#9557: Deriving instances is slow -------------------------------------+------------------------------------- Reporter: Feuerbach | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: #8731 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by nomeata):
Study the generated code to see if it could be abstracted, so that instead of lots of code, there were calls to some suitable shared functions.
Looking at the `Ord` code (which seems to be the largest): * It seems that it could be made much smaller using `<>` (which is `EQ <> x = x` and `y <> _ = y` otherwise) instead of nested case expressions. I guess there would be a performance hit, though. * Do we really have to provide separate definitions for `compare` and `<` and `<=` and `>` and `>=`? Maybe using the default implementation for all methods but `compare` is good enough, and could bring code size down considerably. Overreaching spontaneous idea: Add a method `generalCompare :: r -> r -> r -> a -> a -> r` to the `Ord` class. Implement that in deriving clauses, and have the default implementations use that. (e.g. `(<) = generalCompare True False False`). Should be faster than using `compare` + pattern matching. OTOH. all constructors of `Comparing` are static values, so there is probably not much to win here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9557#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler