IY44051: STD::VECTOR ELEMENT GETS OVERWRITTEN WHEN -O TURNED ON

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• The behaviour of std::vector in the test case below gets
  unexpected if optimization is turned on. It appears that when an
  insert is attempted after erase, the first element is not
  getting pushed forward to the second position. I am if sure if
  this is a runtime or a compiler issue. Starting against the
  library.
  .
  Testcase:
  ==========
  .
  #include <stdio.h>
  #include <string>
  #include <map>
  #include <vector>
  .
  using namespace std;
  .
  typedef map<string, int, less<string> >  MAP;
  typedef vector<MAP::iterator>            VECTOR;
  typedef pair<MAP::iterator, bool>        INSRESULT;
  .
  void print(MAP&, VECTOR&);
  .
  int main(){
     MAP       m;
     VECTOR    v;
     INSRESULT p;
  .
     // Insert three elements
     p = m.insert(MAP::value_type("A", 100));
     v.insert(v.begin(), p.first);
  .
     p = m.insert(MAP::value_type("B", 200));
     v.insert(v.begin()+v.size(), p.first);
  .
     p = m.insert(MAP::value_type("C", 300));
     v.insert(v.begin(), p.first);
  .
     print(m, v);
  .
     m.erase(v[1]);
     v.erase(v.begin()+1);
     printf("\nRemoved first element from m and v\n");
  .
     print(m, v);
  .
     printf("\nInsert (D,400) to m and v\n");
     p = m.insert(MAP::value_type("D", 400));
     v.insert(v.begin(), p.first);
  .
     print(m, v);
  }
  .
  void print(MAP &m, VECTOR &v){
     int i = 0;
     int vlen = v.size();
  .
     printf("\nMap: ");
     for(MAP::iterator it = m.begin(); it!=m.end(); it++){
        printf("\tm[%d] @0x%x: (%s,%d)\n", i, &(*it),
               (*it).first.data(), (*it).second);
        i++;
     }
  .
     printf("Vector:");
     for(i=0; i<vlen; i++){
        printf("\tv[%d] @0x%x: (%s,%d)\n", i, &v[i],
               (*v[i]).first.data(), (*v[i]).second);
     }
  }
  .
  .
  xlC -O -qalias=noansi t.cpp
  .
  .
  Output:
  ========
  Map:    m[0] @0x2020a5a4: (A,100)
          m[1] @0x2020a614: (B,200)
          m[2] @0x2020a684: (C,300)
  Vector: v[0] @0x2020a6a8: (C,300)
          v[1] @0x2020a6ac: (A,100)
          v[2] @0x2020a6b0: (B,200)
  .
  Removed first element from m and v
  .
  Map:    m[0] @0x2020a614: (B,200)
          m[1] @0x2020a684: (C,300)
  Vector: v[0] @0x2020a6a8: (C,300)
          v[1] @0x2020a6ac: (B,200)
  .
  Insert (D,400) to m and v
  .
  Map:    m[0] @0x2020a614: (B,200)
          m[1] @0x2020a684: (C,300)
          m[2] @0x2020a5a4: (D,400)
  Vector: v[0] @0x2020a6a8: (D,400)
          v[1] @0x2020a6ac: (B,200)   <-- Should be C,300
          v[2] @0x2020a6b0: (B,200)
  .
  If optmization is turned off, v[1] will contain (C,300) as
  expected.
  .
  

Local fix

• Disable optimization of the affected module.
  

Problem summary

• The problem cause has been traced to a line of code in the C++
  standard library header xutility, at function copy_backward.
  The problem was caused by the compiler optimizater component,
  not an error in the runtime code.
  

Problem conclusion

• The problem has been fixed in the coming VAC++ V5 PTF.
  

Temporary fix

Comments

APAR Information

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

  IY39459

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

Fix information

• Fixed component name

  VA C++ PROF FOR

• Fixed component ID

  5765F5600

Applicable component levels

• R600 PSN U810710

     UP07/04/30 I 1000

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.