[libcxx-commits] [libcxx] [libc++][PSTL] Add backend for forwaring to mem functions (PR #102448)

[via libcxx-commits]

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@@ -0,0 +1,94 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___PSTL_BACKENDS_FORWARD_TO_MEM_FUNCS_H
+#define _LIBCPP___PSTL_BACKENDS_FORWARD_TO_MEM_FUNCS_H
+
+#include <__algorithm/copy_move_common.h>
+#include <__algorithm/equal.h>
+#include <__config>
+#include <__pstl/backend_fwd.h>
+#include <__pstl/dispatch.h>
+#include <optional>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+namespace __pstl {
+
+template <class _ExecutionPolicy>
+struct __copy<__forward_to_mem_funcs_backend_tag, _ExecutionPolicy> {
+  template <class _Policy,
+            class _In,
+            class _Out,
+            enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_Out*>
+  operator()(_Policy&&, _In* __first, _In* __last, _Out* __result) const noexcept {
+    return std::__constexpr_memmove(__result, __first, __element_count(__last - __first));
+  }
+};
+
+template <class _ExecutionPolicy>
+struct __copy_n<__forward_to_mem_funcs_backend_tag, _ExecutionPolicy> {
+  template <class _Policy,
+            class _In,
+            class _Size,
+            class _Out,
+            enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_Out*>
+  operator()(_Policy&&, _In* __first, _Size __n, _Out* __result) const noexcept {
+    return std::__constexpr_memmove(__result, __first, __element_count(__n));
+  }
+};
+
+template <class _ExecutionPolicy>
+struct __move<__forward_to_mem_funcs_backend_tag, _ExecutionPolicy> {
+  template <class _Policy,
+            class _In,
+            class _Out,
+            enable_if_t<__can_lower_move_assignment_to_memmove<_In, _Out>::value, int> = 0>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_Out*>
+  operator()(_Policy&&, _In* __first, _In* __last, _Out* __result) const noexcept {
+    return std::__constexpr_memmove(__result, __first, __element_count(__last - __first));
+  }
+};
+
+template <class _ExecutionPolicy>
+struct __equal<__forward_to_mem_funcs_backend_tag, _ExecutionPolicy> {
+  template <class _Policy,
+            class _Tp,
+            class _Up,
+            class _Pred,
+            enable_if_t<__can_lower_to_memcmp_equal<_Tp, _Up, _Pred, __identity, __identity>, int> = 0>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<bool>
+  operator()(_Policy&&, _Tp* __first1, _Tp* __last1, _Up* __first2, _Up* __last2) const noexcept {
+    if (__last2 - __first2 != __last1 - __first2)
+      return false;
+    return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
+  }
+};
+
+template <class _ExecutionPolicy>
+struct __equal_3leg<__forward_to_mem_funcs_backend_tag, _ExecutionPolicy> {
+  template <class _Policy,
+            class _Tp,
+            class _Up,
+            class _Pred,
+            enable_if_t<__can_lower_to_memcmp_equal<_Tp, _Up, _Pred, __identity, __identity>, int> = 0>
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<bool>
+  operator()(_Policy&&, _Tp* __first1, _Tp* __last1, _Up* __first2) const noexcept {
+    return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first2));
----------------
strncmp wrote:

Like above, shouldn't the size of `memcmp` be `__element_count(__last1 - __first1)`? What would the subtraction of two potentially foreign pointers yield?

https://github.com/llvm/llvm-project/pull/102448