[Bug fortran/48831] New: check.c: Constant expression (PARAMETER array element) rejected as nonconstant

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48831

           Summary: check.c: Constant expression (PARAMETER array element)
                    rejected as nonconstant
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: major
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org
            Blocks: 32834


I know that this PR is a duplicate of some PR which I cannot find.

http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/d0bd8bd1803b626e
has the following program, which is rejected with:


    i3 = int(0, i2(1))  ! This line gives an error when compiling.
                1
Error: 'kind' argument of 'int' intrinsic at (1) must be a constant


In check.c, there is a simple expr_type == EXPR_CONSTANT check; however, using
gfc_is_constant_expr() doesn't work either as PARAMETER (arrays) are not
recognized as being constant. (EXPR_VARIABLE + FL_PARAMETER.)

I think expr.c's check_init_expr might be better (it is currently static);
however, I have the feeling all checks are wrong.

Note: Fortran 95 distinguishes between initialization and constant expressions,
in Fortran 2003 and Fortran 2008 they have been merged to a single type -
called "initialization expressions" in Fortran 2003 and "constant expressions"
in Fortran 2008.

TODO:
- Find out what F90's constant and init expressions mean
- Make the less powerful call the more powerful, except for -std=f95
- Add checks for init/constant following the F95 pattern everywhere instead of
using the half-baked EXPR_CONST or some made up test which check more, but only
locally (e.g. const_expr + const array, as done in simplify.c)


Note: The case below should unaffected by the const/init change and should be
already valid Fortran 95.

program p1
    implicit none
    integer, parameter  :: i1    = kind(0)
    integer, parameter  :: i2(1) = [i1]
    integer(kind=i2(1)) :: i3

    i3 = int(0, i1)
    print *, i3

    i3 = int(0, i2(1))  ! This line gives an error when compiling.
    print *, i3
end program p1