Implement P0138R2, C++17 construction rules for enum class values

	Implement P0138R2, C++17 construction rules for enum class values
	* cp-tree.h (is_direct_enum_init): Declare.
	* decl.c (is_direct_enum_init): New function.
	(reshape_init): Use it.
	* typeck.c (convert_for_assignment): Likewise.

	* g++.dg/cpp1z/direct-enum-init1.C: New test.

From-SVN: r240449

gcc/cp/ChangeLog

 2016-09-23  Jakub Jelinek  <jakub@redhat.com>
 
+	Implement P0138R2, C++17 construction rules for enum class values
+	* cp-tree.h (is_direct_enum_init): Declare.
+	* decl.c (is_direct_enum_init): New function.
+	(reshape_init): Use it.
+	* typeck.c (convert_for_assignment): Likewise.
+
 	* Make-lang.in (check-c++1z): Pass RUNTESTFLAGS down to
 	make check-g++.
 

gcc/cp/cp-tree.h

@@ -5829,6 +5829,7 @@ extern tree check_elaborated_type_specifier	(enum tag_types, tree, bool);
 extern void warn_extern_redeclared_static	(tree, tree);
 extern tree cxx_comdat_group			(tree);
 extern bool cp_missing_noreturn_ok_p		(tree);
+extern bool is_direct_enum_init			(tree, tree);
 extern void initialize_artificial_var		(tree, vec<constructor_elt, va_gc> *);
 extern tree check_var_type			(tree, tree);
 extern tree reshape_init                        (tree, tree, tsubst_flags_t);

gcc/cp/decl.c

@@ -5581,6 +5581,22 @@ next_initializable_field (tree field)
   return field;
 }
 
+/* Return true for [dcl.init.list] direct-list-initialization from
+   single element of enumeration with a fixed underlying type.  */
+
+bool
+is_direct_enum_init (tree type, tree init)
+{
+  if (cxx_dialect >= cxx1z
+      && TREE_CODE (type) == ENUMERAL_TYPE
+      && ENUM_FIXED_UNDERLYING_TYPE_P (type)
+      && TREE_CODE (init) == CONSTRUCTOR
+      && CONSTRUCTOR_IS_DIRECT_INIT (init)
+      && CONSTRUCTOR_NELTS (init) == 1)
+    return true;
+  return false;
+}
+
 /* Subroutine of reshape_init_array and reshape_init_vector, which does
    the actual work. ELT_TYPE is the element type of the array. MAX_INDEX is an
    INTEGER_CST representing the size of the array minus one (the maximum index),
@@ -6026,6 +6042,17 @@ reshape_init (tree type, tree init, tsubst_flags_t complain)
   if (vec_safe_is_empty (v))
     return init;
 
+  /* Handle [dcl.init.list] direct-list-initialization from
+     single element of enumeration with a fixed underlying type.  */
+  if (is_direct_enum_init (type, init))
+    {
+      tree elt = CONSTRUCTOR_ELT (init, 0)->value;
+      if (check_narrowing (ENUM_UNDERLYING_TYPE (type), elt, complain))
+	return cp_build_c_cast (type, elt, tf_warning_or_error);
+      else
+	return error_mark_node;
+    }
+
   /* Recurse on this CONSTRUCTOR.  */
   d.cur = &(*v)[0];
   d.end = d.cur + v->length ();

gcc/cp/typeck.c

@@ -8266,6 +8266,17 @@ convert_for_assignment (tree type, tree rhs,
   if (TREE_CODE (rhs) == NON_LVALUE_EXPR)
     rhs = TREE_OPERAND (rhs, 0);
 
+  /* Handle [dcl.init.list] direct-list-initialization from
+     single element of enumeration with a fixed underlying type.  */
+  if (is_direct_enum_init (type, rhs))
+    {
+      tree elt = CONSTRUCTOR_ELT (rhs, 0)->value;
+      if (check_narrowing (ENUM_UNDERLYING_TYPE (type), elt, complain))
+	rhs = cp_build_c_cast (type, elt, complain);
+      else
+	rhs = error_mark_node;
+    }
+
   rhstype = TREE_TYPE (rhs);
   coder = TREE_CODE (rhstype);
 

gcc/testsuite/ChangeLog

+2016-09-23  Jakub Jelinek  <jakub@redhat.com>
+
+	Implement P0138R2, C++17 construction rules for enum class values
+	* g++.dg/cpp1z/direct-enum-init1.C: New test.
+
 2016-09-23  David Malcolm  <dmalcolm@redhat.com>
 
 	PR preprocessor/77672