Обсуждение: ahead of time compiling in PostgreSQL?

AOT is referenced at src/backend/jit/README:

   That this is done at query execution time, possibly even only in 
   cases where the relevant task is done a number of times, makes it 
   JIT, rather than ahead-of-time (AOT). Given the way JIT compilation 
   is used in PostgreSQL, the lines between interpretation, AOT and JIT 
   are somewhat blurry.

In what cases does the compilation happen ahead of time?

Thanks,
Viorel