[GHC] #8763: forM_ [1..N] does not get fused (allocates 50% more)

[GHC]

#8763: forM_ [1..N] does not get fused (allocates 50% more)
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        Reporter:  nh2               |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       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 sgraf):

 This happens even in `-O0`. Not sure how to turn case-of-case of (for
 debugging reasons), `-fno-case-of-case` dosn't seem to be a thing anymore.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8763#comment:72>
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