[GHC] #7367: Optimiser / Linker Problem on amd64

[GHC]

#7367: Optimiser / Linker Problem on amd64
--------------------------------------------+------------------------------
        Reporter:  wurmli                   |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:  7.8.1
       Component:  Build System             |          Version:  7.6.1
      Resolution:                           |         Keywords:
Operating System:  Linux                    |     Architecture:  x86_64
 Type of failure:  Runtime performance bug  |  (amd64)
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
--------------------------------------------+------------------------------

Comment (by wurmli):

 May I add to your consideration the following simple example whith the
 same structure and behaviour:


 {{{

 -- ghc --make -threaded -O2 -fllvm -rtsopts heapAndSpeed.hs
 -- ./headAndSpeed +RTS -s

 {-# LANGUAGE BangPatterns #-}

 import System.Environment
 import Control.Applicative
 import Control.Monad

 import Control.Monad.ST

 import qualified Data.STRef as VSM

 -------------------------------------------------------------------
 -- Increment counter by 1

 acc1 :: VSM.STRef s ( Int , Int ) -> ST s ()
 acc1 !v = do{
   (!k,!n) <- VSM.readSTRef v;
   VSM.writeSTRef v (k+1,n)
   }

 -- Increment counter until limit

 whileModify1 :: VSM.STRef s ( Int , Int ) -> ST s ()
 whileModify1 !v = do
   !go <- do{ (k,n) <- VSM.readSTRef v; return (compare k n)}
   case go of
     LT -> do {acc1 v; whileModify1 v}
     EQ -> return ()
     GT -> return ()

 testAcc :: Int -> (Int,Int)
 testAcc n = runST $ do
   v <- VSM.newSTRef (0,n)
   whileModify1 v
   VSM.readSTRef v

 main = do
   let k = 20000000
   putStrLn $ show $ testAcc k
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7367#comment:11>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler