No regression, but new tests still doesn't run. Marked them
as expect fail or skip. Going to work on them later.

simple_logger)

need to be fixed)

introduced Move instruction at IR level.
Intermediate blocks will be inserted for multi-target branch
instructions

we never go back to previous passes, since it is not necessary

now we have 4 passes: fast_inst_sel, fast_reg_alloc, followed
by slow_inst_sel and slow_reg_alloc. This might make the
compilation pipeline more linear

some refactoring: 1. allows reg alloc using other allocators (other than graph coloring), 2. allows retreat to a previous compilation pass

allowing list operands of instructions. Defuse doesnt work. P<T>.clone() is creating new copies of old objects, thus updating cloned objs wont affect the original ones.