PI44519: INLINING OPTIMIZATION CAUSING AUTO_PTR COPY CONSTRUCTOR TO CALL DESTRUCTOR EARLY

APAR status

• Closed as program error.

Error description

• When compiling with optimization with INLINE enabled, auto_ptr
  usage with copy constructors is resulting in incorrect auto_ptr
  behaviour. Specifically, the object being copied is destructed
  during the new auto_ptr initialization instead of transferring
  ownership of the pointer.
  
  
     === TEST CASE ===
  
  #include <memory>
  #include <vector>
  
  class Base
  {
   public:
      Base(): Val1(1) {}
      ~Base()       { printf("dctor '%08X' --> ", this); }
      int GetVal1() { return Val1; }
   protected:
      int Val1;
  };
  
  class Derived : public Base
  {
   public:
      Derived() : Val2(2) {}
      int GetVal2() { return Val2; }
   protected:
      int Val2;
  };
  
  class Derived2 : public Derived
  {
   public:
      Derived2() : Val3(3) {}
      int GetVal3() { return Val3; }
   protected:
      int Val3;
  };
  
  std::auto_ptr<Derived2> func1()
  {
      std::auto_ptr<Derived2> pObj2(new Derived2);
      printf("pDerived2='%08X'; Val2='%d'  --> ", pObj2.get(),
  pObj2->GetVal2());
  
      return pObj2;
  }
  
  void func2()
  {
      std::vector<Derived*> arrObj;
      for (int i = 0; i < 10; i++)
      {
          std::auto_ptr<Derived> pObj(func1());
          printf("pDerived='%08X'; Val2='%d'\n", pObj.get(),
  pObj->GetVal2());
          arrObj.push_back(pObj.release());
      }
  
      for (int i = 0; i < arrObj.size(); i++)
      {
          delete arrObj[i];
      }
  }
  
  int main(int argc,char* argv[])
  {
      func2();
      return 0;
  }
  
  
  
  
     === INCORRECT OUTPUT ===
  > xlC -O2 test.cpp
  ./a.out
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D30'; Val2='2'  --> dctor '25B50D30' -->
  pDerived='25B50D30'; Val2='0'
  pDerived2='25B50D40'; Val2='2'  --> dctor '25B50D40' -->
  pDerived='25B50D40'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D38'; Val2='2'  --> dctor '25B50D38' -->
  pDerived='25B50D38'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  pDerived2='25B50D20'; Val2='2'  --> dctor '25B50D20' -->
  pDerived='25B50D20'; Val2='0'
  dctor '25B50D20' --> dctor '25B50D30' --> dctor '25B50D40' -->
  dctor '25B50D20' --> dctor '25B50D38' --> dctor '25B50D20' -->
  dctor '25B50D20' --> dctor '25B50D20' --> dctor '25B50D20' -->
  dctor '25B50D20' -->
  >
  
     === CORRECT OUTPUT ===
  >./a.out
  pDerived2='25B50D20'; Val2='2'  --> pDerived='25B50D20';
  Val2='2'
  pDerived2='25B50D48'; Val2='2'  --> pDerived='25B50D48';
  Val2='2'
  pDerived2='25B50D70'; Val2='2'  --> pDerived='25B50D70';
  Val2='2'
  pDerived2='25B50DA0'; Val2='2'  --> pDerived='25B50DA0';
  Val2='2'
  pDerived2='25B50D88'; Val2='2'  --> pDerived='25B50D88';
  Val2='2'
  pDerived2='25B50DB8'; Val2='2'  --> pDerived='25B50DB8';
  Val2='2'
  pDerived2='25B50DF0'; Val2='2'  --> pDerived='25B50DF0';
  Val2='2'
  pDerived2='25B50DD0'; Val2='2'  --> pDerived='25B50DD0';
  Val2='2'
  pDerived2='25B50E38'; Val2='2'  --> pDerived='25B50E38';
  Val2='2'
  pDerived2='25B50E50'; Val2='2'  --> pDerived='25B50E50';
  Val2='2'
  dctor '25B50D20' --> dctor '25B50D48' --> dctor '25B50D70' -->
  dctor '25B50DA0' --> dctor '25B50D88' --> dctor '25B50DB8' -->
  dctor '25B50DF0' --> dctor '25B50DD0' --> dctor '25B50E38' -->
  dctor '25B50E50' -->
  >
  

Local fix

• - Do not use optimization
  - Compile with option NOANSIALIAS
  - Manually modify code to call the 'release()' method of the
  auto_ptr used in the copy constructor/initialization
  

Problem summary

Problem conclusion

• Using -D__IBMCPP_AUTO_PTR_REF_CONVS will now enable a new
  implementation of auto_ptr_ref which contains an additional
  member in order to encode the necessary information to reliably
  retrieve the auto_ptr to which it refers. The new implementation
  is not binary-compatible with the old one.
  

Temporary fix

Comments

• RECOMMENDATION TO CUSTOMER:
  If auto_ptr_ref--including symbols for its
  member functions--is not exposed in binary
  interfaces requiring compatibility with the
  old implementation of auto_ptr_ref, then
  enable the new implementation of
  auto_ptr_ref by applying the header update
  and compile all code using auto_ptr_ref
  (explicitly or otherwise) with
  -D__IBMCPP_AUTO_PTR_REF_CONVS.
  

APAR Information

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

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

  PI58817

Modules/Macros

• CRTEC128
  

Fix information

• Fixed component name

  ANSI C++ CLASS

• Fixed component ID

  568819807

Applicable component levels

• R790 PSY

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