LI81681: ISSUE WITH XL UNDERSTANDING CLASS MEMBER VARIABLE OFFSETS W.R.T.POLYMORPHISM AND TEMPLATING

APAR status

• Closed as program error.

Error description

• COMPILER PRODUCES INCORRECT RESULTS FOR CLASS MEMBER VARIABLE
  OFFSETS W.R.T. POLYMORPHISM AND TEMPLATING
  ----------------------------------------------------------------
  
  xlC -std=c++11 testcode.C
  $ ./a.out
  
  
  Actual results:
  
  C:  &B::data2=0x7fffc9d1f910, &A2::data2=0x7fffc9d1f908,
  &B::getData2()=0x7fffc9d1f908, &A2::getData2()=0x7fffc9d1f908
  B:  &data2=0x7fffc9d1f908, &getData2()=0x7fffc9d1f908
  
  
  The expected results:
  
  C:  &B::data2=0x7fffcaf71478, &A2::data2=0x7fffcaf71478,
  &B::getData2()=0x7fffcaf71478, &A2::getData2()=0x7fffcaf71478
  B:  &data2=0x7fffcaf71478, &getData2()=0x7fffcaf71478
  
  ================================================================
  
  Test Case:
  
  #include<stdio.h>
  #include<vector>
  
  template<typename TV>
  struct myvec {
                  protected:
                  std::vector<TV> vec_data;
  };
  
  template<typename TA>
  struct A1 {
                  virtual ~A1() = default;
  };
  
  struct A2 {
                  virtual ~A2() = default;
  protected:
                  myvec<int> data1;
                  myvec<int> data2;
  
                  myvec<int> &getData1(){
                                  return data1;
                  }
                  myvec<int> &getData2(){
                                  return data2;
                  }
  };
  
  template<typename T>
  struct B : public A1<T>, public A2
  {
                  virtual ~B() = default;
  
                  void testB(){
                                  printf("B:  &data2=%p,
  &getData2()=%p\n", &(A2::data2), &getData2());
                  }
  };
  
  template<typename T2>
  struct C : public B<T2>
  {
                  using Parent = B<T2>;
                  virtual ~C() = default;
  
                  void testC(){
                                  printf("C:  &B::data2=%p,
  &A2::data2=%p, &B::getData2()=%p, &A2::getData2()=%p\n",
  &(Parent::data2), &(A2::data2), &(Parent::getData2()),
  &(A2::getData2()));
                  }
  };
  
  int main(void){
  
                  C<double> c;
  
                  c.testC();
                  c.testB();
  
                  return 0;
  }
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users who have test cases similar to the one mentioned in the
  APAR are affected by this issue.
  
  PROBLEM DESCRIPTION:
  The root cause is that the compiler was incorrectly handling
  qualified base class members,
  where the qualified name is more derived than the subobject in
  which the member resides.
  

Problem conclusion

• The compiler has been fixed to handle this scenario.
  

Temporary fix

Comments

APAR Information

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

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

  IJ32578

Fix information

• Fixed component name

  XL C/C++ LINUX

• Fixed component ID

  5725C7310

Applicable component levels