Re: [PATCH] PR fortran/104573 - ICE in resolve_structure_cons, at fortran/resolve.cc:1299

[Mikael Morin <morin-mikael@orange.fr>]

Le 16/02/2022 à 22:20, Harald Anlauf via Fortran a écrit :
> Dear Fortranners,
> 
> while we detect invalid uses of type(*), we may run into other issues
> later when the declared variable is used, leading to an ICE due to a
> NULL pointer dereference.  This is demonstrated by Gerhard's testcase.
> 
> Steve and I came to rather similar fixes, see PR.  Mine is attached.
> 
> Regtested on x86_64-pc-linux-gnu.  OK for mainline?
> 
> Thanks,
> Harald
> 

> diff --git a/gcc/fortran/resolve.cc b/gcc/fortran/resolve.cc
> index 266e41e25b1..2fa1acdbd6d 100644
> --- a/gcc/fortran/resolve.cc
> +++ b/gcc/fortran/resolve.cc
> @@ -1288,15 +1288,17 @@ resolve_structure_cons (gfc_expr *expr, int init)
>  	}
>      }
> 
> -  cons = gfc_constructor_first (expr->value.constructor);
> -
>    /* A constructor may have references if it is the result of substituting a
>       parameter variable.  In this case we just pull out the component we
>       want.  */
>    if (expr->ref)
>      comp = expr->ref->u.c.sym->components;
> -  else
> +  else if (expr->ts.u.derived)
>      comp = expr->ts.u.derived->components;

These unprotected union accesses always make me nervous.
I have tried (hard) to exhibit a case not fixed by your patch,
and I have found the case below that almost qualifies, except that there 
is an ICE before anything can happen.
With a minor tweak to prevent the ICE, the problem does appear.

program p
   type t
     integer :: a
   end type
   character(3), parameter :: x = t(2)
   character(3), parameter :: y = x
   print *, y
end

In that case the character length information occupies the same space as 
a derived type symbol; the else-if condition evaluates to true, and 
everything breaks from there.

So please use a condition on expr->ts.type instead.
I think the relevant values associated with ts->u.derived are 
BT_DERIVED, BT_CLASS and BT_UNION.

OK with that change.

Thanks, and sorry for the time I took before looking at it.