--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/c-family/c-spellcheck.cc	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,121 @@
+/* Find near-matches for macros.
+   Copyright (C) 2016-2018 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/>.  */
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "cpplib.h"
+#include "spellcheck-tree.h"
+#include "c-family/c-spellcheck.h"
+#include "selftest.h"
+
+/* Return true iff STR begin with an underscore and either an uppercase
+   letter or another underscore, and is thus, for C and C++, reserved for
+   use by the implementation.  */
+
+bool
+name_reserved_for_implementation_p (const char *str)
+{
+  if (str[0] != '_')
+    return false;
+  return (str[1] == '_' || ISUPPER(str[1]));
+}
+
+/* Return true iff HASHNODE is a macro that should be offered as a
+   suggestion for a misspelling.  */
+
+static bool
+should_suggest_as_macro_p (cpp_hashnode *hashnode)
+{
+  if (!cpp_macro_p (hashnode))
+    return false;
+
+  /* Don't suggest names reserved for the implementation, but do
+     suggest the builtin macros such as __FILE__, __LINE__ etc.  */
+  if (cpp_user_macro_p (hashnode)
+      && name_reserved_for_implementation_p ((const char *)hashnode->ident.str))
+    return false;
+
+  return true;
+}
+
+/* A callback for cpp_forall_identifiers, for use by best_macro_match's ctor.
+   Process HASHNODE and update the best_macro_match instance pointed to be
+   USER_DATA.  */
+
+static int
+find_closest_macro_cpp_cb (cpp_reader *, cpp_hashnode *hashnode,
+			   void *user_data)
+{
+  if (!should_suggest_as_macro_p (hashnode))
+    return 1;
+
+  best_macro_match *bmm = (best_macro_match *)user_data;
+  bmm->consider (hashnode);
+
+  /* Keep iterating.  */
+  return 1;
+}
+
+/* Constructor for best_macro_match.
+   Use find_closest_macro_cpp_cb to find the closest matching macro to
+   NAME within distance < best_distance_so_far. */
+
+best_macro_match::best_macro_match (tree goal,
+				    edit_distance_t best_distance_so_far,
+				    cpp_reader *reader)
+: best_match <goal_t, candidate_t> (goal, best_distance_so_far)
+{
+  cpp_forall_identifiers (reader, find_closest_macro_cpp_cb, this);
+}
+
+#if CHECKING_P
+
+namespace selftest {
+
+/* Selftests.  */
+
+/* Verify that name_reserved_for_implementation_p is sane.  */
+
+static void
+test_name_reserved_for_implementation_p ()
+{
+  ASSERT_FALSE (name_reserved_for_implementation_p (""));
+  ASSERT_FALSE (name_reserved_for_implementation_p ("foo"));
+  ASSERT_FALSE (name_reserved_for_implementation_p ("_"));
+  ASSERT_FALSE (name_reserved_for_implementation_p ("_foo"));
+  ASSERT_FALSE (name_reserved_for_implementation_p ("_42"));
+  ASSERT_TRUE (name_reserved_for_implementation_p ("_Foo"));
+  ASSERT_TRUE (name_reserved_for_implementation_p ("__"));
+  ASSERT_TRUE (name_reserved_for_implementation_p ("__foo"));
+}
+
+/* Run all of the selftests within this file.  */
+
+void
+c_spellcheck_cc_tests ()
+{
+  test_name_reserved_for_implementation_p ();
+}
+
+} // namespace selftest
+
+#endif /* #if CHECKING_P */