[Bug fortran/30373] New: Option for run-time checking for aliasing amoung dummy arguments

["burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

Some compilers (such as Pathscale, cf. 
http://www.pathscale.com/docs/UserGuide.pdf, section 3.10.2) have an option to
check at run-time for aliasing among Fortran dummy arguments.

(This option "has several friends, and when a customer sees a wrong answer, the
first thing we do (or the customer does, if they've read the docs) is compile
with all of these options, which will quickly lead them to the type of bug.",
Greg Lindahl in c.l.f)

The following examples are invalid (and ill-defined too). Richard Main writes
in c.l.f (link below):

"The code is nonstandard. Some people overstate the restriction in question by
saying that aliasing is disallowed. Aliasing is allowed, but there are
restrictions on it. One of those restrictions is that you may not modify the
value of either of the aliased variables. Thus there is no correct answer and
the compilers are free to do anything they want with it. This is not an error
that compilers are required to catch."


Example 1 (based on the example in the Pathscale manual):

program bar
  implicit none
  real c(100)
  c = 5
  call foo(c,c)
  print *,c(1:5)
contains
  subroutine foo(a,b)
    integer i
    real a(100), b(100)
    do i = 2, 100
      a(i) = b(i) - b(i-1)
    enddo
  end subroutine foo
end program bar

Example 2, based on the first post in
http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/2b4df0a44e704b7f/70c44bc5ea8cafb0

program test
  implicit none
  integer, dimension(3,3) :: n
  call sub(n(1,:),n(1,:))
  write(6,*) n(1,:)
  contains
  subroutine sub(a,b)
    implicit none
    integer, dimension(3), intent(inout) :: a
    integer, dimension(3), intent(inout) :: b
    a=(/4,5,6/)
    b=(/-4,-5,-6/)
  end subroutine
end program test


-- 
           Summary: Option for run-time checking for aliasing amoung dummy
                    arguments
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: enhancement
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: burnus at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=30373