The levels of code optimization that the MPE/iX Optimizer provides
are Level 0, Level 1, and Level 2.
Level 0 optimization is the default optimization level and
provides simple optimizations that
minimize compile time.
Use this level when debugging a program
or running a program that will not be run many times
(for example, a student job program that is run a few times
and discarded).
Level 0 functions include:
Simple branch delay slot scheduling.
Faster register allocation (including copy elimination).
Level 1 optimization is local to basic blocks,
but does not optimize globally.
Use Level 1 to achieve some optimization without spending
excessive time compiling.
Level 1 functions include:
Faster register allocation (including copy elimination).
Level 2 optimization is global optimization.
It provides the greatest saving of space and time
achievable with the Optimizer and produces
the most compact and fastest running program of all the levels.
Use Level 2 when running a debugged program a large number of times.
This is the correct level to choose for most applications.
Level 2 functions are:
All Level 1 optimizations.
Coloring register allocation.
Induction variable elaboration and strength reduction. (An induction variable is a variable dependent on the value of a loop counter.)
Common subexpression elimination.
Loop invariant code motion.
Unused definition elimination.
Promotion of variables to registers.
