#9781: Make list monad operations fuse -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: dfeuer Type: task | Status: closed Priority: normal | Milestone: 7.10.1 Component: Core | Version: 7.9 Libraries | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: | Difficulty: Unknown Unknown/Multiple | Blocked By: Type of failure: Runtime | Related Tickets: performance bug | Test Case: | Blocking: | Differential Revisions: Phab:D455 | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:7 schyler]:
It would be nice to understand why the `mapM` change did anything at all. That's an enormous difference. I wonder how much real code in the wild has similar properties (is it a lack of INLINEing?)
I believe it's either a lack of inlining or an unfortunate effect of full laziness. I haven't tried to dig into that particular one so deeply. Short cut fusion is great stuff, but it's on the finicky side; writing library functions so they don't themselves rely on it seems to be a good idea in many cases. The inliner will be less likely to over-estimate their cost, I believe. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9781#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler