PERF: reduce calls to Hash#[]

lib/arel/engines/sql/christener.rb

@@ -8,11 +8,11 @@ def initialize
       def name_for(relation)
         table = relation.table
         name = table.table_alias || table.name
-        @names[name] ||= []
+        list = @names[name] ||= []
 
-        @names[name] << table unless @names[name].include? table
+        list << table unless list.include? table
 
-        idx = @names[name].index table
+        idx = list.index table
         name + (idx == 0 ? '' : "_#{idx + 1}")
       end
     end