I can see that you get two copies of the same code, which CSE will
#9630: compile-time performance regression (probably due to Generics) -------------------------------------+------------------------------------- Reporter: hvr | Owner: dfeuer Type: bug | Status: new Priority: high | Milestone: 8.2.1 Component: Compiler | Version: 7.9 Resolution: | Keywords: deriving- | perf, Generics Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #9583, #10293, | Differential Rev(s): #13059, #10818 | Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:59 simonpj]: presumably get rid of. That might be worth trying to fix.
But why does it lead to a 26x increase in compilation time? I'd expect
it to be un-noticeable. Well, it's not always going to cause serious problems, and I think this ticket touches several underlying issues, but it bet it ''can'' cause serious trouble. Suppose you have a class with ten methods, and use generic defaults. Now you'll end up with ten dictionaries of ten methods each. Depending on how inlining goes, I suspect that could be quite bad. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9630#comment:60 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler