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

The information in this article applies to:

• Microsoft FORTRAN PowerStation 32 for Windows NT, version 1.0

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

      END

Output

Expected results:

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

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

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