space leak due to optimisations and/or newtypes

[Simon Peyton-Jones]

It sounds like a bad performance bug to me!  Newtypes should not cost efficiency.  Please to submit a Trac bug report.

What would really help is a self-contained program that demonstrates the problem.  Maybe that's what you've supplied.  I'm confused though.  You say
        If I remove any of them (one is enough) then
        the program finishes in about 10 seconds
        and runs in constant space (< 3 MB) with optimisations.

Are you also saying this?
        If I leave all of them in, then the program takes ages and uses
        lots of space, if I use -O.   But it's fine without -O.

Simon

| -----Original Message-----
| From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-users-
| bounces at haskell.org] On Behalf Of Sebastian Fischer
| Sent: 03 June 2009 22:27
| To: glasgow-haskell-users at haskell.org
| Subject: space leak due to optimisations and/or newtypes
|
| Hello,
|
| I have written a Haskell program that runs much more efficiently
| without optimisations than with optimisations.
|
| Compiled without optimisations it finishes in about 15 seconds and
| runs in constant space (< 3 MB), with optimisations (both -O and -O2)
| it consumed all my RAM in less than 30 seconds before I killed it.
|
| The program contains four occurrences of the identity function 'id'.
| All of them are superflous from a declarative point of view. If I
| remove any of them (one is enough) then the program finishes in about
| 10 seconds and runs in constant space (< 3 MB) with optimisations.
|
| The (attached) program is a condensed version of a program that uses
| newtypes. Originally, the identity functions where newtype con- and
| destructors. The original program consumes a lot of memory both with
| and without optimisations. A version where I have inlined some
| newtypes runs in constant space.
|
| I have used GHC 6.10.1 on Mac OS X. Is this behaviour intended, is it
| a known/fixed issue of GHC 6.10.1 or should I file a bug report?
|
| Cheers,
| Sebastian
|
| -------
| {-# LANGUAGE RankNTypes #-}
|
| newtype S a = S { unS :: forall b . (a -> Int -> [b]) -> Int -> [b] }
|
| ret x      = S (\c   -> c x)
| a `bind` f = S (\c   -> unS a (\x -> unS (f x) c))
| zero       = S (\c _ -> [])
| plus a b   = S (\c   -> id (\d -> if d==0 then []
|                                    else id (unS a c) (d-1) ++
|                                         id (unS b c) (d-1)))
|
| runS :: S a -> [a]
| runS a = concatMap (\d -> id (run a) d) [10000]
|
| run :: S a -> Int -> [a]
| run a = unS a (\x _ -> [x])
|
| natSum :: S Int
| natSum = anyof [1..] `bind` \x ->
|           anyof [1..] `bind` \y ->
|           ret (x+y)
|    where anyof = foldr plus zero . map ret
|
| main = print . length $ runS natSum
| -------
|
|
|
| --
| Underestimating the novelty of the future is a time-honored tradition.
| (D.G.)
|
|
|
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