Since there is no compilation error or error message about missing
option, the best I can think of is missing re-build after pass
modification, or the
'hello.bc' has no function inside.
For me, it is quite hard to guess what is going wrong. The listed steps
seems to be
correct, although step 4. is not required: 'opt' is able to work on both
(.bc) and human-readable format (.ll)..