... BTW, looking at these two patches again, I wonder if it'd be
better to put the hackery for SubLink conversion into
identify_current_nestloop_params? That'd remove the need to argue
that we don't have to fix both copies of a nestloop-parameter PHV.
The responsibility doesn't clearly belong to
identify_current_nestloop_params, but it doesn't clearly belong
to create_nestloop_plan either, so neither choice seems superior
from a modularity standpoint.
regards, tom lane