[libcxx-commits] [libcxx] b1482aa - [libc++] Fix incorrect down cast in __tree::operator= (#152285)

[via libcxx-commits]

Author: Nikolas Klauser
Date: 2025-08-06T17:50:53+02:00
New Revision: b1482aa91b16e46cfed46cb4c4c41cfe34dfd434

URL: https://github.com/llvm/llvm-project/commit/b1482aa91b16e46cfed46cb4c4c41cfe34dfd434
DIFF: https://github.com/llvm/llvm-project/commit/b1482aa91b16e46cfed46cb4c4c41cfe34dfd434.diff

LOG: [libc++] Fix incorrect down cast in __tree::operator= (#152285)

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.

Added: 
    

Modified: 
    libcxx/include/__tree

Removed: 
    


################################################################################
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;
 }