7.8 optimizes attoparsec improperly

{-# LANGUAGE OverloadedStrings #-}

import Control.Applicative
import qualified Data.Attoparsec.Text as A
import Data.Text (Text)
import qualified Data.Text as T

testParser :: Text -> Either String Int
testParser f = fmap length
    . A.parseOnly (many (A.char 'b' <|> A.anyChar))
    $ f

main :: IO ()
main = print . testParser $ T.replicate 50000 "a"

On GHC 7.6.3 with -O2:

real    0m0.062s
user    0m0.022s
sys     0m0.007s

On GHC 7.8 tip with -O2:

real    0m12.700s
user    0m12.504s
sys     0m0.165s

On GHC 7.6.3 with -O0:

real    0m0.077s
user    0m0.025s
sys     0m0.007s

On GHC 7.8 tip with -O0:

real    0m0.055s
user    0m0.026s
sys     0m0.007s

This seems to be related to the use of <|>; if I change the program so that the second branch (A.anyChar) is never taken, 7.8 behavior is roughly the same as 7.6 under any optimization level.

Trac metadata

Trac field	Value
Version	7.8.1-rc1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	MacOS X
Architecture