#5642: Deriving Generic of a big type takes a long time and lots of space -------------------------------------+------------------------------------- Reporter: basvandijk | Owner: bgamari Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.3 Resolution: | Keywords: deriving- | perf, Generics Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: T5642 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D2304 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * differential: => Phab:D2304 Comment: I've found a little trick to help reduce the constant factors in deriving `Generic`. (See Phab:D2304 for more details.) One can factor out the topmost `M1` from the derived definitions of `to` and `from` to reduce the number of times GHC has to typecheck an application of `M1`. This in turn leads to a reduction in the number of coercions, which lowers allocation. I tested this trick against basvandijk's 300-constructor datatype, and it saves almost 3 seconds of compilation time and uses ~6.4 times fewer coercions. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5642#comment:38 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler