See https://llvm.org/bugs/show_bug.cgi?id=27115 The problem was that the conversion from 'const enable_shared_from_this<T>*' to 'const T*' didn't work if T inherited enable_shared_from_this as a virtual base class. The fix is to take the original pointer passed to shared_ptr's constructor in the __enable_weak_this method and perform an upcast to 'const T*' instead of performing a downcast from the enable_shared_from_this base. git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@273835 91177308-0d34-0410-b5e6-96231b3b80d8