From 18532a7e816015679561667c7ccd18f83478a17a Mon Sep 17 00:00:00 2001 From: Nikolas Klauser Date: Wed, 6 Aug 2025 12:09:38 +0200 Subject: [PATCH] [libc++] Fix incorrect down cast in __tree::operator= This has been introduced by #151304. This problem is diagnosed by UBSan with optimizations enabled. Since we run UBSan only with optimizations disabled currently, this isn't caught in our CI. We should look into enabling UBSan with optimizations enabled to catch these sorts of issues before landing a patch. --- libcxx/include/__tree | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/libcxx/include/__tree b/libcxx/include/__tree index 6ca1a623536f2..74b20d5b6f814 100644 --- a/libcxx/include/__tree +++ b/libcxx/include/__tree @@ -1388,8 +1388,9 @@ __tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=( if (__root()) __root()->__parent_ = __end_node(); } - __begin_node_ = static_cast<__end_node_pointer>(std::__tree_min(static_cast<__node_base_pointer>(__end_node()))); - __size_ = __t.size(); + __begin_node_ = + __end_node()->__left_ ? static_cast<__end_node_pointer>(std::__tree_min(__end_node()->__left_)) : __end_node(); + __size_ = __t.size(); return *this; }