Vtable incompatibility between GCC 3.0/3.2?

[Stephan Bergmann <stephan dot bergmann at sun dot com>]

Hi all.

I just found out the hard way :)  that there is an incompatibility in 
the vtable layout of GCC 3.0.1 and GCC 3.2.2, see below.  Can anybody 
confirm whether this is a known issue (a deliberate change?), and 
between which two GCC versions the change was introduced?  I did not 
find anything about this in the changes notes.

Thanks a lot in advance,
-Stephan


Compiling file test.cc

  struct Base1 { virtual void fnBase1(); };
  struct Base2 { virtual void fnBase2(); };
  struct Derived: Base1, Base2 {
    Derived();
    void fnBase2();
    virtual void fnDerived();
  };
  Derived::Derived() {}
  void Derived::fnBase2() {}

with

  g++ -S test.cc

shows that the GCC-3.0.1--generated

  vtable for Derived:
    .long 0
    .long typeinfo for Derived
    .long Base1::fnBase1()
    .long Derived::fnDerived()
    .long Derived::fnBase2()
    .long -4
    .long typeinfo for Derived
    .long non-virtual thunk to Derived::fnBase2()

differs from the GCC-3.2.2--generated

  vtable for Derived:
    .long 0
    .long typeinfo for Derived
    .long Base1::fnBase1()
    .long Derived::fnBase2()
    .long Derived::fnDerived()
    .long -4
    .long typeinfo for Derived
    .long non-virtual thunk [nv:-4] to Derived::fnBase2()

in that the slots for fnDerived and fnBase2 have switched positions.