LI75695: WRONG OUTPUT WITH MPI, -O3 AND -QAUTODBL=DBL4

September 2010 Update for XL Fortran Advanced Edition for Blue Gene/L, V11.1

APAR status

• Closed as program error.

Error description

• When compiling and running the following testcase, the output is
  incorrect.  The error is caused by using the MPI compiler
  invocation, -O3 and the -qautodbl=dbl4 option.  Using the
  invocation 'xlf95_r' gives the correct output.  Removing
  -qautodbl=dbl4 or -O3 or adding -qstrict gives the correct
  output.
  
  
   =====   TESTCASE   =====
  
  ===== COMPILE COMMAND:
  mpixlf95_r -O3 -o optim_O3 -qautodbl=dbl4 optim_test.F90
  
  
  PROGRAM optim_test
    IMPLICIT NONE
    INTEGER :: vsp_dim, momnum, ln1,ln2
    COMPLEX, DIMENSION(:,:), ALLOCATABLE :: infield
    COMPLEX, DIMENSION(:), ALLOCATABLE :: mom
    REAL, DIMENSION(:,:), ALLOCATABLE :: mat
    integer :: ierr,n
    ln1=1; ln2=1;
    vsp_dim = 32
    ALLOCATE(infield(1:vsp_dim,ln1:ln2))
    ALLOCATE(mat(1:vsp_dim,ln1:ln2))
    ALLOCATE(mom(ln1:ln2))
    mat = 3.0D0
    infield = CMPLX(1.0d0,4.0d0)
    CALL calc_moments_perf(vsp_dim, infield,mat, mom)
    PRINT*,ln1,': ',mom(ln1)
  CONTAINS
    SUBROUTINE calc_moments_perf(vsp_dim,p_g_1,p_mat,p_mom)
      INTEGER, INTENT(in):: vsp_dim
      COMPLEX, DIMENSION(vsp_dim,ln1:ln2), INTENT(in):: p_g_1
      REAL, DIMENSION(vsp_dim,ln1:ln2), INTENT(in):: p_mat
      COMPLEX, DIMENSION(ln1:ln2), INTENT(out):: p_mom
      COMPLEX, DIMENSION(vsp_dim):: temp
      INTEGER:: n
      temp = p_mat(:,ln1) * p_g_1(:,ln1)
      p_mom(ln1) = SUM(temp,1)
    END SUBROUTINE calc_moments_perf
  END PROGRAM optim_test
  

Local fix

• n/a
  

Problem summary

• USER AFFECTED:
  Users who make use of floating point code.
  
  PROBLEM DESCRIPTION:
  Incorrect output in applications with floating point code.  A
  code optimization was not tracking a floating point register
  correctly thus resulting in an incorrect computation.
  

Problem conclusion

• Dot product reduction was not properly
  tracking the secondary floating point register through a string
  of serialized computations. This meant that it did not correctly
  transform the computation. The method in which it tracks the
  secondary register has been corrected.
  

Temporary fix

Comments

APAR Information

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

  LI74650

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

Fix information

• Fixed component name

  XL FORTRAN AE B

• Fixed component ID

  5799HJG00

Applicable component levels

• RB10 PSN LI74650

     UP06/09/13