Revert "[libc++] Optimize __hash_table::erase(iterator, iterator) (#1…

[boomanaiden154]

…52471)"

This reverts commit e4eccd6.

This was causing ASan failures in some situations involving unordered multimap containers. Details and a reproducer were posted on the original PR (#152471).

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Aiden Grossman (boomanaiden154)

Changes

…52471)"

This reverts commit e4eccd6.

This was causing ASan failures in some situations involving unordered multimap containers. Details and a reproducer were posted on the original PR (#152471).

---

Full diff: https://github.com/llvm/llvm-project/pull/158769.diff

3 Files Affected:

• (modified) libcxx/docs/ReleaseNotes/22.rst (-1)
• (modified) libcxx/include/__hash_table (+28-74)
• (modified) libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/erase_range.pass.cpp (-14)

diff --git a/libcxx/docs/ReleaseNotes/22.rst b/libcxx/docs/ReleaseNotes/22.rst
index e56f0a88db138..2b928a3a26913 100644
--- a/libcxx/docs/ReleaseNotes/22.rst
+++ b/libcxx/docs/ReleaseNotes/22.rst
@@ -57,7 +57,6 @@ Improvements and New Features
   has been improved by up to 3x
 - The performance of ``insert(iterator, iterator)`` of ``map``, ``set``, ``multimap`` and ``multiset`` has been improved
   by up to 2.5x
-- The performance of ``erase(iterator, iterator)`` in the unordered containers has been improved by up to 1.9x
 - The performance of ``map::insert_or_assign`` has been improved by up to 2x
 
 - ``ofstream::write`` has been optimized to pass through large strings to system calls directly instead of copying them
diff --git a/libcxx/include/__hash_table b/libcxx/include/__hash_table
index 2018b5a194e89..2b246f82ce36d 100644
--- a/libcxx/include/__hash_table
+++ b/libcxx/include/__hash_table
@@ -1036,21 +1036,7 @@ private:
   }
   _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(__hash_table&, false_type) _NOEXCEPT {}
 
-  _LIBCPP_HIDE_FROM_ABI void __deallocate_node(__node_pointer __nd) _NOEXCEPT {
-    auto& __alloc = __node_alloc();
-    __node_traits::destroy(__alloc, std::addressof(__nd->__get_value()));
-    std::__destroy_at(std::__to_address(__nd));
-    __node_traits::deallocate(__alloc, __nd, 1);
-  }
-
-  _LIBCPP_HIDE_FROM_ABI void __deallocate_node_list(__next_pointer __np) _NOEXCEPT {
-    while (__np != nullptr) {
-      __next_pointer __next = __np->__next_;
-      __deallocate_node(__np->__upcast());
-      __np = __next;
-    }
-  }
-
+  _LIBCPP_HIDE_FROM_ABI void __deallocate_node(__next_pointer __np) _NOEXCEPT;
   _LIBCPP_HIDE_FROM_ABI __next_pointer __detach() _NOEXCEPT;
 
   template <class _From, class _ValueT = _Tp, __enable_if_t<__is_hash_value_type<_ValueT>::value, int> = 0>
@@ -1188,7 +1174,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::~__hash_table() {
   static_assert(is_copy_constructible<hasher>::value, "Hasher must be copy-constructible.");
 #endif
 
-  __deallocate_node_list(__first_node_.__next_);
+  __deallocate_node(__first_node_.__next_);
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
@@ -1264,7 +1250,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::operator=(const __hash_table& __other)
   // At this point we either have consumed the whole incoming hash table, or we don't have any more nodes to reuse in
   // the destination. Either continue with constructing new nodes, or deallocate the left over nodes.
   if (__own_iter->__next_) {
-    __deallocate_node_list(__own_iter->__next_);
+    __deallocate_node(__own_iter->__next_);
     __own_iter->__next_ = nullptr;
   } else {
     __copy_construct(__other_iter, __own_iter, __current_chash);
@@ -1275,6 +1261,19 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::operator=(const __hash_table& __other)
   return *this;
 }
 
+template <class _Tp, class _Hash, class _Equal, class _Alloc>
+void __hash_table<_Tp, _Hash, _Equal, _Alloc>::__deallocate_node(__next_pointer __np) _NOEXCEPT {
+  __node_allocator& __na = __node_alloc();
+  while (__np != nullptr) {
+    __next_pointer __next    = __np->__next_;
+    __node_pointer __real_np = __np->__upcast();
+    __node_traits::destroy(__na, std::addressof(__real_np->__get_value()));
+    std::__destroy_at(std::addressof(*__real_np));
+    __node_traits::deallocate(__na, __real_np, 1);
+    __np = __next;
+  }
+}
+
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::__next_pointer
 __hash_table<_Tp, _Hash, _Equal, _Alloc>::__detach() _NOEXCEPT {
@@ -1330,11 +1329,11 @@ void __hash_table<_Tp, _Hash, _Equal, _Alloc>::__move_assign(__hash_table& __u,
         }
 #if _LIBCPP_HAS_EXCEPTIONS
       } catch (...) {
-        __deallocate_node_list(__cache);
+        __deallocate_node(__cache);
         throw;
       }
 #endif // _LIBCPP_HAS_EXCEPTIONS
-      __deallocate_node_list(__cache);
+      __deallocate_node(__cache);
     }
     const_iterator __i = __u.begin();
     while (__u.size() != 0)
@@ -1373,11 +1372,11 @@ void __hash_table<_Tp, _Hash, _Equal, _Alloc>::__assign_unique(_InputIterator __
       }
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
-      __deallocate_node_list(__cache);
+      __deallocate_node(__cache);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
-    __deallocate_node_list(__cache);
+    __deallocate_node(__cache);
   }
   for (; __first != __last; ++__first)
     __emplace_unique(*__first);
@@ -1403,11 +1402,11 @@ void __hash_table<_Tp, _Hash, _Equal, _Alloc>::__assign_multi(_InputIterator __f
       }
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
-      __deallocate_node_list(__cache);
+      __deallocate_node(__cache);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
-    __deallocate_node_list(__cache);
+    __deallocate_node(__cache);
   }
   for (; __first != __last; ++__first)
     __emplace_multi(*__first);
@@ -1440,7 +1439,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::end() const _NOEXCEPT {
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 void __hash_table<_Tp, _Hash, _Equal, _Alloc>::clear() _NOEXCEPT {
   if (size() > 0) {
-    __deallocate_node_list(__first_node_.__next_);
+    __deallocate_node(__first_node_.__next_);
     __first_node_.__next_ = nullptr;
     size_type __bc        = bucket_count();
     for (size_type __i = 0; __i < __bc; ++__i)
@@ -1900,57 +1899,12 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::erase(const_iterator __p) {
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
 typename __hash_table<_Tp, _Hash, _Equal, _Alloc>::iterator
 __hash_table<_Tp, _Hash, _Equal, _Alloc>::erase(const_iterator __first, const_iterator __last) {
-  if (__first == __last)
-    return iterator(__last.__node_);
-
-  // current node
-  __next_pointer __current = __first.__node_;
-  size_type __bucket_count = bucket_count();
-  size_t __chash           = std::__constrain_hash(__current->__hash(), __bucket_count);
-  // find previous node
-  __next_pointer __before_first = __bucket_list_[__chash];
-  for (; __before_first->__next_ != __current; __before_first = __before_first->__next_)
-    ;
-
-  __next_pointer __last_node = __last.__node_;
-
-  // If __before_first is in the same bucket (i.e. the first element we erase is not the first in the bucket), clear
-  // this bucket first without re-linking it
-  if (__before_first != __first_node_.__ptr() &&
-      std::__constrain_hash(__before_first->__hash(), __bucket_count) == __chash) {
-    while (__current != __last_node) {
-      if (auto __next_chash = std::__constrain_hash(__current->__hash(), __bucket_count); __next_chash != __chash) {
-        __chash = __next_chash;
-        break;
-      }
-      auto __next = __current->__next_;
-      __deallocate_node(__current->__upcast());
-      __current = __next;
-      --__size_;
-    }
+  for (const_iterator __p = __first; __first != __last; __p = __first) {
+    ++__first;
+    erase(__p);
   }
-
-  while (__current != __last_node) {
-    auto __next = __current->__next_;
-    __deallocate_node(__current->__upcast());
-    __current = __next;
-    --__size_;
-
-    // When switching buckets, set the old bucket to be empty and update the next bucket to have __before_first as its
-    // before-first element
-    if (__next) {
-      if (auto __next_chash = std::__constrain_hash(__next->__hash(), __bucket_count); __next_chash != __chash) {
-        __bucket_list_[__chash] = nullptr;
-        __chash                 = __next_chash;
-        __bucket_list_[__chash] = __before_first;
-      }
-    }
-  }
-
-  // re-link __before_first with __last
-  __before_first->__next_ = __current;
-
-  return iterator(__last.__node_);
+  __next_pointer __np = __last.__node_;
+  return iterator(__np);
 }
 
 template <class _Tp, class _Hash, class _Equal, class _Alloc>
diff --git a/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/erase_range.pass.cpp b/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/erase_range.pass.cpp
index a8a9f5fdbb428..f8a2bdd3fee73 100644
--- a/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/erase_range.pass.cpp
+++ b/libcxx/test/std/containers/unord/unord.multimap/unord.multimap.modifiers/erase_range.pass.cpp
@@ -91,20 +91,6 @@ int main(int, char**) {
     assert(c.size() == 0);
     assert(k == c.end());
   }
-  {   // Make sure we're properly destroying the elements when erasing
-    { // When erasing part of a bucket
-      std::unordered_multimap<int, std::string> map;
-      map.insert(std::make_pair(1, "This is a long string to make sure ASan can detect a memory leak"));
-      map.insert(std::make_pair(1, "This is another long string to make sure ASan can detect a memory leak"));
-      map.erase(++map.begin(), map.end());
-    }
-    { // When erasing the whole bucket
-      std::unordered_multimap<int, std::string> map;
-      map.insert(std::make_pair(1, "This is a long string to make sure ASan can detect a memory leak"));
-      map.insert(std::make_pair(1, "This is another long string to make sure ASan can detect a memory leak"));
-      map.erase(map.begin(), map.end());
-    }
-  }
 #if TEST_STD_VER >= 11
   {
     typedef std::unordered_multimap<int,

[alexfh]

@boomanaiden154 could you take a look at the pre-merge check failures?

[boomanaiden154]

These tests are broken at head. https://github.com/llvm/llvm-project/actions/workflows/libcxx-build-and-test.yaml shows all of the recent workflow runs hitting the same failures on MacOS.

The armv7 builder was interrupted, so the failure there is also not related.

[boomanaiden154]

https://github.com/llvm/llvm-project/actions/runs/17790938555 is the last scheduled job on main which shows the same failures as here.

I talked with @philnik777 on Discord in #libcxx and he said we are good to revert for now.

I have also double checked that reverting this patch fixes the ASan failures we are seeing internally.