[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 nomeata):

 A comment in `SetLevels` (which I just came across) in the code indicates
 that this problem should have been taken care of:

 {{{
           -- We are keen to float something to the top level, even if it
 does not
           -- escape a lambda, because then it needs no allocation.  But
 it's controlled
           -- by a flag, because doing this too early loses opportunities
 for RULES
           -- which (needless to say) are important in some nofib programs
           -- (gcd is an example).
 }}}


 So either my assumption is wrong, or this does not work as desired.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:3>
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