[libc++] Refactor ranges::{min, max, min_element, max_element} to use std::__min_element (#132418)

Previously, ranges::min_element delegated to ranges::__min_element_impl, which
duplicated the definition of std::__min_element. This patch updates
ranges::min_element to directly call std::__min_element, which allows
removing the redundant code in ranges::__min_element_impl.

Upon removal of ranges::__min_element_impl, the other ranges algorithms
ranges::{min,max,max_element}, which previously delegated to ranges::__min_element_impl,
have been updated to call std::__min_element instead.

This refactoring unifies the implementation across these algorithms,
ensuring that future optimizations or maintenance work only need to be
applied in one place.

Author: winner245

libcxx/include/__algorithm/min_element.h

@@ -29,7 +29,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Comp, class _Iter, class _Sent, class _Proj>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iter
-__min_element(_Iter __first, _Sent __last, _Comp __comp, _Proj& __proj) {
+__min_element(_Iter __first, _Sent __last, _Comp& __comp, _Proj& __proj) {
   if (__first == __last)
     return __first;
 

libcxx/include/__algorithm/ranges_max.h

@@ -9,7 +9,7 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_MAX_H
 #define _LIBCPP___ALGORITHM_RANGES_MAX_H
 
-#include <__algorithm/ranges_min_element.h>
+#include <__algorithm/min_element.h>
 #include <__assert>
 #include <__concepts/copyable.h>
 #include <__config>
@@ -57,7 +57,7 @@ struct __max {
         __il.begin() != __il.end(), "initializer_list must contain at least one element");
 
     auto __comp_lhs_rhs_swapped = [&](auto&& __lhs, auto&& __rhs) -> bool { return std::invoke(__comp, __rhs, __lhs); };
-    return *ranges::__min_element_impl(__il.begin(), __il.end(), __comp_lhs_rhs_swapped, __proj);
+    return *std::__min_element(__il.begin(), __il.end(), __comp_lhs_rhs_swapped, __proj);
   }
 
   template <input_range _Rp,
@@ -75,7 +75,7 @@ struct __max {
       auto __comp_lhs_rhs_swapped = [&](auto&& __lhs, auto&& __rhs) -> bool {
         return std::invoke(__comp, __rhs, __lhs);
       };
-      return *ranges::__min_element_impl(std::move(__first), std::move(__last), __comp_lhs_rhs_swapped, __proj);
+      return *std::__min_element(std::move(__first), std::move(__last), __comp_lhs_rhs_swapped, __proj);
     } else {
       range_value_t<_Rp> __result = *__first;
       while (++__first != __last) {

libcxx/include/__algorithm/ranges_max_element.h

@@ -9,7 +9,7 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_MAX_ELEMENT_H
 #define _LIBCPP___ALGORITHM_RANGES_MAX_ELEMENT_H
 
-#include <__algorithm/ranges_min_element.h>
+#include <__algorithm/min_element.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
@@ -40,7 +40,7 @@ struct __max_element {
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip
   operator()(_Ip __first, _Sp __last, _Comp __comp = {}, _Proj __proj = {}) const {
     auto __comp_lhs_rhs_swapped = [&](auto&& __lhs, auto&& __rhs) -> bool { return std::invoke(__comp, __rhs, __lhs); };
-    return ranges::__min_element_impl(__first, __last, __comp_lhs_rhs_swapped, __proj);
+    return std::__min_element(__first, __last, __comp_lhs_rhs_swapped, __proj);
   }
 
   template <forward_range _Rp,
@@ -49,7 +49,7 @@ struct __max_element {
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Rp>
   operator()(_Rp&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
     auto __comp_lhs_rhs_swapped = [&](auto&& __lhs, auto&& __rhs) -> bool { return std::invoke(__comp, __rhs, __lhs); };
-    return ranges::__min_element_impl(ranges::begin(__r), ranges::end(__r), __comp_lhs_rhs_swapped, __proj);
+    return std::__min_element(ranges::begin(__r), ranges::end(__r), __comp_lhs_rhs_swapped, __proj);
   }
 };
 

libcxx/include/__algorithm/ranges_min.h

@@ -9,7 +9,7 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_MIN_H
 #define _LIBCPP___ALGORITHM_RANGES_MIN_H
 
-#include <__algorithm/ranges_min_element.h>
+#include <__algorithm/min_element.h>
 #include <__assert>
 #include <__concepts/copyable.h>
 #include <__config>
@@ -54,7 +54,7 @@ struct __min {
   operator()(initializer_list<_Tp> __il, _Comp __comp = {}, _Proj __proj = {}) const {
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
         __il.begin() != __il.end(), "initializer_list must contain at least one element");
-    return *ranges::__min_element_impl(__il.begin(), __il.end(), __comp, __proj);
+    return *std::__min_element(__il.begin(), __il.end(), __comp, __proj);
   }
 
   template <input_range _Rp,
@@ -67,7 +67,7 @@ struct __min {
     auto __last  = ranges::end(__r);
     _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__first != __last, "range must contain at least one element");
     if constexpr (forward_range<_Rp> && !__is_cheap_to_copy<range_value_t<_Rp>>) {
-      return *ranges::__min_element_impl(__first, __last, __comp, __proj);
+      return *std::__min_element(__first, __last, __comp, __proj);
     } else {
       range_value_t<_Rp> __result = *__first;
       while (++__first != __last) {

libcxx/include/__algorithm/ranges_min_element.h

@@ -9,6 +9,7 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_MIN_ELEMENT_H
 #define _LIBCPP___ALGORITHM_RANGES_MIN_ELEMENT_H
 
+#include <__algorithm/min_element.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
@@ -32,36 +33,22 @@ _LIBCPP_PUSH_MACROS
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
-
-// TODO(ranges): `ranges::min_element` can now simply delegate to `std::__min_element`.
-template <class _Ip, class _Sp, class _Proj, class _Comp>
-_LIBCPP_HIDE_FROM_ABI constexpr _Ip __min_element_impl(_Ip __first, _Sp __last, _Comp& __comp, _Proj& __proj) {
-  if (__first == __last)
-    return __first;
-
-  _Ip __i = __first;
-  while (++__i != __last)
-    if (std::invoke(__comp, std::invoke(__proj, *__i), std::invoke(__proj, *__first)))
-      __first = __i;
-  return __first;
-}
-
 struct __min_element {
   template <forward_iterator _Ip,
             sentinel_for<_Ip> _Sp,
             class _Proj                                             = identity,
             indirect_strict_weak_order<projected<_Ip, _Proj>> _Comp = ranges::less>
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr _Ip
   operator()(_Ip __first, _Sp __last, _Comp __comp = {}, _Proj __proj = {}) const {
-    return ranges::__min_element_impl(__first, __last, __comp, __proj);
+    return std::__min_element(__first, __last, __comp, __proj);
   }
 
   template <forward_range _Rp,
             class _Proj                                                         = identity,
             indirect_strict_weak_order<projected<iterator_t<_Rp>, _Proj>> _Comp = ranges::less>
   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Rp>
   operator()(_Rp&& __r, _Comp __comp = {}, _Proj __proj = {}) const {
-    return ranges::__min_element_impl(ranges::begin(__r), ranges::end(__r), __comp, __proj);
+    return std::__min_element(ranges::begin(__r), ranges::end(__r), __comp, __proj);
   }
 };