Trends in Functional Programming V. 6 (Repost)

Compiler writers often face a choice between implementing a simple, non-optimizing
transformation pass that generates poor code which will require subsequent
optimization, and implementing a complex, optimizing transformation pass
that avoids generating poor code in the first place. A two-pass strategy is compelling
because it is simpler to implement correctly, but its disadvantage is that
the intermediate data structures can be large and traversing them unnecessarily
can be costly. In a system performing just-in-time compilation or run-time code
generation, the costs associated with a two-pass compilation strategy can render
it impractical. A one-pass optimizing transformation is compelling because it
avoids generating intermediate data structures requiring further optimization, but
its disadvantage is that the transformation is more difficult to implement.