[GHC] #10992: Performance regression

[GHC]

#10992: Performance regression
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           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:
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 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>
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