#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 RyanGlScott): Per SPJ's request, I've reposted some sleuthing I did in [https://phabricator.haskell.org/D2304#67314 the comments] of Phab:D2304. I decided to my changes on the 300-constructor sum type mentioned at the top of this ticket. I manually implemented a `Generic` instance for this datatype three times, and put each one in its own file: * [https://gist.github.com/RyanGlScott/e1ef13b59440200e696f5ca0c23dfb8c #file-gen_v1-hs Gen_v1.hs], which contains a `Generic` instance as GHC derives it currently (without the changes in Phab:D2304) * [https://gist.github.com/RyanGlScott/e1ef13b59440200e696f5ca0c23dfb8c #file-gen_v2-hs Gen_v2.hs], which is like `Gen_v1.hs` except that it factors out the topmost `M1` in `from`/`to` (i.e., with the changes in Phab:D2304) * [https://gist.github.com/RyanGlScott/e1ef13b59440200e696f5ca0c23dfb8c #file-gen_v3-hs Gen_v3.hs], which is like `Gen_v1.hs` except that it both (1) factors out the topmost `M1` in `from`/`to` and (2) factors out common occurrences of `L1`/`R1` in `to` I compiled each file with `ghc -O2 -v3 +RTS -s` and dumped the results to logs. Here are the highlights: * [https://gist.githubusercontent.com/RyanGlScott/e1ef13b59440200e696f5ca0c23df... Gen_v1.txt] * `{terms: 16,282, types: 2,563,921, coercions: 639,012}` * `7,781,716,432 bytes allocated in the heap` * `Total time 8.708s ( 8.719s elapsed)` * [https://gist.githubusercontent.com/RyanGlScott/e1ef13b59440200e696f5ca0c23df... Gen_v2.txt] * `{terms: 16,288, types: 2,924,492, coercions: 9,950}` * `4,479,400,544 bytes allocated in the heap` * `Total time 5.580s ( 5.590s elapsed)` * [https://gist.githubusercontent.com/RyanGlScott/e1ef13b59440200e696f5ca0c23df... Gen_v3.txt] * `{terms: 16,288, types: 2,924,492, coercions: 9,950}` * `4,016,934,848 bytes allocated in the heap` * `Total time 4.990s ( 5.006s elapsed)` There is a huge difference between `v1` and `v2`, as suspected. There is a difference between `v2` and `v3` in that it allocated fewer bytes on the heap, but interestingly, `v3` has the exact same number of types and coercions, so I'm not sure where the improvement is coming from. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5642#comment:39 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler