[libcxx-commits] [libcxx] [libc++] Optimize heap operations (PR #159917)
via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Oct 1 07:02:19 PDT 2025
https://github.com/nukyan updated https://github.com/llvm/llvm-project/pull/159917
>From d7714681a78a9604f2d3c16da022e85c347174e9 Mon Sep 17 00:00:00 2001
From: Yang Kun <ikspress at outlook.com>
Date: Sun, 14 Sep 2025 19:52:05 +0800
Subject: [PATCH] [libc++] Optimize heap operations
---
libcxx/include/__algorithm/make_heap.h | 6 +--
.../include/__algorithm/partial_sort_copy.h | 5 +-
libcxx/include/__algorithm/pop_heap.h | 36 +++++++-------
libcxx/include/__algorithm/push_heap.h | 48 +++++++++----------
libcxx/include/__algorithm/ranges_pop_heap.h | 4 +-
libcxx/include/__algorithm/sift_down.h | 29 +++++------
libcxx/include/__algorithm/sort_heap.h | 4 +-
7 files changed, 66 insertions(+), 66 deletions(-)
diff --git a/libcxx/include/__algorithm/make_heap.h b/libcxx/include/__algorithm/make_heap.h
index 8aff8ce588568..2bd26eb00aa02 100644
--- a/libcxx/include/__algorithm/make_heap.h
+++ b/libcxx/include/__algorithm/make_heap.h
@@ -45,11 +45,11 @@ __make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compar
if (__n > 1) {
// start from the first parent, there is no need to consider children
- for (__diff_t __start = (__sift_down_n - 2) / 2; __start >= 0; --__start) {
- std::__sift_down<_AlgPolicy, __assume_both_children>(__first, __comp_ref, __sift_down_n, __start);
+ for (__diff_t __start = __sift_down_n / 2; __start != 0;) {
+ std::__sift_down<_AlgPolicy, __assume_both_children>(__first, __comp_ref, __sift_down_n, --__start);
}
if _LIBCPP_CONSTEXPR (__assume_both_children)
- std::__sift_up<_AlgPolicy>(__first, __last, __comp, __n);
+ std::__sift_up<_AlgPolicy>(__first, --__last, __comp);
}
}
diff --git a/libcxx/include/__algorithm/partial_sort_copy.h b/libcxx/include/__algorithm/partial_sort_copy.h
index 2230dfc9cc4ad..0b8a0fb7e2830 100644
--- a/libcxx/include/__algorithm/partial_sort_copy.h
+++ b/libcxx/include/__algorithm/partial_sort_copy.h
@@ -52,16 +52,17 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator, _Random
_RandomAccessIterator __r = __result_first;
auto&& __projected_comp = std::__make_projected(__comp, __proj2);
- if (__r != __result_last) {
+ if (__result_first != __result_last) {
for (; __first != __last && __r != __result_last; ++__first, (void)++__r)
*__r = *__first;
std::__make_heap<_AlgPolicy>(__result_first, __r, __projected_comp);
typename iterator_traits<_RandomAccessIterator>::difference_type __len = __r - __result_first;
- for (; __first != __last; ++__first)
+ for (; __first != __last; ++__first) {
if (std::__invoke(__comp, std::__invoke(__proj1, *__first), std::__invoke(__proj2, *__result_first))) {
*__result_first = *__first;
std::__sift_down<_AlgPolicy, false>(__result_first, __projected_comp, __len, 0);
}
+ }
std::__sort_heap<_AlgPolicy>(__result_first, __r, __projected_comp);
}
diff --git a/libcxx/include/__algorithm/pop_heap.h b/libcxx/include/__algorithm/pop_heap.h
index 6d23830097ff9..57f079ace0d6e 100644
--- a/libcxx/include/__algorithm/pop_heap.h
+++ b/libcxx/include/__algorithm/pop_heap.h
@@ -33,28 +33,20 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
__pop_heap(_RandomAccessIterator __first,
- _RandomAccessIterator __last,
+ _RandomAccessIterator __bottom,
_Compare& __comp,
typename iterator_traits<_RandomAccessIterator>::difference_type __len) {
- // Calling `pop_heap` on an empty range is undefined behavior, but in practice it will be a no-op.
- _LIBCPP_ASSERT_PEDANTIC(__len > 0, "The heap given to pop_heap must be non-empty");
+ using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
- __comp_ref_type<_Compare> __comp_ref = __comp;
+ value_type __top = _IterOps<_AlgPolicy>::__iter_move(__first); // create a hole at __first
+ _RandomAccessIterator __hole = std::__floyd_sift_down<_AlgPolicy>(__first, __comp, __len);
- using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
- if (__len > 1) {
- value_type __top = _IterOps<_AlgPolicy>::__iter_move(__first); // create a hole at __first
- _RandomAccessIterator __hole = std::__floyd_sift_down<_AlgPolicy>(__first, __comp_ref, __len);
- --__last;
-
- if (__hole == __last) {
- *__hole = std::move(__top);
- } else {
- *__hole = _IterOps<_AlgPolicy>::__iter_move(__last);
- ++__hole;
- *__last = std::move(__top);
- std::__sift_up<_AlgPolicy>(__first, __hole, __comp_ref, __hole - __first);
- }
+ if (__hole == __bottom) {
+ *__hole = std::move(__top);
+ } else {
+ *__hole = _IterOps<_AlgPolicy>::__iter_move(__bottom);
+ *__bottom = std::move(__top);
+ std::__sift_up<_AlgPolicy>(__first, __hole, __comp);
}
}
@@ -64,8 +56,14 @@ pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare _
static_assert(std::is_copy_constructible<_RandomAccessIterator>::value, "Iterators must be copy constructible.");
static_assert(std::is_copy_assignable<_RandomAccessIterator>::value, "Iterators must be copy assignable.");
+ // Calling `pop_heap` on an empty range is undefined behavior, but in practice it will be a no-op.
+ _LIBCPP_ASSERT_PEDANTIC(__len > 0, "The heap given to pop_heap must be non-empty");
+
+ __comp_ref_type<_Compare> __comp_ref = __comp;
+
typename iterator_traits<_RandomAccessIterator>::difference_type __len = __last - __first;
- std::__pop_heap<_ClassicAlgPolicy>(std::move(__first), std::move(__last), __comp, __len);
+ if (__len > 1)
+ std::__pop_heap<_ClassicAlgPolicy>(std::move(__first), std::move(--__last), __comp_ref, __len);
}
template <class _RandomAccessIterator>
diff --git a/libcxx/include/__algorithm/push_heap.h b/libcxx/include/__algorithm/push_heap.h
index ec0b445f2b70f..0de948bcc0226 100644
--- a/libcxx/include/__algorithm/push_heap.h
+++ b/libcxx/include/__algorithm/push_heap.h
@@ -29,37 +29,35 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
-__sift_up(_RandomAccessIterator __first,
- _RandomAccessIterator __last,
- _Compare&& __comp,
- typename iterator_traits<_RandomAccessIterator>::difference_type __len) {
- using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
-
- if (__len > 1) {
- __len = (__len - 2) / 2;
- _RandomAccessIterator __ptr = __first + __len;
-
- if (__comp(*__ptr, *--__last)) {
- value_type __t(_IterOps<_AlgPolicy>::__iter_move(__last));
- do {
- *__last = _IterOps<_AlgPolicy>::__iter_move(__ptr);
- __last = __ptr;
- if (__len == 0)
- break;
- __len = (__len - 1) / 2;
- __ptr = __first + __len;
- } while (__comp(*__ptr, __t));
-
- *__last = std::move(__t);
- }
+__sift_up(_RandomAccessIterator __first, _RandomAccessIterator __bottom, _Compare&& __comp) {
+ using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
+ using value_type = typename iterator_traits<_RandomAccessIterator>::value_type;
+
+ difference_type __parent = __bottom - __first;
+ _LIBCPP_ASSERT_INTERNAL(__parent > 0, "shouldn't be called unless __bottom - __first > 0");
+ __parent = (__parent - 1) / 2;
+ _RandomAccessIterator __parent_i = __first + __parent;
+
+ if (__comp(*__parent_i, *__bottom)) {
+ value_type __t(_IterOps<_AlgPolicy>::__iter_move(__bottom));
+ do {
+ *__bottom = _IterOps<_AlgPolicy>::__iter_move(__parent_i);
+ __bottom = __parent_i;
+ if (__parent == 0)
+ break;
+ __parent = (__parent - 1) / 2;
+ __parent_i = __first + __parent;
+ } while (__comp(*__parent_i, __t));
+
+ *__bottom = std::move(__t);
}
}
template <class _AlgPolicy, class _RandomAccessIterator, class _Compare>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
__push_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare& __comp) {
- typename iterator_traits<_RandomAccessIterator>::difference_type __len = __last - __first;
- std::__sift_up<_AlgPolicy, __comp_ref_type<_Compare> >(std::move(__first), std::move(__last), __comp, __len);
+ if (__first != __last)
+ std::__sift_up<_AlgPolicy, __comp_ref_type<_Compare> >(std::move(__first), std::move(--__last), __comp);
}
template <class _RandomAccessIterator, class _Compare>
diff --git a/libcxx/include/__algorithm/ranges_pop_heap.h b/libcxx/include/__algorithm/ranges_pop_heap.h
index eccf54c094e3d..b6e994464a1f5 100644
--- a/libcxx/include/__algorithm/ranges_pop_heap.h
+++ b/libcxx/include/__algorithm/ranges_pop_heap.h
@@ -48,7 +48,9 @@ struct __pop_heap {
auto __len = __last_iter - __first;
auto&& __projected_comp = std::__make_projected(__comp, __proj);
- std::__pop_heap<_RangeAlgPolicy>(std::move(__first), __last_iter, __projected_comp, __len);
+
+ if (__len > 1)
+ std::__pop_heap<_RangeAlgPolicy>(std::move(__first), ranges::prev(__last_iter), __projected_comp, __len);
return __last_iter;
}
diff --git a/libcxx/include/__algorithm/sift_down.h b/libcxx/include/__algorithm/sift_down.h
index e01c9b2b00f86..3a8956bfc267a 100644
--- a/libcxx/include/__algorithm/sift_down.h
+++ b/libcxx/include/__algorithm/sift_down.h
@@ -38,7 +38,7 @@ __sift_down(_RandomAccessIterator __first,
// right-child of __start is at 2 * __start + 2
difference_type __child = __start;
- if (__len < 2 || (__len - 2) / 2 < __child)
+ if (__len < 2)
return;
__child = 2 * __child + 1;
@@ -62,7 +62,7 @@ __sift_down(_RandomAccessIterator __first,
__first[__start] = _Ops::__iter_move(__first + __child);
__start = __child;
- if ((__len - 2) / 2 < __child)
+ if (__len / 2 - 1 < __child)
break;
// recompute the child based off of the updated parent
@@ -85,16 +85,18 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _RandomAccessIterator __floy
_RandomAccessIterator __first,
_Compare&& __comp,
typename iterator_traits<_RandomAccessIterator>::difference_type __len) {
- using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
- _LIBCPP_ASSERT_INTERNAL(__len >= 2, "shouldn't be called unless __len >= 2");
+ _LIBCPP_ASSERT_INTERNAL(__len > 1, "shouldn't be called unless __len > 1");
- _RandomAccessIterator __hole = __first;
- _RandomAccessIterator __child_i = __first;
- difference_type __child = 0;
+ using _Ops = _IterOps<_AlgPolicy>;
- while (true) {
- __child_i += difference_type(__child + 1);
- __child = 2 * __child + 1;
+ typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
+
+ difference_type __child = 1;
+ _RandomAccessIterator __hole = __first, __child_i = __first;
+
+ do {
+ __child_i += __child;
+ __child *= 2;
if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
// right-child exists and is greater than left-child
@@ -103,13 +105,12 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _RandomAccessIterator __floy
}
// swap __hole with its largest child
- *__hole = _IterOps<_AlgPolicy>::__iter_move(__child_i);
+ *__hole = _Ops::__iter_move(__child_i);
__hole = __child_i;
// if __hole is now a leaf, we're done
- if (__child > (__len - 2) / 2)
- return __hole;
- }
+ } while (__child <= __len / 2);
+ return __hole;
}
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/__algorithm/sort_heap.h b/libcxx/include/__algorithm/sort_heap.h
index f20b110c7fd12..f2d73ab793650 100644
--- a/libcxx/include/__algorithm/sort_heap.h
+++ b/libcxx/include/__algorithm/sort_heap.h
@@ -36,8 +36,8 @@ __sort_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compar
__comp_ref_type<_Compare> __comp_ref = __comp;
using difference_type = typename iterator_traits<_RandomAccessIterator>::difference_type;
- for (difference_type __n = __last - __first; __n > 1; --__last, (void)--__n)
- std::__pop_heap<_AlgPolicy>(__first, __last, __comp_ref, __n);
+ for (difference_type __n = __last - __first; __n > 1; --__n)
+ std::__pop_heap<_AlgPolicy>(__first, --__last, __comp_ref, __n);
std::__check_strict_weak_ordering_sorted(__first, __saved_last, __comp_ref);
}
More information about the libcxx-commits
mailing list