Coercion causes "impossible" error
The following, heavily-redacted version of a function in text
is causing GHC to die after reporting that the impossible happened.
module Encoding where
import Data.ByteString as B
import Data.ByteString.Internal as B
import Data.Text.Internal (Text(..), safe, textP)
import Data.Word (Word8)
import Foreign.C.Types (CSize)
import Foreign.ForeignPtr (withForeignPtr, ForeignPtr)
import Foreign.Ptr (Ptr, minusPtr, plusPtr)
-- | Encode text using UTF-8 encoding.
encodeUtf8 :: Text -> ByteString
encodeUtf8 (Text arr off len) = inlinePerformIO $ do
let size0 = max len 4
mallocByteString size0 >>= start size0 off 0
where
-- start :: Int -> Int -> Int -> ForeignPtr Word8 -> IO ByteString
start size n0 m0 fp = withForeignPtr fp $ go n0 m0
where
offLen = off + len
go n m ptr
| n == offLen = return (PS fp 0 m)
| otherwise = do
let ensure k act
| size-m >= k = act
| otherwise = do
let newSize = size
fp' <- mallocByteString newSize
start newSize n m fp'
{-# INLINE ensure #-}
ensure 4 $ return $ PS fp 0 m
$ ghc -fext-core Encoding.hs
[1 of 1] Compiling Encoding ( Encoding.hs, Encoding.o )
ghc: panic! (the 'impossible' happened)
(GHC version 7.6.3 for x86_64-unknown-linux):
make_exp (App _ (Coercion _))
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Note that it only happens when I try to make GHC output the Core, it will happily compile otherwise. The crash can also be prevented by uncommenting the type-annotation or removing the inline-annotation.
Trac metadata
Trac field | Value |
---|---|
Version | 7.6.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |