Re: [PATCH] Fortran: restrictions on integer arguments to SYSTEM_CLOCK [PR112609]

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

On Sat, Nov 18, 2023 at 11:12:55PM +0100, Harald Anlauf wrote:
> 
> Fortran 2023 added restrictions on integer arguments to SYSTEM_CLOCK.
> The attached patch implements these.
> 
> I was struggling with the way we should handle features that are sort-of
> deleted in a new standard, but not described as such in the standard,
> which is why we do not have GFC_STD_F2023_DEL.  As -std=gnu should not
> apply this restriction, I came up with the solution in the patch.
> While playing, I hit a gcc_unreachable in notify_std_msg due to a
> missing case, also fixed.
> 
> Interestingly, the standard now has a recommendation:
> 
> 16.9.202 SYSTEM_CLOCK
> 
> It it recommended that all references to SYSTEM_CLOCK use integer
> arguments with a decimal exponent range of at least 18. ...
> 
> In case the user chooses integer(4), shall we emit a warning
> e.g. under -pedantic, or some other flag?  This is not done
> in the patch, but could be added.
> 
> Regtested on x86_64-pc-linux-gnu.  OK for mainline?
> 

Not in its current form.

>  {
> +  int first_int_kind = -1;
> +  bool f2023 = ((gfc_option.allow_std & GFC_STD_F2023) != 0
> +		&& (gfc_option.allow_std & GFC_STD_GNU) == 0);
> +

If you use the gfc_notify_std(), then you should not need the
above check on GFC_STD_GNU as it should include GFC_STD_F2023.

> 
> +      if (f2023 && count->ts.kind < gfc_default_integer_kind)
> +	{
> +	  gfc_error ("Fortran 2023: COUNT argument to SYSTEM_CLOCK "
> +		     "at %L must have kind of at least default integer",
> +		     &count->where);
> +	  return false;
> +	}

Elsewhere in the FE, gfortran uses gfc_notify_std() to enforce 
requirements of a Fortran standard.  The above would be 

      if (count->ts.kind < gfc_default_integer_kind
          && gfc_notify_std (GFC_STD_F2023, "COUNT argument to SYSTEM_CLOCK "
                             "at %L must have kind of at least default integer",
                             &count->where))

Note, gfc_notify_std() should add the 'Fortran 2023: ' string,
if not, that should be fixed.

Of course, I seldom provide patches if others don't have a comment
then do as you like.

-- 
Steve