--- a/gcc/ada/libgnat/a-direct.adb	Thu Oct 25 07:37:49 2018 +0900
+++ b/gcc/ada/libgnat/a-direct.adb	Thu Feb 13 11:34:05 2020 +0900
@@ -6,7 +6,7 @@
 --                                                                          --
 --                                 B o d y                                  --
 --                                                                          --
---          Copyright (C) 2004-2018, Free Software Foundation, Inc.         --
+--          Copyright (C) 2004-2019, Free Software Foundation, Inc.         --
 --                                                                          --
 -- GNAT is free software;  you can  redistribute it  and/or modify it under --
 -- terms of the  GNU General Public License as published  by the Free Soft- --
@@ -33,6 +33,8 @@
 with Ada.Calendar.Formatting;    use Ada.Calendar.Formatting;
 with Ada.Characters.Handling;    use Ada.Characters.Handling;
 with Ada.Directories.Validity;   use Ada.Directories.Validity;
+with Ada.Directories.Hierarchical_File_Names;
+use Ada.Directories.Hierarchical_File_Names;
 with Ada.Strings.Fixed;
 with Ada.Strings.Maps;           use Ada.Strings.Maps;
 with Ada.Strings.Unbounded;      use Ada.Strings.Unbounded;
@@ -224,31 +226,22 @@
               Strings.Fixed.Index (Name, Dir_Seps, Going => Strings.Backward);
 
          begin
-            if Last_DS = 0 then
-
-               --  There is no directory separator, returns "." representing
-               --  the current working directory.
-
-               return ".";
-
             --  If Name indicates a root directory, raise Use_Error, because
             --  it has no containing directory.
 
-            elsif Name = "/"
-              or else
-                (Windows
-                  and then
-                  (Name = "\"
-                      or else
-                        (Name'Length = 3
-                          and then Name (Name'Last - 1 .. Name'Last) = ":\"
-                          and then (Name (Name'First) in 'a' .. 'z'
-                                     or else
-                                       Name (Name'First) in 'A' .. 'Z'))))
+            if Is_Parent_Directory_Name (Name)
+              or else Is_Current_Directory_Name (Name)
+              or else Is_Root_Directory_Name (Name)
             then
                raise Use_Error with
                  "directory """ & Name & """ has no containing directory";
 
+            elsif Last_DS = 0 then
+               --  There is no directory separator, so return ".", representing
+               --  the current working directory.
+
+               return ".";
+
             else
                declare
                   Last   : Positive := Last_DS - Name'First + 1;
@@ -262,31 +255,14 @@
                   --  number on Windows.
 
                   while Last > 1 loop
-                     exit when
-                       Result (Last) /= '/'
-                         and then
-                       Result (Last) /= Directory_Separator;
-
-                     exit when Windows
-                       and then Last = 3
-                       and then Result (2) = ':'
-                       and then
-                         (Result (1) in 'A' .. 'Z'
-                           or else
-                          Result (1) in 'a' .. 'z');
+                     exit when Is_Root_Directory_Name (Result (1 .. Last))
+                                 or else (Result (Last) /= Directory_Separator
+                                           and then Result (Last) /= '/');
 
                      Last := Last - 1;
                   end loop;
 
-                  --  Special case of "..": the current directory may be a root
-                  --  directory.
-
-                  if Last = 2 and then Result (1 .. 2) = ".." then
-                     return Containing_Directory (Current_Directory);
-
-                  else
-                     return Result (1 .. Last);
-                  end if;
+                  return Result (1 .. Last);
                end;
             end if;
          end;
@@ -806,6 +782,20 @@
                end if;
 
                if Exists = 1 then
+                  --  Ignore special directories "." and ".."
+
+                  if (Full_Name'Length > 1
+                       and then
+                         Full_Name
+                            (Full_Name'Last - 1 .. Full_Name'Last) = "\.")
+                    or else
+                     (Full_Name'Length > 2
+                        and then
+                          Full_Name
+                            (Full_Name'Last - 2 .. Full_Name'Last) = "\..")
+                  then
+                     Exists := 0;
+                  end if;
 
                   --  Now check if the file kind matches the filter
 
@@ -1280,17 +1270,31 @@
       function Simple_Name_Internal (Path : String) return String is
          Cut_Start : Natural :=
            Strings.Fixed.Index (Path, Dir_Seps, Going => Strings.Backward);
-         Cut_End   : Natural;
+
+         --  Cut_End points to the last simple name character
+
+         Cut_End   : Natural := Path'Last;
 
       begin
-         --  Cut_Start pointS to the first simple name character
+         --  Root directories are considered simple
+
+         if Is_Root_Directory_Name (Path) then
+            return Path;
+         end if;
+
+         --  Handle trailing directory separators
+
+         if Cut_Start = Path'Last then
+            Cut_End   := Path'Last - 1;
+            Cut_Start := Strings.Fixed.Index
+                           (Path (Path'First .. Path'Last - 1),
+                             Dir_Seps, Going => Strings.Backward);
+         end if;
+
+         --  Cut_Start points to the first simple name character
 
          Cut_Start := (if Cut_Start = 0 then Path'First else Cut_Start + 1);
 
-         --  Cut_End point to the last simple name character
-
-         Cut_End := Path'Last;
-
          Check_For_Standard_Dirs : declare
             BN : constant String := Path (Cut_Start .. Cut_End);
 
@@ -1301,7 +1305,7 @@
 
          begin
             if BN = "." or else BN = ".." then
-               return "";
+               return BN;
 
             elsif Has_Drive_Letter
               and then BN'Length > 2