Preprocessing can add clauses for optimizing

After a query is parsed and normalized, but before the optimizer begins its analysis, the query is preprocessed to increase the number of clauses that can be optimized:

The changes made by preprocessing are transparent unless you are examining the output of query tuning tools such as showplan, statistics io, or dbcc traceon(302). If you run queries that benefit from the addition of optimized search arguments, you see the added clauses: