Nested SPECIALIZEd functions cause error: "Symbol _BadUTF8_zdf1_closure already defined."

The utf8-string package (in particular, the module Code.Binary.UTF8.Generic) does not compile under ghc-6.9.20080825.

I tried stripping down that module and believe the problem occurs when a SPECIALIZEd function calls another SPECIALIZEd function:

{-# LANGUAGE FlexibleInstances #-}
module BadUTF8 where

import Data.Word

class UTF8Bytes b where

instance UTF8Bytes [Word8] where

{-# SPECIALIZE myfoldr :: (Char -> a -> a) -> a -> [Word8]      -> a #-}
myfoldr :: UTF8Bytes b => (Char -> a -> a) -> a -> b -> a
myfoldr _ x _ = x

{-# SPECIALIZE toString :: [Word8] -> String #-}
toString :: UTF8Bytes b => b -> String
toString bs = myfoldr (:) [] bs

Compiling using ghc-6.9.20080825 without -O, or ghc-6.8.3 with or without -O, does not produce an error. However, ghc-6.9.20080825 with optimization produces:

judah-jacobsons-computer:tmp judah$ ~/tmp/ghc-stage/bin/ghc --make -O BadUTF8.hs
[1 of 1] Compiling BadUTF8          ( BadUTF8.hs, BadUTF8.o )

/var/folders/Pm/Pm4yd68oG4qqe-gsgn56W++++TI/-Tmp-/ghc88501_0/ghc88501_0.s:81:0:
    FATAL:Symbol _BadUTF8_zdf1_closure already defined.

Trac metadata

Trac field	Value
Version	6.9
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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