SpecConstr pass hangs

From Stack Overflow:

The code

{-# LANGUAGE BangPatterns #-}
{-# OPTIONS_GHC -O2 #-}

import qualified Data.Vector.Unboxed.Mutable as MV
import Data.Vector.Unboxed ((!))
import qualified Data.Vector.Unboxed as V
import Control.Monad (forM_)

similar :: V.Vector Char -> Int
similar v = l + sum (map (similar' 1 1) checks)
  where
    (l,checks) = let h = V.head v in V.foldl'  
        (\(i,is) c -> if c == h then (i+1,i:is) else (i+1,is)) (1,[]) (V.tail v)
    similar' !r !n !i = if i < l-1 && v!(n) == v!(i+1) then similar' (r+1) (n+1) (i+1)
        else r

main :: IO ()
main = do
    n <- getLine
    v <- MV.replicate (read n) 0
    forM_ [1..read n] $ \n' -> do
      v' <- getLine
      MV.unsafeWrite v (n'-1) (similar . V.fromList $ v')
    V.unsafeFreeze v >>= V.mapM_ print

causes GHC to hang in the !SpecConstr pass.

Versions 7.0.* compiled it just fine, 7.2.* to 7.6.1 hang.

Trac metadata

Trac field	Value
Version	7.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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