LI75795: OPTIMIZING AWAY IF CAUSING FP EXCEPTION

November 2010 Update for XL C/C++ for Linux, V11.1
XL C/C++ for Linux Fix Pack 9 (August 2013 Update) for 11.1
April 2011 Update for XL C/C++ for Linux, V11.1
July 2011 Update for XL C/C++ for Linux, V11.1
October 2011 Update for XL C/C++ for Linux, V11.1
June 2012 Update for XL C/C++ for Linux, V11.1
October 2012 Update for XL C/C++ for Linux, V11.1
XL C/C++ for Linux Fix Pack 8 (June 2013 Update) for 11.1

APAR status

• Closed as program error.

Error description

• When compiling the following test case with -qstrict and
  optimization that uses HOT transformations, the IF statement is
  being optimized away, resulting in incorrect behaviour.
  
  
     =====  TEST CASE  =====
  
  xlc -O3 -qstrict -qflttrap test.c -lm
  
  #include <stdio.h>
  #include <math.h>
  #include <fptrap.h>
  
  double x = -1;
  
  int main()
  {
    int i, j;
    double sum;
  
    (void) fp_enable(TRP_INVALID);
  
    sum = 0;
    if (x > 0)
      sum += log(x);
    printf("sum %g\n", sum);
  
    for (i = 0; i < 1; i++)
      for (j = 0; j < 1; j++)
        ;
  
    return 0;
  }
  

Local fix

• Compile with -qnohot
  

Problem summary

• PROBLEM DESCRIPTION:
  Floating point expressions are speculated even with -qflttrap.
  
  USERS AFFECTED:
  Any user specifying -qflttrap and -qhot and above.
  

Problem conclusion

• Issue was corrected.
  

Temporary fix

Comments

APAR Information

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

  IZ81030

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

Fix information

• Fixed component name

  XL C/C++ FOR LI

• Fixed component ID

  5724X1400

Applicable component levels

• RB10 PSN IZ81030

     UP06/09/13