Re: [PATCH] c++: Add !TYPE_P assert to type_dependent_expression_p [PR99080]

[Marek Polacek <polacek@redhat.com>]

On Fri, May 27, 2022 at 11:52:12AM -0400, Jason Merrill wrote:
> On 5/26/22 20:33, Marek Polacek wrote:
> > As discussed here:
> > <https://gcc.gnu.org/pipermail/gcc-patches/2021-February/564629.html>,
> > type_dependent_expression_p should not be called with a type argument.
> > 
> > I promised I'd add an assert so here it is.  One place needed adjusting,
> > the comment explains why.
> > 
> > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
> > 
> > 	PR c++/99080
> > 
> > gcc/cp/ChangeLog:
> > 
> > 	* pt.cc (type_dependent_expression_p): Assert !TYPE_P.
> > 	* semantics.cc (finish_id_expression_1): Don't call
> > 	type_dependent_expression_p for a type.
> > ---
> >   gcc/cp/pt.cc        | 2 ++
> >   gcc/cp/semantics.cc | 4 +++-
> >   2 files changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> > index 24bbe2f4060..89156cb88b4 100644
> > --- a/gcc/cp/pt.cc
> > +++ b/gcc/cp/pt.cc
> > @@ -27727,6 +27727,8 @@ type_dependent_expression_p (tree expression)
> >     if (expression == NULL_TREE || expression == error_mark_node)
> >       return false;
> > +  gcc_checking_assert (!TYPE_P (expression));
> > +
> >     STRIP_ANY_LOCATION_WRAPPER (expression);
> >     /* An unresolved name is always dependent.  */
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index cd7a2818feb..7f8502f49b0 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -4141,7 +4141,9 @@ finish_id_expression_1 (tree id_expression,
> >       }
> >     else
> >       {
> > -      bool dependent_p = type_dependent_expression_p (decl);
> > +      /* DECL could be e.g. UNBOUND_CLASS_TEMPLATE which is a type which
> > +	 t_d_e_p doesn't accept.  */
> > +      bool dependent_p = !TYPE_P (decl) && type_dependent_expression_p (decl);
> 
> Maybe instead we could handle UNBOUND_CLASS_TEMPLATE at a higher level in
> the function, like with an 'else if' before this 'else'?

Maybe, but I think I'd have to duplicate (parts of) this block:

 4227       else if (scope)
 4228         {
 4229           if (TREE_CODE (decl) == SCOPE_REF)
 4230             {
 4231               gcc_assert (same_type_p (scope, TREE_OPERAND (decl, 0)));
 4232               decl = TREE_OPERAND (decl, 1);
 4233             }
 4234
 4235           decl = (adjust_result_of_qualified_name_lookup
 4236                   (decl, scope, current_nonlambda_class_type()));
 4237
 4238           cp_warn_deprecated_use_scopes (scope);
 4239
 4240           if (TYPE_P (scope))
 4241             decl = finish_qualified_id_expr (scope,
 4242                                              decl,
 4243                                              done,
 4244                                              address_p,
 4245                                              template_p,
 4246                                              template_arg_p,
 4247                                              tf_warning_or_error);
 4248           else
 4249             decl = convert_from_reference (decl);
 4250         }

Would that be acceptable?  Can't do

  else if (TREE_CODE (decl) == UNBOUND_CLASS_TEMPLATE)
    {
      gcc_checking_assert (scope);
      *idk = CP_ID_KIND_QUALIFIED;
      goto do_scope;
    }
because that will complain about skipping the initialization of dependent_p.

Here's a patch with the partial duplication, which passes dg.exp:

-- >8 --
As discussed here:
<https://gcc.gnu.org/pipermail/gcc-patches/2021-February/564629.html>,
type_dependent_expression_p should not be called with a type argument.

I promised I'd add an assert so here it is.  One place needed adjusting.

	PR c++/99080

gcc/cp/ChangeLog:

	* pt.cc (type_dependent_expression_p): Assert !TYPE_P.
	* semantics.cc (finish_id_expression_1): Handle UNBOUND_CLASS_TEMPLATE
	specifically.
---
 gcc/cp/pt.cc        |  2 ++
 gcc/cp/semantics.cc | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 24bbe2f4060..89156cb88b4 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -27727,6 +27727,8 @@ type_dependent_expression_p (tree expression)
   if (expression == NULL_TREE || expression == error_mark_node)
     return false;
 
+  gcc_checking_assert (!TYPE_P (expression));
+
   STRIP_ANY_LOCATION_WRAPPER (expression);
 
   /* An unresolved name is always dependent.  */
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index cdc91a38e25..f62b0a4a736 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -4139,6 +4139,17 @@ finish_id_expression_1 (tree id_expression,
 	}
       return r;
     }
+  else if (TREE_CODE (decl) == UNBOUND_CLASS_TEMPLATE)
+    {
+      gcc_checking_assert (scope);
+      *idk = CP_ID_KIND_QUALIFIED;
+      decl = (adjust_result_of_qualified_name_lookup
+	      (decl, scope, current_nonlambda_class_type()));
+      cp_warn_deprecated_use_scopes (scope);
+      decl = finish_qualified_id_expr (scope, decl, done, address_p,
+				       template_p, template_arg_p,
+				       tf_warning_or_error);
+    }
   else
     {
       bool dependent_p = type_dependent_expression_p (decl);

base-commit: d822f4bbd714c6595f70cc68888dcebecfb6662d
-- 
2.36.1