#10992: Performance regression --------------------------------------+--------------------------------- Reporter: aleator | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: performane | Operating System: Linux Architecture: x86_64 (amd64) | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------------+--------------------------------- For some reason Data.List.sum is much slower than the naive recursive definition for it. Does not seem happen in 7.8. {{{#!hs import Data.List import Criterion.Main sum1 [] = 0 sum1 (x:xs) = x + sum1 xs sum2 = foldr (+) 0 sum3 = foldl' (+) 0 sum4 = getSum #. foldMap Sum main = do let els = [1..100000] defaultMain [ bench "sum0" $ whnf (sum :: [Int] -> Int) els ,bench "sum" $ whnf (sum :: [Int] -> Int) els ,bench "sum1" $ whnf (sum1:: [Int] -> Int) els ,bench "sum2" $ whnf (sum2:: [Int] -> Int) els ,bench "sum3" $ whnf (sum3:: [Int] -> Int) els ,bench "sum4" $ whnf (sum4:: [Int] -> Int) els ] {- benchmarking sum0 time 128.0 ms (121.7 ms .. 133.8 ms) 0.997 R² (0.994 R² .. 1.000 R²) mean 132.8 ms (130.1 ms .. 136.3 ms) std dev 4.622 ms (2.980 ms .. 6.577 ms) variance introduced by outliers: 11% (moderately inflated) benchmarking sum time 131.0 ms (125.7 ms .. 136.7 ms) 0.998 R² (0.993 R² .. 1.000 R²) mean 131.9 ms (128.6 ms .. 136.7 ms) std dev 5.971 ms (2.903 ms .. 9.649 ms) variance introduced by outliers: 11% (moderately inflated) benchmarking sum1 time 26.29 ms (25.43 ms .. 27.24 ms) 0.995 R² (0.991 R² .. 0.998 R²) mean 26.30 ms (25.73 ms .. 26.98 ms) std dev 1.293 ms (953.2 μs .. 1.804 ms) variance introduced by outliers: 15% (moderately inflated) benchmarking sum2 time 26.39 ms (25.49 ms .. 27.26 ms) 0.995 R² (0.991 R² .. 0.998 R²) mean 26.33 ms (25.77 ms .. 26.95 ms) std dev 1.295 ms (941.5 μs .. 1.878 ms) variance introduced by outliers: 15% (moderately inflated) benchmarking sum3 time 7.695 ms (7.670 ms .. 7.722 ms) 1.000 R² (1.000 R² .. 1.000 R²) mean 7.703 ms (7.691 ms .. 7.733 ms) std dev 51.21 μs (25.43 μs .. 99.41 μs) benchmarking sum4 time 26.29 ms (25.40 ms .. 27.21 ms) 0.995 R² (0.989 R² .. 0.998 R²) mean 26.36 ms (25.88 ms .. 27.08 ms) std dev 1.364 ms (954.5 μs .. 1.899 ms) variance introduced by outliers: 20% (moderately inflated) -} }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10992 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler