LI77073: INCORRECT VIRTUAL TEMPLATE ERROR

November 2012 Update for XL C/C++ for Blue Gene/Q, V12.1
February 2013 Update for XL C/C++ for Blue Gene/Q, V12.1

APAR status

• Closed as program error.

Error description

• The compiler generates an incorrect virtual template error
  message for the test case mentioned below:
  
  $cat test.cpp
  namespace sc{
  
  template <class T>
  class  Ref {};
  }
  
  
  namespace sc {
  
  
    struct DistArray4Dimensions {
      public:
        static const DistArray4Dimensions& default_dim() { return
  default_dim_; }
  
      private:
        static DistArray4Dimensions default_dim_;
  
    };
  
  
  class DistArray4 {
    public:
      virtual Ref<DistArray4> clone(const DistArray4Dimensions&
  dim = DistArray4Dimensions::default_dim()) =0;
  };
  
  
  }
  
  namespace sc {
  
  class DistArray4_MPIIOFile: public DistArray4 {
  
    protected:
      template <typename Derived> Ref<DistArray4> clone(const
  DistArray4Dimensions& dim =
  
  DistArray4Dimensions::default_dim());
  };
  }
  $
  
  
  ===== ACTUAL OUTPUT:
  $bgxlC -qarch=450d -qtune=450  -c test.cpp
  "test.cpp", line 34.49: 1540-1158 (S) The function template
  "sc::DistArray4_MPIIOFile::clone" must not be declared as
  virtual.
  $
  
  ===== EXPECTED OUTPUT:
  Should compile clean.
  

Local fix

• n/a
  

Problem summary

• USERS AFFECTED:
  Users with member function templates which have the same name
  and parameter list as a base class virtual function are
  affected by this issue.
  
  PROBLEM DESCRIPTION:
  A template function which otherwise has the same name and
  parameter list
  as a base class virtual function may be incorrectly rejected
  with a message
  indicating that the template function may not be declared
  virtual.
  
  struct A {
  virtual void foo();
  };
  
  struct B : A {
  template <typename T>
  void foo();  // error message produced for this line
  };
  
  The function is actually not declared virtual; however, it was
  mistakenly
  considered to override the base class virtual function.
  
  Specializations of member template functions should never be
  considered to
  override members of a base class.
  

Problem conclusion

• A check was implemented to recognize that member function
  templates never override virtual functions.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  LI76710

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  XL C/C++ FOR BG

• Fixed component ID

  5799AG100

Applicable component levels

• RC10 PSN LI76710

     UP06/09/13