#7258: Compiling DynFlags is jolly slow -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.1 Resolution: | Keywords: deriving-perf Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by tdammers): Replying to [comment:37 bgamari]:
While chatting with tdammers about this I had a peek at the core; it seems that 5000 terms of the 7000 terms in the simplified core of `W2` are in `creadPrec_rdaO`. Moreover, much of this is repetition. I've proposed an approach for dealing with this in #14364.
I've just done a bit more profiling, and it turns out that removing the derived `Read` instance from the `W3` example (`W2` extended to 500 fields) cuts overall compilation time down from 25.5 seconds to 3.6. So it seems that the edge case isn't just "constructors with many fields", but rather, "derived `Read` instances for constructors with many fields". -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7258#comment:40 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler