If I understood your question, the following info may be what you're looking for.
ExecNestLoop gets the join qualifications and passes them to ExecQual
for each outer tuple. Each qualification is checked in ExecQual
using the ExecEvalExpr macro which calls the function pointer evalfunc
for each E
ExecQual evaluates join conditions one at a time.It captures one condition and
passes it to function ExecEvalExpr which is actually a macro that invokes
another function evalfunc( which is a function pointer that is set to the
function PostgreSQL wants to use to evaluate the expression. It's of
