VolcanoPlanner now takes the "originalRoot" as the input for materialized-view substitution, so the programs used in Prepare.optimize() will not be applied to these substituted rels. For example, a correlated subquery will be de-correlated but its equivalents with materialization substitutions will not be de-correlated. So it would be nice to have a way for the substituted rels to run specific programs too before starting volcano planning.
The easiest solution might be using the new "root" for materialization substitution instead, but it would be based on the assumption that those "pre-processing" programs are simple ones like de-correlation and field-trimming. In order to allow a more general pre-processing program set, one that could have different optimization output for the original rel and for the materialization substituted rels, we'd better have an interface or some approach to run pre-processing programs for rels after materialization substitution.