LI75296: -O3 ORDERING EVALUATING EXTRA OPERATION

May 2010 Update for XL Fortran for Linux, V12.1
January 2012 Update for XL Fortran for Linux, V12.1
January 2011 Update for XL Fortran for Linux, V12.1
June 2011 Update for XL Fortran for Linux, V12.1
XL Fortran for Linux Fix Pack 8 (January 2014 Update) for 12.1

APAR status

• Closed as program error.

Error description

• When compiling code similar to the snippet below at -O3,
  instruction ordering can cause the multiplication operation to
  execute in cases where 'foo(i) != bar'.  The 'a' variable is not
  set, as the execution is a result of reordering.  Sometimes this
  behaviour is undesired, and may cause problems.
  
     if (foo(i) == bar) then
       a = 0.
     else
       a = foo(i) * b
     endif
  

Local fix

• N/A
  

Problem summary

• USERS AFFECTED:
  Users with -O3 and higher.
  
  PROBLEM DESCRIPTION:
  Internal code reordering allows for the multiply to be
  executed.  The -qstrict=guards compiler option should avoid
  this reordering, but is failing in this case.
  

Problem conclusion

• The compiler is performing speculation on a multiply and
  reordering it.  The behaviour of the -qstrict=guards option has
  been corrected to avoid this reordering.
  

Temporary fix

Comments

APAR Information

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

  IZ67132

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

Fix information

• Fixed component name

  XL FORTRAN RHEL

• Fixed component ID

  5724U8410

Applicable component levels

• RC10 PSN IZ67132

     UP06/09/13