gcc-3.4: critical C++ bug, too many destructors

[Andrew Pinski]

On Apr 13, 2004, at 10:01, Michael Veksler wrote:

> I think that gcc-3.4.0 should be delayed until a fix is committed.
> The following example illustrates how specialized allocators break
> much of STL code.
>
>   $ cat t3.cc
>   #include <iostream>
>
>   #define DEBUG std::cout << __PRETTY_FUNCTION__ << "\n"
>   template <class T>
>   class A {
>   public:
>     A() { DEBUG; }
>     template <class U>
>     A(const U&) { DEBUG; }
>     ~A() { DEBUG; }
>   };
>
>   template <class T1, class T2>
>   class B : public A<T1> {
>   public:
>     B(const A<T1> & var = A<T2>()) : A<T1>(var) {}
>   };
>
>   int main()
>   {
>     B<int, double> b;
>   }

Note changing DEBUG to print out this you can see what is going on here
and adding a DEBUG in the B construtor.

A<T>::A() [with T = double] 0xbffec900
A<T>::A(constU&) [with U = A<double>, T = int] 0xbffec910
B<T1, T2>::B(constA<T1>&) [with T1 = int, T2 = double] 0xbffec920
A<T>::~A() [with T = int] 0xbffec910
A<T>::~A() [with T = double] 0xbffec900
A<T>::~A() [with T = int] 0xbffec920


Note the code is also equivalent to:

#include <iostream>
#define DEBUG std::cout << __PRETTY_FUNCTION__ << " " <<(void*)this 
<<"\n"
   template <class T>
   class A {
   public:
     A() { DEBUG; }
     template <class U>
     A(const U&) { DEBUG; }
     ~A() { DEBUG; }
   };

   template <class T1, class T2>
   class B : public A<T1> {
   public:
     B(const A<T1> & var) : A<T1>(var) {DEBUG;}
   };

   int main()
   {
     A<double> d;
     B<int, double> b(d);
   }

Which has the same (similar, just the order of the deconstructors are 
different) output:
A<T>::A() [with T = double] 0xbffec920
A<T>::A(constU&) [with U = A<double>, T = int] 0xbffec900
B<T1, T2>::B(constA<T1>&) [with T1 = int, T2 = double] 0xbffec910
A<T>::~A() [with T = int] 0xbffec900
A<T>::~A() [with T = int] 0xbffec910
A<T>::~A() [with T = double] 0xbffec920


So this is not a bug.

Thanks,
Andrew Pinski