How does postgres store the join predicate for a relation in a given query

Hi all,

When you fire a query in postgresql, it will first parse the query and
create the data structures for storing various aspects of the query and
executing the query. (Like RangeTblEntry, PlannerInfo, RangeOptInfo etc.).

I want to know how does postgresql stores the join predicates of a query.
Like which data structure is used to store the join predicates.

How can we find the join predicates applied on a relation from relid, Oid
or RangeTblEntry ?

I want to construct a join graph for a given query, for which I need the
join predicates between two relations.

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Thanks,
Gourav Kumar