[Patch] Fortran: Fix intrinsic null() handling [PR99651]

[Tobias Burnus]

Hi Paul,

On 23.03.21 18:34, Paul Richard Thomas wrote:
> I took something of a detour in reviewing this patch. Although short,
> understanding it is not straightforward!

I concur – and as I wrote both in the patch email and in the PR, it is
not straight forward which message is showing with which setting.

Actually, I think there are many straight-forward ways to fix it
"properly" but they tend to hide some nicer error messages in favour of
a more generic one. Only by taking into account all the diagnostic and
hidden/delayed diagnostic, the patch becomes complex. (-:

> Your patch works as advertised and regtests OK (with the patch for
> PR93660 on board as well). Is NULL the only case where this can happen?

I am not sure whether any other code would profit form getting one of
the attributes conditionally assigned in intrinsic.c.

Otherwise, I think that's the only code which verifies like that it in
such a way whether an intrinsic function was used. I think the reason
that it does so is because 'null' is turned early during parsing into
EXPR_NULL, which is not a function and, hence, bypasses some of the
later checking code in resolve.c.


> Just to aid my understanding, I tried:
> diff --git a/gcc/fortran/primary.c b/gcc/fortran/primary.c
>
> --- a/gcc/fortran/primary.c
> +++ b/gcc/fortran/primary.c
> @@ -3922,6 +3922,9 @@ gfc_match_rvalue (gfc_expr **result)
>        if (m == MATCH_NO)
>         m = MATCH_YES;
>
> +      if (!strcmp (sym->name, "NULL") || !strcmp (sym->name, "null"))
> +       sym->attr.intrinsic = 1;
> +
>        break;
>
>      generic_function:
>
> which also works and regtests OK. (I couldn't remember whether
> sym->name is upper or lower case at this stage.)

Should be always lowercase, I think. But I am also not sure that your
aid-understanding patch will work correctly with 'external null' or a
use-/host-associated/interface 'null' procedure or some array variable.
Inside intrinsic.c, we are at least sure that we did get an intrinsic
function after having passed all intrinsic checks.

Tobias

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