[PATCH v25 32/33] c++: Implement __is_invocable built-in trait

[Ken Matsui <kmatsui@gcc.gnu.org>]

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.
	(is_invocable_p): New function.
	* method.h: New file to export build_trait_object in method.cc.

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/method.h                          |  28 ++
 gcc/cp/semantics.cc                      | 135 +++++++++
 gcc/testsuite/g++.dg/ext/has-builtin-1.C |   3 +
 gcc/testsuite/g++.dg/ext/is_invocable1.C | 337 +++++++++++++++++++++++
 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 +++
 9 files changed, 733 insertions(+)
 create mode 100644 gcc/cp/method.h
 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 9fce36e12d1..29bf548d30a 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3754,6 +3754,12 @@ 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 05514a51c21..b8b7608c122 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -71,6 +71,7 @@ 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/method.h b/gcc/cp/method.h
new file mode 100644
index 00000000000..1aec8ec5cfd
--- /dev/null
+++ b/gcc/cp/method.h
@@ -0,0 +1,28 @@
+/* Functions exported by method.cc.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 3, or (at your option)
+any later version.
+
+GCC is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_CP_METHOD_H
+#define GCC_CP_METHOD_H 1
+
+#include "tree.h"
+
+/* In method.cc  */
+extern tree build_trait_object (tree type);
+
+#endif  /* GCC_CP_METHOD_H  */
diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc
index 7cccbae5287..cc2e400531a 100644
--- a/gcc/cp/semantics.cc
+++ b/gcc/cp/semantics.cc
@@ -45,6 +45,10 @@ along with GCC; see the file COPYING3.  If not see
 #include "gomp-constants.h"
 #include "predict.h"
 #include "memmodel.h"
+#include "method.h"
+
+#include "print-tree.h"
+#include "tree-pretty-print.h"
 
 /* There routines provide a modular interface to perform many parsing
    operations.  They may therefore be used during actual parsing, or
@@ -11714,6 +11718,133 @@ classtype_has_nothrow_assign_or_copy_p (tree type, bool assign_p)
   return saw_copy;
 }
 
+/* Return true if FN_TYPE is invocable with the given ARG_TYPES.  */
+
+static bool
+is_invocable_p (tree fn_type, tree arg_types)
+{
+  /* ARG_TYPES must be a TREE_VEC.  */
+  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);
+
+  /* std::is_invocable 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)
+    /* A pointer to data member with non-one argument is not invocable.  */
+    return false;
+
+  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
+    /* A pointer to member function with no arguments is not invocable.  */
+    return false;
+
+  /* Construct an expression of a pointer to member.  */
+  tree datum;
+  if (is_ptrdatamem || is_ptrmemfunc)
+    {
+      tree datum_type = TREE_VEC_ELT (arg_types, 0);
+
+      /* Dereference datum.  */
+      if (CLASS_TYPE_P (datum_type))
+	{
+	  bool is_refwrap = false;
+
+	  tree datum_decl = TYPE_NAME (TYPE_MAIN_VARIANT (datum_type));
+	  if (decl_in_std_namespace_p (datum_decl))
+	    {
+	      tree name = DECL_NAME (datum_decl);
+	      if (name && (id_equal (name, "reference_wrapper")))
+		{
+		  /* Handle std::reference_wrapper.  */
+		  is_refwrap = true;
+		  datum_type = cp_build_reference_type (datum_type, false);
+		}
+	    }
+
+	  datum = build_trait_object (datum_type);
+
+	  /* If datum_type was not std::reference_wrapper, check if it has
+	     operator*() overload.  If datum_type was std::reference_wrapper,
+	     avoid dereferencing the datum twice.  */
+	  if (!is_refwrap)
+	    if (get_class_binding (datum_type, get_identifier ("operator*")))
+	      /* Handle operator*().  */
+	      datum = build_x_indirect_ref (UNKNOWN_LOCATION, datum,
+					    RO_UNARY_STAR, NULL_TREE,
+					    tf_none);
+	}
+      else if (POINTER_TYPE_P (datum_type))
+	datum = build_trait_object (TREE_TYPE (datum_type));
+      else
+	datum = build_trait_object (datum_type);
+    }
+
+  /* Build a function expression.  */
+  tree fn;
+  if (is_ptrdatamem)
+    fn = build_m_component_ref (datum, build_trait_object (fn_type), tf_none);
+  else if (is_ptrmemfunc)
+    fn = build_trait_object (TYPE_PTRMEMFUNC_FN_TYPE (fn_type));
+  else
+    fn = build_trait_object (fn_type);
+
+  /* Construct arguments to the function and an expression of a call.  */
+  if (!is_ptrdatamem)
+    {
+      releasing_vec args;
+
+      if (is_ptrmemfunc)
+	{
+	  /* A pointer to member function is internally converted to a pointer
+	     to function that takes a pointer to the dereferenced datum type
+	     as its first argument and original arguments afterward.  If the
+	     function is a const member function, the first argument also
+	     requires a const datum pointer and vice-versa.  */
+
+	  tree datum_type = TREE_TYPE (datum);
+	  if (TYPE_REF_P (datum_type))
+	    datum_type = TREE_TYPE (datum_type);
+
+	  datum = build_trait_object (build_pointer_type (datum_type));
+	  vec_safe_push (args, datum);
+	}
+
+      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);
+	}
+
+      fn = finish_call_expr (fn, &args, false, false, tf_none);
+    }
+
+  if (error_operand_p (fn))
+    return false;
+
+  return true;
+}
+
 /* Return true if DERIVED is pointer interconvertible base of BASE.  */
 
 static bool
@@ -12181,6 +12312,9 @@ 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 is_invocable_p (type1, type2);
+
     case CPTK_IS_LAYOUT_COMPATIBLE:
       return layout_compatible_type_p (type1, type2);
 
@@ -12390,6 +12524,7 @@ 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 b1430e9bd8b..3a9bda1ee03 100644
--- a/gcc/testsuite/g++.dg/ext/has-builtin-1.C
+++ b/gcc/testsuite/g++.dg/ext/has-builtin-1.C
@@ -92,6 +92,9 @@
 #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..2fd3906b571
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable1.C
@@ -0,0 +1,337 @@
+// { 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& ) );
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..e2b0c5ef406
--- /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
-- 
2.42.0