On 5/2/24 16:12, Ken Matsui wrote:
This patch implements built-in trait for std::is_invocable.

gcc/cp/ChangeLog:

        * cp-trait.def: Define __is_invocable.
        * constraint.cc (diagnose_trait_expr): Handle CPTK_IS_INVOCABLE.
        * semantics.cc (trait_expr_value): Likewise.
        (finish_trait_expr): Likewise.
        * cp-tree.h (build_invoke): New function.
        * method.cc (build_invoke): New function.

gcc/testsuite/ChangeLog:

        * g++.dg/ext/has-builtin-1.C: Test existence of __is_invocable.
        * g++.dg/ext/is_invocable1.C: New test.
        * g++.dg/ext/is_invocable2.C: New test.
        * g++.dg/ext/is_invocable3.C: New test.
        * g++.dg/ext/is_invocable4.C: New test.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
  gcc/cp/constraint.cc                     |   6 +
  gcc/cp/cp-trait.def                      |   1 +
  gcc/cp/cp-tree.h                         |   2 +
  gcc/cp/method.cc                         | 134 +++++++++
  gcc/cp/semantics.cc                      |   5 +
  gcc/testsuite/g++.dg/ext/has-builtin-1.C |   3 +
  gcc/testsuite/g++.dg/ext/is_invocable1.C | 349 +++++++++++++++++++++++
  gcc/testsuite/g++.dg/ext/is_invocable2.C | 139 +++++++++
  gcc/testsuite/g++.dg/ext/is_invocable3.C |  51 ++++
  gcc/testsuite/g++.dg/ext/is_invocable4.C |  33 +++
  10 files changed, 723 insertions(+)
  create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable1.C
  create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable2.C
  create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable3.C
  create mode 100644 gcc/testsuite/g++.dg/ext/is_invocable4.C

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index c28d7bf428e..6d14ef7dcc7 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -3792,6 +3792,12 @@ diagnose_trait_expr (tree expr, tree args)
      case CPTK_IS_FUNCTION:
        inform (loc, "  %qT is not a function", t1);
        break;
+    case CPTK_IS_INVOCABLE:
+      if (!t2)
+    inform (loc, "  %qT is not invocable", t1);
+      else
+    inform (loc, "  %qT is not invocable by %qE", t1, t2);
+      break;
      case CPTK_IS_LAYOUT_COMPATIBLE:
        inform (loc, "  %qT is not layout compatible with %qT", t1, t2);
        break;
diff --git a/gcc/cp/cp-trait.def b/gcc/cp/cp-trait.def
index b1c875a6e7d..4e420d5390a 100644
--- a/gcc/cp/cp-trait.def
+++ b/gcc/cp/cp-trait.def
@@ -75,6 +75,7 @@ DEFTRAIT_EXPR (IS_EMPTY, "__is_empty", 1)
  DEFTRAIT_EXPR (IS_ENUM, "__is_enum", 1)
  DEFTRAIT_EXPR (IS_FINAL, "__is_final", 1)
  DEFTRAIT_EXPR (IS_FUNCTION, "__is_function", 1)
+DEFTRAIT_EXPR (IS_INVOCABLE, "__is_invocable", -1)
  DEFTRAIT_EXPR (IS_LAYOUT_COMPATIBLE, "__is_layout_compatible", 2)
  DEFTRAIT_EXPR (IS_LITERAL_TYPE, "__is_literal_type", 1)
  DEFTRAIT_EXPR (IS_MEMBER_FUNCTION_POINTER, "__is_member_function_pointer", 1)
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 1938ada0268..83dc20e1130 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7338,6 +7338,8 @@ extern tree get_copy_assign                       (tree);
  extern tree get_default_ctor                  (tree);
  extern tree get_dtor                          (tree, tsubst_flags_t);
  extern tree build_stub_object                 (tree);
+extern tree build_invoke                       (tree, const_tree,
+                                                tsubst_flags_t);
  extern tree strip_inheriting_ctors            (tree);
  extern tree inherited_ctor_binfo              (tree);
  extern bool base_ctor_omit_inherited_parms    (tree);
diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 08a3d34fb01..faf932258e6 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -1928,6 +1928,140 @@ build_trait_object (tree type)
    return build_stub_object (type);
  }
+/* [func.require] Build an expression of INVOKE(FN_TYPE, ARG_TYPES...). If the
+   given is not invocable, returns error_mark_node.  */
+
+tree
+build_invoke (tree fn_type, const_tree arg_types, tsubst_flags_t complain)
+{
+  if (error_operand_p (fn_type) || error_operand_p (arg_types))
+    return error_mark_node;
+
+  gcc_assert (TYPE_P (fn_type));
+  gcc_assert (TREE_CODE (arg_types) == TREE_VEC);
+
+  /* Access check is required to determine if the given is invocable.  */
+  deferring_access_check_sentinel acs (dk_no_deferred);
+
+  /* INVOKE is an unevaluated context.  */
+  cp_unevaluated cp_uneval_guard;
+
+  bool is_ptrdatamem;
+  bool is_ptrmemfunc;
+  if (TREE_CODE (fn_type) == REFERENCE_TYPE)
+    {
+      tree deref_fn_type = TREE_TYPE (fn_type);
+      is_ptrdatamem = TYPE_PTRDATAMEM_P (deref_fn_type);
+      is_ptrmemfunc = TYPE_PTRMEMFUNC_P (deref_fn_type);
+
+      /* Dereference fn_type if it is a pointer to member.  */
+      if (is_ptrdatamem || is_ptrmemfunc)
+       fn_type = deref_fn_type;
+    }
+  else
+    {
+      is_ptrdatamem = TYPE_PTRDATAMEM_P (fn_type);
+      is_ptrmemfunc = TYPE_PTRMEMFUNC_P (fn_type);
+    }
+
+  if (is_ptrdatamem && TREE_VEC_LENGTH (arg_types) != 1)
+    {
+      if (complain & tf_error)
+       error ("pointer to data member type %qT can only be invoked with "
+              "one argument", fn_type);
+      return error_mark_node;
+    }
+
+  if (is_ptrmemfunc && TREE_VEC_LENGTH (arg_types) == 0)
+    {
+      if (complain & tf_error)
+       error ("pointer to member function type %qT must be invoked with "
+              "at least one argument", fn_type);
+      return error_mark_node;
+    }
+
+  /* Construct an expression of a pointer to member.  */
+  tree ptrmem_expr;
+  if (is_ptrdatamem || is_ptrmemfunc)
+    {
+      tree datum_type = TREE_VEC_ELT (arg_types, 0);
+
+      /* datum must be a class type or a reference/pointer to a class type.  */
+      if (!(CLASS_TYPE_P (datum_type)
+           || ((TYPE_REF_P (datum_type) || POINTER_TYPE_P (datum_type))
+               && CLASS_TYPE_P (TREE_TYPE (datum_type)))))
+       {
+         if (complain & tf_error)
+           error ("first argument type %qT of a pointer to member must be"
+                  "a class type or a reference/pointer to a class type",
+                  datum_type);
+         return error_mark_node;
+       }
+
+      bool is_refwrap = false;
+      if (CLASS_TYPE_P (datum_type))
+       {
+         /* 1.2 & 1.5: Handle std::reference_wrapper.  */
+         tree datum_decl = TYPE_NAME (TYPE_MAIN_VARIANT (datum_type));
+         if (decl_in_std_namespace_p (datum_decl))
+           {
+             const_tree name = DECL_NAME (datum_decl);
+             if (name && (id_equal (name, "reference_wrapper")))
+               {
+                 /* Retrieve T from std::reference_wrapper<T>,
+                    i.e., decltype(datum.get()).  */
+                 datum_type = TREE_VEC_ELT (TYPE_TI_ARGS (datum_type), 0);
+                 is_refwrap = true;
+               }
+           }
+       }
+
+      tree ptrmem_class_type = TYPE_PTRMEM_CLASS_TYPE (fn_type);
+      const bool ptrmem_is_base_of_datum =
+       (NON_UNION_CLASS_TYPE_P (ptrmem_class_type)
+        && NON_UNION_CLASS_TYPE_P (datum_type)

Why NON_UNION?  That doesn't seem to be based on anything in the standard.

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

+        && (same_type_ignoring_top_level_qualifiers_p (ptrmem_class_type,
+                                                       datum_type)
+            || DERIVED_FROM_P (ptrmem_class_type, datum_type)));
+
+      tree datum_expr = build_trait_object (datum_type);
+      if (!ptrmem_is_base_of_datum && !is_refwrap && !TYPE_REF_P (datum_type))

...so we shouldn't need to check TYPE_REF_P here.

Jason

+       /* 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);
+      /* 1.1, 1.2, 1.4, & 1.5: Otherwise.  */
+
+      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))
+       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.

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