I see the following constructs:

new X will free the memory if X constructor throws.

operator new() can be overloaded.

The canonical definition of an operator new overload is void *operator new(heap h) and the corrisponding operator delete.

The most common operator new overload is pacement new, which is void *operator new(void *p) { return p; }

You almost always cannot call delete on the pointer given to placement new.

This leads to a single question.

How is memory cleaned up when X constructor throws and an overloaded new is used?