[GHC] #8763: forM_ [1..N] does not get fused (10 times slower than go function)

[GHC]

#8763: forM_ [1..N] does not get fused (10 times slower than go function)
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        Reporter:  nh2                      |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler                 |          Version:  7.6.3
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by nh2):

 Replying to [comment:9 daniel.is.fischer]:
 > The simple example doesn't use the same list in different places

 Unfortunately, I still get no difference in performance even if I
 duplicate the loops to

   forM_ [1.._MAX] $ \i -> do
     UM.unsafeWrite v 0 i
   forM_ [1.._MAX] $ \i -> do
     UM.unsafeWrite v 0 i

 Any idea?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:11>
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