[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 daniel.is.fischer):

 Slight correction, @Niklas, it's not a suspicion that it's the floating
 out of the list to the top-level and consequently the use of the list for
 looping instead of unboxed `Int#`s, that is direct from the core (`-ddump-
 simpl` is your friend in all matters related to performance). The question
 is under which exact circumstances GHC floats the list out. To answer
 that, you need somebody knowing how GHC works.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:15>
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