LI80905: -QSMP=OMP CAUSING INCORRECT OUTPUT AT RUNTIME

APAR status

• Closed as program error.

Error description

• The exe generated from the resulting test case produces
  incorrect output when compiled with -qsmp=omp:
  
  ===== COMPILE COMMAND:
  xlC -qsmp=omp test.cpp
  
  $ cat test.cpp
  #include <iostream>
  using namespace std;
  
  int main(int argc, char **argv)
  {
    int size = 4;
    int dim = 3;
    float in[12], out[12];
    float * __restrict__ x = out;
    float * __restrict__ y = out + 4;
    float * __restrict__ z = out + 8;
    for(int i=0; i<size*dim; i++)
      in[i] = out[i] = 0.0f;
    in[3] = in[4] = in[5] = 1.6f;
    #pragma omp simd
    for(int i=0; i<size; i++)
    {
      x[i] = in[i*dim];
      y[i] = in[i*dim+1];
      z[i] = in[i*dim+2];
    }
    cout << "check out " << out[1] << " " << out [5] << " " << out
  [9] << std::endl;
    return 0;
  }
  $
  
  
  
  ===== ACTUAL OUTPUT:
  $ ./a.out
  check out 0 0 1.6
  $
  
  
  ===== EXPECTED OUTPUT:
  $ ./a.out
  check out 1.6 1.6 1.6
  $
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Clients using -qsmp=omp maybe affected by this issue
  
  PROBLEM DESCRIPTION:
  An internal optimization causing certain variables to be
  privatized was causing an incorrect output at runtime
  

Problem conclusion

• This optimization has now 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:

  IJ16748

Fix information

• Fixed component name

  XL C/C++ LINUX

• Fixed component ID

  5725C7310

Applicable component levels