[Bug fortran/45016] New: Support pointer assignment with bound-spec; wrong bounds for pointer assignment

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

This PR is about two related topics:
a) Wrong code: Fortran 90+: The lower bound shall be the same as the one of the
object on the RHS
b) F2003+ pointer assignment with bounds-spec

Related to PR 29785 (bounds remapping).

 * * *

a) WRONG CODE

The test case should print twice a lower bound of 2, but currently it prints
"1" for the lower bound of pointer "p":

!-------------------------------
integer, target :: a(2:5,2:5)
integer, pointer :: p(:,:)
!p(-1:,-1:) => a
p => a
print *, 'a: ', lbound(a)
print *, 'p: ', lbound(p)
end
!-------------------------------


Fortran 90 has:

"R736 pointer-assignment-stmt is pointer-object => target"
"If the target is not a pointer, the
pointer assignment statement associates the pointer-object with the target. If
the target is a pointer that is associated, the pointer-object is associated
with the same object as the target."

Due to the bounds-spec (cf. below) Fortran 2003 is more explicit:

"[...] the extent of a dimension of data-pointer-object is the extent of the
corresponding dimension of data-target. [...] the lower bound of each dimension
is the result of the intrinsic function LBOUND (13.7.60) applied to the
corresponding dimension of data-target. The upper bound of each dimension is
one less than the sum of the lower bound and the extent."

b) BOUND SPEC

(cf. 1.7 in the F2003 intro at
ftp://ftp.nag.co.uk/sc22wg5/N1601-N1650/N1648.pdf)

The following program should have a lower bound of "-1" for the pointer "p".
(Works, e.g., with the Cray compiler.)

Older gfortrans, e.g. 4.3, accepted this and set the lower bound to 1. Current
gfortran reports:
  Error: Pointer assignment to non-POINTER at (1)

!--------------------------------
integer, target :: a(2:5,2:5)
integer, pointer :: p(:,:)
p(-1:,-1:) => a
print *, 'a: ', lbound(a) ! OK, prints "2 2"
print *, 'p: ', lbound(p) ! WRONG: prints "1 1", expected: "-1 -1"
end
!--------------------------------

While Fortran 95 only has:
"R736 pointer-assignment-stmt  is  pointer-object => target"

Fortran 2003 (and F2008 as R733) have:
"R735 pointer-assignment-stmt is data-pointer-object [ (bounds-spec-list) ] =>
data-target
                              or data-pointer-object (bounds-remapping-list )
=> data-target
                              or proc-pointer-object => proc-target"

Further Fortran 2008 quotes (mostly identical to F2003, cf. also item (a)):

C716 (R733) If bounds-spec-list is specified, the number of bounds-specs shall
equal the rank of data-pointer-object.

C718 (R733) If bounds-remapping-list is not specified, the ranks of
data-pointer-object and data-target shall be the same.

R735 bounds-spec   is   lower-bound-expr :

[Remark: Note that only a lower bound can be specified; no upper or stride]

"If no bounds-remapping-list is specified, the extent of a dimension of the
pointer object is the extent of the corresponding dimension of the pointer
target. If bounds-spec-list appears, it specifies the lower bounds; otherwise,
the lower bound of each dimension is the result of the intrinsic function
LBOUND (13.7.90) applied to the corresponding dimension of the pointer target.
The upper bound of each dimension is one less than the sum of
the lower bound and the extent."

Expected: The bounds are correctly set. Additionally, the bounds are rejected
with -std=f95,


-- 
           Summary: Support pointer assignment with bound-spec; wrong bounds
                    for pointer assignment
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          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=45016