There are many instruction ctors that call the setName method of the Value base class, which can throw a bad_alloc exception in OOM situations. In such situations special User delete operators are called which are not implemented yet.
Note that some User subclasses change the information which is required to calculate the storage pointer of a User object (e.g.NumUserOperands). Those subclasses need an operator delete that restores the changed information to its original value. Example: GlobalVariable.h