[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:  (none)
            Type:  bug               |               Status:  infoneeded
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  7.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #7206             |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by George):

 Replying to [comment:36 osa1]:
 > Sorry for the confusion -- it turns out GHC 8.2.2 already optimizes
 this. Perhaps this can be closed or we may need a new reproducer.

 I have a very similar program where, with 8.4.1, the forM_ version
 allocates 50% more than the version with recursive go but both versions
 run in about the same time . Is it worth giving that code here in this bug
 or should I enter a new bug referencing this one?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:39>
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