class A {
public:
  int a;
  virtual void v();
};
 
class B : public virtual A {
public:
  int b;
  virtual void w();
};
 
class C : public virtual A {
public:
  int c;
  virtual void x();
};
 
class D : public B, public C {
public:
  int d;
  virtual void y();
};

                                   +-----------------------+
                                   |   20 (vbase_offset)   |
                                   +-----------------------+
                                   |     0 (top_offset)    |
                                   +-----------------------+
                                   | ptr to typeinfo for D |
                      +----------> +-----------------------+
d --> +----------+    |            |         B::w()        |
      |  vtable  |----+            +-----------------------+
      +----------+                 |         D::y()        |
      |     b    |                 +-----------------------+
      +----------+                 |   12 (vbase_offset)   |
      |  vtable  |---------+       +-----------------------+
      +----------+         |       |    -8 (top_offset)    |
      |     c    |         |       +-----------------------+
      +----------+         |       | ptr to typeinfo for D |
      |     d    |         +-----> +-----------------------+
      +----------+                 |         C::x()        |
      |  vtable  |----+            +-----------------------+
      +----------+    |            |    0 (vbase_offset)   |
      |     a    |    |            +-----------------------+
      +----------+    |            |   -20 (top_offset)    |
                      |            +-----------------------+
                      |            | ptr to typeinfo for D |
                      +----------> +-----------------------+
                                   |         A::v()        |
                                   +-----------------------+