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Subject: [Bug fortran/55207] New: Automatic deallocation of variables declared in the main program
Date: Sun, 04 Nov 2012 18:27:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55207

             Bug #: 55207
           Summary: Automatic deallocation of variables declared in the
                    main program
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: janus@gcc.gnu.org


Although F95/F03/F08 only require automatic deallocation of local unsaved
variables upon termination of a procedure, gfortran currently also does it upon
termination of the main program.

Simple test case (for both scalars and arrays):

program main
  integer, allocatable :: i
  integer, allocatable, dimension(:) :: j
  allocate(i)
  allocate(j(1:5))
end program


The dump shows a block which automatically deallocates the variables at the end
of the main program:

  finally
    {
      if (j.data != 0B)
        {
          __builtin_free ((void *) j.data);
        }
      j.data = 0B;
      if (i != 0B)
        {
          __builtin_free ((void *) i);
        }
    }


>>From F08:6.7.3.2:

"When the execution of a procedure is terminated by execution of a RETURN or
END statement, an unsaved allocatable local variable of the procedure retains
its allocation and definition status if it is a function result variable or a
subobject thereof; otherwise, it is deallocated."

This mentions only *procedures*, not the main program. Moreover, variables
declared in the main program are implicitly SAVEd in F08, cf. chapter 5.3.16:

"A variable, common block, or procedure pointer declared in the scoping unit of
a main program, module, or submodule implicitly has the SAVE attribute, which
may be confirmed by explicit specification. If a common block has the SAVE
attribute in any other kind of scoping unit, it shall have the SAVE attribute
in every scoping unit that is not of a main program, module, or submodule."

Currently we miss to flag this via attr.save = SAVE_IMPLICIT.

In F95 it is basically impossible to detect whether a compiler does
end-of-program auto-dealloc. However, in F03 it can be detected by using a
FINAL procedure, since deallocation (automatic or explicit) also implies
finalization (for finalizable variables).