Secrets of the Glasgow Haskell Compiler inliner Simon Marlow Simon Peyton Jones Microsoft Research Ltd, Cambridge Microsoft Research Ltd, Cambridge
[email protected] [email protected] Septemb er 1, 1999 A ma jor issue for any compiler, esp ecially for one that Abstract inlines heavily,is name capture. Our initial brute-force solution involved inconvenient plumbing, and wehave Higher-order languages, such as Haskell, encourage the pro- now evolved a simple and e ective alternative Sec- grammer to build abstractions by comp osing functions. A tion 3. go o d compiler must inline many of these calls to recover an eciently executable program. At rst wewere very conservative ab out inlining recur- sive de nitions; that is, we did not inline them at all. In principle, inlining is dead simple: just replace the call But we found that this strategy o ccasionally b ehaved of a function by an instance of its b o dy. But any compiler- very badly. After a series of failed hacks we develop ed writer will tell you that inlining is a black art, full of delicate a simple, obviously-correct algorithm that do es the job compromises that work together to give go o d p erformance b eautifully Section 4. without unnecessary co de bloat. Because the compiler do es so much inlining, it is im- The purp ose of this pap er is, therefore, to articulate the p ortant to get as much as p ossible done in each pass key lessons we learned from a full-scale \pro duction" inliner, over the program.