return VM_Address.fromInt(VM_Interface.readAvailableBitsWord(base) & ~GC_FORWARDING_MASK);
return VM_Interface.readAvailableBitsWord(base).and(GC_FORWARDING_MASK.not()).toAddress();
  static VM_Address getForwardingPtr(VM_Address base) throws VM_PragmaUninterruptible, VM_PragmaInline {    return VM_Address.fromInt(VM_Interface.readAvailableBitsWord(base) & ~GC_FORWARDING_MASK);  }