#8766: length [Integer] is twice as slow but length [Int] is 10 times faster --------------------------------------------+------------------------------ Reporter: George | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime performance bug | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: --------------------------------------------+------------------------------ Comment (by hvr): Replying to [comment:2 nomeata]:
The improvement for `Int` is most likely from 82f56e5 (#876). But I guess the important point of the ticket is the regression for `Integer`.
I was getting to that (needed to verify something first though): The Core for {{{#!hs intlen = length [1..(2^(30::Int))::Integer] }}} Otoh, looks differs as following: GHC 7.6.3: {{{ intlen1 = enumDeltaToInteger intlen3 intlen3 intlen2 }}} vs. GHC 7.8.20140130: {{{ intlen1 = enumDeltaToIntegerFB (incLen) I# intlen3 intlen3 intlen2 }}} The use of `enumDeltaToIntegerFB` instead of `enumDeltaToInteger` accounts for the speed difference. I've verified that by copying the definition from `GHC.Enum` into the test-code and using `enumDeltaToInteger` directly with GHC 7.8.20140130 which resulted in a slightly better runtime than for GHC 7.6.3 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8766#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler