For the most part, provided they are actually valid, the objects will be compiled on request. Even so you should consider manually compiling them yourself. I've seen systems with lots of code dependencies grind to a halt due to a cascade effect of compilations.

An easy way to do this is to use either:

$ORACLE_HOME/rdbms/admin/ultrp.sql

or

DBMS_UTILITY.COMPILE_SCHEMA

Cheers