[libcxx-commits] [libcxx] [libc++] Overhaul the PSTL dispatching mechanism (PR #88131)

[Louis Dionne via libcxx-commits]

================
@@ -509,67 +151,31 @@ equal(_ExecutionPolicy&& __policy,
       _Pred __pred) {
   _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator1, "equal requires ForwardIterators");
   _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator2, "equal requires ForwardIterators");
-  auto __res = std::__equal(__policy, std::move(__first1), std::move(__last1), std::move(__first2), std::move(__pred));
-  if (!__res)
-    std::__throw_bad_alloc();
-  return *__res;
+  using _Implementation = __pstl::__dispatch<__pstl::__equal_3leg, __pstl::__current_configuration, _RawPolicy>;
+  return __pstl::__handle_exception<_Implementation>(
+      std::forward<_ExecutionPolicy>(__policy),
+      std::move(__first1),
+      std::move(__last1),
+      std::move(__first2),
+      std::move(__pred));
 }
 
 template <class _ExecutionPolicy,
           class _ForwardIterator1,
           class _ForwardIterator2,
-          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
 _LIBCPP_HIDE_FROM_ABI bool
 equal(_ExecutionPolicy&& __policy, _ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2) {
   _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator1, "equal requires ForwardIterators");
   _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator2, "equal requires ForwardIterators");
-  auto __res = std::__equal(__policy, std::move(__first1), std::move(__last1), std::move(__first2), std::equal_to{});
-  if (!__res)
-    std::__throw_bad_alloc();
-  return *__res;
-}
-
-template <class _ExecutionPolicy,
-          class _ForwardIterator1,
-          class _ForwardIterator2,
-          class _Pred,
-          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
-          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
-[[nodiscard]] _LIBCPP_HIDE_FROM_ABI optional<bool>
-__equal(_ExecutionPolicy&& __policy,
-        _ForwardIterator1&& __first1,
-        _ForwardIterator1&& __last1,
-        _ForwardIterator2&& __first2,
-        _ForwardIterator2&& __last2,
-        _Pred&& __pred) noexcept {
-  return std::__pstl_frontend_dispatch(
-      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_equal, _RawPolicy),
-      [&__policy](_ForwardIterator1 __g_first1,
-                  _ForwardIterator1 __g_last1,
-                  _ForwardIterator2 __g_first2,
-                  _ForwardIterator2 __g_last2,
-                  _Pred __g_pred) -> optional<bool> {
-        if constexpr (__has_random_access_iterator_category<_ForwardIterator1>::value &&
-                      __has_random_access_iterator_category<_ForwardIterator2>::value) {
-          if (__g_last1 - __g_first1 != __g_last2 - __g_first2)
-            return false;
-          return std::__equal(
-              __policy, std::move(__g_first1), std::move(__g_last1), std::move(__g_first2), std::move(__g_pred));
-        } else {
-          (void)__policy; // Avoid unused lambda capture warning
-          return std::equal(
-              std::move(__g_first1),
-              std::move(__g_last1),
-              std::move(__g_first2),
-              std::move(__g_last2),
-              std::move(__g_pred));
-        }
-      },
+  using _Implementation = __pstl::__dispatch<__pstl::__equal_3leg, __pstl::__current_configuration, _RawPolicy>;
----------------
ldionne wrote:

This variant of `std::equal` is often referred to as the "3 leg" version because it takes 3 iterators `[first1, last1)` and `first2` as opposed to "4 legs" which would be `[first1, last1)` and `[first2, last2)`. It's not an official term or anything, but I needed something to differentiate between the two.

https://github.com/llvm/llvm-project/pull/88131