I have a problem with optimizing the Haskell module.
There is a main module.
{-# LANGUAGE OverloadedStrings #-}
module Main where
import Control.DeepSeq
import Formatting
import Formatting.Clock
import System.Clock
import Data.Array
size :: Int
size = 200 :: Int
stdMult :: (Ix a, Ix b, Ix c, Num d) =>
Array (a,b) d -> Array (b,c) d -> Array (a,c) d
stdMult x y = array resultBounds
[((i,j), sum [ x!(i,k) * y!(k,j) | k <- range (lj,uj)])
| i <- range (li,ui),
j <- range (lj',uj') ]
where ((li,lj),(ui,uj)) = bounds x
((li',lj'),(ui',uj')) = bounds y
resultBounds
| (lj,uj)==(li',ui') = ((li,lj'),(ui,uj'))
| otherwise = error "error"
main :: IO ()
main = do
let a = array ((1,1),(size, size)) [((i,j), 2*i-j) |
i <- range (1,size),
j <- range (1,size)]
let b = array ((1,1),(size, size)) [((i,j), 2*i+3*j) |
i <- range (1,size)`,
j <- range (1,size)]
start <- getTime ProcessCPUTime
let
c = stdMult a b
end <- c `deepseq` getTime ProcessCPUTime
fprint (timeSpecs % "\n") start end
return()
When stdMultin the main module, everything works fine. I am replacing stdMultwith another module. When I do not use ghc optimization, the runtime is the same. When I use the ghc -O3 options, when stdMultduring the execution of the main module it decreases, but when stdMultin the other module the execution time remains almost unchanged! For example, when stdMultin Main I have a time of 3 seconds, and when stdMultnot in Main, I have a time of 30 seconds, for a matrix 500x500.
It is very strange!