#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: | -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"9649fc0ae45e006c2ed54cc5ea2414158949fadb/ghc" 9649fc0a/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="9649fc0ae45e006c2ed54cc5ea2414158949fadb" Refactor derived Generic instances to reduce allocations Previously, derived implementations of `to`/`from` in `Generic` instances were wastefully putting extra `M1`s in every case, which led to an O(n) increase in the number of coercions, resulting in a slowdown during the typechecker phase. This factors out the common `M1` in every case of a `to`/`from` definition so that the typechecker has far fewer coercions to deal with. For a datatype with 300 constructors, this change has been observed to save almost 3 seconds of compilation time. This is one step towards coming up with a solution for #5642. Test Plan: ./validate Reviewers: hvr, austin, simonpj, bgamari Reviewed By: bgamari Subscribers: basvandijk, carter, thomie, osa1 Differential Revision: https://phabricator.haskell.org/D2304 GHC Trac Issues: #5642 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5642#comment:41> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler