LI76239: INCORRECT LOGICAL EXPRESSION EVALUATION

January 2012 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

• The following small test case demonstates that the xlf compiler
  have a bug in the evaluation of logical expressions:
  
  ...
   integer*4 x/1/, y/2000/
  ...
       ((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)) evaluates
  to true
       .not.((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)) also
  comes out true.
  
  This issue affects XLF V12.1 and XLF V13.1.
  
  
  ===== TESTCASE:
  $cat test_case.f
        program IBM BROKEN FORTRAN
        integer*4 x/1/, y/2000/
  
  c THIS EXPRESSION SHOULD EVALUATE TO TRUE
        write (*,*)'
  ((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x))'
       + ,
  ((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x))
        if (((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)))
  then
        write (*,*) '-OK-: EVALUATES TO TRUE'
        end if
  c THIS EXPRESSION SHOULD EVALUATE TO FALSE
        write
  (*,*)'.not.((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x))'
       + ,
  .not.((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x))
  c ON IBM, IT ERRONEOUSLY EVALUATES TO TRUE
        if (.not.((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)))
  then
        write (*,*) '*ERROR*: EVALUATES TO TRUE'
        else
        write (*,*) '-OK-: EVALUATES TO FALSE'
        end if
  
        end
  
  ===== COMPILE COMMAND:
  xlf test_case.f
  
  $./a.out
        ((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)) T
   -OK-: EVALUATES TO TRUE
   .not.((.not.((x.eq.1).and.(y.lt.1000))).and.(1.eq.x)) T
   *ERROR*: EVALUATES TO TRUE
  

Local fix

• N/A
  

Problem summary

• PROBLEM DESCRIPTION: Certain combinations of negated
  short-circuit expressions were evaluated incorrectly.
  
  USERS AFFECTED: Users that depend on short-circuit evaluation.
  

Problem conclusion

• Problem is fixed in the short-circuit expression generator.
  Apply recommended PTF.
  

Temporary fix

Comments

APAR Information

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

  IZ89350

• 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 IZ89350

     UP06/09/13