[vector] #32: Performance of concatMap and O2/Odph

[vector]

#32: Performance of concatMap and O2/Odph
--------------------+-------------------------------------------------------
Reporter:  choener  |       Owner:     
    Type:  defect   |      Status:  new
Priority:  minor    |   Milestone:     
 Version:  0.6      |    Keywords:     
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 This one is fun, I get slowdowns of up to 10.000x which is especially nice
 in code that is called often ;-) (why exactly, I do not know yet, it
 should be more like x5 - 10x)
 -Odph adversely effects runtime performance here!

 The code below differs only in the "makes it slow" line.

 {{{
 module Main where

 import qualified Data.Vector.Unboxed as VU
 import Criterion.Main

 iL = 4
 jL = 100

 good :: Int -> Int -> VU.Vector (Int,Int)
 good i j = {-# CORE "good" #-}
   VU.map (\(k,l) -> (k-l,l)) $
   VU.concatMap (
     \d -> VU.map (\d' -> (d,d'))
           $ VU.enumFromN 3 (d-5))    -- for each distance, all possible
 left/right combinations
   $ VU.enumFromN 8 (min 23 (j-i-13)) -- diagonal distance or number of
 unpaired nucleotides -2.
 {-# INLINE good #-}


 bad :: Int -> Int -> VU.Vector (Int,Int)
 bad i j = {-# CORE "bad" #-}
   VU.map (\(k,l) -> (i+k,j-l)) $ -- this part makes it slow!
   VU.map (\(k,l) -> (k-l,l)) $
   VU.concatMap (
     \d -> VU.map (\d' -> (d,d'))
           $ VU.enumFromN 3 (d-5))    -- for each distance, all possible
 left/right combinations
   $ VU.enumFromN 8 (min 23 (j-i-13)) -- diagonal distance or number of
 unpaired nucleotides -2.
 {-# INLINE bad #-}

 main = defaultMain
    [ bench "good" $ whnf (\j -> VU.sum $ VU.map (\(k,l) -> k+l) $ good iL
 j) jL
    , bench "bad" $ whnf (\j -> VU.sum $ VU.map (\(k,l) -> k+l) $ bad iL j)
 jL
    ]
 }}}

-- 
Ticket URL: <http://trac.haskell.org/vector/ticket/32>
vector <http://trac.haskell.org/vector>
Package vector