Undecidability of program optimization
In your example, you consider a size optimizer, that is a program that 


  takes a program $P$, and returns an equivalent program $P'$ such that there is no other program $P''$ also equivalent to $P$ but strictly smaller than $P'$.


With such a perfect size optimizer, you could build a decision procedure for this question


  Is an input program $P$ equivalent to any program of at most $33$ characters? 


But this is a non trivial property of program semantics. Rice Theorem says that such properties are undecidable.