[libc++][pstl] Merge all frontend functions for the PSTL (#89219)

This is an intermediate step towards the PSTL dispatching mechanism
rework. It will make it a lot easier to track the upcoming front-end
changes. After the rework, there are basically no implementation details
in the front-end, so the definition of each algorithm will become much
simpler. Otherwise, it wouldn't make sense to define all the algorithms
in the same header.

2 files changed, 80 insertions, 115 deletions

diff --git a/libcxx/include/__numeric/pstl_transform_reduce.h b/libcxx/include/__numeric/pstl.h
index fe41b1c..05559b4 100644
--- a/libcxx/include/__numeric/pstl_transform_reduce.h
+++ b/libcxx/include/__numeric/pstl.h
@@ -6,13 +6,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef _LIBCPP___NUMERIC_PSTL_TRANSFORM_REDUCE_H
-#define _LIBCPP___NUMERIC_PSTL_TRANSFORM_REDUCE_H
+#ifndef _LIBCPP___NUMERIC_PSTL_H
+#define _LIBCPP___NUMERIC_PSTL_H
 
 #include <__algorithm/pstl_frontend_dispatch.h>
 #include <__config>
+#include <__functional/identity.h>
 #include <__functional/operations.h>
 #include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
 #include <__numeric/transform_reduce.h>
 #include <__pstl/configuration.h>
 #include <__type_traits/is_execution_policy.h>
@@ -153,10 +155,85 @@ _LIBCPP_HIDE_FROM_ABI _Tp transform_reduce(
   return *std::move(__res);
 }
 
+template <class>
+void __pstl_reduce();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _BinaryOperation                              = plus<>,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_Tp>
+__reduce(_ExecutionPolicy&& __policy,
+         _ForwardIterator&& __first,
+         _ForwardIterator&& __last,
+         _Tp&& __init,
+         _BinaryOperation&& __op = {}) noexcept {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_reduce, _RawPolicy),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Tp __g_init, _BinaryOperation __g_op) {
+        return std::__transform_reduce(
+            __policy, std::move(__g_first), std::move(__g_last), std::move(__g_init), std::move(__g_op), __identity{});
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__init),
+      std::move(__op));
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _BinaryOperation                              = plus<>,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+reduce(_ExecutionPolicy&& __policy,
+       _ForwardIterator __first,
+       _ForwardIterator __last,
+       _Tp __init,
+       _BinaryOperation __op = {}) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "reduce requires ForwardIterators");
+  auto __res = std::__reduce(__policy, std::move(__first), std::move(__last), std::move(__init), std::move(__op));
+  if (!__res)
+    std::__throw_bad_alloc();
+  return *std::move(__res);
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<__iter_value_type<_ForwardIterator>>
+__reduce(_ExecutionPolicy&& __policy, _ForwardIterator&& __first, _ForwardIterator&& __last) noexcept {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_reduce, _RawPolicy),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last) {
+        return std::__reduce(
+            __policy, std::move(__g_first), std::move(__g_last), __iter_value_type<_ForwardIterator>());
+      },
+      std::move(__first),
+      std::move(__last));
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI __iter_value_type<_ForwardIterator>
+reduce(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "reduce requires ForwardIterators");
+  auto __res = std::__reduce(__policy, std::move(__first), std::move(__last));
+  if (!__res)
+    std::__throw_bad_alloc();
+  return *std::move(__res);
+}
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
 
 _LIBCPP_POP_MACROS
 
-#endif // _LIBCPP___NUMERIC_PSTL_TRANSFORM_REDUCE_H
+#endif // _LIBCPP___NUMERIC_PSTL_H
diff --git a/libcxx/include/__numeric/pstl_reduce.h b/libcxx/include/__numeric/pstl_reduce.h
deleted file mode 100644
index d678b94..0000000
--- a/libcxx/include/__numeric/pstl_reduce.h
+++ /dev/null
@@ -1,112 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// 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___NUMERIC_PSTL_REDUCE_H
-#define _LIBCPP___NUMERIC_PSTL_REDUCE_H
-
-#include <__algorithm/pstl_frontend_dispatch.h>
-#include <__config>
-#include <__functional/identity.h>
-#include <__iterator/cpp17_iterator_concepts.h>
-#include <__iterator/iterator_traits.h>
-#include <__numeric/pstl_transform_reduce.h>
-#include <__type_traits/is_execution_policy.h>
-
-#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
-#  pragma GCC system_header
-#endif
-
-_LIBCPP_PUSH_MACROS
-#include <__undef_macros>
-
-#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
-
-_LIBCPP_BEGIN_NAMESPACE_STD
-
-template <class>
-void __pstl_reduce();
-
-template <class _ExecutionPolicy,
-          class _ForwardIterator,
-          class _Tp,
-          class _BinaryOperation                              = plus<>,
-          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
-          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<_Tp>
-__reduce(_ExecutionPolicy&& __policy,
-         _ForwardIterator&& __first,
-         _ForwardIterator&& __last,
-         _Tp&& __init,
-         _BinaryOperation&& __op = {}) noexcept {
-  return std::__pstl_frontend_dispatch(
-      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_reduce, _RawPolicy),
-      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Tp __g_init, _BinaryOperation __g_op) {
-        return std::__transform_reduce(
-            __policy, std::move(__g_first), std::move(__g_last), std::move(__g_init), std::move(__g_op), __identity{});
-      },
-      std::move(__first),
-      std::move(__last),
-      std::move(__init),
-      std::move(__op));
-}
-
-template <class _ExecutionPolicy,
-          class _ForwardIterator,
-          class _Tp,
-          class _BinaryOperation                              = plus<>,
-          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
-          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI _Tp
-reduce(_ExecutionPolicy&& __policy,
-       _ForwardIterator __first,
-       _ForwardIterator __last,
-       _Tp __init,
-       _BinaryOperation __op = {}) {
-  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "reduce requires ForwardIterators");
-  auto __res = std::__reduce(__policy, std::move(__first), std::move(__last), std::move(__init), std::move(__op));
-  if (!__res)
-    std::__throw_bad_alloc();
-  return *std::move(__res);
-}
-
-template <class _ExecutionPolicy,
-          class _ForwardIterator,
-          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
-          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<__iter_value_type<_ForwardIterator>>
-__reduce(_ExecutionPolicy&& __policy, _ForwardIterator&& __first, _ForwardIterator&& __last) noexcept {
-  return std::__pstl_frontend_dispatch(
-      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_reduce, _RawPolicy),
-      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last) {
-        return std::__reduce(
-            __policy, std::move(__g_first), std::move(__g_last), __iter_value_type<_ForwardIterator>());
-      },
-      std::move(__first),
-      std::move(__last));
-}
-
-template <class _ExecutionPolicy,
-          class _ForwardIterator,
-          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
-          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-_LIBCPP_HIDE_FROM_ABI __iter_value_type<_ForwardIterator>
-reduce(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last) {
-  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator, "reduce requires ForwardIterators");
-  auto __res = std::__reduce(__policy, std::move(__first), std::move(__last));
-  if (!__res)
-    std::__throw_bad_alloc();
-  return *std::move(__res);
-}
-
-_LIBCPP_END_NAMESPACE_STD
-
-#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
-
-_LIBCPP_POP_MACROS
-
-#endif // _LIBCPP___NUMERIC_PSTL_REDUCE_H