strange space usage

This program:

module Main (main) where

import System.IO.Unsafe

main :: IO ()
main = do writeFile "wibbleflibble" (replicate 100 'z')
          bs <- getCs $ g $ replicate 1000000 "flibble"
          print $ last bs

getCs :: [FilePath] -> IO String
getCs [] = return ""
getCs (c : cs) = do x <- readFile c
                    xs <- unsafeInterleaveIO $ getCs cs
                    return (x ++ xs)

g :: [FilePath] -> [FilePath]
g is = map f is

f :: FilePath -> FilePath 
f fn = "wibble" ++ fn

when run:

$ ghc -fforce-recomp -Wall --make -O2 -prof -auto-all z.hs -o z
$ ./z +RTS -h -p

shows that around 100k is used by f (h.png). Running with

$ ./z +RTS -hcf -hy -p

shows that it is all of type [] (hcf_hy.png). That seems like a large amount of space for a 13 character filename, so it smells to me like something is wrong somewhere.

If we inline g:

module Main (main) where

import System.IO.Unsafe

main :: IO ()
main = do writeFile "wibbleflibble" (replicate 100 'z')
          bs <- getCs $ map f $ replicate 1000000 "flibble"
          print $ last bs

getCs :: [FilePath] -> IO String
getCs [] = return ""
getCs (c : cs) = do x <- readFile c
                    xs <- unsafeInterleaveIO $ getCs cs
                    return (x ++ xs)

f :: FilePath -> FilePath 
f fn = "wibble" ++ fn

then it all disappears (h2.png).

Trac metadata

Trac field	Value
Version	6.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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