[v14,23/26] c++: Implement __is_invocable built-in trait

Message ID	20240228192843.188979-24-kmatsui@gcc.gnu.org
State	New
Headers	show Return-Path: <gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org> DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org D72553858C62 From: Ken Matsui <kmatsui@gcc.gnu.org> To: gcc-patches@gcc.gnu.org Cc: libstdc++@gcc.gnu.org, Ken Matsui <kmatsui@gcc.gnu.org> Subject: [PATCH v14 23/26] c++: Implement __is_invocable built-in trait Date: Wed, 28 Feb 2024 11:26:28 -0800 Message-ID: <20240228192843.188979-24-kmatsui@gcc.gnu.org> In-Reply-To: <20240228192843.188979-1-kmatsui@gcc.gnu.org> References: <20240221093616.4001742-1-kmatsui@gcc.gnu.org> <20240228192843.188979-1-kmatsui@gcc.gnu.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: list Errors-To: gcc-patches-bounces+incoming=patchwork.ozlabs.org@gcc.gnu.org
Series	Optimize more type traits \| expand [v14,00/26] Optimize more type traits [v14,01/26] c++: Implement __is_const built-in trait [v14,02/26] libstdc++: Optimize std::is_const compilation performance [v14,03/26] c++: Implement __is_volatile built-in trait [v14,04/26] libstdc++: Optimize std::is_volatile compilation performance [v14,05/26] c++: Implement __is_pointer built-in trait [v14,06/26] libstdc++: Optimize std::is_pointer compilation performance [v14,07/26] c++: Implement __is_unbounded_array built-in trait [v14,08/26] libstdc++: Optimize std::is_unbounded_array compilation performance [v14,09/26] c++: Implement __add_pointer built-in trait [v14,10/26] libstdc++: Optimize std::add_pointer compilation performance [v14,11/26] c++: Implement __remove_extent built-in trait [v14,12/26] libstdc++: Optimize std::remove_extent compilation performance [v14,13/26] c++: Implement __remove_all_extents built-in trait [v14,14/26] libstdc++: Optimize std::remove_all_extents compilation performance [v14,15/26] c++: Implement __add_lvalue_reference built-in trait [v14,16/26] libstdc++: Optimize std::add_lvalue_reference compilation performance [v14,17/26] c++: Implement __add_rvalue_reference built-in trait [v14,18/26] libstdc++: Optimize std::add_rvalue_reference compilation performance [v14,19/26] c++: Implement __decay built-in trait [v14,20/26] libstdc++: Optimize std::decay compilation performance [v14,21/26] c++: Implement __rank built-in trait [v14,22/26] libstdc++: Optimize std::rank compilation performance [v14,23/26] c++: Implement __is_invocable built-in trait [v14,24/26] libstdc++: Optimize std::is_invocable compilation performance [v14,25/26] c++: Implement __is_nothrow_invocable built-in trait [v14,26/26] libstdc++: Optimize std::is_nothrow_invocable compilation performance

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20240228192843.188979-24-kmatsui@gcc.gnu.org

State

New

Headers

DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org D72553858C62
From: Ken Matsui <kmatsui@gcc.gnu.org>
To: gcc-patches@gcc.gnu.org
Cc: libstdc++@gcc.gnu.org, Ken Matsui <kmatsui@gcc.gnu.org>
Subject: [PATCH v14 23/26] c++: Implement __is_invocable built-in trait
Date: Wed, 28 Feb 2024 11:26:28 -0800
Message-ID: <20240228192843.188979-24-kmatsui@gcc.gnu.org>
In-Reply-To: <20240228192843.188979-1-kmatsui@gcc.gnu.org>
References: <20240221093616.4001742-1-kmatsui@gcc.gnu.org>
 <20240228192843.188979-1-kmatsui@gcc.gnu.org>
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Series

Optimize more type traits | expand

Commit Message

Ken Matsui Feb. 28, 2024, 7:26 p.m. UTC

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                         | 132 +++++++++
 gcc/cp/semantics.cc                      |   4 +
 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, 720 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

Comments

Patrick Palka March 8, 2024, 5:17 p.m. UTC | #1

On Wed, 28 Feb 2024, 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.

Thanks, this looks great!  This generic build_invoke function could be
used for invoke_result etc as well, and it could also cache the built-up
call across __is_invocable and __is_nothrow_invocable checks on the same
arguments (which is a common pattern in the standard library).  LGTM

> 
> 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                         | 132 +++++++++
>  gcc/cp/semantics.cc                      |   4 +
>  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, 720 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 23ea66d9c12..c87b126fdb1 100644
> --- a/gcc/cp/constraint.cc
> +++ b/gcc/cp/constraint.cc
> @@ -3791,6 +3791,12 @@ 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 85056c8140b..6cb2b55f4ea 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 334c11396c2..261d3a71faa 100644
> --- a/gcc/cp/cp-tree.h
> +++ b/gcc/cp/cp-tree.h
> @@ -7334,6 +7334,8 @@ 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 98c10e6a8b5..953f1bed6fc 100644
> --- a/gcc/cp/method.cc
> +++ b/gcc/cp/method.cc
> @@ -1928,6 +1928,138 @@ 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 (fn_type == error_mark_node || arg_types == error_mark_node)
> +    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)
> +    /* Only a pointer to data member with one argument is invocable.  */

Just one note, if/when build_invoke gets a caller that passes tf_error
(for e.g. elaborating why is_invocable is false, or why invoke_result
is ill-formed) these error_mark_node code paths will need to issue
diagnostics b.

> +    return error_mark_node;
> +
> +  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
> +    /* A pointer to member function with no arguments is not invocable.  */
> +    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 (TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
> +        {
> +	  if (!CLASS_TYPE_P (TREE_TYPE (datum_type)))
> +	    return error_mark_node;
> +        }
> +      else if (!CLASS_TYPE_P (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 datum_expr = build_trait_object (datum_type);
> +      tree fn_expr = build_trait_object (fn_type);
> +      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr, complain);
> +
> +      if (error_operand_p (ptrmem_expr) && !is_refwrap)
> +	{
> +	  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)
> +	     && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
> +							    datum_type)
> +		 || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
> +
> +	  if (!ptrmem_is_base_of_datum)
> +	    {
> +	      /* 1.3 & 1.6: Try to dereference datum_expr.  */
> +	      datum_expr = build_x_indirect_ref (UNKNOWN_LOCATION, datum_expr,
> +						 RO_UNARY_STAR, NULL_TREE,
> +						 complain);
> +	      /* Rebuild ptrmem_expr.  */
> +	      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr,
> +						   complain);
> +	    }
> +	}
> +      /* 1.1 & 1.4: Otherwise.  */
> +
> +      if (error_operand_p (ptrmem_expr))
> +	return error_mark_node;
> +
> +      if (is_ptrdatamem)
> +	return ptrmem_expr;
> +    }
> +
> +  /* Construct expressions for arguments to INVOKE.  For a pointer to member
> +     function, the first argument, which is the object, is not arguments to
> +     the function.  */
> +  releasing_vec args;
> +  for (int i = is_ptrmemfunc ? 1 : 0; i < TREE_VEC_LENGTH (arg_types); ++i)
> +    {
> +      tree arg_type = TREE_VEC_ELT (arg_types, i);
> +      tree arg = build_trait_object (arg_type);
> +      vec_safe_push (args, arg);
> +    }
> +
> +  tree invoke_expr;
> +  if (is_ptrmemfunc)
> +    invoke_expr = build_offset_ref_call_from_tree (ptrmem_expr, &args,
> +						   complain);
> +  else  /* 1.7.  */
> +    invoke_expr = finish_call_expr (build_trait_object (fn_type), &args, false,
> +				    false, complain);
> +  return invoke_expr;
> +}
> +
>  /* Determine which function will be called when looking up NAME in TYPE,
>     called with a single ARGTYPE argument, or no argument if ARGTYPE is
>     null.  FLAGS and COMPLAIN are as for build_new_method_call.
> diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> index 7242db75248..149c0631d62 100644
> --- a/gcc/cp/semantics.cc
> +++ b/gcc/cp/semantics.cc
> @@ -12467,6 +12467,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
>      case CPTK_IS_FUNCTION:
>        return type_code1 == FUNCTION_TYPE;
>  
> +    case CPTK_IS_INVOCABLE:
> +      return !error_operand_p (build_invoke (type1, type2, tf_none));
> +
>      case CPTK_IS_LAYOUT_COMPATIBLE:
>        return layout_compatible_type_p (type1, type2);
>  
> @@ -12682,6 +12685,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
>        break;
>  
>      case CPTK_IS_CONVERTIBLE:
> +    case CPTK_IS_INVOCABLE:
>      case CPTK_IS_NOTHROW_ASSIGNABLE:
>      case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
>      case CPTK_IS_NOTHROW_CONVERTIBLE:
> diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> index 7f7b27f7aa7..d2a7ebdf25c 100644
> --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> @@ -104,6 +104,9 @@
>  #if !__has_builtin (__is_function)
>  # error "__has_builtin (__is_function) failed"
>  #endif
> +#if !__has_builtin (__is_invocable)
> +# error "__has_builtin (__is_invocable) failed"
> +#endif
>  #if !__has_builtin (__is_layout_compatible)
>  # error "__has_builtin (__is_layout_compatible) failed"
>  #endif
> diff --git a/gcc/testsuite/g++.dg/ext/is_invocable1.C b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> new file mode 100644
> index 00000000000..d21ae1d1958
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> @@ -0,0 +1,349 @@
> +// { dg-do compile { target c++11 } }
> +
> +#define SA(X) static_assert((X),#X)
> +
> +using func_type_v0 = void(*)();
> +
> +SA(   __is_invocable( func_type_v0 ) );
> +SA( ! __is_invocable( func_type_v0, int ) );
> +
> +using func_type_i0 = int(*)();
> +
> +SA(   __is_invocable( func_type_i0 ) );
> +SA( ! __is_invocable( func_type_i0, int ) );
> +
> +using func_type_l0 = int&(*)();
> +
> +SA(   __is_invocable( func_type_l0 ) );
> +SA( ! __is_invocable( func_type_l0(int) ) );
> +
> +using func_type_ii = int(*)(int);
> +
> +SA( ! __is_invocable( func_type_ii ) );
> +SA(   __is_invocable( func_type_ii, int ) );
> +
> +using func_type_il = int(*)(int&);
> +
> +SA( ! __is_invocable( func_type_il ) );
> +SA( ! __is_invocable( func_type_il, int ) );
> +SA(   __is_invocable( func_type_il, int& ) );
> +
> +using func_type_ir = int(*)(int&&);
> +
> +SA( ! __is_invocable( func_type_ir ) );
> +SA( ! __is_invocable( func_type_ir, int& ) );
> +SA(   __is_invocable( func_type_ir, int ) );
> +SA(   __is_invocable( func_type_ir, int&& ) );
> +
> +struct A { };
> +
> +using mem_type_i = int A::*;
> +
> +SA( ! __is_invocable( mem_type_i ) );
> +SA( ! __is_invocable( mem_type_i, int ) );
> +SA( ! __is_invocable( mem_type_i, int* ) );
> +SA( ! __is_invocable( mem_type_i, int& ) );
> +SA( ! __is_invocable( mem_type_i, int&& ) );
> +SA(   __is_invocable( mem_type_i, A ) );
> +SA(   __is_invocable( mem_type_i, A* ) );
> +SA(   __is_invocable( mem_type_i, A& ) );
> +SA(   __is_invocable( mem_type_i, A&& ) );
> +SA(   __is_invocable( mem_type_i, const A& ) );
> +SA( ! __is_invocable( mem_type_i, A&, int ) );
> +
> +using memfun_type_i = int (A::*)();
> +
> +SA( ! __is_invocable( memfun_type_i ) );
> +SA( ! __is_invocable( memfun_type_i, int ) );
> +SA( ! __is_invocable( memfun_type_i, int* ) );
> +SA( ! __is_invocable( memfun_type_i, int& ) );
> +SA( ! __is_invocable( memfun_type_i, int&& ) );
> +SA(   __is_invocable( memfun_type_i, A ) );
> +SA(   __is_invocable( memfun_type_i, A* ) );
> +SA(   __is_invocable( memfun_type_i, A& ) );
> +SA(   __is_invocable( memfun_type_i, A&& ) );
> +SA( ! __is_invocable( memfun_type_i, const A& ) );
> +SA( ! __is_invocable( memfun_type_i, A&, int ) );
> +
> +using memfun_type_ic = int (A::*)() const;
> +
> +SA( ! __is_invocable( memfun_type_ic ) );
> +SA( ! __is_invocable( memfun_type_ic, int ) );
> +SA( ! __is_invocable( memfun_type_ic, int& ) );
> +SA(   __is_invocable( memfun_type_ic, A& ) );
> +SA(   __is_invocable( memfun_type_ic, A* ) );
> +SA( ! __is_invocable( memfun_type_ic, A&, int ) );
> +SA( ! __is_invocable( memfun_type_ic, A*, int& ) );
> +SA(   __is_invocable( memfun_type_ic, const A& ) );
> +SA(   __is_invocable( memfun_type_ic, const A* ) );
> +SA( ! __is_invocable( memfun_type_ic, const A&, int& ) );
> +SA( ! __is_invocable( memfun_type_ic, const A*, int ) );
> +
> +using memfun_type_iic = int& (A::*)(int&) const;
> +
> +SA( ! __is_invocable( memfun_type_iic ) );
> +SA( ! __is_invocable( memfun_type_iic, int ) );
> +SA( ! __is_invocable( memfun_type_iic, int& ) );
> +SA( ! __is_invocable( memfun_type_iic, A&, int ) );
> +SA(   __is_invocable( memfun_type_iic, A&, int& ) );
> +SA( ! __is_invocable( memfun_type_iic, A*, int ) );
> +SA(   __is_invocable( memfun_type_iic, A*, int& ) );
> +SA( ! __is_invocable( memfun_type_iic, const A&, int ) );
> +SA( ! __is_invocable( memfun_type_iic, const A&, int&, int ) );
> +SA(   __is_invocable( memfun_type_iic, const A&, int& ) );
> +SA(   __is_invocable( memfun_type_iic, const A*, int& ) );
> +
> +struct B {
> +  int& operator()();
> +  long& operator()() const;
> +  bool& operator()(int);
> +private:
> +  void operator()(int, int);
> +};
> +using CB = const B;
> +
> +SA(   __is_invocable( B ) );
> +SA(   __is_invocable( B& ) );
> +SA(   __is_invocable( B&& ) );
> +SA( ! __is_invocable( B* ) );
> +SA(   __is_invocable( CB ) );
> +SA(   __is_invocable( CB& ) );
> +SA( ! __is_invocable( CB* ) );
> +
> +SA(   __is_invocable( B, int ) );
> +SA(   __is_invocable( B&, int ) );
> +SA(   __is_invocable( B&&, int ) );
> +SA( ! __is_invocable( B*, int ) );
> +SA( ! __is_invocable( CB, int ) );
> +SA( ! __is_invocable( CB&, int ) );
> +SA( ! __is_invocable( CB*, int ) );
> +
> +SA( ! __is_invocable( B, int, int ) );
> +SA( ! __is_invocable( B&, int, int ) );
> +SA( ! __is_invocable( B&&, int, int ) );
> +SA( ! __is_invocable( B*, int, int ) );
> +SA( ! __is_invocable( CB, int, int ) );
> +SA( ! __is_invocable( CB&, int, int ) );
> +SA( ! __is_invocable( CB*, int, int ) );
> +
> +struct C : B { int& operator()() = delete; };
> +using CC = const C;
> +
> +SA( ! __is_invocable( C ) );
> +SA( ! __is_invocable( C& ) );
> +SA( ! __is_invocable( C&& ) );
> +SA( ! __is_invocable( C* ) );
> +SA( ! __is_invocable( CC ) );
> +SA( ! __is_invocable( CC& ) );
> +SA( ! __is_invocable( CC* ) );
> +
> +struct D { B operator*(); };
> +using CD = const D;
> +
> +SA( ! __is_invocable( D ) );
> +
> +struct E { void v(); };
> +using CE = const E;
> +
> +SA( ! __is_invocable( E ) );
> +SA( ! __is_invocable( void (E::*)() ) );
> +SA(   __is_invocable( void (E::*)(), E ) );
> +SA(   __is_invocable( void (E::*)(), E* ) );
> +SA( ! __is_invocable( void (E::*)(), CE ) );
> +
> +struct F : E {};
> +using CF = const F;
> +
> +SA( ! __is_invocable( F ) );
> +SA(   __is_invocable( void (E::*)(), F ) );
> +SA(   __is_invocable( void (E::*)(), F* ) );
> +SA( ! __is_invocable( void (E::*)(), CF ) );
> +
> +struct G { E operator*(); };
> +using CG = const G;
> +
> +SA( ! __is_invocable( G ) );
> +SA(   __is_invocable( void (E::*)(), G ) );
> +SA( ! __is_invocable( void (E::*)(), G* ) );
> +SA( ! __is_invocable( void (E::*)(), CG ) );
> +
> +struct H { E& operator*(); };
> +using CH = const H;
> +
> +SA( ! __is_invocable( H ) );
> +SA(   __is_invocable( void (E::*)(), H ) );
> +SA( ! __is_invocable( void (E::*)(), H* ) );
> +SA( ! __is_invocable( void (E::*)(), CH ) );
> +
> +struct I { E&& operator*(); };
> +using CI = const I;
> +
> +SA( ! __is_invocable( I ) );
> +SA(   __is_invocable( void (E::*)(), I ) );
> +SA( ! __is_invocable( void (E::*)(), I* ) );
> +SA( ! __is_invocable( void (E::*)(), CI ) );
> +
> +struct K { E* operator*(); };
> +using CK = const K;
> +
> +SA( ! __is_invocable( K ) );
> +SA( ! __is_invocable( void (E::*)(), K ) );
> +SA( ! __is_invocable( void (E::*)(), K* ) );
> +SA( ! __is_invocable( void (E::*)(), CK ) );
> +
> +struct L { CE operator*(); };
> +using CL = const L;
> +
> +SA( ! __is_invocable( L ) );
> +SA( ! __is_invocable( void (E::*)(), L ) );
> +SA( ! __is_invocable( void (E::*)(), L* ) );
> +SA( ! __is_invocable( void (E::*)(), CL ) );
> +
> +struct M {
> +  int i;
> +private:
> +  long l;
> +};
> +using CM = const M;
> +
> +SA( ! __is_invocable( M ) );
> +SA( ! __is_invocable( M& ) );
> +SA( ! __is_invocable( M&& ) );
> +SA( ! __is_invocable( M* ) );
> +SA( ! __is_invocable( CM ) );
> +SA( ! __is_invocable( CM& ) );
> +SA( ! __is_invocable( CM* ) );
> +
> +SA( ! __is_invocable( int M::* ) );
> +SA(   __is_invocable( int M::*, M ) );
> +SA(   __is_invocable( int M::*, M& ) );
> +SA(   __is_invocable( int M::*, M&& ) );
> +SA(   __is_invocable( int M::*, M* ) );
> +SA(   __is_invocable( int M::*, CM ) );
> +SA(   __is_invocable( int M::*, CM& ) );
> +SA(   __is_invocable( int M::*, CM* ) );
> +SA( ! __is_invocable( int M::*, int ) );
> +
> +SA( ! __is_invocable( int CM::* ) );
> +SA(   __is_invocable( int CM::*, M ) );
> +SA(   __is_invocable( int CM::*, M& ) );
> +SA(   __is_invocable( int CM::*, M&& ) );
> +SA(   __is_invocable( int CM::*, M* ) );
> +SA(   __is_invocable( int CM::*, CM ) );
> +SA(   __is_invocable( int CM::*, CM& ) );
> +SA(   __is_invocable( int CM::*, CM* ) );
> +SA( ! __is_invocable( int CM::*, int ) );
> +
> +SA( ! __is_invocable( long M::* ) );
> +SA(   __is_invocable( long M::*, M ) );
> +SA(   __is_invocable( long M::*, M& ) );
> +SA(   __is_invocable( long M::*, M&& ) );
> +SA(   __is_invocable( long M::*, M* ) );
> +SA(   __is_invocable( long M::*, CM ) );
> +SA(   __is_invocable( long M::*, CM& ) );
> +SA(   __is_invocable( long M::*, CM* ) );
> +SA( ! __is_invocable( long M::*, long ) );
> +
> +SA( ! __is_invocable( long CM::* ) );
> +SA(   __is_invocable( long CM::*, M ) );
> +SA(   __is_invocable( long CM::*, M& ) );
> +SA(   __is_invocable( long CM::*, M&& ) );
> +SA(   __is_invocable( long CM::*, M* ) );
> +SA(   __is_invocable( long CM::*, CM ) );
> +SA(   __is_invocable( long CM::*, CM& ) );
> +SA(   __is_invocable( long CM::*, CM* ) );
> +SA( ! __is_invocable( long CM::*, long ) );
> +
> +SA( ! __is_invocable( short M::* ) );
> +SA(   __is_invocable( short M::*, M ) );
> +SA(   __is_invocable( short M::*, M& ) );
> +SA(   __is_invocable( short M::*, M&& ) );
> +SA(   __is_invocable( short M::*, M* ) );
> +SA(   __is_invocable( short M::*, CM ) );
> +SA(   __is_invocable( short M::*, CM& ) );
> +SA(   __is_invocable( short M::*, CM* ) );
> +SA( ! __is_invocable( short M::*, short ) );
> +
> +SA( ! __is_invocable( short CM::* ) );
> +SA(   __is_invocable( short CM::*, M ) );
> +SA(   __is_invocable( short CM::*, M& ) );
> +SA(   __is_invocable( short CM::*, M&& ) );
> +SA(   __is_invocable( short CM::*, M* ) );
> +SA(   __is_invocable( short CM::*, CM ) );
> +SA(   __is_invocable( short CM::*, CM& ) );
> +SA(   __is_invocable( short CM::*, CM* ) );
> +SA( ! __is_invocable( short CM::*, short ) );
> +
> +struct N { M operator*(); };
> +SA(   __is_invocable( int M::*, N ) );
> +SA( ! __is_invocable( int M::*, N* ) );
> +
> +struct O { M& operator*(); };
> +SA(   __is_invocable( int M::*, O ) );
> +SA( ! __is_invocable( int M::*, O* ) );
> +
> +struct P { M&& operator*(); };
> +SA(   __is_invocable( int M::*, P ) );
> +SA( ! __is_invocable( int M::*, P* ) );
> +
> +struct Q { M* operator*(); };
> +SA( ! __is_invocable( int M::*, Q ) );
> +SA( ! __is_invocable( int M::*, Q* ) );
> +
> +struct R { void operator()(int = 0); };
> +
> +SA(   __is_invocable( R ) );
> +SA(   __is_invocable( R, int ) );
> +SA( ! __is_invocable( R, int, int ) );
> +
> +struct S { void operator()(int, ...); };
> +
> +SA( ! __is_invocable( S ) );
> +SA(   __is_invocable( S, int ) );
> +SA(   __is_invocable( S, int, int ) );
> +SA(   __is_invocable( S, int, int, int ) );
> +
> +void fn1() {}
> +
> +SA(   __is_invocable( decltype(fn1) ) );
> +
> +void fn2(int arr[10]);
> +
> +SA(   __is_invocable( decltype(fn2), int[10] ) );
> +SA(   __is_invocable( decltype(fn2), int(&)[10] ) );
> +SA(   __is_invocable( decltype(fn2), int(&&)[10] ) );
> +SA( ! __is_invocable( decltype(fn2), int(*)[10] ) );
> +SA( ! __is_invocable( decltype(fn2), int(*&)[10] ) );
> +SA( ! __is_invocable( decltype(fn2), int(*&&)[10] ) );
> +SA(   __is_invocable( decltype(fn2), int[] ) );
> +
> +auto lambda = []() {};
> +
> +SA(   __is_invocable( decltype(lambda) ) );
> +
> +template <typename Func, typename... Args>
> +struct can_invoke {
> +    static constexpr bool value = __is_invocable( Func, Args... );
> +};
> +
> +SA(   can_invoke<decltype(lambda)>::value );
> +
> +struct T {
> +  void func() const {}
> +  int data;
> +};
> +
> +SA(   __is_invocable( decltype(&T::func)&, T& ) );
> +SA(   __is_invocable( decltype(&T::data)&, T& ) );
> +
> +struct U { };
> +struct V : U { U& operator*() = delete; };
> +SA(   __is_invocable( int U::*, V ) );
> +
> +struct W : private U { U& operator*(); };
> +SA( ! __is_invocable( int U::*, W ) );
> +
> +struct X { int m; };
> +struct Y { X& operator*(); };
> +struct Z : Y { };
> +SA(   __is_invocable(int X::*, Z) );
> diff --git a/gcc/testsuite/g++.dg/ext/is_invocable2.C b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> new file mode 100644
> index 00000000000..a68aefd3e13
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> @@ -0,0 +1,139 @@
> +// { dg-do compile { target c++11 } }
> +// __is_invocable should handle std::reference_wrapper correctly.
> +
> +#include <functional>
> +
> +#define SA(X) static_assert((X),#X)
> +
> +using std::reference_wrapper;
> +
> +using func_type_v0 = void(*)();
> +
> +SA(   __is_invocable( reference_wrapper<func_type_v0> ) );
> +SA( ! __is_invocable( reference_wrapper<func_type_v0>, int ) );
> +
> +using func_type_i0 = int(*)();
> +
> +SA(   __is_invocable( reference_wrapper<func_type_i0> ) );
> +SA( ! __is_invocable( reference_wrapper<func_type_i0>, int ) );
> +
> +using func_type_l0 = int&(*)();
> +
> +SA(   __is_invocable( reference_wrapper<func_type_l0> ) );
> +SA( ! __is_invocable( reference_wrapper<func_type_l0(int)> ) );
> +
> +using func_type_ii = int(*)(int);
> +
> +SA( ! __is_invocable( reference_wrapper<func_type_ii> ) );
> +SA(   __is_invocable( reference_wrapper<func_type_ii>, int ) );
> +
> +using func_type_il = int(*)(int&);
> +
> +SA( ! __is_invocable( reference_wrapper<func_type_il> ) );
> +SA( ! __is_invocable( reference_wrapper<func_type_il>, int ) );
> +SA(   __is_invocable( reference_wrapper<func_type_il>, int& ) );
> +
> +using func_type_ir = int(*)(int&&);
> +
> +SA( ! __is_invocable( reference_wrapper<func_type_ir> ) );
> +SA( ! __is_invocable( reference_wrapper<func_type_ir>, int& ) );
> +SA(   __is_invocable( reference_wrapper<func_type_ir>, int ) );
> +SA(   __is_invocable( reference_wrapper<func_type_ir>, int&& ) );
> +
> +struct A { };
> +
> +using mem_type_i = int A::*;
> +
> +SA( ! __is_invocable( reference_wrapper<mem_type_i> ) );
> +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int ) );
> +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int* ) );
> +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int& ) );
> +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int&& ) );
> +SA(   __is_invocable( reference_wrapper<mem_type_i>, A ) );
> +SA(   __is_invocable( reference_wrapper<mem_type_i>, A* ) );
> +SA(   __is_invocable( reference_wrapper<mem_type_i>, A& ) );
> +SA(   __is_invocable( reference_wrapper<mem_type_i>, A&& ) );
> +
> +using memfun_type_i = int (A::*)();
> +
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i> ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int* ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int&& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A* ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A&& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, const A& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, A&, int ) );
> +
> +using memfun_type_ic = int (A::*)() const;
> +
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic> ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A* ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A&, int ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A*, int& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A* ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A&, int& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A*, int ) );
> +
> +using memfun_type_iic = int& (A::*)(int&) const;
> +
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic> ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A&, int ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A&, int& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A*, int ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A*, int& ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int ) );
> +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int&, int ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int& ) );
> +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A*, int& ) );
> +
> +struct B {
> +  int& operator()();
> +  long& operator()() const;
> +  bool& operator()(int);
> +private:
> +  void operator()(int, int);
> +};
> +using CB = const B;
> +
> +SA(   __is_invocable( reference_wrapper<B> ) );
> +SA(   __is_invocable( reference_wrapper<B>& ) );
> +SA(   __is_invocable( reference_wrapper<B>&& ) );
> +SA(   __is_invocable( reference_wrapper<CB> ) );
> +SA(   __is_invocable( reference_wrapper<CB>& ) );
> +SA(   __is_invocable( reference_wrapper<B>, int ) );
> +SA( ! __is_invocable( reference_wrapper<B>&, int, int ) );
> +
> +struct C : B { int& operator()() = delete; };
> +using CC = const C;
> +
> +SA( ! __is_invocable( reference_wrapper<C> ) );
> +SA( ! __is_invocable( reference_wrapper<C>& ) );
> +SA( ! __is_invocable( reference_wrapper<C>&& ) );
> +SA( ! __is_invocable( reference_wrapper<CC> ) );
> +SA( ! __is_invocable( reference_wrapper<CC>& ) );
> +
> +struct D { B operator*(); };
> +using CD = const D;
> +
> +SA( ! __is_invocable( reference_wrapper<D> ) );
> +SA( ! __is_invocable( reference_wrapper<D>& ) );
> +SA( ! __is_invocable( reference_wrapper<D>&& ) );
> +SA( ! __is_invocable( reference_wrapper<D>* ) );
> +SA( ! __is_invocable( reference_wrapper<D*> ) );
> +SA( ! __is_invocable( reference_wrapper<D*>* ) );
> +
> +std::function<void()> fn = []() {};
> +auto refwrap = std::ref(fn);
> +
> +SA(   __is_invocable( decltype(fn) ) );
> +SA(   __is_invocable( decltype(refwrap) ) );
> diff --git a/gcc/testsuite/g++.dg/ext/is_invocable3.C b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> new file mode 100644
> index 00000000000..8699b0a53ca
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> @@ -0,0 +1,51 @@
> +// { dg-do compile { target c++11 } }
> +// __is_invocable should handle incomplete class correctly.
> +
> +#define SA(X) static_assert((X),#X)
> +
> +struct Incomplete;
> +
> +SA( ! __is_invocable( Incomplete ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( Incomplete, int ) ); // { dg-error "incomplete type" }
> +
> +SA( ! __is_invocable( int, Incomplete, int ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( int, Incomplete ) ); // { dg-error "incomplete type" }
> +
> +SA( ! __is_invocable( Incomplete, Incomplete() ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( Incomplete, Incomplete(int), int ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( Incomplete, Incomplete(int, int), int, int ) ); // { dg-error "incomplete type" }
> +
> +SA( ! __is_invocable( Incomplete, Incomplete(), int, int ) ); // { dg-error "incomplete type" }
> +
> +SA( ! __is_invocable( int(Incomplete), Incomplete ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( int(int, Incomplete), int, Incomplete ) ); // { dg-error "incomplete type" }
> +SA( ! __is_invocable( int(int, Incomplete), Incomplete, int ) ); // { dg-error "incomplete type" }
> +
> +SA(   __is_invocable( int(Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( int(int, Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> +
> +SA(   __is_invocable( int(Incomplete&&), Incomplete&& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( int(int, Incomplete&&), int, Incomplete&& ) ); // { dg-bogus "incomplete type" }
> +
> +SA(   __is_invocable( int(const Incomplete&&), const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( int(int, const Incomplete&&), int, const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> +
> +SA(   __is_invocable( int(const Incomplete&), const Incomplete& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( int(int, const Incomplete&), int, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> +
> +SA(   __is_invocable( int(const Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( int(int, const Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> +
> +SA(   __is_invocable( int Incomplete::*, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> +SA( ! __is_invocable( void (Incomplete::*)(long&), const Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> +SA(   __is_invocable( void (Incomplete::*)(long&) const, Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> +
> +template <typename T>
> +struct Holder { T t; };
> +
> +SA(   __is_invocable( int(Holder<Incomplete>&), Holder<Incomplete>& ) ); // { dg-bogus "incomplete type" }
> +
> +// Define Incomplete, which is now not incomplete.
> +struct Incomplete { void operator()(); };
> +
> +SA(   __is_invocable( Incomplete ) ); // { dg-bogus "incomplete type" }
> diff --git a/gcc/testsuite/g++.dg/ext/is_invocable4.C b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> new file mode 100644
> index 00000000000..d1efccf08f8
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> @@ -0,0 +1,33 @@
> +// { dg-do compile { target c++11 } }
> +// Failed access check should be a substitution failure, not an error.
> +
> +#define SA(X) static_assert((X),#X)
> +
> +template<bool B>
> +struct bool_constant { static constexpr bool value = B; };
> +
> +template<typename _Fn, typename... _ArgTypes>
> +struct is_invocable
> +: public bool_constant<__is_invocable(_Fn, _ArgTypes...)>
> +{ };
> +
> +#if __cpp_variable_templates
> +template<typename _Fn, typename... _ArgTypes>
> +constexpr bool is_invocable_v = __is_invocable(_Fn, _ArgTypes...);
> +#endif
> +
> +class Private
> +{
> +  void operator()() const
> +  {
> +    SA( ! is_invocable<Private>::value );
> +#if __cpp_variable_templates
> +    SA( ! is_invocable_v<Private> );
> +#endif
> +  }
> +};
> +
> +SA( ! is_invocable<Private>::value );
> +#if __cpp_variable_templates
> +SA( ! is_invocable_v<Private> );
> +#endif
> -- 
> 2.44.0
> 
>

Ken Matsui March 8, 2024, 5:38 p.m. UTC | #2

On Fri, Mar 8, 2024 at 9:17 AM Patrick Palka <ppalka@redhat.com> wrote:
>
> On Wed, 28 Feb 2024, 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.
>
> Thanks, this looks great!  This generic build_invoke function could be
> used for invoke_result etc as well, and it could also cache the built-up
> call across __is_invocable and __is_nothrow_invocable checks on the same
> arguments (which is a common pattern in the standard library).  LGTM

Thank you!!!  Yes, I will also work on those features!

>
> >
> > 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                         | 132 +++++++++
> >  gcc/cp/semantics.cc                      |   4 +
> >  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, 720 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 23ea66d9c12..c87b126fdb1 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3791,6 +3791,12 @@ 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 85056c8140b..6cb2b55f4ea 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 334c11396c2..261d3a71faa 100644
> > --- a/gcc/cp/cp-tree.h
> > +++ b/gcc/cp/cp-tree.h
> > @@ -7334,6 +7334,8 @@ 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 98c10e6a8b5..953f1bed6fc 100644
> > --- a/gcc/cp/method.cc
> > +++ b/gcc/cp/method.cc
> > @@ -1928,6 +1928,138 @@ 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 (fn_type == error_mark_node || arg_types == error_mark_node)
> > +    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)
> > +    /* Only a pointer to data member with one argument is invocable.  */
>
> Just one note, if/when build_invoke gets a caller that passes tf_error
> (for e.g. elaborating why is_invocable is false, or why invoke_result
> is ill-formed) these error_mark_node code paths will need to issue
> diagnostics b.

Oh I see.  I will update this patch.  Thank you!

>
> > +    return error_mark_node;
> > +
> > +  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
> > +    /* A pointer to member function with no arguments is not invocable.  */
> > +    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 (TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
> > +        {
> > +       if (!CLASS_TYPE_P (TREE_TYPE (datum_type)))
> > +         return error_mark_node;
> > +        }
> > +      else if (!CLASS_TYPE_P (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 datum_expr = build_trait_object (datum_type);
> > +      tree fn_expr = build_trait_object (fn_type);
> > +      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr, complain);
> > +
> > +      if (error_operand_p (ptrmem_expr) && !is_refwrap)
> > +     {
> > +       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)
> > +          && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
> > +                                                         datum_type)
> > +              || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
> > +
> > +       if (!ptrmem_is_base_of_datum)
> > +         {
> > +           /* 1.3 & 1.6: Try to dereference datum_expr.  */
> > +           datum_expr = build_x_indirect_ref (UNKNOWN_LOCATION, datum_expr,
> > +                                              RO_UNARY_STAR, NULL_TREE,
> > +                                              complain);
> > +           /* Rebuild ptrmem_expr.  */
> > +           ptrmem_expr = build_m_component_ref (datum_expr, fn_expr,
> > +                                                complain);
> > +         }
> > +     }
> > +      /* 1.1 & 1.4: Otherwise.  */
> > +
> > +      if (error_operand_p (ptrmem_expr))
> > +     return error_mark_node;
> > +
> > +      if (is_ptrdatamem)
> > +     return ptrmem_expr;
> > +    }
> > +
> > +  /* Construct expressions for arguments to INVOKE.  For a pointer to member
> > +     function, the first argument, which is the object, is not arguments to
> > +     the function.  */
> > +  releasing_vec args;
> > +  for (int i = is_ptrmemfunc ? 1 : 0; i < TREE_VEC_LENGTH (arg_types); ++i)
> > +    {
> > +      tree arg_type = TREE_VEC_ELT (arg_types, i);
> > +      tree arg = build_trait_object (arg_type);
> > +      vec_safe_push (args, arg);
> > +    }
> > +
> > +  tree invoke_expr;
> > +  if (is_ptrmemfunc)
> > +    invoke_expr = build_offset_ref_call_from_tree (ptrmem_expr, &args,
> > +                                                complain);
> > +  else  /* 1.7.  */
> > +    invoke_expr = finish_call_expr (build_trait_object (fn_type), &args, false,
> > +                                 false, complain);
> > +  return invoke_expr;
> > +}
> > +
> >  /* Determine which function will be called when looking up NAME in TYPE,
> >     called with a single ARGTYPE argument, or no argument if ARGTYPE is
> >     null.  FLAGS and COMPLAIN are as for build_new_method_call.
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index 7242db75248..149c0631d62 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -12467,6 +12467,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
> >      case CPTK_IS_FUNCTION:
> >        return type_code1 == FUNCTION_TYPE;
> >
> > +    case CPTK_IS_INVOCABLE:
> > +      return !error_operand_p (build_invoke (type1, type2, tf_none));
> > +
> >      case CPTK_IS_LAYOUT_COMPATIBLE:
> >        return layout_compatible_type_p (type1, type2);
> >
> > @@ -12682,6 +12685,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
> >        break;
> >
> >      case CPTK_IS_CONVERTIBLE:
> > +    case CPTK_IS_INVOCABLE:
> >      case CPTK_IS_NOTHROW_ASSIGNABLE:
> >      case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
> >      case CPTK_IS_NOTHROW_CONVERTIBLE:
> > diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > index 7f7b27f7aa7..d2a7ebdf25c 100644
> > --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > @@ -104,6 +104,9 @@
> >  #if !__has_builtin (__is_function)
> >  # error "__has_builtin (__is_function) failed"
> >  #endif
> > +#if !__has_builtin (__is_invocable)
> > +# error "__has_builtin (__is_invocable) failed"
> > +#endif
> >  #if !__has_builtin (__is_layout_compatible)
> >  # error "__has_builtin (__is_layout_compatible) failed"
> >  #endif
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable1.C b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > new file mode 100644
> > index 00000000000..d21ae1d1958
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > @@ -0,0 +1,349 @@
> > +// { dg-do compile { target c++11 } }
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +using func_type_v0 = void(*)();
> > +
> > +SA(   __is_invocable( func_type_v0 ) );
> > +SA( ! __is_invocable( func_type_v0, int ) );
> > +
> > +using func_type_i0 = int(*)();
> > +
> > +SA(   __is_invocable( func_type_i0 ) );
> > +SA( ! __is_invocable( func_type_i0, int ) );
> > +
> > +using func_type_l0 = int&(*)();
> > +
> > +SA(   __is_invocable( func_type_l0 ) );
> > +SA( ! __is_invocable( func_type_l0(int) ) );
> > +
> > +using func_type_ii = int(*)(int);
> > +
> > +SA( ! __is_invocable( func_type_ii ) );
> > +SA(   __is_invocable( func_type_ii, int ) );
> > +
> > +using func_type_il = int(*)(int&);
> > +
> > +SA( ! __is_invocable( func_type_il ) );
> > +SA( ! __is_invocable( func_type_il, int ) );
> > +SA(   __is_invocable( func_type_il, int& ) );
> > +
> > +using func_type_ir = int(*)(int&&);
> > +
> > +SA( ! __is_invocable( func_type_ir ) );
> > +SA( ! __is_invocable( func_type_ir, int& ) );
> > +SA(   __is_invocable( func_type_ir, int ) );
> > +SA(   __is_invocable( func_type_ir, int&& ) );
> > +
> > +struct A { };
> > +
> > +using mem_type_i = int A::*;
> > +
> > +SA( ! __is_invocable( mem_type_i ) );
> > +SA( ! __is_invocable( mem_type_i, int ) );
> > +SA( ! __is_invocable( mem_type_i, int* ) );
> > +SA( ! __is_invocable( mem_type_i, int& ) );
> > +SA( ! __is_invocable( mem_type_i, int&& ) );
> > +SA(   __is_invocable( mem_type_i, A ) );
> > +SA(   __is_invocable( mem_type_i, A* ) );
> > +SA(   __is_invocable( mem_type_i, A& ) );
> > +SA(   __is_invocable( mem_type_i, A&& ) );
> > +SA(   __is_invocable( mem_type_i, const A& ) );
> > +SA( ! __is_invocable( mem_type_i, A&, int ) );
> > +
> > +using memfun_type_i = int (A::*)();
> > +
> > +SA( ! __is_invocable( memfun_type_i ) );
> > +SA( ! __is_invocable( memfun_type_i, int ) );
> > +SA( ! __is_invocable( memfun_type_i, int* ) );
> > +SA( ! __is_invocable( memfun_type_i, int& ) );
> > +SA( ! __is_invocable( memfun_type_i, int&& ) );
> > +SA(   __is_invocable( memfun_type_i, A ) );
> > +SA(   __is_invocable( memfun_type_i, A* ) );
> > +SA(   __is_invocable( memfun_type_i, A& ) );
> > +SA(   __is_invocable( memfun_type_i, A&& ) );
> > +SA( ! __is_invocable( memfun_type_i, const A& ) );
> > +SA( ! __is_invocable( memfun_type_i, A&, int ) );
> > +
> > +using memfun_type_ic = int (A::*)() const;
> > +
> > +SA( ! __is_invocable( memfun_type_ic ) );
> > +SA( ! __is_invocable( memfun_type_ic, int ) );
> > +SA( ! __is_invocable( memfun_type_ic, int& ) );
> > +SA(   __is_invocable( memfun_type_ic, A& ) );
> > +SA(   __is_invocable( memfun_type_ic, A* ) );
> > +SA( ! __is_invocable( memfun_type_ic, A&, int ) );
> > +SA( ! __is_invocable( memfun_type_ic, A*, int& ) );
> > +SA(   __is_invocable( memfun_type_ic, const A& ) );
> > +SA(   __is_invocable( memfun_type_ic, const A* ) );
> > +SA( ! __is_invocable( memfun_type_ic, const A&, int& ) );
> > +SA( ! __is_invocable( memfun_type_ic, const A*, int ) );
> > +
> > +using memfun_type_iic = int& (A::*)(int&) const;
> > +
> > +SA( ! __is_invocable( memfun_type_iic ) );
> > +SA( ! __is_invocable( memfun_type_iic, int ) );
> > +SA( ! __is_invocable( memfun_type_iic, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, A&, int ) );
> > +SA(   __is_invocable( memfun_type_iic, A&, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, A*, int ) );
> > +SA(   __is_invocable( memfun_type_iic, A*, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, const A&, int ) );
> > +SA( ! __is_invocable( memfun_type_iic, const A&, int&, int ) );
> > +SA(   __is_invocable( memfun_type_iic, const A&, int& ) );
> > +SA(   __is_invocable( memfun_type_iic, const A*, int& ) );
> > +
> > +struct B {
> > +  int& operator()();
> > +  long& operator()() const;
> > +  bool& operator()(int);
> > +private:
> > +  void operator()(int, int);
> > +};
> > +using CB = const B;
> > +
> > +SA(   __is_invocable( B ) );
> > +SA(   __is_invocable( B& ) );
> > +SA(   __is_invocable( B&& ) );
> > +SA( ! __is_invocable( B* ) );
> > +SA(   __is_invocable( CB ) );
> > +SA(   __is_invocable( CB& ) );
> > +SA( ! __is_invocable( CB* ) );
> > +
> > +SA(   __is_invocable( B, int ) );
> > +SA(   __is_invocable( B&, int ) );
> > +SA(   __is_invocable( B&&, int ) );
> > +SA( ! __is_invocable( B*, int ) );
> > +SA( ! __is_invocable( CB, int ) );
> > +SA( ! __is_invocable( CB&, int ) );
> > +SA( ! __is_invocable( CB*, int ) );
> > +
> > +SA( ! __is_invocable( B, int, int ) );
> > +SA( ! __is_invocable( B&, int, int ) );
> > +SA( ! __is_invocable( B&&, int, int ) );
> > +SA( ! __is_invocable( B*, int, int ) );
> > +SA( ! __is_invocable( CB, int, int ) );
> > +SA( ! __is_invocable( CB&, int, int ) );
> > +SA( ! __is_invocable( CB*, int, int ) );
> > +
> > +struct C : B { int& operator()() = delete; };
> > +using CC = const C;
> > +
> > +SA( ! __is_invocable( C ) );
> > +SA( ! __is_invocable( C& ) );
> > +SA( ! __is_invocable( C&& ) );
> > +SA( ! __is_invocable( C* ) );
> > +SA( ! __is_invocable( CC ) );
> > +SA( ! __is_invocable( CC& ) );
> > +SA( ! __is_invocable( CC* ) );
> > +
> > +struct D { B operator*(); };
> > +using CD = const D;
> > +
> > +SA( ! __is_invocable( D ) );
> > +
> > +struct E { void v(); };
> > +using CE = const E;
> > +
> > +SA( ! __is_invocable( E ) );
> > +SA( ! __is_invocable( void (E::*)() ) );
> > +SA(   __is_invocable( void (E::*)(), E ) );
> > +SA(   __is_invocable( void (E::*)(), E* ) );
> > +SA( ! __is_invocable( void (E::*)(), CE ) );
> > +
> > +struct F : E {};
> > +using CF = const F;
> > +
> > +SA( ! __is_invocable( F ) );
> > +SA(   __is_invocable( void (E::*)(), F ) );
> > +SA(   __is_invocable( void (E::*)(), F* ) );
> > +SA( ! __is_invocable( void (E::*)(), CF ) );
> > +
> > +struct G { E operator*(); };
> > +using CG = const G;
> > +
> > +SA( ! __is_invocable( G ) );
> > +SA(   __is_invocable( void (E::*)(), G ) );
> > +SA( ! __is_invocable( void (E::*)(), G* ) );
> > +SA( ! __is_invocable( void (E::*)(), CG ) );
> > +
> > +struct H { E& operator*(); };
> > +using CH = const H;
> > +
> > +SA( ! __is_invocable( H ) );
> > +SA(   __is_invocable( void (E::*)(), H ) );
> > +SA( ! __is_invocable( void (E::*)(), H* ) );
> > +SA( ! __is_invocable( void (E::*)(), CH ) );
> > +
> > +struct I { E&& operator*(); };
> > +using CI = const I;
> > +
> > +SA( ! __is_invocable( I ) );
> > +SA(   __is_invocable( void (E::*)(), I ) );
> > +SA( ! __is_invocable( void (E::*)(), I* ) );
> > +SA( ! __is_invocable( void (E::*)(), CI ) );
> > +
> > +struct K { E* operator*(); };
> > +using CK = const K;
> > +
> > +SA( ! __is_invocable( K ) );
> > +SA( ! __is_invocable( void (E::*)(), K ) );
> > +SA( ! __is_invocable( void (E::*)(), K* ) );
> > +SA( ! __is_invocable( void (E::*)(), CK ) );
> > +
> > +struct L { CE operator*(); };
> > +using CL = const L;
> > +
> > +SA( ! __is_invocable( L ) );
> > +SA( ! __is_invocable( void (E::*)(), L ) );
> > +SA( ! __is_invocable( void (E::*)(), L* ) );
> > +SA( ! __is_invocable( void (E::*)(), CL ) );
> > +
> > +struct M {
> > +  int i;
> > +private:
> > +  long l;
> > +};
> > +using CM = const M;
> > +
> > +SA( ! __is_invocable( M ) );
> > +SA( ! __is_invocable( M& ) );
> > +SA( ! __is_invocable( M&& ) );
> > +SA( ! __is_invocable( M* ) );
> > +SA( ! __is_invocable( CM ) );
> > +SA( ! __is_invocable( CM& ) );
> > +SA( ! __is_invocable( CM* ) );
> > +
> > +SA( ! __is_invocable( int M::* ) );
> > +SA(   __is_invocable( int M::*, M ) );
> > +SA(   __is_invocable( int M::*, M& ) );
> > +SA(   __is_invocable( int M::*, M&& ) );
> > +SA(   __is_invocable( int M::*, M* ) );
> > +SA(   __is_invocable( int M::*, CM ) );
> > +SA(   __is_invocable( int M::*, CM& ) );
> > +SA(   __is_invocable( int M::*, CM* ) );
> > +SA( ! __is_invocable( int M::*, int ) );
> > +
> > +SA( ! __is_invocable( int CM::* ) );
> > +SA(   __is_invocable( int CM::*, M ) );
> > +SA(   __is_invocable( int CM::*, M& ) );
> > +SA(   __is_invocable( int CM::*, M&& ) );
> > +SA(   __is_invocable( int CM::*, M* ) );
> > +SA(   __is_invocable( int CM::*, CM ) );
> > +SA(   __is_invocable( int CM::*, CM& ) );
> > +SA(   __is_invocable( int CM::*, CM* ) );
> > +SA( ! __is_invocable( int CM::*, int ) );
> > +
> > +SA( ! __is_invocable( long M::* ) );
> > +SA(   __is_invocable( long M::*, M ) );
> > +SA(   __is_invocable( long M::*, M& ) );
> > +SA(   __is_invocable( long M::*, M&& ) );
> > +SA(   __is_invocable( long M::*, M* ) );
> > +SA(   __is_invocable( long M::*, CM ) );
> > +SA(   __is_invocable( long M::*, CM& ) );
> > +SA(   __is_invocable( long M::*, CM* ) );
> > +SA( ! __is_invocable( long M::*, long ) );
> > +
> > +SA( ! __is_invocable( long CM::* ) );
> > +SA(   __is_invocable( long CM::*, M ) );
> > +SA(   __is_invocable( long CM::*, M& ) );
> > +SA(   __is_invocable( long CM::*, M&& ) );
> > +SA(   __is_invocable( long CM::*, M* ) );
> > +SA(   __is_invocable( long CM::*, CM ) );
> > +SA(   __is_invocable( long CM::*, CM& ) );
> > +SA(   __is_invocable( long CM::*, CM* ) );
> > +SA( ! __is_invocable( long CM::*, long ) );
> > +
> > +SA( ! __is_invocable( short M::* ) );
> > +SA(   __is_invocable( short M::*, M ) );
> > +SA(   __is_invocable( short M::*, M& ) );
> > +SA(   __is_invocable( short M::*, M&& ) );
> > +SA(   __is_invocable( short M::*, M* ) );
> > +SA(   __is_invocable( short M::*, CM ) );
> > +SA(   __is_invocable( short M::*, CM& ) );
> > +SA(   __is_invocable( short M::*, CM* ) );
> > +SA( ! __is_invocable( short M::*, short ) );
> > +
> > +SA( ! __is_invocable( short CM::* ) );
> > +SA(   __is_invocable( short CM::*, M ) );
> > +SA(   __is_invocable( short CM::*, M& ) );
> > +SA(   __is_invocable( short CM::*, M&& ) );
> > +SA(   __is_invocable( short CM::*, M* ) );
> > +SA(   __is_invocable( short CM::*, CM ) );
> > +SA(   __is_invocable( short CM::*, CM& ) );
> > +SA(   __is_invocable( short CM::*, CM* ) );
> > +SA( ! __is_invocable( short CM::*, short ) );
> > +
> > +struct N { M operator*(); };
> > +SA(   __is_invocable( int M::*, N ) );
> > +SA( ! __is_invocable( int M::*, N* ) );
> > +
> > +struct O { M& operator*(); };
> > +SA(   __is_invocable( int M::*, O ) );
> > +SA( ! __is_invocable( int M::*, O* ) );
> > +
> > +struct P { M&& operator*(); };
> > +SA(   __is_invocable( int M::*, P ) );
> > +SA( ! __is_invocable( int M::*, P* ) );
> > +
> > +struct Q { M* operator*(); };
> > +SA( ! __is_invocable( int M::*, Q ) );
> > +SA( ! __is_invocable( int M::*, Q* ) );
> > +
> > +struct R { void operator()(int = 0); };
> > +
> > +SA(   __is_invocable( R ) );
> > +SA(   __is_invocable( R, int ) );
> > +SA( ! __is_invocable( R, int, int ) );
> > +
> > +struct S { void operator()(int, ...); };
> > +
> > +SA( ! __is_invocable( S ) );
> > +SA(   __is_invocable( S, int ) );
> > +SA(   __is_invocable( S, int, int ) );
> > +SA(   __is_invocable( S, int, int, int ) );
> > +
> > +void fn1() {}
> > +
> > +SA(   __is_invocable( decltype(fn1) ) );
> > +
> > +void fn2(int arr[10]);
> > +
> > +SA(   __is_invocable( decltype(fn2), int[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int(&)[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int(&&)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*&)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*&&)[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int[] ) );
> > +
> > +auto lambda = []() {};
> > +
> > +SA(   __is_invocable( decltype(lambda) ) );
> > +
> > +template <typename Func, typename... Args>
> > +struct can_invoke {
> > +    static constexpr bool value = __is_invocable( Func, Args... );
> > +};
> > +
> > +SA(   can_invoke<decltype(lambda)>::value );
> > +
> > +struct T {
> > +  void func() const {}
> > +  int data;
> > +};
> > +
> > +SA(   __is_invocable( decltype(&T::func)&, T& ) );
> > +SA(   __is_invocable( decltype(&T::data)&, T& ) );
> > +
> > +struct U { };
> > +struct V : U { U& operator*() = delete; };
> > +SA(   __is_invocable( int U::*, V ) );
> > +
> > +struct W : private U { U& operator*(); };
> > +SA( ! __is_invocable( int U::*, W ) );
> > +
> > +struct X { int m; };
> > +struct Y { X& operator*(); };
> > +struct Z : Y { };
> > +SA(   __is_invocable(int X::*, Z) );
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable2.C b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > new file mode 100644
> > index 00000000000..a68aefd3e13
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > @@ -0,0 +1,139 @@
> > +// { dg-do compile { target c++11 } }
> > +// __is_invocable should handle std::reference_wrapper correctly.
> > +
> > +#include <functional>
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +using std::reference_wrapper;
> > +
> > +using func_type_v0 = void(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_v0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_v0>, int ) );
> > +
> > +using func_type_i0 = int(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_i0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_i0>, int ) );
> > +
> > +using func_type_l0 = int&(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_l0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_l0(int)> ) );
> > +
> > +using func_type_ii = int(*)(int);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_ii> ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ii>, int ) );
> > +
> > +using func_type_il = int(*)(int&);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_il> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_il>, int ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_il>, int& ) );
> > +
> > +using func_type_ir = int(*)(int&&);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_ir> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_ir>, int& ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int&& ) );
> > +
> > +struct A { };
> > +
> > +using mem_type_i = int A::*;
> > +
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i> ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int* ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int&& ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A* ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A&& ) );
> > +
> > +using memfun_type_i = int (A::*)();
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int&& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A* ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A&& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, const A& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, A&, int ) );
> > +
> > +using memfun_type_ic = int (A::*)() const;
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A&, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A*, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A&, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A*, int ) );
> > +
> > +using memfun_type_iic = int& (A::*)(int&) const;
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A&, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A&, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A*, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A*, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int&, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A*, int& ) );
> > +
> > +struct B {
> > +  int& operator()();
> > +  long& operator()() const;
> > +  bool& operator()(int);
> > +private:
> > +  void operator()(int, int);
> > +};
> > +using CB = const B;
> > +
> > +SA(   __is_invocable( reference_wrapper<B> ) );
> > +SA(   __is_invocable( reference_wrapper<B>& ) );
> > +SA(   __is_invocable( reference_wrapper<B>&& ) );
> > +SA(   __is_invocable( reference_wrapper<CB> ) );
> > +SA(   __is_invocable( reference_wrapper<CB>& ) );
> > +SA(   __is_invocable( reference_wrapper<B>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<B>&, int, int ) );
> > +
> > +struct C : B { int& operator()() = delete; };
> > +using CC = const C;
> > +
> > +SA( ! __is_invocable( reference_wrapper<C> ) );
> > +SA( ! __is_invocable( reference_wrapper<C>& ) );
> > +SA( ! __is_invocable( reference_wrapper<C>&& ) );
> > +SA( ! __is_invocable( reference_wrapper<CC> ) );
> > +SA( ! __is_invocable( reference_wrapper<CC>& ) );
> > +
> > +struct D { B operator*(); };
> > +using CD = const D;
> > +
> > +SA( ! __is_invocable( reference_wrapper<D> ) );
> > +SA( ! __is_invocable( reference_wrapper<D>& ) );
> > +SA( ! __is_invocable( reference_wrapper<D>&& ) );
> > +SA( ! __is_invocable( reference_wrapper<D>* ) );
> > +SA( ! __is_invocable( reference_wrapper<D*> ) );
> > +SA( ! __is_invocable( reference_wrapper<D*>* ) );
> > +
> > +std::function<void()> fn = []() {};
> > +auto refwrap = std::ref(fn);
> > +
> > +SA(   __is_invocable( decltype(fn) ) );
> > +SA(   __is_invocable( decltype(refwrap) ) );
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable3.C b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > new file mode 100644
> > index 00000000000..8699b0a53ca
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > @@ -0,0 +1,51 @@
> > +// { dg-do compile { target c++11 } }
> > +// __is_invocable should handle incomplete class correctly.
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +struct Incomplete;
> > +
> > +SA( ! __is_invocable( Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( int, Incomplete, int ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int, Incomplete ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( Incomplete, Incomplete() ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, Incomplete(int), int ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, Incomplete(int, int), int, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( Incomplete, Incomplete(), int, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( int(Incomplete), Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int(int, Incomplete), int, Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int(int, Incomplete), Incomplete, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA(   __is_invocable( int(Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(Incomplete&&), Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, Incomplete&&), int, Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&&), const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&&), int, const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&), const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&), int, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int Incomplete::*, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA( ! __is_invocable( void (Incomplete::*)(long&), const Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( void (Incomplete::*)(long&) const, Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > +
> > +template <typename T>
> > +struct Holder { T t; };
> > +
> > +SA(   __is_invocable( int(Holder<Incomplete>&), Holder<Incomplete>& ) ); // { dg-bogus "incomplete type" }
> > +
> > +// Define Incomplete, which is now not incomplete.
> > +struct Incomplete { void operator()(); };
> > +
> > +SA(   __is_invocable( Incomplete ) ); // { dg-bogus "incomplete type" }
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable4.C b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > new file mode 100644
> > index 00000000000..d1efccf08f8
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > @@ -0,0 +1,33 @@
> > +// { dg-do compile { target c++11 } }
> > +// Failed access check should be a substitution failure, not an error.
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +template<bool B>
> > +struct bool_constant { static constexpr bool value = B; };
> > +
> > +template<typename _Fn, typename... _ArgTypes>
> > +struct is_invocable
> > +: public bool_constant<__is_invocable(_Fn, _ArgTypes...)>
> > +{ };
> > +
> > +#if __cpp_variable_templates
> > +template<typename _Fn, typename... _ArgTypes>
> > +constexpr bool is_invocable_v = __is_invocable(_Fn, _ArgTypes...);
> > +#endif
> > +
> > +class Private
> > +{
> > +  void operator()() const
> > +  {
> > +    SA( ! is_invocable<Private>::value );
> > +#if __cpp_variable_templates
> > +    SA( ! is_invocable_v<Private> );
> > +#endif
> > +  }
> > +};
> > +
> > +SA( ! is_invocable<Private>::value );
> > +#if __cpp_variable_templates
> > +SA( ! is_invocable_v<Private> );
> > +#endif
> > --
> > 2.44.0
> >
> >
>

Ken Matsui March 15, 2024, 1:53 a.m. UTC | #3

On Fri, Mar 8, 2024 at 9:17 AM Patrick Palka <ppalka@redhat.com> wrote:
>
> On Wed, 28 Feb 2024, 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.
>
> Thanks, this looks great!  This generic build_invoke function could be
> used for invoke_result etc as well, and it could also cache the built-up
> call across __is_invocable and __is_nothrow_invocable checks on the same
> arguments (which is a common pattern in the standard library).  LGTM
>
> >
> > 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                         | 132 +++++++++
> >  gcc/cp/semantics.cc                      |   4 +
> >  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, 720 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 23ea66d9c12..c87b126fdb1 100644
> > --- a/gcc/cp/constraint.cc
> > +++ b/gcc/cp/constraint.cc
> > @@ -3791,6 +3791,12 @@ 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 85056c8140b..6cb2b55f4ea 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 334c11396c2..261d3a71faa 100644
> > --- a/gcc/cp/cp-tree.h
> > +++ b/gcc/cp/cp-tree.h
> > @@ -7334,6 +7334,8 @@ 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 98c10e6a8b5..953f1bed6fc 100644
> > --- a/gcc/cp/method.cc
> > +++ b/gcc/cp/method.cc
> > @@ -1928,6 +1928,138 @@ 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 (fn_type == error_mark_node || arg_types == error_mark_node)
> > +    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)
> > +    /* Only a pointer to data member with one argument is invocable.  */
>
> Just one note, if/when build_invoke gets a caller that passes tf_error
> (for e.g. elaborating why is_invocable is false, or why invoke_result
> is ill-formed) these error_mark_node code paths will need to issue
> diagnostics b.

Which function should we use for diagnostics - error, error_at, or
something else?  If we opt for error_at, which location information do
we want to use?

>
> > +    return error_mark_node;
> > +
> > +  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
> > +    /* A pointer to member function with no arguments is not invocable.  */
> > +    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 (TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
> > +        {
> > +       if (!CLASS_TYPE_P (TREE_TYPE (datum_type)))
> > +         return error_mark_node;
> > +        }
> > +      else if (!CLASS_TYPE_P (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 datum_expr = build_trait_object (datum_type);
> > +      tree fn_expr = build_trait_object (fn_type);
> > +      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr, complain);
> > +
> > +      if (error_operand_p (ptrmem_expr) && !is_refwrap)
> > +     {
> > +       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)
> > +          && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
> > +                                                         datum_type)
> > +              || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
> > +
> > +       if (!ptrmem_is_base_of_datum)
> > +         {
> > +           /* 1.3 & 1.6: Try to dereference datum_expr.  */
> > +           datum_expr = build_x_indirect_ref (UNKNOWN_LOCATION, datum_expr,
> > +                                              RO_UNARY_STAR, NULL_TREE,
> > +                                              complain);
> > +           /* Rebuild ptrmem_expr.  */
> > +           ptrmem_expr = build_m_component_ref (datum_expr, fn_expr,
> > +                                                complain);
> > +         }
> > +     }
> > +      /* 1.1 & 1.4: Otherwise.  */
> > +
> > +      if (error_operand_p (ptrmem_expr))
> > +     return error_mark_node;
> > +
> > +      if (is_ptrdatamem)
> > +     return ptrmem_expr;
> > +    }
> > +
> > +  /* Construct expressions for arguments to INVOKE.  For a pointer to member
> > +     function, the first argument, which is the object, is not arguments to
> > +     the function.  */
> > +  releasing_vec args;
> > +  for (int i = is_ptrmemfunc ? 1 : 0; i < TREE_VEC_LENGTH (arg_types); ++i)
> > +    {
> > +      tree arg_type = TREE_VEC_ELT (arg_types, i);
> > +      tree arg = build_trait_object (arg_type);
> > +      vec_safe_push (args, arg);
> > +    }
> > +
> > +  tree invoke_expr;
> > +  if (is_ptrmemfunc)
> > +    invoke_expr = build_offset_ref_call_from_tree (ptrmem_expr, &args,
> > +                                                complain);
> > +  else  /* 1.7.  */
> > +    invoke_expr = finish_call_expr (build_trait_object (fn_type), &args, false,
> > +                                 false, complain);
> > +  return invoke_expr;
> > +}
> > +
> >  /* Determine which function will be called when looking up NAME in TYPE,
> >     called with a single ARGTYPE argument, or no argument if ARGTYPE is
> >     null.  FLAGS and COMPLAIN are as for build_new_method_call.
> > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > index 7242db75248..149c0631d62 100644
> > --- a/gcc/cp/semantics.cc
> > +++ b/gcc/cp/semantics.cc
> > @@ -12467,6 +12467,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
> >      case CPTK_IS_FUNCTION:
> >        return type_code1 == FUNCTION_TYPE;
> >
> > +    case CPTK_IS_INVOCABLE:
> > +      return !error_operand_p (build_invoke (type1, type2, tf_none));
> > +
> >      case CPTK_IS_LAYOUT_COMPATIBLE:
> >        return layout_compatible_type_p (type1, type2);
> >
> > @@ -12682,6 +12685,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
> >        break;
> >
> >      case CPTK_IS_CONVERTIBLE:
> > +    case CPTK_IS_INVOCABLE:
> >      case CPTK_IS_NOTHROW_ASSIGNABLE:
> >      case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
> >      case CPTK_IS_NOTHROW_CONVERTIBLE:
> > diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > index 7f7b27f7aa7..d2a7ebdf25c 100644
> > --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > @@ -104,6 +104,9 @@
> >  #if !__has_builtin (__is_function)
> >  # error "__has_builtin (__is_function) failed"
> >  #endif
> > +#if !__has_builtin (__is_invocable)
> > +# error "__has_builtin (__is_invocable) failed"
> > +#endif
> >  #if !__has_builtin (__is_layout_compatible)
> >  # error "__has_builtin (__is_layout_compatible) failed"
> >  #endif
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable1.C b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > new file mode 100644
> > index 00000000000..d21ae1d1958
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > @@ -0,0 +1,349 @@
> > +// { dg-do compile { target c++11 } }
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +using func_type_v0 = void(*)();
> > +
> > +SA(   __is_invocable( func_type_v0 ) );
> > +SA( ! __is_invocable( func_type_v0, int ) );
> > +
> > +using func_type_i0 = int(*)();
> > +
> > +SA(   __is_invocable( func_type_i0 ) );
> > +SA( ! __is_invocable( func_type_i0, int ) );
> > +
> > +using func_type_l0 = int&(*)();
> > +
> > +SA(   __is_invocable( func_type_l0 ) );
> > +SA( ! __is_invocable( func_type_l0(int) ) );
> > +
> > +using func_type_ii = int(*)(int);
> > +
> > +SA( ! __is_invocable( func_type_ii ) );
> > +SA(   __is_invocable( func_type_ii, int ) );
> > +
> > +using func_type_il = int(*)(int&);
> > +
> > +SA( ! __is_invocable( func_type_il ) );
> > +SA( ! __is_invocable( func_type_il, int ) );
> > +SA(   __is_invocable( func_type_il, int& ) );
> > +
> > +using func_type_ir = int(*)(int&&);
> > +
> > +SA( ! __is_invocable( func_type_ir ) );
> > +SA( ! __is_invocable( func_type_ir, int& ) );
> > +SA(   __is_invocable( func_type_ir, int ) );
> > +SA(   __is_invocable( func_type_ir, int&& ) );
> > +
> > +struct A { };
> > +
> > +using mem_type_i = int A::*;
> > +
> > +SA( ! __is_invocable( mem_type_i ) );
> > +SA( ! __is_invocable( mem_type_i, int ) );
> > +SA( ! __is_invocable( mem_type_i, int* ) );
> > +SA( ! __is_invocable( mem_type_i, int& ) );
> > +SA( ! __is_invocable( mem_type_i, int&& ) );
> > +SA(   __is_invocable( mem_type_i, A ) );
> > +SA(   __is_invocable( mem_type_i, A* ) );
> > +SA(   __is_invocable( mem_type_i, A& ) );
> > +SA(   __is_invocable( mem_type_i, A&& ) );
> > +SA(   __is_invocable( mem_type_i, const A& ) );
> > +SA( ! __is_invocable( mem_type_i, A&, int ) );
> > +
> > +using memfun_type_i = int (A::*)();
> > +
> > +SA( ! __is_invocable( memfun_type_i ) );
> > +SA( ! __is_invocable( memfun_type_i, int ) );
> > +SA( ! __is_invocable( memfun_type_i, int* ) );
> > +SA( ! __is_invocable( memfun_type_i, int& ) );
> > +SA( ! __is_invocable( memfun_type_i, int&& ) );
> > +SA(   __is_invocable( memfun_type_i, A ) );
> > +SA(   __is_invocable( memfun_type_i, A* ) );
> > +SA(   __is_invocable( memfun_type_i, A& ) );
> > +SA(   __is_invocable( memfun_type_i, A&& ) );
> > +SA( ! __is_invocable( memfun_type_i, const A& ) );
> > +SA( ! __is_invocable( memfun_type_i, A&, int ) );
> > +
> > +using memfun_type_ic = int (A::*)() const;
> > +
> > +SA( ! __is_invocable( memfun_type_ic ) );
> > +SA( ! __is_invocable( memfun_type_ic, int ) );
> > +SA( ! __is_invocable( memfun_type_ic, int& ) );
> > +SA(   __is_invocable( memfun_type_ic, A& ) );
> > +SA(   __is_invocable( memfun_type_ic, A* ) );
> > +SA( ! __is_invocable( memfun_type_ic, A&, int ) );
> > +SA( ! __is_invocable( memfun_type_ic, A*, int& ) );
> > +SA(   __is_invocable( memfun_type_ic, const A& ) );
> > +SA(   __is_invocable( memfun_type_ic, const A* ) );
> > +SA( ! __is_invocable( memfun_type_ic, const A&, int& ) );
> > +SA( ! __is_invocable( memfun_type_ic, const A*, int ) );
> > +
> > +using memfun_type_iic = int& (A::*)(int&) const;
> > +
> > +SA( ! __is_invocable( memfun_type_iic ) );
> > +SA( ! __is_invocable( memfun_type_iic, int ) );
> > +SA( ! __is_invocable( memfun_type_iic, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, A&, int ) );
> > +SA(   __is_invocable( memfun_type_iic, A&, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, A*, int ) );
> > +SA(   __is_invocable( memfun_type_iic, A*, int& ) );
> > +SA( ! __is_invocable( memfun_type_iic, const A&, int ) );
> > +SA( ! __is_invocable( memfun_type_iic, const A&, int&, int ) );
> > +SA(   __is_invocable( memfun_type_iic, const A&, int& ) );
> > +SA(   __is_invocable( memfun_type_iic, const A*, int& ) );
> > +
> > +struct B {
> > +  int& operator()();
> > +  long& operator()() const;
> > +  bool& operator()(int);
> > +private:
> > +  void operator()(int, int);
> > +};
> > +using CB = const B;
> > +
> > +SA(   __is_invocable( B ) );
> > +SA(   __is_invocable( B& ) );
> > +SA(   __is_invocable( B&& ) );
> > +SA( ! __is_invocable( B* ) );
> > +SA(   __is_invocable( CB ) );
> > +SA(   __is_invocable( CB& ) );
> > +SA( ! __is_invocable( CB* ) );
> > +
> > +SA(   __is_invocable( B, int ) );
> > +SA(   __is_invocable( B&, int ) );
> > +SA(   __is_invocable( B&&, int ) );
> > +SA( ! __is_invocable( B*, int ) );
> > +SA( ! __is_invocable( CB, int ) );
> > +SA( ! __is_invocable( CB&, int ) );
> > +SA( ! __is_invocable( CB*, int ) );
> > +
> > +SA( ! __is_invocable( B, int, int ) );
> > +SA( ! __is_invocable( B&, int, int ) );
> > +SA( ! __is_invocable( B&&, int, int ) );
> > +SA( ! __is_invocable( B*, int, int ) );
> > +SA( ! __is_invocable( CB, int, int ) );
> > +SA( ! __is_invocable( CB&, int, int ) );
> > +SA( ! __is_invocable( CB*, int, int ) );
> > +
> > +struct C : B { int& operator()() = delete; };
> > +using CC = const C;
> > +
> > +SA( ! __is_invocable( C ) );
> > +SA( ! __is_invocable( C& ) );
> > +SA( ! __is_invocable( C&& ) );
> > +SA( ! __is_invocable( C* ) );
> > +SA( ! __is_invocable( CC ) );
> > +SA( ! __is_invocable( CC& ) );
> > +SA( ! __is_invocable( CC* ) );
> > +
> > +struct D { B operator*(); };
> > +using CD = const D;
> > +
> > +SA( ! __is_invocable( D ) );
> > +
> > +struct E { void v(); };
> > +using CE = const E;
> > +
> > +SA( ! __is_invocable( E ) );
> > +SA( ! __is_invocable( void (E::*)() ) );
> > +SA(   __is_invocable( void (E::*)(), E ) );
> > +SA(   __is_invocable( void (E::*)(), E* ) );
> > +SA( ! __is_invocable( void (E::*)(), CE ) );
> > +
> > +struct F : E {};
> > +using CF = const F;
> > +
> > +SA( ! __is_invocable( F ) );
> > +SA(   __is_invocable( void (E::*)(), F ) );
> > +SA(   __is_invocable( void (E::*)(), F* ) );
> > +SA( ! __is_invocable( void (E::*)(), CF ) );
> > +
> > +struct G { E operator*(); };
> > +using CG = const G;
> > +
> > +SA( ! __is_invocable( G ) );
> > +SA(   __is_invocable( void (E::*)(), G ) );
> > +SA( ! __is_invocable( void (E::*)(), G* ) );
> > +SA( ! __is_invocable( void (E::*)(), CG ) );
> > +
> > +struct H { E& operator*(); };
> > +using CH = const H;
> > +
> > +SA( ! __is_invocable( H ) );
> > +SA(   __is_invocable( void (E::*)(), H ) );
> > +SA( ! __is_invocable( void (E::*)(), H* ) );
> > +SA( ! __is_invocable( void (E::*)(), CH ) );
> > +
> > +struct I { E&& operator*(); };
> > +using CI = const I;
> > +
> > +SA( ! __is_invocable( I ) );
> > +SA(   __is_invocable( void (E::*)(), I ) );
> > +SA( ! __is_invocable( void (E::*)(), I* ) );
> > +SA( ! __is_invocable( void (E::*)(), CI ) );
> > +
> > +struct K { E* operator*(); };
> > +using CK = const K;
> > +
> > +SA( ! __is_invocable( K ) );
> > +SA( ! __is_invocable( void (E::*)(), K ) );
> > +SA( ! __is_invocable( void (E::*)(), K* ) );
> > +SA( ! __is_invocable( void (E::*)(), CK ) );
> > +
> > +struct L { CE operator*(); };
> > +using CL = const L;
> > +
> > +SA( ! __is_invocable( L ) );
> > +SA( ! __is_invocable( void (E::*)(), L ) );
> > +SA( ! __is_invocable( void (E::*)(), L* ) );
> > +SA( ! __is_invocable( void (E::*)(), CL ) );
> > +
> > +struct M {
> > +  int i;
> > +private:
> > +  long l;
> > +};
> > +using CM = const M;
> > +
> > +SA( ! __is_invocable( M ) );
> > +SA( ! __is_invocable( M& ) );
> > +SA( ! __is_invocable( M&& ) );
> > +SA( ! __is_invocable( M* ) );
> > +SA( ! __is_invocable( CM ) );
> > +SA( ! __is_invocable( CM& ) );
> > +SA( ! __is_invocable( CM* ) );
> > +
> > +SA( ! __is_invocable( int M::* ) );
> > +SA(   __is_invocable( int M::*, M ) );
> > +SA(   __is_invocable( int M::*, M& ) );
> > +SA(   __is_invocable( int M::*, M&& ) );
> > +SA(   __is_invocable( int M::*, M* ) );
> > +SA(   __is_invocable( int M::*, CM ) );
> > +SA(   __is_invocable( int M::*, CM& ) );
> > +SA(   __is_invocable( int M::*, CM* ) );
> > +SA( ! __is_invocable( int M::*, int ) );
> > +
> > +SA( ! __is_invocable( int CM::* ) );
> > +SA(   __is_invocable( int CM::*, M ) );
> > +SA(   __is_invocable( int CM::*, M& ) );
> > +SA(   __is_invocable( int CM::*, M&& ) );
> > +SA(   __is_invocable( int CM::*, M* ) );
> > +SA(   __is_invocable( int CM::*, CM ) );
> > +SA(   __is_invocable( int CM::*, CM& ) );
> > +SA(   __is_invocable( int CM::*, CM* ) );
> > +SA( ! __is_invocable( int CM::*, int ) );
> > +
> > +SA( ! __is_invocable( long M::* ) );
> > +SA(   __is_invocable( long M::*, M ) );
> > +SA(   __is_invocable( long M::*, M& ) );
> > +SA(   __is_invocable( long M::*, M&& ) );
> > +SA(   __is_invocable( long M::*, M* ) );
> > +SA(   __is_invocable( long M::*, CM ) );
> > +SA(   __is_invocable( long M::*, CM& ) );
> > +SA(   __is_invocable( long M::*, CM* ) );
> > +SA( ! __is_invocable( long M::*, long ) );
> > +
> > +SA( ! __is_invocable( long CM::* ) );
> > +SA(   __is_invocable( long CM::*, M ) );
> > +SA(   __is_invocable( long CM::*, M& ) );
> > +SA(   __is_invocable( long CM::*, M&& ) );
> > +SA(   __is_invocable( long CM::*, M* ) );
> > +SA(   __is_invocable( long CM::*, CM ) );
> > +SA(   __is_invocable( long CM::*, CM& ) );
> > +SA(   __is_invocable( long CM::*, CM* ) );
> > +SA( ! __is_invocable( long CM::*, long ) );
> > +
> > +SA( ! __is_invocable( short M::* ) );
> > +SA(   __is_invocable( short M::*, M ) );
> > +SA(   __is_invocable( short M::*, M& ) );
> > +SA(   __is_invocable( short M::*, M&& ) );
> > +SA(   __is_invocable( short M::*, M* ) );
> > +SA(   __is_invocable( short M::*, CM ) );
> > +SA(   __is_invocable( short M::*, CM& ) );
> > +SA(   __is_invocable( short M::*, CM* ) );
> > +SA( ! __is_invocable( short M::*, short ) );
> > +
> > +SA( ! __is_invocable( short CM::* ) );
> > +SA(   __is_invocable( short CM::*, M ) );
> > +SA(   __is_invocable( short CM::*, M& ) );
> > +SA(   __is_invocable( short CM::*, M&& ) );
> > +SA(   __is_invocable( short CM::*, M* ) );
> > +SA(   __is_invocable( short CM::*, CM ) );
> > +SA(   __is_invocable( short CM::*, CM& ) );
> > +SA(   __is_invocable( short CM::*, CM* ) );
> > +SA( ! __is_invocable( short CM::*, short ) );
> > +
> > +struct N { M operator*(); };
> > +SA(   __is_invocable( int M::*, N ) );
> > +SA( ! __is_invocable( int M::*, N* ) );
> > +
> > +struct O { M& operator*(); };
> > +SA(   __is_invocable( int M::*, O ) );
> > +SA( ! __is_invocable( int M::*, O* ) );
> > +
> > +struct P { M&& operator*(); };
> > +SA(   __is_invocable( int M::*, P ) );
> > +SA( ! __is_invocable( int M::*, P* ) );
> > +
> > +struct Q { M* operator*(); };
> > +SA( ! __is_invocable( int M::*, Q ) );
> > +SA( ! __is_invocable( int M::*, Q* ) );
> > +
> > +struct R { void operator()(int = 0); };
> > +
> > +SA(   __is_invocable( R ) );
> > +SA(   __is_invocable( R, int ) );
> > +SA( ! __is_invocable( R, int, int ) );
> > +
> > +struct S { void operator()(int, ...); };
> > +
> > +SA( ! __is_invocable( S ) );
> > +SA(   __is_invocable( S, int ) );
> > +SA(   __is_invocable( S, int, int ) );
> > +SA(   __is_invocable( S, int, int, int ) );
> > +
> > +void fn1() {}
> > +
> > +SA(   __is_invocable( decltype(fn1) ) );
> > +
> > +void fn2(int arr[10]);
> > +
> > +SA(   __is_invocable( decltype(fn2), int[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int(&)[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int(&&)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*&)[10] ) );
> > +SA( ! __is_invocable( decltype(fn2), int(*&&)[10] ) );
> > +SA(   __is_invocable( decltype(fn2), int[] ) );
> > +
> > +auto lambda = []() {};
> > +
> > +SA(   __is_invocable( decltype(lambda) ) );
> > +
> > +template <typename Func, typename... Args>
> > +struct can_invoke {
> > +    static constexpr bool value = __is_invocable( Func, Args... );
> > +};
> > +
> > +SA(   can_invoke<decltype(lambda)>::value );
> > +
> > +struct T {
> > +  void func() const {}
> > +  int data;
> > +};
> > +
> > +SA(   __is_invocable( decltype(&T::func)&, T& ) );
> > +SA(   __is_invocable( decltype(&T::data)&, T& ) );
> > +
> > +struct U { };
> > +struct V : U { U& operator*() = delete; };
> > +SA(   __is_invocable( int U::*, V ) );
> > +
> > +struct W : private U { U& operator*(); };
> > +SA( ! __is_invocable( int U::*, W ) );
> > +
> > +struct X { int m; };
> > +struct Y { X& operator*(); };
> > +struct Z : Y { };
> > +SA(   __is_invocable(int X::*, Z) );
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable2.C b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > new file mode 100644
> > index 00000000000..a68aefd3e13
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > @@ -0,0 +1,139 @@
> > +// { dg-do compile { target c++11 } }
> > +// __is_invocable should handle std::reference_wrapper correctly.
> > +
> > +#include <functional>
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +using std::reference_wrapper;
> > +
> > +using func_type_v0 = void(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_v0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_v0>, int ) );
> > +
> > +using func_type_i0 = int(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_i0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_i0>, int ) );
> > +
> > +using func_type_l0 = int&(*)();
> > +
> > +SA(   __is_invocable( reference_wrapper<func_type_l0> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_l0(int)> ) );
> > +
> > +using func_type_ii = int(*)(int);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_ii> ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ii>, int ) );
> > +
> > +using func_type_il = int(*)(int&);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_il> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_il>, int ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_il>, int& ) );
> > +
> > +using func_type_ir = int(*)(int&&);
> > +
> > +SA( ! __is_invocable( reference_wrapper<func_type_ir> ) );
> > +SA( ! __is_invocable( reference_wrapper<func_type_ir>, int& ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int ) );
> > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int&& ) );
> > +
> > +struct A { };
> > +
> > +using mem_type_i = int A::*;
> > +
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i> ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int* ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int&& ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A* ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A&& ) );
> > +
> > +using memfun_type_i = int (A::*)();
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int&& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A* ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A&& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, const A& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, A&, int ) );
> > +
> > +using memfun_type_ic = int (A::*)() const;
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A&, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A*, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A* ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A&, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A*, int ) );
> > +
> > +using memfun_type_iic = int& (A::*)(int&) const;
> > +
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic> ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A&, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A&, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A*, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A*, int& ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int ) );
> > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int&, int ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int& ) );
> > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A*, int& ) );
> > +
> > +struct B {
> > +  int& operator()();
> > +  long& operator()() const;
> > +  bool& operator()(int);
> > +private:
> > +  void operator()(int, int);
> > +};
> > +using CB = const B;
> > +
> > +SA(   __is_invocable( reference_wrapper<B> ) );
> > +SA(   __is_invocable( reference_wrapper<B>& ) );
> > +SA(   __is_invocable( reference_wrapper<B>&& ) );
> > +SA(   __is_invocable( reference_wrapper<CB> ) );
> > +SA(   __is_invocable( reference_wrapper<CB>& ) );
> > +SA(   __is_invocable( reference_wrapper<B>, int ) );
> > +SA( ! __is_invocable( reference_wrapper<B>&, int, int ) );
> > +
> > +struct C : B { int& operator()() = delete; };
> > +using CC = const C;
> > +
> > +SA( ! __is_invocable( reference_wrapper<C> ) );
> > +SA( ! __is_invocable( reference_wrapper<C>& ) );
> > +SA( ! __is_invocable( reference_wrapper<C>&& ) );
> > +SA( ! __is_invocable( reference_wrapper<CC> ) );
> > +SA( ! __is_invocable( reference_wrapper<CC>& ) );
> > +
> > +struct D { B operator*(); };
> > +using CD = const D;
> > +
> > +SA( ! __is_invocable( reference_wrapper<D> ) );
> > +SA( ! __is_invocable( reference_wrapper<D>& ) );
> > +SA( ! __is_invocable( reference_wrapper<D>&& ) );
> > +SA( ! __is_invocable( reference_wrapper<D>* ) );
> > +SA( ! __is_invocable( reference_wrapper<D*> ) );
> > +SA( ! __is_invocable( reference_wrapper<D*>* ) );
> > +
> > +std::function<void()> fn = []() {};
> > +auto refwrap = std::ref(fn);
> > +
> > +SA(   __is_invocable( decltype(fn) ) );
> > +SA(   __is_invocable( decltype(refwrap) ) );
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable3.C b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > new file mode 100644
> > index 00000000000..8699b0a53ca
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > @@ -0,0 +1,51 @@
> > +// { dg-do compile { target c++11 } }
> > +// __is_invocable should handle incomplete class correctly.
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +struct Incomplete;
> > +
> > +SA( ! __is_invocable( Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( int, Incomplete, int ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int, Incomplete ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( Incomplete, Incomplete() ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, Incomplete(int), int ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( Incomplete, Incomplete(int, int), int, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( Incomplete, Incomplete(), int, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA( ! __is_invocable( int(Incomplete), Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int(int, Incomplete), int, Incomplete ) ); // { dg-error "incomplete type" }
> > +SA( ! __is_invocable( int(int, Incomplete), Incomplete, int ) ); // { dg-error "incomplete type" }
> > +
> > +SA(   __is_invocable( int(Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(Incomplete&&), Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, Incomplete&&), int, Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&&), const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&&), int, const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&), const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&), int, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int(const Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( int(int, const Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +
> > +SA(   __is_invocable( int Incomplete::*, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > +SA( ! __is_invocable( void (Incomplete::*)(long&), const Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > +SA(   __is_invocable( void (Incomplete::*)(long&) const, Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > +
> > +template <typename T>
> > +struct Holder { T t; };
> > +
> > +SA(   __is_invocable( int(Holder<Incomplete>&), Holder<Incomplete>& ) ); // { dg-bogus "incomplete type" }
> > +
> > +// Define Incomplete, which is now not incomplete.
> > +struct Incomplete { void operator()(); };
> > +
> > +SA(   __is_invocable( Incomplete ) ); // { dg-bogus "incomplete type" }
> > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable4.C b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > new file mode 100644
> > index 00000000000..d1efccf08f8
> > --- /dev/null
> > +++ b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > @@ -0,0 +1,33 @@
> > +// { dg-do compile { target c++11 } }
> > +// Failed access check should be a substitution failure, not an error.
> > +
> > +#define SA(X) static_assert((X),#X)
> > +
> > +template<bool B>
> > +struct bool_constant { static constexpr bool value = B; };
> > +
> > +template<typename _Fn, typename... _ArgTypes>
> > +struct is_invocable
> > +: public bool_constant<__is_invocable(_Fn, _ArgTypes...)>
> > +{ };
> > +
> > +#if __cpp_variable_templates
> > +template<typename _Fn, typename... _ArgTypes>
> > +constexpr bool is_invocable_v = __is_invocable(_Fn, _ArgTypes...);
> > +#endif
> > +
> > +class Private
> > +{
> > +  void operator()() const
> > +  {
> > +    SA( ! is_invocable<Private>::value );
> > +#if __cpp_variable_templates
> > +    SA( ! is_invocable_v<Private> );
> > +#endif
> > +  }
> > +};
> > +
> > +SA( ! is_invocable<Private>::value );
> > +#if __cpp_variable_templates
> > +SA( ! is_invocable_v<Private> );
> > +#endif
> > --
> > 2.44.0
> >
> >
>

Ken Matsui March 15, 2024, 6:34 a.m. UTC | #4

On Thu, Mar 14, 2024 at 6:53 PM Ken Matsui <kmatsui@cs.washington.edu> wrote:
>
> On Fri, Mar 8, 2024 at 9:17 AM Patrick Palka <ppalka@redhat.com> wrote:
> >
> > On Wed, 28 Feb 2024, 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.
> >
> > Thanks, this looks great!  This generic build_invoke function could be
> > used for invoke_result etc as well, and it could also cache the built-up
> > call across __is_invocable and __is_nothrow_invocable checks on the same
> > arguments (which is a common pattern in the standard library).  LGTM
> >
> > >
> > > 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                         | 132 +++++++++
> > >  gcc/cp/semantics.cc                      |   4 +
> > >  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, 720 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 23ea66d9c12..c87b126fdb1 100644
> > > --- a/gcc/cp/constraint.cc
> > > +++ b/gcc/cp/constraint.cc
> > > @@ -3791,6 +3791,12 @@ 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 85056c8140b..6cb2b55f4ea 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 334c11396c2..261d3a71faa 100644
> > > --- a/gcc/cp/cp-tree.h
> > > +++ b/gcc/cp/cp-tree.h
> > > @@ -7334,6 +7334,8 @@ 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 98c10e6a8b5..953f1bed6fc 100644
> > > --- a/gcc/cp/method.cc
> > > +++ b/gcc/cp/method.cc
> > > @@ -1928,6 +1928,138 @@ 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 (fn_type == error_mark_node || arg_types == error_mark_node)
> > > +    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)
> > > +    /* Only a pointer to data member with one argument is invocable.  */
> >
> > Just one note, if/when build_invoke gets a caller that passes tf_error
> > (for e.g. elaborating why is_invocable is false, or why invoke_result
> > is ill-formed) these error_mark_node code paths will need to issue
> > diagnostics b.
>
> Which function should we use for diagnostics - error, error_at, or
> something else?  If we opt for error_at, which location information do
> we want to use?
>

Never mind, I can follow your finish_type_pack_element implementation :)

> >
> > > +    return error_mark_node;
> > > +
> > > +  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
> > > +    /* A pointer to member function with no arguments is not invocable.  */
> > > +    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 (TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
> > > +        {
> > > +       if (!CLASS_TYPE_P (TREE_TYPE (datum_type)))
> > > +         return error_mark_node;
> > > +        }
> > > +      else if (!CLASS_TYPE_P (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 datum_expr = build_trait_object (datum_type);
> > > +      tree fn_expr = build_trait_object (fn_type);
> > > +      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr, complain);
> > > +
> > > +      if (error_operand_p (ptrmem_expr) && !is_refwrap)
> > > +     {
> > > +       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)
> > > +          && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
> > > +                                                         datum_type)
> > > +              || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
> > > +
> > > +       if (!ptrmem_is_base_of_datum)
> > > +         {
> > > +           /* 1.3 & 1.6: Try to dereference datum_expr.  */
> > > +           datum_expr = build_x_indirect_ref (UNKNOWN_LOCATION, datum_expr,
> > > +                                              RO_UNARY_STAR, NULL_TREE,
> > > +                                              complain);
> > > +           /* Rebuild ptrmem_expr.  */
> > > +           ptrmem_expr = build_m_component_ref (datum_expr, fn_expr,
> > > +                                                complain);
> > > +         }
> > > +     }
> > > +      /* 1.1 & 1.4: Otherwise.  */
> > > +
> > > +      if (error_operand_p (ptrmem_expr))
> > > +     return error_mark_node;
> > > +
> > > +      if (is_ptrdatamem)
> > > +     return ptrmem_expr;
> > > +    }
> > > +
> > > +  /* Construct expressions for arguments to INVOKE.  For a pointer to member
> > > +     function, the first argument, which is the object, is not arguments to
> > > +     the function.  */
> > > +  releasing_vec args;
> > > +  for (int i = is_ptrmemfunc ? 1 : 0; i < TREE_VEC_LENGTH (arg_types); ++i)
> > > +    {
> > > +      tree arg_type = TREE_VEC_ELT (arg_types, i);
> > > +      tree arg = build_trait_object (arg_type);
> > > +      vec_safe_push (args, arg);
> > > +    }
> > > +
> > > +  tree invoke_expr;
> > > +  if (is_ptrmemfunc)
> > > +    invoke_expr = build_offset_ref_call_from_tree (ptrmem_expr, &args,
> > > +                                                complain);
> > > +  else  /* 1.7.  */
> > > +    invoke_expr = finish_call_expr (build_trait_object (fn_type), &args, false,
> > > +                                 false, complain);
> > > +  return invoke_expr;
> > > +}
> > > +
> > >  /* Determine which function will be called when looking up NAME in TYPE,
> > >     called with a single ARGTYPE argument, or no argument if ARGTYPE is
> > >     null.  FLAGS and COMPLAIN are as for build_new_method_call.
> > > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
> > > index 7242db75248..149c0631d62 100644
> > > --- a/gcc/cp/semantics.cc
> > > +++ b/gcc/cp/semantics.cc
> > > @@ -12467,6 +12467,9 @@ trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
> > >      case CPTK_IS_FUNCTION:
> > >        return type_code1 == FUNCTION_TYPE;
> > >
> > > +    case CPTK_IS_INVOCABLE:
> > > +      return !error_operand_p (build_invoke (type1, type2, tf_none));
> > > +
> > >      case CPTK_IS_LAYOUT_COMPATIBLE:
> > >        return layout_compatible_type_p (type1, type2);
> > >
> > > @@ -12682,6 +12685,7 @@ finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
> > >        break;
> > >
> > >      case CPTK_IS_CONVERTIBLE:
> > > +    case CPTK_IS_INVOCABLE:
> > >      case CPTK_IS_NOTHROW_ASSIGNABLE:
> > >      case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
> > >      case CPTK_IS_NOTHROW_CONVERTIBLE:
> > > diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > > index 7f7b27f7aa7..d2a7ebdf25c 100644
> > > --- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > > +++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
> > > @@ -104,6 +104,9 @@
> > >  #if !__has_builtin (__is_function)
> > >  # error "__has_builtin (__is_function) failed"
> > >  #endif
> > > +#if !__has_builtin (__is_invocable)
> > > +# error "__has_builtin (__is_invocable) failed"
> > > +#endif
> > >  #if !__has_builtin (__is_layout_compatible)
> > >  # error "__has_builtin (__is_layout_compatible) failed"
> > >  #endif
> > > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable1.C b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > > new file mode 100644
> > > index 00000000000..d21ae1d1958
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
> > > @@ -0,0 +1,349 @@
> > > +// { dg-do compile { target c++11 } }
> > > +
> > > +#define SA(X) static_assert((X),#X)
> > > +
> > > +using func_type_v0 = void(*)();
> > > +
> > > +SA(   __is_invocable( func_type_v0 ) );
> > > +SA( ! __is_invocable( func_type_v0, int ) );
> > > +
> > > +using func_type_i0 = int(*)();
> > > +
> > > +SA(   __is_invocable( func_type_i0 ) );
> > > +SA( ! __is_invocable( func_type_i0, int ) );
> > > +
> > > +using func_type_l0 = int&(*)();
> > > +
> > > +SA(   __is_invocable( func_type_l0 ) );
> > > +SA( ! __is_invocable( func_type_l0(int) ) );
> > > +
> > > +using func_type_ii = int(*)(int);
> > > +
> > > +SA( ! __is_invocable( func_type_ii ) );
> > > +SA(   __is_invocable( func_type_ii, int ) );
> > > +
> > > +using func_type_il = int(*)(int&);
> > > +
> > > +SA( ! __is_invocable( func_type_il ) );
> > > +SA( ! __is_invocable( func_type_il, int ) );
> > > +SA(   __is_invocable( func_type_il, int& ) );
> > > +
> > > +using func_type_ir = int(*)(int&&);
> > > +
> > > +SA( ! __is_invocable( func_type_ir ) );
> > > +SA( ! __is_invocable( func_type_ir, int& ) );
> > > +SA(   __is_invocable( func_type_ir, int ) );
> > > +SA(   __is_invocable( func_type_ir, int&& ) );
> > > +
> > > +struct A { };
> > > +
> > > +using mem_type_i = int A::*;
> > > +
> > > +SA( ! __is_invocable( mem_type_i ) );
> > > +SA( ! __is_invocable( mem_type_i, int ) );
> > > +SA( ! __is_invocable( mem_type_i, int* ) );
> > > +SA( ! __is_invocable( mem_type_i, int& ) );
> > > +SA( ! __is_invocable( mem_type_i, int&& ) );
> > > +SA(   __is_invocable( mem_type_i, A ) );
> > > +SA(   __is_invocable( mem_type_i, A* ) );
> > > +SA(   __is_invocable( mem_type_i, A& ) );
> > > +SA(   __is_invocable( mem_type_i, A&& ) );
> > > +SA(   __is_invocable( mem_type_i, const A& ) );
> > > +SA( ! __is_invocable( mem_type_i, A&, int ) );
> > > +
> > > +using memfun_type_i = int (A::*)();
> > > +
> > > +SA( ! __is_invocable( memfun_type_i ) );
> > > +SA( ! __is_invocable( memfun_type_i, int ) );
> > > +SA( ! __is_invocable( memfun_type_i, int* ) );
> > > +SA( ! __is_invocable( memfun_type_i, int& ) );
> > > +SA( ! __is_invocable( memfun_type_i, int&& ) );
> > > +SA(   __is_invocable( memfun_type_i, A ) );
> > > +SA(   __is_invocable( memfun_type_i, A* ) );
> > > +SA(   __is_invocable( memfun_type_i, A& ) );
> > > +SA(   __is_invocable( memfun_type_i, A&& ) );
> > > +SA( ! __is_invocable( memfun_type_i, const A& ) );
> > > +SA( ! __is_invocable( memfun_type_i, A&, int ) );
> > > +
> > > +using memfun_type_ic = int (A::*)() const;
> > > +
> > > +SA( ! __is_invocable( memfun_type_ic ) );
> > > +SA( ! __is_invocable( memfun_type_ic, int ) );
> > > +SA( ! __is_invocable( memfun_type_ic, int& ) );
> > > +SA(   __is_invocable( memfun_type_ic, A& ) );
> > > +SA(   __is_invocable( memfun_type_ic, A* ) );
> > > +SA( ! __is_invocable( memfun_type_ic, A&, int ) );
> > > +SA( ! __is_invocable( memfun_type_ic, A*, int& ) );
> > > +SA(   __is_invocable( memfun_type_ic, const A& ) );
> > > +SA(   __is_invocable( memfun_type_ic, const A* ) );
> > > +SA( ! __is_invocable( memfun_type_ic, const A&, int& ) );
> > > +SA( ! __is_invocable( memfun_type_ic, const A*, int ) );
> > > +
> > > +using memfun_type_iic = int& (A::*)(int&) const;
> > > +
> > > +SA( ! __is_invocable( memfun_type_iic ) );
> > > +SA( ! __is_invocable( memfun_type_iic, int ) );
> > > +SA( ! __is_invocable( memfun_type_iic, int& ) );
> > > +SA( ! __is_invocable( memfun_type_iic, A&, int ) );
> > > +SA(   __is_invocable( memfun_type_iic, A&, int& ) );
> > > +SA( ! __is_invocable( memfun_type_iic, A*, int ) );
> > > +SA(   __is_invocable( memfun_type_iic, A*, int& ) );
> > > +SA( ! __is_invocable( memfun_type_iic, const A&, int ) );
> > > +SA( ! __is_invocable( memfun_type_iic, const A&, int&, int ) );
> > > +SA(   __is_invocable( memfun_type_iic, const A&, int& ) );
> > > +SA(   __is_invocable( memfun_type_iic, const A*, int& ) );
> > > +
> > > +struct B {
> > > +  int& operator()();
> > > +  long& operator()() const;
> > > +  bool& operator()(int);
> > > +private:
> > > +  void operator()(int, int);
> > > +};
> > > +using CB = const B;
> > > +
> > > +SA(   __is_invocable( B ) );
> > > +SA(   __is_invocable( B& ) );
> > > +SA(   __is_invocable( B&& ) );
> > > +SA( ! __is_invocable( B* ) );
> > > +SA(   __is_invocable( CB ) );
> > > +SA(   __is_invocable( CB& ) );
> > > +SA( ! __is_invocable( CB* ) );
> > > +
> > > +SA(   __is_invocable( B, int ) );
> > > +SA(   __is_invocable( B&, int ) );
> > > +SA(   __is_invocable( B&&, int ) );
> > > +SA( ! __is_invocable( B*, int ) );
> > > +SA( ! __is_invocable( CB, int ) );
> > > +SA( ! __is_invocable( CB&, int ) );
> > > +SA( ! __is_invocable( CB*, int ) );
> > > +
> > > +SA( ! __is_invocable( B, int, int ) );
> > > +SA( ! __is_invocable( B&, int, int ) );
> > > +SA( ! __is_invocable( B&&, int, int ) );
> > > +SA( ! __is_invocable( B*, int, int ) );
> > > +SA( ! __is_invocable( CB, int, int ) );
> > > +SA( ! __is_invocable( CB&, int, int ) );
> > > +SA( ! __is_invocable( CB*, int, int ) );
> > > +
> > > +struct C : B { int& operator()() = delete; };
> > > +using CC = const C;
> > > +
> > > +SA( ! __is_invocable( C ) );
> > > +SA( ! __is_invocable( C& ) );
> > > +SA( ! __is_invocable( C&& ) );
> > > +SA( ! __is_invocable( C* ) );
> > > +SA( ! __is_invocable( CC ) );
> > > +SA( ! __is_invocable( CC& ) );
> > > +SA( ! __is_invocable( CC* ) );
> > > +
> > > +struct D { B operator*(); };
> > > +using CD = const D;
> > > +
> > > +SA( ! __is_invocable( D ) );
> > > +
> > > +struct E { void v(); };
> > > +using CE = const E;
> > > +
> > > +SA( ! __is_invocable( E ) );
> > > +SA( ! __is_invocable( void (E::*)() ) );
> > > +SA(   __is_invocable( void (E::*)(), E ) );
> > > +SA(   __is_invocable( void (E::*)(), E* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CE ) );
> > > +
> > > +struct F : E {};
> > > +using CF = const F;
> > > +
> > > +SA( ! __is_invocable( F ) );
> > > +SA(   __is_invocable( void (E::*)(), F ) );
> > > +SA(   __is_invocable( void (E::*)(), F* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CF ) );
> > > +
> > > +struct G { E operator*(); };
> > > +using CG = const G;
> > > +
> > > +SA( ! __is_invocable( G ) );
> > > +SA(   __is_invocable( void (E::*)(), G ) );
> > > +SA( ! __is_invocable( void (E::*)(), G* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CG ) );
> > > +
> > > +struct H { E& operator*(); };
> > > +using CH = const H;
> > > +
> > > +SA( ! __is_invocable( H ) );
> > > +SA(   __is_invocable( void (E::*)(), H ) );
> > > +SA( ! __is_invocable( void (E::*)(), H* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CH ) );
> > > +
> > > +struct I { E&& operator*(); };
> > > +using CI = const I;
> > > +
> > > +SA( ! __is_invocable( I ) );
> > > +SA(   __is_invocable( void (E::*)(), I ) );
> > > +SA( ! __is_invocable( void (E::*)(), I* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CI ) );
> > > +
> > > +struct K { E* operator*(); };
> > > +using CK = const K;
> > > +
> > > +SA( ! __is_invocable( K ) );
> > > +SA( ! __is_invocable( void (E::*)(), K ) );
> > > +SA( ! __is_invocable( void (E::*)(), K* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CK ) );
> > > +
> > > +struct L { CE operator*(); };
> > > +using CL = const L;
> > > +
> > > +SA( ! __is_invocable( L ) );
> > > +SA( ! __is_invocable( void (E::*)(), L ) );
> > > +SA( ! __is_invocable( void (E::*)(), L* ) );
> > > +SA( ! __is_invocable( void (E::*)(), CL ) );
> > > +
> > > +struct M {
> > > +  int i;
> > > +private:
> > > +  long l;
> > > +};
> > > +using CM = const M;
> > > +
> > > +SA( ! __is_invocable( M ) );
> > > +SA( ! __is_invocable( M& ) );
> > > +SA( ! __is_invocable( M&& ) );
> > > +SA( ! __is_invocable( M* ) );
> > > +SA( ! __is_invocable( CM ) );
> > > +SA( ! __is_invocable( CM& ) );
> > > +SA( ! __is_invocable( CM* ) );
> > > +
> > > +SA( ! __is_invocable( int M::* ) );
> > > +SA(   __is_invocable( int M::*, M ) );
> > > +SA(   __is_invocable( int M::*, M& ) );
> > > +SA(   __is_invocable( int M::*, M&& ) );
> > > +SA(   __is_invocable( int M::*, M* ) );
> > > +SA(   __is_invocable( int M::*, CM ) );
> > > +SA(   __is_invocable( int M::*, CM& ) );
> > > +SA(   __is_invocable( int M::*, CM* ) );
> > > +SA( ! __is_invocable( int M::*, int ) );
> > > +
> > > +SA( ! __is_invocable( int CM::* ) );
> > > +SA(   __is_invocable( int CM::*, M ) );
> > > +SA(   __is_invocable( int CM::*, M& ) );
> > > +SA(   __is_invocable( int CM::*, M&& ) );
> > > +SA(   __is_invocable( int CM::*, M* ) );
> > > +SA(   __is_invocable( int CM::*, CM ) );
> > > +SA(   __is_invocable( int CM::*, CM& ) );
> > > +SA(   __is_invocable( int CM::*, CM* ) );
> > > +SA( ! __is_invocable( int CM::*, int ) );
> > > +
> > > +SA( ! __is_invocable( long M::* ) );
> > > +SA(   __is_invocable( long M::*, M ) );
> > > +SA(   __is_invocable( long M::*, M& ) );
> > > +SA(   __is_invocable( long M::*, M&& ) );
> > > +SA(   __is_invocable( long M::*, M* ) );
> > > +SA(   __is_invocable( long M::*, CM ) );
> > > +SA(   __is_invocable( long M::*, CM& ) );
> > > +SA(   __is_invocable( long M::*, CM* ) );
> > > +SA( ! __is_invocable( long M::*, long ) );
> > > +
> > > +SA( ! __is_invocable( long CM::* ) );
> > > +SA(   __is_invocable( long CM::*, M ) );
> > > +SA(   __is_invocable( long CM::*, M& ) );
> > > +SA(   __is_invocable( long CM::*, M&& ) );
> > > +SA(   __is_invocable( long CM::*, M* ) );
> > > +SA(   __is_invocable( long CM::*, CM ) );
> > > +SA(   __is_invocable( long CM::*, CM& ) );
> > > +SA(   __is_invocable( long CM::*, CM* ) );
> > > +SA( ! __is_invocable( long CM::*, long ) );
> > > +
> > > +SA( ! __is_invocable( short M::* ) );
> > > +SA(   __is_invocable( short M::*, M ) );
> > > +SA(   __is_invocable( short M::*, M& ) );
> > > +SA(   __is_invocable( short M::*, M&& ) );
> > > +SA(   __is_invocable( short M::*, M* ) );
> > > +SA(   __is_invocable( short M::*, CM ) );
> > > +SA(   __is_invocable( short M::*, CM& ) );
> > > +SA(   __is_invocable( short M::*, CM* ) );
> > > +SA( ! __is_invocable( short M::*, short ) );
> > > +
> > > +SA( ! __is_invocable( short CM::* ) );
> > > +SA(   __is_invocable( short CM::*, M ) );
> > > +SA(   __is_invocable( short CM::*, M& ) );
> > > +SA(   __is_invocable( short CM::*, M&& ) );
> > > +SA(   __is_invocable( short CM::*, M* ) );
> > > +SA(   __is_invocable( short CM::*, CM ) );
> > > +SA(   __is_invocable( short CM::*, CM& ) );
> > > +SA(   __is_invocable( short CM::*, CM* ) );
> > > +SA( ! __is_invocable( short CM::*, short ) );
> > > +
> > > +struct N { M operator*(); };
> > > +SA(   __is_invocable( int M::*, N ) );
> > > +SA( ! __is_invocable( int M::*, N* ) );
> > > +
> > > +struct O { M& operator*(); };
> > > +SA(   __is_invocable( int M::*, O ) );
> > > +SA( ! __is_invocable( int M::*, O* ) );
> > > +
> > > +struct P { M&& operator*(); };
> > > +SA(   __is_invocable( int M::*, P ) );
> > > +SA( ! __is_invocable( int M::*, P* ) );
> > > +
> > > +struct Q { M* operator*(); };
> > > +SA( ! __is_invocable( int M::*, Q ) );
> > > +SA( ! __is_invocable( int M::*, Q* ) );
> > > +
> > > +struct R { void operator()(int = 0); };
> > > +
> > > +SA(   __is_invocable( R ) );
> > > +SA(   __is_invocable( R, int ) );
> > > +SA( ! __is_invocable( R, int, int ) );
> > > +
> > > +struct S { void operator()(int, ...); };
> > > +
> > > +SA( ! __is_invocable( S ) );
> > > +SA(   __is_invocable( S, int ) );
> > > +SA(   __is_invocable( S, int, int ) );
> > > +SA(   __is_invocable( S, int, int, int ) );
> > > +
> > > +void fn1() {}
> > > +
> > > +SA(   __is_invocable( decltype(fn1) ) );
> > > +
> > > +void fn2(int arr[10]);
> > > +
> > > +SA(   __is_invocable( decltype(fn2), int[10] ) );
> > > +SA(   __is_invocable( decltype(fn2), int(&)[10] ) );
> > > +SA(   __is_invocable( decltype(fn2), int(&&)[10] ) );
> > > +SA( ! __is_invocable( decltype(fn2), int(*)[10] ) );
> > > +SA( ! __is_invocable( decltype(fn2), int(*&)[10] ) );
> > > +SA( ! __is_invocable( decltype(fn2), int(*&&)[10] ) );
> > > +SA(   __is_invocable( decltype(fn2), int[] ) );
> > > +
> > > +auto lambda = []() {};
> > > +
> > > +SA(   __is_invocable( decltype(lambda) ) );
> > > +
> > > +template <typename Func, typename... Args>
> > > +struct can_invoke {
> > > +    static constexpr bool value = __is_invocable( Func, Args... );
> > > +};
> > > +
> > > +SA(   can_invoke<decltype(lambda)>::value );
> > > +
> > > +struct T {
> > > +  void func() const {}
> > > +  int data;
> > > +};
> > > +
> > > +SA(   __is_invocable( decltype(&T::func)&, T& ) );
> > > +SA(   __is_invocable( decltype(&T::data)&, T& ) );
> > > +
> > > +struct U { };
> > > +struct V : U { U& operator*() = delete; };
> > > +SA(   __is_invocable( int U::*, V ) );
> > > +
> > > +struct W : private U { U& operator*(); };
> > > +SA( ! __is_invocable( int U::*, W ) );
> > > +
> > > +struct X { int m; };
> > > +struct Y { X& operator*(); };
> > > +struct Z : Y { };
> > > +SA(   __is_invocable(int X::*, Z) );
> > > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable2.C b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > > new file mode 100644
> > > index 00000000000..a68aefd3e13
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/ext/is_invocable2.C
> > > @@ -0,0 +1,139 @@
> > > +// { dg-do compile { target c++11 } }
> > > +// __is_invocable should handle std::reference_wrapper correctly.
> > > +
> > > +#include <functional>
> > > +
> > > +#define SA(X) static_assert((X),#X)
> > > +
> > > +using std::reference_wrapper;
> > > +
> > > +using func_type_v0 = void(*)();
> > > +
> > > +SA(   __is_invocable( reference_wrapper<func_type_v0> ) );
> > > +SA( ! __is_invocable( reference_wrapper<func_type_v0>, int ) );
> > > +
> > > +using func_type_i0 = int(*)();
> > > +
> > > +SA(   __is_invocable( reference_wrapper<func_type_i0> ) );
> > > +SA( ! __is_invocable( reference_wrapper<func_type_i0>, int ) );
> > > +
> > > +using func_type_l0 = int&(*)();
> > > +
> > > +SA(   __is_invocable( reference_wrapper<func_type_l0> ) );
> > > +SA( ! __is_invocable( reference_wrapper<func_type_l0(int)> ) );
> > > +
> > > +using func_type_ii = int(*)(int);
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<func_type_ii> ) );
> > > +SA(   __is_invocable( reference_wrapper<func_type_ii>, int ) );
> > > +
> > > +using func_type_il = int(*)(int&);
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<func_type_il> ) );
> > > +SA( ! __is_invocable( reference_wrapper<func_type_il>, int ) );
> > > +SA(   __is_invocable( reference_wrapper<func_type_il>, int& ) );
> > > +
> > > +using func_type_ir = int(*)(int&&);
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<func_type_ir> ) );
> > > +SA( ! __is_invocable( reference_wrapper<func_type_ir>, int& ) );
> > > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int ) );
> > > +SA(   __is_invocable( reference_wrapper<func_type_ir>, int&& ) );
> > > +
> > > +struct A { };
> > > +
> > > +using mem_type_i = int A::*;
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<mem_type_i> ) );
> > > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int* ) );
> > > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<mem_type_i>, int&& ) );
> > > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A ) );
> > > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A* ) );
> > > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A& ) );
> > > +SA(   __is_invocable( reference_wrapper<mem_type_i>, A&& ) );
> > > +
> > > +using memfun_type_i = int (A::*)();
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i> ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int* ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int&& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A* ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_i>, A&& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, const A& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_i>, A&, int ) );
> > > +
> > > +using memfun_type_ic = int (A::*)() const;
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic> ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A* ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A&, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A*, int& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A* ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A&, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A*, int ) );
> > > +
> > > +using memfun_type_iic = int& (A::*)(int&) const;
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic> ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A&, int ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A&, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A*, int ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A*, int& ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int&, int ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int& ) );
> > > +SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A*, int& ) );
> > > +
> > > +struct B {
> > > +  int& operator()();
> > > +  long& operator()() const;
> > > +  bool& operator()(int);
> > > +private:
> > > +  void operator()(int, int);
> > > +};
> > > +using CB = const B;
> > > +
> > > +SA(   __is_invocable( reference_wrapper<B> ) );
> > > +SA(   __is_invocable( reference_wrapper<B>& ) );
> > > +SA(   __is_invocable( reference_wrapper<B>&& ) );
> > > +SA(   __is_invocable( reference_wrapper<CB> ) );
> > > +SA(   __is_invocable( reference_wrapper<CB>& ) );
> > > +SA(   __is_invocable( reference_wrapper<B>, int ) );
> > > +SA( ! __is_invocable( reference_wrapper<B>&, int, int ) );
> > > +
> > > +struct C : B { int& operator()() = delete; };
> > > +using CC = const C;
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<C> ) );
> > > +SA( ! __is_invocable( reference_wrapper<C>& ) );
> > > +SA( ! __is_invocable( reference_wrapper<C>&& ) );
> > > +SA( ! __is_invocable( reference_wrapper<CC> ) );
> > > +SA( ! __is_invocable( reference_wrapper<CC>& ) );
> > > +
> > > +struct D { B operator*(); };
> > > +using CD = const D;
> > > +
> > > +SA( ! __is_invocable( reference_wrapper<D> ) );
> > > +SA( ! __is_invocable( reference_wrapper<D>& ) );
> > > +SA( ! __is_invocable( reference_wrapper<D>&& ) );
> > > +SA( ! __is_invocable( reference_wrapper<D>* ) );
> > > +SA( ! __is_invocable( reference_wrapper<D*> ) );
> > > +SA( ! __is_invocable( reference_wrapper<D*>* ) );
> > > +
> > > +std::function<void()> fn = []() {};
> > > +auto refwrap = std::ref(fn);
> > > +
> > > +SA(   __is_invocable( decltype(fn) ) );
> > > +SA(   __is_invocable( decltype(refwrap) ) );
> > > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable3.C b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > > new file mode 100644
> > > index 00000000000..8699b0a53ca
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/ext/is_invocable3.C
> > > @@ -0,0 +1,51 @@
> > > +// { dg-do compile { target c++11 } }
> > > +// __is_invocable should handle incomplete class correctly.
> > > +
> > > +#define SA(X) static_assert((X),#X)
> > > +
> > > +struct Incomplete;
> > > +
> > > +SA( ! __is_invocable( Incomplete ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( Incomplete, int ) ); // { dg-error "incomplete type" }
> > > +
> > > +SA( ! __is_invocable( int, Incomplete, int ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( int, Incomplete ) ); // { dg-error "incomplete type" }
> > > +
> > > +SA( ! __is_invocable( Incomplete, Incomplete() ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( Incomplete, Incomplete(int), int ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( Incomplete, Incomplete(int, int), int, int ) ); // { dg-error "incomplete type" }
> > > +
> > > +SA( ! __is_invocable( Incomplete, Incomplete(), int, int ) ); // { dg-error "incomplete type" }
> > > +
> > > +SA( ! __is_invocable( int(Incomplete), Incomplete ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( int(int, Incomplete), int, Incomplete ) ); // { dg-error "incomplete type" }
> > > +SA( ! __is_invocable( int(int, Incomplete), Incomplete, int ) ); // { dg-error "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int(Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( int(int, Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int(Incomplete&&), Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( int(int, Incomplete&&), int, Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int(const Incomplete&&), const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( int(int, const Incomplete&&), int, const Incomplete&& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int(const Incomplete&), const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( int(int, const Incomplete&), int, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int(const Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( int(int, const Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +SA(   __is_invocable( int Incomplete::*, const Incomplete& ) ); // { dg-bogus "incomplete type" }
> > > +SA( ! __is_invocable( void (Incomplete::*)(long&), const Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > > +SA(   __is_invocable( void (Incomplete::*)(long&) const, Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +template <typename T>
> > > +struct Holder { T t; };
> > > +
> > > +SA(   __is_invocable( int(Holder<Incomplete>&), Holder<Incomplete>& ) ); // { dg-bogus "incomplete type" }
> > > +
> > > +// Define Incomplete, which is now not incomplete.
> > > +struct Incomplete { void operator()(); };
> > > +
> > > +SA(   __is_invocable( Incomplete ) ); // { dg-bogus "incomplete type" }
> > > diff --git a/gcc/testsuite/g++.dg/ext/is_invocable4.C b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > > new file mode 100644
> > > index 00000000000..d1efccf08f8
> > > --- /dev/null
> > > +++ b/gcc/testsuite/g++.dg/ext/is_invocable4.C
> > > @@ -0,0 +1,33 @@
> > > +// { dg-do compile { target c++11 } }
> > > +// Failed access check should be a substitution failure, not an error.
> > > +
> > > +#define SA(X) static_assert((X),#X)
> > > +
> > > +template<bool B>
> > > +struct bool_constant { static constexpr bool value = B; };
> > > +
> > > +template<typename _Fn, typename... _ArgTypes>
> > > +struct is_invocable
> > > +: public bool_constant<__is_invocable(_Fn, _ArgTypes...)>
> > > +{ };
> > > +
> > > +#if __cpp_variable_templates
> > > +template<typename _Fn, typename... _ArgTypes>
> > > +constexpr bool is_invocable_v = __is_invocable(_Fn, _ArgTypes...);
> > > +#endif
> > > +
> > > +class Private
> > > +{
> > > +  void operator()() const
> > > +  {
> > > +    SA( ! is_invocable<Private>::value );
> > > +#if __cpp_variable_templates
> > > +    SA( ! is_invocable_v<Private> );
> > > +#endif
> > > +  }
> > > +};
> > > +
> > > +SA( ! is_invocable<Private>::value );
> > > +#if __cpp_variable_templates
> > > +SA( ! is_invocable_v<Private> );
> > > +#endif
> > > --
> > > 2.44.0
> > >
> > >
> >

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 23ea66d9c12..c87b126fdb1 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3791,6 +3791,12 @@  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 85056c8140b..6cb2b55f4ea 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 334c11396c2..261d3a71faa 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7334,6 +7334,8 @@  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 98c10e6a8b5..953f1bed6fc 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -1928,6 +1928,138 @@  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 (fn_type == error_mark_node || arg_types == error_mark_node)
+    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)
+    /* Only a pointer to data member with one argument is invocable.  */
+    return error_mark_node;
+
+  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
+    /* A pointer to member function with no arguments is not invocable.  */
+    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 (TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
+        {
+	  if (!CLASS_TYPE_P (TREE_TYPE (datum_type)))
+	    return error_mark_node;
+        }
+      else if (!CLASS_TYPE_P (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 datum_expr = build_trait_object (datum_type);
+      tree fn_expr = build_trait_object (fn_type);
+      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr, complain);
+
+      if (error_operand_p (ptrmem_expr) && !is_refwrap)
+	{
+	  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)
+	     && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
+							    datum_type)
+		 || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
+
+	  if (!ptrmem_is_base_of_datum)
+	    {
+	      /* 1.3 & 1.6: Try to dereference datum_expr.  */
+	      datum_expr = build_x_indirect_ref (UNKNOWN_LOCATION, datum_expr,
+						 RO_UNARY_STAR, NULL_TREE,
+						 complain);
+	      /* Rebuild ptrmem_expr.  */
+	      ptrmem_expr = build_m_component_ref (datum_expr, fn_expr,
+						   complain);
+	    }
+	}
+      /* 1.1 & 1.4: Otherwise.  */
+
+      if (error_operand_p (ptrmem_expr))
+	return error_mark_node;
+
+      if (is_ptrdatamem)
+	return ptrmem_expr;
+    }
+
+  /* Construct expressions for arguments to INVOKE.  For a pointer to member
+     function, the first argument, which is the object, is not arguments to
+     the function.  */
+  releasing_vec args;
+  for (int i = is_ptrmemfunc ? 1 : 0; i < TREE_VEC_LENGTH (arg_types); ++i)
+    {
+      tree arg_type = TREE_VEC_ELT (arg_types, i);
+      tree arg = build_trait_object (arg_type);
+      vec_safe_push (args, arg);
+    }
+
+  tree invoke_expr;
+  if (is_ptrmemfunc)
+    invoke_expr = build_offset_ref_call_from_tree (ptrmem_expr, &args,
+						   complain);
+  else  /* 1.7.  */
+    invoke_expr = finish_call_expr (build_trait_object (fn_type), &args, false,
+				    false, complain);
+  return invoke_expr;
+}
+
 /* Determine which function will be called when looking up NAME in TYPE,
    called with a single ARGTYPE argument, or no argument if ARGTYPE is
    null.  FLAGS and COMPLAIN are as for build_new_method_call.
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 7242db75248..149c0631d62 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -12467,6 +12467,9 @@  trait_expr_value (cp_trait_kind kind, tree type1, tree type2)
     case CPTK_IS_FUNCTION:
       return type_code1 == FUNCTION_TYPE;
 
+    case CPTK_IS_INVOCABLE:
+      return !error_operand_p (build_invoke (type1, type2, tf_none));
+
     case CPTK_IS_LAYOUT_COMPATIBLE:
       return layout_compatible_type_p (type1, type2);
 
@@ -12682,6 +12685,7 @@  finish_trait_expr (location_t loc, cp_trait_kind kind, tree type1, tree type2)
       break;
 
     case CPTK_IS_CONVERTIBLE:
+    case CPTK_IS_INVOCABLE:
     case CPTK_IS_NOTHROW_ASSIGNABLE:
     case CPTK_IS_NOTHROW_CONSTRUCTIBLE:
     case CPTK_IS_NOTHROW_CONVERTIBLE:
diff --git a/gcc/testsuite/g++.dg/ext/has-builtin-1.C b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
index 7f7b27f7aa7..d2a7ebdf25c 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -104,6 +104,9 @@ 
 #if !__has_builtin (__is_function)
 # error "__has_builtin (__is_function) failed"
 #endif
+#if !__has_builtin (__is_invocable)
+# error "__has_builtin (__is_invocable) failed"
+#endif
 #if !__has_builtin (__is_layout_compatible)
 # error "__has_builtin (__is_layout_compatible) failed"
 #endif
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable1.C b/gcc/testsuite/g++.dg/ext/is_invocable1.C
new file mode 100644
index 00000000000..d21ae1d1958
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
@@ -0,0 +1,349 @@ 
+// { dg-do compile { target c++11 } }
+
+#define SA(X) static_assert((X),#X)
+
+using func_type_v0 = void(*)();
+
+SA(   __is_invocable( func_type_v0 ) );
+SA( ! __is_invocable( func_type_v0, int ) );
+
+using func_type_i0 = int(*)();
+
+SA(   __is_invocable( func_type_i0 ) );
+SA( ! __is_invocable( func_type_i0, int ) );
+
+using func_type_l0 = int&(*)();
+
+SA(   __is_invocable( func_type_l0 ) );
+SA( ! __is_invocable( func_type_l0(int) ) );
+
+using func_type_ii = int(*)(int);
+
+SA( ! __is_invocable( func_type_ii ) );
+SA(   __is_invocable( func_type_ii, int ) );
+
+using func_type_il = int(*)(int&);
+
+SA( ! __is_invocable( func_type_il ) );
+SA( ! __is_invocable( func_type_il, int ) );
+SA(   __is_invocable( func_type_il, int& ) );
+
+using func_type_ir = int(*)(int&&);
+
+SA( ! __is_invocable( func_type_ir ) );
+SA( ! __is_invocable( func_type_ir, int& ) );
+SA(   __is_invocable( func_type_ir, int ) );
+SA(   __is_invocable( func_type_ir, int&& ) );
+
+struct A { };
+
+using mem_type_i = int A::*;
+
+SA( ! __is_invocable( mem_type_i ) );
+SA( ! __is_invocable( mem_type_i, int ) );
+SA( ! __is_invocable( mem_type_i, int* ) );
+SA( ! __is_invocable( mem_type_i, int& ) );
+SA( ! __is_invocable( mem_type_i, int&& ) );
+SA(   __is_invocable( mem_type_i, A ) );
+SA(   __is_invocable( mem_type_i, A* ) );
+SA(   __is_invocable( mem_type_i, A& ) );
+SA(   __is_invocable( mem_type_i, A&& ) );
+SA(   __is_invocable( mem_type_i, const A& ) );
+SA( ! __is_invocable( mem_type_i, A&, int ) );
+
+using memfun_type_i = int (A::*)();
+
+SA( ! __is_invocable( memfun_type_i ) );
+SA( ! __is_invocable( memfun_type_i, int ) );
+SA( ! __is_invocable( memfun_type_i, int* ) );
+SA( ! __is_invocable( memfun_type_i, int& ) );
+SA( ! __is_invocable( memfun_type_i, int&& ) );
+SA(   __is_invocable( memfun_type_i, A ) );
+SA(   __is_invocable( memfun_type_i, A* ) );
+SA(   __is_invocable( memfun_type_i, A& ) );
+SA(   __is_invocable( memfun_type_i, A&& ) );
+SA( ! __is_invocable( memfun_type_i, const A& ) );
+SA( ! __is_invocable( memfun_type_i, A&, int ) );
+
+using memfun_type_ic = int (A::*)() const;
+
+SA( ! __is_invocable( memfun_type_ic ) );
+SA( ! __is_invocable( memfun_type_ic, int ) );
+SA( ! __is_invocable( memfun_type_ic, int& ) );
+SA(   __is_invocable( memfun_type_ic, A& ) );
+SA(   __is_invocable( memfun_type_ic, A* ) );
+SA( ! __is_invocable( memfun_type_ic, A&, int ) );
+SA( ! __is_invocable( memfun_type_ic, A*, int& ) );
+SA(   __is_invocable( memfun_type_ic, const A& ) );
+SA(   __is_invocable( memfun_type_ic, const A* ) );
+SA( ! __is_invocable( memfun_type_ic, const A&, int& ) );
+SA( ! __is_invocable( memfun_type_ic, const A*, int ) );
+
+using memfun_type_iic = int& (A::*)(int&) const;
+
+SA( ! __is_invocable( memfun_type_iic ) );
+SA( ! __is_invocable( memfun_type_iic, int ) );
+SA( ! __is_invocable( memfun_type_iic, int& ) );
+SA( ! __is_invocable( memfun_type_iic, A&, int ) );
+SA(   __is_invocable( memfun_type_iic, A&, int& ) );
+SA( ! __is_invocable( memfun_type_iic, A*, int ) );
+SA(   __is_invocable( memfun_type_iic, A*, int& ) );
+SA( ! __is_invocable( memfun_type_iic, const A&, int ) );
+SA( ! __is_invocable( memfun_type_iic, const A&, int&, int ) );
+SA(   __is_invocable( memfun_type_iic, const A&, int& ) );
+SA(   __is_invocable( memfun_type_iic, const A*, int& ) );
+
+struct B {
+  int& operator()();
+  long& operator()() const;
+  bool& operator()(int);
+private:
+  void operator()(int, int);
+};
+using CB = const B;
+
+SA(   __is_invocable( B ) );
+SA(   __is_invocable( B& ) );
+SA(   __is_invocable( B&& ) );
+SA( ! __is_invocable( B* ) );
+SA(   __is_invocable( CB ) );
+SA(   __is_invocable( CB& ) );
+SA( ! __is_invocable( CB* ) );
+
+SA(   __is_invocable( B, int ) );
+SA(   __is_invocable( B&, int ) );
+SA(   __is_invocable( B&&, int ) );
+SA( ! __is_invocable( B*, int ) );
+SA( ! __is_invocable( CB, int ) );
+SA( ! __is_invocable( CB&, int ) );
+SA( ! __is_invocable( CB*, int ) );
+
+SA( ! __is_invocable( B, int, int ) );
+SA( ! __is_invocable( B&, int, int ) );
+SA( ! __is_invocable( B&&, int, int ) );
+SA( ! __is_invocable( B*, int, int ) );
+SA( ! __is_invocable( CB, int, int ) );
+SA( ! __is_invocable( CB&, int, int ) );
+SA( ! __is_invocable( CB*, int, int ) );
+
+struct C : B { int& operator()() = delete; };
+using CC = const C;
+
+SA( ! __is_invocable( C ) );
+SA( ! __is_invocable( C& ) );
+SA( ! __is_invocable( C&& ) );
+SA( ! __is_invocable( C* ) );
+SA( ! __is_invocable( CC ) );
+SA( ! __is_invocable( CC& ) );
+SA( ! __is_invocable( CC* ) );
+
+struct D { B operator*(); };
+using CD = const D;
+
+SA( ! __is_invocable( D ) );
+
+struct E { void v(); };
+using CE = const E;
+
+SA( ! __is_invocable( E ) );
+SA( ! __is_invocable( void (E::*)() ) );
+SA(   __is_invocable( void (E::*)(), E ) );
+SA(   __is_invocable( void (E::*)(), E* ) );
+SA( ! __is_invocable( void (E::*)(), CE ) );
+
+struct F : E {};
+using CF = const F;
+
+SA( ! __is_invocable( F ) );
+SA(   __is_invocable( void (E::*)(), F ) );
+SA(   __is_invocable( void (E::*)(), F* ) );
+SA( ! __is_invocable( void (E::*)(), CF ) );
+
+struct G { E operator*(); };
+using CG = const G;
+
+SA( ! __is_invocable( G ) );
+SA(   __is_invocable( void (E::*)(), G ) );
+SA( ! __is_invocable( void (E::*)(), G* ) );
+SA( ! __is_invocable( void (E::*)(), CG ) );
+
+struct H { E& operator*(); };
+using CH = const H;
+
+SA( ! __is_invocable( H ) );
+SA(   __is_invocable( void (E::*)(), H ) );
+SA( ! __is_invocable( void (E::*)(), H* ) );
+SA( ! __is_invocable( void (E::*)(), CH ) );
+
+struct I { E&& operator*(); };
+using CI = const I;
+
+SA( ! __is_invocable( I ) );
+SA(   __is_invocable( void (E::*)(), I ) );
+SA( ! __is_invocable( void (E::*)(), I* ) );
+SA( ! __is_invocable( void (E::*)(), CI ) );
+
+struct K { E* operator*(); };
+using CK = const K;
+
+SA( ! __is_invocable( K ) );
+SA( ! __is_invocable( void (E::*)(), K ) );
+SA( ! __is_invocable( void (E::*)(), K* ) );
+SA( ! __is_invocable( void (E::*)(), CK ) );
+
+struct L { CE operator*(); };
+using CL = const L;
+
+SA( ! __is_invocable( L ) );
+SA( ! __is_invocable( void (E::*)(), L ) );
+SA( ! __is_invocable( void (E::*)(), L* ) );
+SA( ! __is_invocable( void (E::*)(), CL ) );
+
+struct M {
+  int i;
+private:
+  long l;
+};
+using CM = const M;
+
+SA( ! __is_invocable( M ) );
+SA( ! __is_invocable( M& ) );
+SA( ! __is_invocable( M&& ) );
+SA( ! __is_invocable( M* ) );
+SA( ! __is_invocable( CM ) );
+SA( ! __is_invocable( CM& ) );
+SA( ! __is_invocable( CM* ) );
+
+SA( ! __is_invocable( int M::* ) );
+SA(   __is_invocable( int M::*, M ) );
+SA(   __is_invocable( int M::*, M& ) );
+SA(   __is_invocable( int M::*, M&& ) );
+SA(   __is_invocable( int M::*, M* ) );
+SA(   __is_invocable( int M::*, CM ) );
+SA(   __is_invocable( int M::*, CM& ) );
+SA(   __is_invocable( int M::*, CM* ) );
+SA( ! __is_invocable( int M::*, int ) );
+
+SA( ! __is_invocable( int CM::* ) );
+SA(   __is_invocable( int CM::*, M ) );
+SA(   __is_invocable( int CM::*, M& ) );
+SA(   __is_invocable( int CM::*, M&& ) );
+SA(   __is_invocable( int CM::*, M* ) );
+SA(   __is_invocable( int CM::*, CM ) );
+SA(   __is_invocable( int CM::*, CM& ) );
+SA(   __is_invocable( int CM::*, CM* ) );
+SA( ! __is_invocable( int CM::*, int ) );
+
+SA( ! __is_invocable( long M::* ) );
+SA(   __is_invocable( long M::*, M ) );
+SA(   __is_invocable( long M::*, M& ) );
+SA(   __is_invocable( long M::*, M&& ) );
+SA(   __is_invocable( long M::*, M* ) );
+SA(   __is_invocable( long M::*, CM ) );
+SA(   __is_invocable( long M::*, CM& ) );
+SA(   __is_invocable( long M::*, CM* ) );
+SA( ! __is_invocable( long M::*, long ) );
+
+SA( ! __is_invocable( long CM::* ) );
+SA(   __is_invocable( long CM::*, M ) );
+SA(   __is_invocable( long CM::*, M& ) );
+SA(   __is_invocable( long CM::*, M&& ) );
+SA(   __is_invocable( long CM::*, M* ) );
+SA(   __is_invocable( long CM::*, CM ) );
+SA(   __is_invocable( long CM::*, CM& ) );
+SA(   __is_invocable( long CM::*, CM* ) );
+SA( ! __is_invocable( long CM::*, long ) );
+
+SA( ! __is_invocable( short M::* ) );
+SA(   __is_invocable( short M::*, M ) );
+SA(   __is_invocable( short M::*, M& ) );
+SA(   __is_invocable( short M::*, M&& ) );
+SA(   __is_invocable( short M::*, M* ) );
+SA(   __is_invocable( short M::*, CM ) );
+SA(   __is_invocable( short M::*, CM& ) );
+SA(   __is_invocable( short M::*, CM* ) );
+SA( ! __is_invocable( short M::*, short ) );
+
+SA( ! __is_invocable( short CM::* ) );
+SA(   __is_invocable( short CM::*, M ) );
+SA(   __is_invocable( short CM::*, M& ) );
+SA(   __is_invocable( short CM::*, M&& ) );
+SA(   __is_invocable( short CM::*, M* ) );
+SA(   __is_invocable( short CM::*, CM ) );
+SA(   __is_invocable( short CM::*, CM& ) );
+SA(   __is_invocable( short CM::*, CM* ) );
+SA( ! __is_invocable( short CM::*, short ) );
+
+struct N { M operator*(); };
+SA(   __is_invocable( int M::*, N ) );
+SA( ! __is_invocable( int M::*, N* ) );
+
+struct O { M& operator*(); };
+SA(   __is_invocable( int M::*, O ) );
+SA( ! __is_invocable( int M::*, O* ) );
+
+struct P { M&& operator*(); };
+SA(   __is_invocable( int M::*, P ) );
+SA( ! __is_invocable( int M::*, P* ) );
+
+struct Q { M* operator*(); };
+SA( ! __is_invocable( int M::*, Q ) );
+SA( ! __is_invocable( int M::*, Q* ) );
+
+struct R { void operator()(int = 0); };
+
+SA(   __is_invocable( R ) );
+SA(   __is_invocable( R, int ) );
+SA( ! __is_invocable( R, int, int ) );
+
+struct S { void operator()(int, ...); };
+
+SA( ! __is_invocable( S ) );
+SA(   __is_invocable( S, int ) );
+SA(   __is_invocable( S, int, int ) );
+SA(   __is_invocable( S, int, int, int ) );
+
+void fn1() {}
+
+SA(   __is_invocable( decltype(fn1) ) );
+
+void fn2(int arr[10]);
+
+SA(   __is_invocable( decltype(fn2), int[10] ) );
+SA(   __is_invocable( decltype(fn2), int(&)[10] ) );
+SA(   __is_invocable( decltype(fn2), int(&&)[10] ) );
+SA( ! __is_invocable( decltype(fn2), int(*)[10] ) );
+SA( ! __is_invocable( decltype(fn2), int(*&)[10] ) );
+SA( ! __is_invocable( decltype(fn2), int(*&&)[10] ) );
+SA(   __is_invocable( decltype(fn2), int[] ) );
+
+auto lambda = []() {};
+
+SA(   __is_invocable( decltype(lambda) ) );
+
+template <typename Func, typename... Args>
+struct can_invoke {
+    static constexpr bool value = __is_invocable( Func, Args... );
+};
+
+SA(   can_invoke<decltype(lambda)>::value );
+
+struct T {
+  void func() const {}
+  int data;
+};
+
+SA(   __is_invocable( decltype(&T::func)&, T& ) );
+SA(   __is_invocable( decltype(&T::data)&, T& ) );
+
+struct U { };
+struct V : U { U& operator*() = delete; };
+SA(   __is_invocable( int U::*, V ) );
+
+struct W : private U { U& operator*(); };
+SA( ! __is_invocable( int U::*, W ) );
+
+struct X { int m; };
+struct Y { X& operator*(); };
+struct Z : Y { };
+SA(   __is_invocable(int X::*, Z) );
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable2.C b/gcc/testsuite/g++.dg/ext/is_invocable2.C
new file mode 100644
index 00000000000..a68aefd3e13
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable2.C
@@ -0,0 +1,139 @@ 
+// { dg-do compile { target c++11 } }
+// __is_invocable should handle std::reference_wrapper correctly.
+
+#include <functional>
+
+#define SA(X) static_assert((X),#X)
+
+using std::reference_wrapper;
+
+using func_type_v0 = void(*)();
+
+SA(   __is_invocable( reference_wrapper<func_type_v0> ) );
+SA( ! __is_invocable( reference_wrapper<func_type_v0>, int ) );
+
+using func_type_i0 = int(*)();
+
+SA(   __is_invocable( reference_wrapper<func_type_i0> ) );
+SA( ! __is_invocable( reference_wrapper<func_type_i0>, int ) );
+
+using func_type_l0 = int&(*)();
+
+SA(   __is_invocable( reference_wrapper<func_type_l0> ) );
+SA( ! __is_invocable( reference_wrapper<func_type_l0(int)> ) );
+
+using func_type_ii = int(*)(int);
+
+SA( ! __is_invocable( reference_wrapper<func_type_ii> ) );
+SA(   __is_invocable( reference_wrapper<func_type_ii>, int ) );
+
+using func_type_il = int(*)(int&);
+
+SA( ! __is_invocable( reference_wrapper<func_type_il> ) );
+SA( ! __is_invocable( reference_wrapper<func_type_il>, int ) );
+SA(   __is_invocable( reference_wrapper<func_type_il>, int& ) );
+
+using func_type_ir = int(*)(int&&);
+
+SA( ! __is_invocable( reference_wrapper<func_type_ir> ) );
+SA( ! __is_invocable( reference_wrapper<func_type_ir>, int& ) );
+SA(   __is_invocable( reference_wrapper<func_type_ir>, int ) );
+SA(   __is_invocable( reference_wrapper<func_type_ir>, int&& ) );
+
+struct A { };
+
+using mem_type_i = int A::*;
+
+SA( ! __is_invocable( reference_wrapper<mem_type_i> ) );
+SA( ! __is_invocable( reference_wrapper<mem_type_i>, int ) );
+SA( ! __is_invocable( reference_wrapper<mem_type_i>, int* ) );
+SA( ! __is_invocable( reference_wrapper<mem_type_i>, int& ) );
+SA( ! __is_invocable( reference_wrapper<mem_type_i>, int&& ) );
+SA(   __is_invocable( reference_wrapper<mem_type_i>, A ) );
+SA(   __is_invocable( reference_wrapper<mem_type_i>, A* ) );
+SA(   __is_invocable( reference_wrapper<mem_type_i>, A& ) );
+SA(   __is_invocable( reference_wrapper<mem_type_i>, A&& ) );
+
+using memfun_type_i = int (A::*)();
+
+SA( ! __is_invocable( reference_wrapper<memfun_type_i> ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int* ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, int&& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_i>, A ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_i>, A* ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_i>, A& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_i>, A&& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, const A& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_i>, A&, int ) );
+
+using memfun_type_ic = int (A::*)() const;
+
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic> ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, int& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_ic>, A* ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A&, int ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, A*, int& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_ic>, const A* ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A&, int& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_ic>, const A*, int ) );
+
+using memfun_type_iic = int& (A::*)(int&) const;
+
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic> ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, int& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A&, int ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A&, int& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, A*, int ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_iic>, A*, int& ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int ) );
+SA( ! __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int&, int ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A&, int& ) );
+SA(   __is_invocable( reference_wrapper<memfun_type_iic>, const A*, int& ) );
+
+struct B {
+  int& operator()();
+  long& operator()() const;
+  bool& operator()(int);
+private:
+  void operator()(int, int);
+};
+using CB = const B;
+
+SA(   __is_invocable( reference_wrapper<B> ) );
+SA(   __is_invocable( reference_wrapper<B>& ) );
+SA(   __is_invocable( reference_wrapper<B>&& ) );
+SA(   __is_invocable( reference_wrapper<CB> ) );
+SA(   __is_invocable( reference_wrapper<CB>& ) );
+SA(   __is_invocable( reference_wrapper<B>, int ) );
+SA( ! __is_invocable( reference_wrapper<B>&, int, int ) );
+
+struct C : B { int& operator()() = delete; };
+using CC = const C;
+
+SA( ! __is_invocable( reference_wrapper<C> ) );
+SA( ! __is_invocable( reference_wrapper<C>& ) );
+SA( ! __is_invocable( reference_wrapper<C>&& ) );
+SA( ! __is_invocable( reference_wrapper<CC> ) );
+SA( ! __is_invocable( reference_wrapper<CC>& ) );
+
+struct D { B operator*(); };
+using CD = const D;
+
+SA( ! __is_invocable( reference_wrapper<D> ) );
+SA( ! __is_invocable( reference_wrapper<D>& ) );
+SA( ! __is_invocable( reference_wrapper<D>&& ) );
+SA( ! __is_invocable( reference_wrapper<D>* ) );
+SA( ! __is_invocable( reference_wrapper<D*> ) );
+SA( ! __is_invocable( reference_wrapper<D*>* ) );
+
+std::function<void()> fn = []() {};
+auto refwrap = std::ref(fn);
+
+SA(   __is_invocable( decltype(fn) ) );
+SA(   __is_invocable( decltype(refwrap) ) );
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable3.C b/gcc/testsuite/g++.dg/ext/is_invocable3.C
new file mode 100644
index 00000000000..8699b0a53ca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable3.C
@@ -0,0 +1,51 @@ 
+// { dg-do compile { target c++11 } }
+// __is_invocable should handle incomplete class correctly.
+
+#define SA(X) static_assert((X),#X)
+
+struct Incomplete;
+
+SA( ! __is_invocable( Incomplete ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( Incomplete, int ) ); // { dg-error "incomplete type" }
+
+SA( ! __is_invocable( int, Incomplete, int ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( int, Incomplete ) ); // { dg-error "incomplete type" }
+
+SA( ! __is_invocable( Incomplete, Incomplete() ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( Incomplete, Incomplete(int), int ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( Incomplete, Incomplete(int, int), int, int ) ); // { dg-error "incomplete type" }
+
+SA( ! __is_invocable( Incomplete, Incomplete(), int, int ) ); // { dg-error "incomplete type" }
+
+SA( ! __is_invocable( int(Incomplete), Incomplete ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( int(int, Incomplete), int, Incomplete ) ); // { dg-error "incomplete type" }
+SA( ! __is_invocable( int(int, Incomplete), Incomplete, int ) ); // { dg-error "incomplete type" }
+
+SA(   __is_invocable( int(Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( int(int, Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
+
+SA(   __is_invocable( int(Incomplete&&), Incomplete&& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( int(int, Incomplete&&), int, Incomplete&& ) ); // { dg-bogus "incomplete type" }
+
+SA(   __is_invocable( int(const Incomplete&&), const Incomplete&& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( int(int, const Incomplete&&), int, const Incomplete&& ) ); // { dg-bogus "incomplete type" }
+
+SA(   __is_invocable( int(const Incomplete&), const Incomplete& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( int(int, const Incomplete&), int, const Incomplete& ) ); // { dg-bogus "incomplete type" }
+
+SA(   __is_invocable( int(const Incomplete&), Incomplete& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( int(int, const Incomplete&), int, Incomplete& ) ); // { dg-bogus "incomplete type" }
+
+SA(   __is_invocable( int Incomplete::*, const Incomplete& ) ); // { dg-bogus "incomplete type" }
+SA( ! __is_invocable( void (Incomplete::*)(long&), const Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
+SA(   __is_invocable( void (Incomplete::*)(long&) const, Incomplete*, long& ) ); // { dg-bogus "incomplete type" }
+
+template <typename T>
+struct Holder { T t; };
+
+SA(   __is_invocable( int(Holder<Incomplete>&), Holder<Incomplete>& ) ); // { dg-bogus "incomplete type" }
+
+// Define Incomplete, which is now not incomplete.
+struct Incomplete { void operator()(); };
+
+SA(   __is_invocable( Incomplete ) ); // { dg-bogus "incomplete type" }
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable4.C b/gcc/testsuite/g++.dg/ext/is_invocable4.C
new file mode 100644
index 00000000000..d1efccf08f8
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable4.C
@@ -0,0 +1,33 @@ 
+// { dg-do compile { target c++11 } }
+// Failed access check should be a substitution failure, not an error.
+
+#define SA(X) static_assert((X),#X)
+
+template<bool B>
+struct bool_constant { static constexpr bool value = B; };
+
+template<typename _Fn, typename... _ArgTypes>
+struct is_invocable
+: public bool_constant<__is_invocable(_Fn, _ArgTypes...)>
+{ };
+
+#if __cpp_variable_templates
+template<typename _Fn, typename... _ArgTypes>
+constexpr bool is_invocable_v = __is_invocable(_Fn, _ArgTypes...);
+#endif
+
+class Private
+{
+  void operator()() const
+  {
+    SA( ! is_invocable<Private>::value );
+#if __cpp_variable_templates
+    SA( ! is_invocable_v<Private> );
+#endif
+  }
+};
+
+SA( ! is_invocable<Private>::value );
+#if __cpp_variable_templates
+SA( ! is_invocable_v<Private> );
+#endif

[v14,23/26] c++: Implement __is_invocable built-in trait

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