[gfortran] Fix PR 12841: Passing NULL to a subroutine

[Tobias Schlüter <tobias dot schlueter at physik dot uni-muenchen dot de>]

This needed two independent fixes:
1. when NULL appears in an arglist we don't want to compare shape and 
rank of the parameters
2. when building the function call EXPR_NULL does not need its address 
taken, because it already returns an address. Maybe it would be better 
to have it handled the same way as other pointers, but this seemed out 
of reach, as we use the backend's null_pointer_node.

Unfortunately, or number of total bugs is not lowered by this, because 
while investigating this bug, I ran into what is now PR15754.

- Tobi

Index: interface.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/interface.c,v
retrieving revision 1.4
diff -u -p -r1.4 interface.c
--- interface.c 27 May 2004 12:35:12 -0000      1.4
+++ interface.c 31 May 2004 22:37:18 -0000
@@ -1096,7 +1096,8 @@ compare_parameter (gfc_symbol * formal,
       return compare_interfaces (formal, actual->symtree->n.sym, 0);
     }

-  if (!gfc_compare_types (&formal->ts, &actual->ts))
+  if (actual->expr_type != EXPR_NULL
+      && !gfc_compare_types (&formal->ts, &actual->ts))
     return 0;

   if (symbol_rank (formal) == actual->rank)
@@ -1235,7 +1236,8 @@ compare_actual_formal (gfc_actual_arglis
          return 0;
        }

-      if (compare_pointer (f->sym, a->expr) == 0)
+      if (a->expr->expr_type != EXPR_NULL
+         && compare_pointer (f->sym, a->expr) == 0)
        {
          if (where)
            gfc_error ("Actual argument for '%s' must be a pointer at %L",
Index: trans-expr.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/fortran/trans-expr.c,v
retrieving revision 1.7
diff -u -p -r1.7 trans-expr.c
--- trans-expr.c        30 May 2004 14:37:24 -0000      1.7
+++ trans-expr.c        31 May 2004 22:37:18 -0000
@@ -1099,10 +1099,12 @@ gfc_conv_function_call (gfc_se * se, gfc
          if (argss == gfc_ss_terminator)
             {
              gfc_conv_expr_reference (&parmse, arg->expr);
-              if (formal && formal->sym->attr.pointer)
+              if (formal && formal->sym->attr.pointer
+                 && arg->expr->expr_type != EXPR_NULL)
                 {
                   /* Scalar pointer dummy args require an extra level of
-                     indirection.  */
+                     indirection. The null pointer already contains
+                    this level of indirection. */
                   parmse.expr = gfc_build_addr_expr (NULL, parmse.expr);
                 }
             }