Does it make sense to break a large query into separate functions?

Greetings,

I have a domain specific language implementation that ends up as sql after
an automatic transformation/code generation phase.
The complexity of the generated sql queries can be significant, with lots
of self joins and many other criteria injected into sql.

I've just noticed that some parts of the autogenerated queries can be
functions on their own. Would moving these parts to their own functions
help the query planner?

There are any two tables and all queries use them, so I thought the query
planner may be able to do better if I let it deal with smaller queries
rather than one quite large one. I don't know how the query planner works
when there are calls to other functions from a function though.

Changing the code generator would take time, so I decided to ask for more
educated input than mine.

Best regards
Seref