LI75145: ISSUES WITH 64 BIT ADD OPERATION AT -O2

October 2009 Update for XL C/C++ for Linux, V10.1
June 2011 Update for XL C/C++ for Linux, V10.1
XL C/C++ for Linux Fix Pack 8 (January 2014 Update) for 10.1
August 2010 Update for XL C/C++ for Linux, V10.1
January 2011 Update for XL C/C++ for Linux, V10.1
January 2012 Update for XL C/C++ for Linux, V10.1
July 2012 Update for XL C/C++ for Linux, V10.1

APAR status

• Closed as program error.

Error description

• The following test case abends at runtime when compiled with the
  following options:
  
  /* compile with xlc -q64 -O */
  
  int index[10];
  int n = 10;
  int forward=0;
  
  main () {
    int i, start, end, step;
    if (forward)
    {
      start=0; end=10; step=1;
    } else {
      start=n-1; end=-1; step=-1;
    }
    for (i=start; i != end; i+=step)
      index[(unsigned int) i] = i;
  }
  

Local fix

• Using the type 'long' instead of 'int' for the variables in 64
  bit will help work around this issue.
  

Problem summary

• Users using -q64 and -O2 and higher with
  certain loops with 'int' loop indicies and runtime
  computed bounds (not contants) maybe affected by this issue.
  
  The compiler generates incorrect code that
  will often lead to a SEGV.  The problem is in the
  'Reassociation' optimization when zero extension is being done.
  

Problem conclusion

• Fixed reassociation to be smarter when
  zero extension is being done.
  

Temporary fix

Comments

APAR Information

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

  IZ45789

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

Fix information

• Fixed component name

  XL C/C++ SLES10

• Fixed component ID

  5724U8300

Applicable component levels

• RA10 PSN IZ45789

     UP06/09/13