-mpa=n
Enable the procedure abstraction optimization up to level n. If n is zero,
the optimization is disabled. If n is 1, first level of abstraction is allowed;
that is, instruction sequences in the source code may be abstracted
into a subroutine. If n is 2, a second level of abstraction is allowed; that
is, instructions that were put into a subroutine in the first level may be
abstracted into a subroutine one level deeper. This pattern continues
for larger values of n.
The net effect is to limit the subroutine call nesting depth to a maximum
of n.