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

[Jason Merrill <jason@redhat.com>]

On 5/27/22 12:43, Marek Polacek wrote:
> 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()));

This call should have no effect, it only affects BASELINKs.  OK without 
this statement.

> +      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