[libc++] Simplify and clean up heap operations #159917
Open
+69
−69
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
Thank you for submitting a Pull Request (PR) to the LLVM Project! This PR will be automatically labeled and the relevant teams will be notified. If you wish to, you can add reviewers by using the "Reviewers" section on this page. If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers. If you have further questions, they may be answered by the LLVM GitHub User Guide. You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums. |
llvmbot
added
the
libc++
|
@llvm/pr-subscribers-libcxx Author: None (nukyan) ChangesReopening for #121480, these changes are intended to clean up the code and a little bit performance improving. Here is the output of Full diff: https://github.com/llvm/llvm-project/pull/159917.diff 7 Files Affected:
diff --git a/libcxx/include/__algorithm/make_heap.h b/libcxx/include/__algorithm/make_heap.h
index 8cfeda2b59811..9de58fc65ce21 100644
--- a/libcxx/include/__algorithm/make_heap.h
+++ b/libcxx/include/__algorithm/make_heap.h
@@ -36,7 +36,7 @@ __make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compar
using __diff_t = __iter_diff_t<_RandomAccessIterator>;
const __diff_t __n = __last - __first;
- static const bool __assume_both_children = is_arithmetic<__iter_value_type<_RandomAccessIterator> >::value;
+ constexpr bool __assume_both_children = is_arithmetic<__iter_value_type<_RandomAccessIterator> >::value;
// While it would be correct to always assume we have both children, in practice we observed this to be a performance
// improvement only for arithmetic types.
@@ -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..6f2b59ca59b1a 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
@@ -85,29 +85,34 @@ _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;
- if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
- // right-child exists and is greater than left-child
- ++__child_i;
- ++__child;
+ difference_type __child = 1;
+ _RandomAccessIterator __hole = __first, __child_i = __first;
+
+ while (true) {
+ __child_i += __child;
+ __child *= 2;
+
+ if (__child < __len) {
+ _RandomAccessIterator __right_i = _Ops::next(__child_i);
+ if (__comp(*__child_i, *__right_i)) {
+ // right-child exists and is greater than left-child
+ __child_i = __right_i;
+ ++__child;
+ }
}
// 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)
+ if (__child > __len / 2)
return __hole;
}
}
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);
}
|
nukyan
commented
Sep 20, 2025
|
Looking at the benchmark results, I don't see anything with a clear gain. Did I miss something? |
I primarily cleaned up some unnecessary boundary checks in Additionally, I noticed we can set __child to 1 and use |
nukyan
force-pushed
the
libcxx_heap
branch
2 times, most recently
from
b68506b to
d771468
Compare
|
I'm not sure why CI is always failed on AIX with a strange error. It works fine both on my computer (x86_64) and other builds. |
nukyan
changed the title
Hi, could you please take a look when you have a moment? It's a small change focus on simplify and clean up codes in libc++. I've thoroughly tested the changes, and they are working as expected. 😄 |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Reopening for #121480, these changes are intended to clean up the code and a little bit performance improving.
Here is the output of
libcxx/test/benchmarks/algorithms/make_heap.bench.cpp.