changes towards a canonical representation of comparisons: * new createNullCheckGuard helper method on CiLoweringTool * replaced NullCheckNode with IsNullNode * GuardNode and FixedGuardNode can be negated * keep a list of conditions that are true/false in CheckCastEliminationPhase * FixedGuardNode has only one condition * GraphBuilderPhase creates canonical CompareNodes * BooleanNodes can negate their usages * added junit test for canonicalized compares * removed junit test for negated instanceof * added more thorough graph comparison for junit tests * CheckCastEliminationPhase keeps track of conditions that are known to be true/false

var f = new CombineFilter("Combine Filter");
f.addRule(new CombineFilter.CombineRule(new Properties.RegexpPropertyMatcher("class", ".*"), new Properties.RegexpPropertyMatcher("class", "BeginNode"), false, "shortName"));
f.addRule(new CombineFilter.CombineRule(new Properties.RegexpPropertyMatcher("class", "EndNode"), new Properties.RegexpPropertyMatcher("class", ".*"), true, "shortName"));
f.apply(graph);