[GHC] #6082: Program compiled with 7.4.1 runs many times slower than compiled with 7.2.2

[GHC]

#6082: Program compiled with 7.4.1 runs many times slower than compiled with 7.2.2
----------------------------------+-----------------------------------------
    Reporter:  gchrupala          |       Owner:  pcapriotti             
        Type:  bug                |      Status:  new                    
    Priority:  high               |   Milestone:  7.4.3                  
   Component:  libraries (other)  |     Version:  7.4.1                  
    Keywords:                     |          Os:  Unknown/Multiple       
Architecture:  Unknown/Multiple   |     Failure:  Runtime performance bug
  Difficulty:  Unknown            |    Testcase:                         
   Blockedby:                     |    Blocking:                         
     Related:                     |  
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Changes (by pcapriotti):

  * component:  Compiler => libraries (other)


Comment:

 The problem seems to have been introduced in the last version of the
 `array` library. Here is a minimal test case:

 {{{
 import Control.Monad
 import Data.Array.ST
 import Data.Array.Unboxed
 import Control.Monad.ST

 type DenseVector i = UArray i Float

 main = do
   let lo = (0,0)
       hi = (1000,1000)
       m = test (lo, hi)
   print $ bounds m

 test bounds = m
   where m = runSTUArray $ do
               params <- newArray bounds 0
               replicateM_ 10000 $ do
                 params' <- {-# SCC "freeze" #-} unsafeFreeze params
                 let _ = params' :: DenseVector (Int,Int)
                 return ()
               return params

 foo :: DenseVector (Int,Int) -> ST s ()
 foo _ = return ()
 }}}

 The `unsafeFreeze` call is significantly slower with `array-0.4.0.0` than
 `array-0.3.0.3`.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6082#comment:5>
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