[Bug fortran/43331] New: Cray pointers generate bogus IL for the middle-end

[rguenth at gcc dot gnu dot org]

I have a patch that exposes this and causes a "miscompile" of
gfortran.dg/cray_pointers_2.f90.  Reduced testcase:

! { dg-do run }
! { dg-options "-fcray-pointer -fbounds-check" }
! Series of routines for testing a Cray pointer implementation
program craytest
  call ptr5
end program craytest

subroutine ptr5
  logical :: intne
  integer :: i
  integer, parameter :: n = 9
  integer itarg1 (n)
  integer ipte1 (*)

  pointer(iptr4,ipte1)

  iptr4 = loc(itarg1)

  do, i=1,n
     ipte1(i) = i
     if (intne(ipte1(i), itarg1(i))) then
        ! Error #143
        call abort()
     endif
  end do

end subroutine ptr5

! Separate function calls to break Cray pointer-indifferent optimization
logical function intne(ii,jj)
  integer :: i,j
  intne = ii.ne.jj
  if (intne) then
     write (*,*) ii," doesn't equal ",jj
  endif
end function intne


where we can see the following IL created by the FE:

ptr5 ()
{
  integer(kind=4) i;
  integer(kind=8) iptr4;
  integer(kind=4) ipte1[1] [value-expr: *(integer(kind=4)[1] *) iptr4];
  integer(kind=4) itarg1[9];

  {
    integer(kind=8) D.1548;

    D.1548 = (integer(kind=8)) &itarg1;
    iptr4 = D.1548;
  }
...
            ipte1[NON_LVALUE_EXPR <SAVE_EXPR <(integer(kind=8)) i>> + -1] = i;
...
            if (intne (&ipte1[NON_LVALUE_EXPR <SAVE_EXPR <(integer(kind=8)) i>>
+ -1], &itarg1[NON_LVALUE_EXPR <SAVE_EXPR <(integer(kind=8)) i>> + -1]))


you can clearly see that substituting the value-expr
*(integer(kind=4)[1] *) iptr4 for ipte1 will expose an array size of 1 (!)
to the middle-end, which it will happily oblige to and optimize
&ipte1[i - 1] to &ipte1[0].

If the array size is not known the FE should generate
*(integer(kind=4)[] *) iptr4


-- 
           Summary: Cray pointers generate bogus IL for the middle-end
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43331