] == 2) && (origin_simd_2[0] == 1));
+
+    static_assert(noexcept(ex::swap(std::move(origin_simd_1[0]), value)));
+    ex::swap(std::move(origin_simd_1[0]), value);
+    assert((origin_simd_1[0] == 3) && (value == 2));
+
+    static_assert(noexcept(ex::swap(value, std::move(origin_simd_2[0]))));
+    ex::swap(value, std::move(origin_simd_2[0]));
+    assert((value == 1) && (origin_simd_2[0] == 2));
+  }
+};
+
+template <class T, std::size_t>
+struct CheckMaskRefSwap {
+  template <class SimdAbi>
+  void operator()() {
+    ex::simd_mask<T, SimdAbi> origin_mask_1(true);
+    ex::simd_mask<T, SimdAbi> origin_mask_2(false);
+    bool value = true;
+
+    static_assert(noexcept(ex::swap(std::move(origin_mask_1[0]), std::move(origin_mask_2[0]))));
+    ex::swap(std::move(origin_mask_1[0]), std::move(origin_mask_2[0]));
+    assert((origin_mask_1[0] == false) && (origin_mask_2[0] == true));
+
+    static_assert(noexcept(ex::swap(std::move(origin_mask_1[0]), value)));
+    ex::swap(std::move(origin_mask_1[0]), value);
+    assert((origin_mask_1[0] == true) && (value == false));
+
+    static_assert(noexcept(ex::swap(value, std::move(origin_mask_2[0]))));
+    ex::swap(value, std::move(origin_mask_2[0]));
+    assert((value == true) && (origin_mask_2[0] == false));
+  }
+};
+
+int main(int, char**) {
+  test_all_simd_abi<CheckSimdRefSwap>();
+  test_all_simd_abi<CheckMaskRefSwap>();
+  return 0;
+}