Re: [PATCH v18 23/26] c++: Implement __is_invocable built-in trait

[Jason Merrill <jason@redhat.com>]

On 5/2/24 16:47, Ken Matsui wrote:
> On Thu, May 2, 2024 at 1:38 PM Jason Merrill <jason@redhat.com> wrote:
>>
>> On 5/2/24 16:12, Ken Matsui wrote:
>>> This patch implements built-in trait for std::is_invocable.
>>>
>>> gcc/cp/ChangeLog:
>>>
>>>        * cp-trait.def: Define __is_invocable.
>>>        * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_INVOCABLE.
>>>        * semantics.cc (trait_expr_value): Likewise.
>>>        (finish_trait_expr): Likewise.
>>>        * cp-tree.h (build_invoke): New function.
>>>        * method.cc (build_invoke): New function.
>>>
>>> gcc/testsuite/ChangeLog:
>>>
>>>        * g++.dg/ext/has-builtin-1.C: Test existence of __is_invocable.
>>>        * g++.dg/ext/is_invocable1.C: New test.
>>>        * g++.dg/ext/is_invocable2.C: New test.
>>>        * g++.dg/ext/is_invocable3.C: New test.
>>>        * g++.dg/ext/is_invocable4.C: New test.
>>>
>>> Signed-off-by: Ken Matsui <kmatsui@gcc.gnu.org>
>>> ---
>>>    gcc/cp/constraint.cc                     |   6 +
>>>    gcc/cp/cp-trait.def                      |   1 +
>>>    gcc/cp/cp-tree.h                         |   2 +
>>>    gcc/cp/method.cc                         | 134 +++++++++
>>>    gcc/cp/semantics.cc                      |   5 +
>>>    gcc/testsuite/g++.dg/ext/has-builtin-1.C |   3 +
>>>    gcc/testsuite/g++.dg/ext/is_invocable1.C | 349 +++++++++++++++++++++++
>>>    gcc/testsuite/g++.dg/ext/is_invocable2.C | 139 +++++++++
>>>    gcc/testsuite/g++.dg/ext/is_invocable3.C |  51 ++++
>>>    gcc/testsuite/g++.dg/ext/is_invocable4.C |  33 +++
>>>    10 files changed, 723 insertions(+)
>>>    create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable1.C
>>>    create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable2.C
>>>    create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable3.C
>>>    create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable4.C
>>>
>>> diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
>>> index c28d7bf428e..6d14ef7dcc7 100644
>>> --- a/gcc/cp/constraint.cc
>>> +++ b/gcc/cp/constraint.cc
>>> @@ -3792,6 +3792,12 @@ diagnose_trait_expr (tree expr, tree args)
>>>        case CPTK_IS_FUNCTION:
>>>          inform (loc, "  %qT is not a function", t1);
>>>          break;
>>> +    case CPTK_IS_INVOCABLE:
>>> +      if (!t2)
>>> +    inform (loc, "  %qT is not invocable", t1);
>>> +      else
>>> +    inform (loc, "  %qT is not invocable by %qE", t1, t2);
>>> +      break;
>>>        case CPTK_IS_LAYOUT_COMPATIBLE:
>>>          inform (loc, "  %qT is not layout compatible with %qT", t1, t2);
>>>          break;
>>> diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
>>> index b1c875a6e7d..4e420d5390a 100644
>>> --- a/gcc/cp/cp-trait.def
>>> +++ b/gcc/cp/cp-trait.def
>>> @@ -75,6 +75,7 @@ DEFTRAIT_EXPR (IS_EMPTY, "__is_empty", 1)
>>>    DEFTRAIT_EXPR (IS_ENUM, "__is_enum", 1)
>>>    DEFTRAIT_EXPR (IS_FINAL, "__is_final", 1)
>>>    DEFTRAIT_EXPR (IS_FUNCTION, "__is_function", 1)
>>> +DEFTRAIT_EXPR (IS_INVOCABLE, "__is_invocable", -1)
>>>    DEFTRAIT_EXPR (IS_LAYOUT_COMPATIBLE, "__is_layout_compatible", 2)
>>>    DEFTRAIT_EXPR (IS_LITERAL_TYPE, "__is_literal_type", 1)
>>>    DEFTRAIT_EXPR (IS_MEMBER_FUNCTION_POINTER, "__is_member_function_pointer", 1)
>>> diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
>>> index 1938ada0268..83dc20e1130 100644
>>> --- a/gcc/cp/cp-tree.h
>>> +++ b/gcc/cp/cp-tree.h
>>> @@ -7338,6 +7338,8 @@ extern tree get_copy_assign                     (tree);
>>>    extern tree get_default_ctor                        (tree);
>>>    extern tree get_dtor                                (tree, tsubst_flags_t);
>>>    extern tree build_stub_object                       (tree);
>>> +extern tree build_invoke                     (tree, const_tree,
>>> +                                              tsubst_flags_t);
>>>    extern tree strip_inheriting_ctors          (tree);
>>>    extern tree inherited_ctor_binfo            (tree);
>>>    extern bool base_ctor_omit_inherited_parms  (tree);
>>> diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
>>> index 08a3d34fb01..faf932258e6 100644
>>> --- a/gcc/cp/method.cc
>>> +++ b/gcc/cp/method.cc
>>> @@ -1928,6 +1928,140 @@ build_trait_object (tree type)
>>>      return build_stub_object (type);
>>>    }
>>>
>>> +/* [func.require] Build an expression of INVOKE(FN_TYPE, ARG_TYPES...).  If the
>>> +   given is not invocable, returns error_mark_node.  */
>>> +
>>> +tree
>>> +build_invoke (tree fn_type, const_tree arg_types, tsubst_flags_t complain)
>>> +{
>>> +  if (error_operand_p (fn_type) || error_operand_p (arg_types))
>>> +    return error_mark_node;
>>> +
>>> +  gcc_assert (TYPE_P (fn_type));
>>> +  gcc_assert (TREE_CODE (arg_types) == TREE_VEC);
>>> +
>>> +  /* Access check is required to determine if the given is invocable.  */
>>> +  deferring_access_check_sentinel acs (dk_no_deferred);
>>> +
>>> +  /* INVOKE is an unevaluated context.  */
>>> +  cp_unevaluated cp_uneval_guard;
>>> +
>>> +  bool is_ptrdatamem;
>>> +  bool is_ptrmemfunc;
>>> +  if (TREE_CODE (fn_type) == REFERENCE_TYPE)
>>> +    {
>>> +      tree deref_fn_type = TREE_TYPE (fn_type);
>>> +      is_ptrdatamem = TYPE_PTRDATAMEM_P (deref_fn_type);
>>> +      is_ptrmemfunc = TYPE_PTRMEMFUNC_P (deref_fn_type);
>>> +
>>> +      /* Dereference fn_type if it is a pointer to member.  */
>>> +      if (is_ptrdatamem || is_ptrmemfunc)
>>> +     fn_type = deref_fn_type;
>>> +    }
>>> +  else
>>> +    {
>>> +      is_ptrdatamem = TYPE_PTRDATAMEM_P (fn_type);
>>> +      is_ptrmemfunc = TYPE_PTRMEMFUNC_P (fn_type);
>>> +    }
>>> +
>>> +  if (is_ptrdatamem && TREE_VEC_LENGTH (arg_types) != 1)
>>> +    {
>>> +      if (complain & tf_error)
>>> +     error ("pointer to data member type %qT can only be invoked with "
>>> +            "one argument", fn_type);
>>> +      return error_mark_node;
>>> +    }
>>> +
>>> +  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
>>> +    {
>>> +      if (complain & tf_error)
>>> +     error ("pointer to member function type %qT must be invoked with "
>>> +            "at least one argument", fn_type);
>>> +      return error_mark_node;
>>> +    }
>>> +
>>> +  /* Construct an expression of a pointer to member.  */
>>> +  tree ptrmem_expr;
>>> +  if (is_ptrdatamem || is_ptrmemfunc)
>>> +    {
>>> +      tree datum_type = TREE_VEC_ELT (arg_types, 0);
>>> +
>>> +      /* datum must be a class type or a reference/pointer to a class type.  */
>>> +      if (!(CLASS_TYPE_P (datum_type)
>>> +         || ((TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
>>> +             && CLASS_TYPE_P (TREE_TYPE (datum_type)))))
>>> +     {
>>> +       if (complain & tf_error)
>>> +         error ("first argument type %qT of a pointer to member must be"
>>> +                "a class type or a reference/pointer to a class type",
>>> +                datum_type);
>>> +       return error_mark_node;
>>> +     }
>>> +
>>> +      bool is_refwrap = false;
>>> +      if (CLASS_TYPE_P (datum_type))
>>> +     {
>>> +       /* 1.2 & 1.5: Handle std::reference_wrapper.  */
>>> +       tree datum_decl = TYPE_NAME (TYPE_MAIN_VARIANT (datum_type));
>>> +       if (decl_in_std_namespace_p (datum_decl))
>>> +         {
>>> +           const_tree name = DECL_NAME (datum_decl);
>>> +           if (name && (id_equal (name, "reference_wrapper")))
>>> +             {
>>> +               /* Retrieve T from std::reference_wrapper<T>,
>>> +                  i.e., decltype(datum.get()).  */
>>> +               datum_type = TREE_VEC_ELT (TYPE_TI_ARGS (datum_type), 0);
>>> +               is_refwrap = true;
>>> +             }
>>> +         }
>>> +     }
>>> +
>>> +      tree ptrmem_class_type = TYPE_PTRMEM_CLASS_TYPE (fn_type);
>>> +      const bool ptrmem_is_base_of_datum =
>>> +     (NON_UNION_CLASS_TYPE_P (ptrmem_class_type)
>>> +      && NON_UNION_CLASS_TYPE_P (datum_type)
>>
>> Why NON_UNION?  That doesn't seem to be based on anything in the standard.
> 
> This comes from the __is_base_of implementation in semantics.cc:
> 
>      case CPTK_IS_BASE_OF:
>        return (NON_UNION_CLASS_TYPE_P (type1) && NON_UNION_CLASS_TYPE_P (type2)
>        && (same_type_ignoring_top_level_qualifiers_p (type1, type2)
>    || DERIVED_FROM_P (type1, type2)));

OK, but non-union isn't a requirement for is_same, but you're applying 
that requirement for the same-type case as well as for the base case.

>> This check and the one for reference_wrapper need to ignore
>> REFERENCE_TYPE; INVOKE is defined in terms of expressions, and the type
>> of an expression is never a reference.

> I think ptrmem_is_base_of_datum and is_refwrap checks are ignoring
> REFERENCE_TYPE, leading to false, ...

I mean they need to look through REFERENCE_TYPE; if the first argument 
is reference to reference_wrapper, we need to use the reference_wrapper 
handling.  Likewise if it's a reference to T or a base of T.

>>> +      && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
>>> +                                                     datum_type)
>>> +          || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
>>> +
>>> +      tree datum_expr = build_trait_object (datum_type);
>>> +      if (!ptrmem_is_base_of_datum && !is_refwrap && !TYPE_REF_P (datum_type))
>>
>> ...so we shouldn't need to check TYPE_REF_P here.

> ... which is why I think we need to check TYPE_REF_P here.

The standard says that if t1 isn't either same, base, or 
reference_wrapper, we dereference it.  There's no exception for 
references because they shouldn't get this far.

Jason