Re: typespec in forall and implied-do

[Steve Kargl <sgk@troutmask.apl.washington.edu>]

On Sun, Nov 20, 2022 at 10:28:40PM +0100, Harald Anlauf via Fortran wrote:
> Steve,
> 
> for unknown reasons I cannot reply to your mail on gmane,
> so trying directly via mailing list.
> 
> I tried your patch, and it works on the supplied testcases.
> 
> However, there is a scoping issue for the declaration of the
> index variable, as can be seen by the following variation:
> 
> program foo
>   use iso_fortran_env, only : k => real_kinds
>   implicit none
>   integer, parameter :: n = size(k)
>   integer(8) :: i
> !!$  integer, parameter :: &
> !!$       &  p(n) = [(precision(real(1.,k(i))), integer :: i = 1, n)]
>   integer, parameter :: &
>        &  q(n) = [(kind(i), integer(2) :: i = 1, n)]
>   integer, parameter :: &
>        &  r(n) = [(storage_size(i), integer(1) :: i = 1, n)]
> !!$  print *, p
>   print *, q
>   print *, r
> end program foo
> 
> After your patch, gfortran prints:
> 
>            8           8           8           8
>           64          64          64          64
> 
> This suggests that the integer kind is taken from the host decl,
> which is kind=8, and not the local one (2 or 1).
> 
> Crayftn (which chokes on your original testcase):
> 
>  3*2
>  3*8
> 
> This is what I expect.
> 
> Intel doesn't accept storage_size() here, which is a bug.
> Commenting the uses of array r, I then get:
> 
>            2           2           2
> 
> At least this agrees with Cray.
> 
> Can you have another look at this?
> 

Unfortunately, gfortran does not define a namespace for an implied-do
index and uses a kludge by adding the attr.implied_index attribute to
the symbol.  Unfortunately**2, gfortran uses gfc_match_iterator for 
all places that 'i = start, stop [,step]' and there is no way to know
if what is being parsed.  With the introduction of an optional typespec,
there is no easy way to deal with it in a clean way.  Things get messy
quickly when trying to deal with implicit typing and explicitly typed
symbols.  So, if the implied-do index has previously been typed such as

    integer(8) i
    print *, (i, integer(2) i=1, 3)

the integer(2) is ignored.  That's this part of the gfc_match_iterator
diff

+  if (seen_ts && var->ts.type == BT_UNKNOWN)
+    {
+      var->ts.type = ts.type;
+      var->ts.kind = ts.kind;
+      var->symtree->n.sym->ts.type = ts.type;
+      var->symtree->n.sym->ts.kind = ts.kind;
+    }

Perhaps, a better way would be to simply create a shadow symbol
if a typespec appears in an iterator 

    print *, (i, integer i=1,3)

would become 

    print *, (_i, integer _i=1,3)

The issue is then that implied-do object list needs to be walked
and all occurrence of i must be replaced with _i.

-- 
Steve