id	summary	reporter	owner	description	type	status	priority	milestone	version	resolution	keywords	cc
32	Performance of concatMap and O2/Odph	choener		"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
   ]
}}}
"	defect	closed	critical	0.7.1	0.6	fixed