[Haskell-cafe] GHC vs GCC

[Jason Dagit]

On Fri, Mar 26, 2010 at 10:46 AM, Rafael Cunha de Almeida <
almeidaraf at gmail.com> wrote:

> Hello,
>
> During a talk with a friend I came up with two programs, one written in
> C and another in haskell.
>
> Haskell
>        main :: IO ()
>        main = print $ rangeI 0 0
>
>        rangeK :: Int -> Int -> Int -> Int -> Int
>        rangeK i j k acc
>            | k < 1000 =
>                if i * i + j * j + k * k `mod` 7 == 0
>                then rangeK i j (k+1) (acc+1)
>                else rangeK i j (k+1) acc
>            | otherwise = acc
>
>        rangeJ :: Int -> Int -> Int -> Int
>        rangeJ i j acc
>            | j < 1000 = rangeJ i (j+1) (acc + rangeK i j 0 0)
>            | otherwise = acc
>
>        rangeI :: Int -> Int -> Int
>        rangeI i acc
>            | i < 1000 = rangeI (i+1) (acc + (rangeJ i 0 0))
>            | otherwise = acc
>

You might try using bang patterns.  It's possible that GHC didn't detect the
strictness.  Only way I know to check is to look at the core.  Use something
like ghc-core from Hackage to view it.  Ideally the core is using Int#
instead of Int and avoiding lots of boxing.



> I compiled the haskell code with ghc -O3 and I compiled the C code with
> gcc -O3. The execution time of the programs were dramatically different.
> You can test it yourselves, but here is the time I've got in my system:
>

You might try -Odph .

See http://book.realworldhaskell.org/read/profiling-and-optimization.htmlfor
more ideas.

Jason
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