do final cleanup after planning.

-subquery_planner()

pull up subqueries from rangetable, if possible

simplify constant expressions

canonicalize qual

Attempt to reduce WHERE clause to either CNF or DNF canonical form.

CNF (top-level-AND) is preferred, since the optimizer can then use

any of the AND subclauses to filter tuples; but quals that are in

or close to DNF form will suffer exponential expansion if we try to

force them to CNF. In pathological cases either transform may expand

the qual unreasonably; so we may have to leave it un-normalized,

thereby reducing the accuracy of selectivity estimates.

Attempt to simplify WHERE clause to the most useful form; this includes

flattening nested AND/ORs and detecting clauses that are duplicated in

different branches of an OR.

simplify constant expressions

process sublinks

convert Vars of outer query levels into Params

--grouping_planner()