Speed up syntactic_implication() for constants.

* src/ltlvisit/syntimpl.cc (syntactic_implication): Do not
create visitors if arguments are constant.

ChangeLog

+2010-04-15  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
+
+	Speed up syntactic_implication() for constants.
+
+	* src/ltlvisit/syntimpl.cc (syntactic_implication): Do not
+	create visitors if arguments are constant.
+
 2010-04-15  Alexandre Duret-Lutz  <adl@lrde.epita.fr>
 
 	Fix simplification of "a M true" as Fa.

src/ltlvisit/syntimpl.cc

@@ -616,13 +616,13 @@ namespace spot
     {
       if (f1 == f2)
 	return true;
-      inf_left_recurse_visitor v1(f2);
-      inf_right_recurse_visitor v2(f1);
-
       if (f2 == constant::true_instance()
 	  || f1 == constant::false_instance())
 	return true;
 
+      inf_left_recurse_visitor v1(f2);
+      inf_right_recurse_visitor v2(f1);
+
       const_cast<formula*>(f1)->accept(v1);
       if (v1.result())
 	return true;