[GHC] #10414: Buggy behavior with threaded runtime (-N1 working, -N2 getting into <<loop>>)

[GHC]

#10414: Buggy behavior with threaded runtime (-N1 working, -N2 getting into
<<loop>>)
-------------------------------------+-------------------------------------
        Reporter:  exio4             |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Incorrect result  |  Unknown/Multiple
  at runtime                         |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by michaelt):

 And a bit more compressed, for what it may be worth:

 {{{#!hs

 {-# LANGUAGE MagicHash, UnboxedTuples #-}
 import GHC.Exts
 newtype Eval a = Eval {runEval :: State# RealWorld -> (# State# RealWorld,
 a #)}

 -- inline sequence ::  [Eval a] -> Eval [a]
 well_sequenced ::  [Eval a] -> Eval [a]
 well_sequenced = foldr op (Eval $ \s -> (# s, [] #))  where
   op e es = Eval $ \s -> case runEval e s of
                     (# s', a #) -> case runEval es s' of
                       (# s'', as #) -> (# s'', a : as #)

 -- seemingly demonic use of spark#
 ill_sequenced ::  [Eval a] -> Eval [a]
 ill_sequenced  as = Eval $ spark# (case well_sequenced as of
              Eval f -> case f realWorld# of  (# _, a' #) -> a')

 main :: IO ()
 main = print ((layer . layer . layer . layer . layer) show 'y')
   where
   layer :: (Char -> String) -> (Char -> String)
   layer f = (\(Eval x) -> case x realWorld# of (# _, as #) -> concat as)
         . well_sequenced
         . map ill_sequenced
         . map (map (\x -> Eval $ \s -> (# s, x #)))
         . chunk'
         . concatMap f
         . show

 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10414#comment:15>
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