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Q108461: FIX: DO Loop/Computed GOTO Errors with /Ox and /4Yb

Article: Q108461
Product(s): Microsoft Fortran Compiler
Version(s): 1.0
Operating System(s): 
Keyword(s): 
Last Modified: 24-MAR-2000

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The information in this article applies to:

- Microsoft Fortran Powerstation 32 for Windows NT, version 1.0 
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SYMPTOMS
========

DO loops may not function properly when compiled with both optimization for time
(/Ox) and extended error handling (/4Yb or $DEBUG). A similar problem exists
using computed GOTO statements.

RESOLUTION
==========

Do not compile with /Ox and /4Yb at the same time. Use the Visual Workbench
debugger to track down run-time errors that occur when using /Ox.

STATUS
======

Microsoft has confirmed this to be a problem in Microsoft FORTRAN PowerStation
32 for Windows NT, version 1.0. This problem was fixed in FORTRAN PowerStation,
version 4.0.

MORE INFORMATION
================

The following code illustrates the DO loop problem when compiling with /Ox and
/4Yb:

Sample Code #1
--------------

  c FORTRAN Compile options needed: /Ox /4Yb
        ieof = 0
        DO i = 1, 4
          IF ( i .EQ. 4 )  ieof = 999
          i1 = i + 1
          WRITE (*,1000) i, i1, ieof
        ENDDO
  1000  FORMAT (3i6)
        END

Output
------

Expected results:

  1     2     0
  2     3     0
  3     4     0
  4     5   999

Results with -Ox -4Yb:

  1     2     0
  1     2     0
  2     3     0
  3     4     0

The sample program below executes in an infinite loop when compiling with /Ox and
/4Yb:

Sample Code #2
--------------

  c FORTRAN Compile options needed: /Ox /4Yb
        J = 0
      1 CONTINUE
        WRITE(*,*) 'Label 1'
        WRITE(*,*) 'J = ', J

        J = J + 1
        IF (J.EQ.2) THEN
       K = 1
        ELSE
       K = 1
        ENDIF

        WRITE(*,*) 'J = ', J
        GOTO(1,2), J        ! Computed GOTO always branches to label 1

      2 CONTINUE
        WRITE(*,*) 'Label 2'
        END

Additional query words: 1.00

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbFortranSearch kbZNotKeyword2 kbFORTRANPower32100NT
Version           : :1.0
Issue type        : kbbug
Solution Type     : kbfix

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