Fix range type signed-ness heuristic

diff --git a/gdb/gdbtypes.c b/gdb/gdbtypes.c
index a43d9265ad2..5e8a486d28f 100644
--- a/gdb/gdbtypes.c
+++ b/gdb/gdbtypes.c
@@ -958,7 +958,13 @@  create_range_type (struct type *result_type, struct type *index_type,
 
   if (index_type->code () == TYPE_CODE_FIXED_POINT)
     result_type->set_is_unsigned (index_type->is_unsigned ());
-  /* Note that the signed-ness of a range type can't simply be copied
+  else if (index_type->is_unsigned ())
+    {
+      /* If the underlying type is unsigned, then the range
+	 necessarily is.  */
+      result_type->set_is_unsigned (true);
+    }
+  /* Otherwise, the signed-ness of a range type can't simply be copied
      from the underlying type.  Consider a case where the underlying
      type is 'int', but the range type can hold 0..65535, and where
      the range is further specified to fit into 16 bits.  In this
@@ -966,13 +972,15 @@  create_range_type (struct type *result_type, struct type *index_type,
      range values will cause an unwanted sign extension.  So, we have
      some heuristics here instead.  */
   else if (low_bound->kind () == PROP_CONST && low_bound->const_val () >= 0)
-    result_type->set_is_unsigned (true);
-  /* Ada allows the declaration of range types whose upper bound is
-     less than the lower bound, so checking the lower bound is not
-     enough.  Make sure we do not mark a range type whose upper bound
-     is negative as unsigned.  */
-  if (high_bound->kind () == PROP_CONST && high_bound->const_val () < 0)
-    result_type->set_is_unsigned (false);
+    {
+      result_type->set_is_unsigned (true);
+      /* Ada allows the declaration of range types whose upper bound is
+	 less than the lower bound, so checking the lower bound is not
+	 enough.  Make sure we do not mark a range type whose upper bound
+	 is negative as unsigned.  */
+      if (high_bound->kind () == PROP_CONST && high_bound->const_val () < 0)
+	result_type->set_is_unsigned (false);
+    }
 
   result_type->set_endianity_is_not_default
     (index_type->endianity_is_not_default ());
diff --git a/gdb/testsuite/gdb.ada/unsigned_last.exp b/gdb/testsuite/gdb.ada/unsigned_last.exp
new file mode 100644
index 00000000000..f07d9483bbd
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/unsigned_last.exp
@@ -0,0 +1,38 @@ 
+# Copyright 2022 Free Software Foundation, Inc.
+#
+# This program 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 of the License, or
+# (at your option) any later version.
+#
+# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# Check that 'Last correctly results in an unsigned integer in when
+# the underlying type is unsigned.
+
+load_lib "ada.exp"
+
+if { [skip_ada_tests] } { return -1 }
+
+standard_ada_testfile main
+
+if {[gdb_compile_ada "${srcfile}" "${binfile}" executable {debug}] != ""} {
+  return -1
+}
+
+clean_restart ${testfile}
+
+set bp_location [gdb_get_line_number "START" ${testdir}/main.adb]
+runto "main.adb:$bp_location"
+
+# Check that both X and Unsigned_64'Last are printed as unsigned
+# values.  Previously the heuristic used when determining if a range
+# type was unsigned did not catch the latter case.
+gdb_test "print x" "= 18446744073709551615"
+gdb_test "print Unsigned_64'Last" "= 18446744073709551615"
diff --git a/gdb/testsuite/gdb.ada/unsigned_last/main.adb b/gdb/testsuite/gdb.ada/unsigned_last/main.adb
new file mode 100644
index 00000000000..f01e27e8ccc
--- /dev/null
+++ b/gdb/testsuite/gdb.ada/unsigned_last/main.adb
@@ -0,0 +1,22 @@ 
+--  Copyright 2022 Free Software Foundation, Inc.
+--
+--  This program 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 of the License, or
+--  (at your option) any later version.
+--
+--  This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+with Interfaces;
+
+procedure Main is
+   X : Interfaces.Unsigned_64 := Interfaces.Unsigned_64'Last;
+begin
+   null; -- START
+end Main;