#7270: Incorrect optimization with Data.ByteString.append
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Reporter: ocheron | Owner: duncan
Type: bug | Status: new
Priority: highest | Milestone: 7.6.2
Component: libraries (other) | Version: 7.6.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Incorrect result at runtime
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Changes (by igloo):
* owner: igloo => duncan
* priority: normal => highest
* milestone: => 7.6.2
Comment:
Thanks for the report. This is due to bytestring's misuse of its
`inlinePerformIO`; Duncan knows what to do.
Here's a small standalone program demonstrating the problem:
{{{
{-# LANGUAGE BangPatterns, MagicHash, UnboxedTuples #-}
module Main (main) where
import GHC.Base
import GHC.ForeignPtr
import Foreign
main :: IO ()
main = do let !r = make 68
!s = make 70
dump r
dump s
dump :: ForeignPtr Word8 -> IO ()
dump fp = do print fp
withForeignPtr fp $ \p -> do x <- peek p
print x
make :: Word8 -> ForeignPtr Word8
make w = inlinePerformIO $ do fp <- mallocPlainForeignPtrBytes 1
withForeignPtr fp $ \p -> poke p w
return fp
inlinePerformIO :: IO a -> a
inlinePerformIO (IO m) = case m realWorld# of (# _, r #) -> r
}}}
{{{
$ ghc --make q -O
$ ./q
0x00007f95b0706010
68
0x00007f95b0706010
68
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7270#comment:3>
GHC <http://www.haskell.org/ghc/>
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