Abstract
Eight years ago Compiling without continuations introduced the idea of so-called join points as a powerful optimisation tool in a functional language compiler. Since then join points have become more and more deeply entwined in GHC’s optimisation passes; for example they are treated specially by the Simplifier and its Occurrence Analyser, and a dedicated pass called Exitification makes a join-point-specific transformation
With the perspective of this experience, I am convinced that any serious functional compiler should use join points (or something equivalent): it’s a powerful and re-usable idea. Yet beyond the initial paper, none of what we have learned has appeared in print. In this talk I will share the lessons of the last eight years of using join points in practice in GHC.