[GHC] #10034: Regression in mapM_ performance

[GHC]

#10034: Regression in mapM_ performance
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        Reporter:  dfeuer            |                   Owner:  ekmett
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.10.1
       Component:  Core Libraries    |                 Version:  7.10.1-rc2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:  Phab:D632
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Comment (by simonpj):

 I still don't follow from comment:2 where the performance loss you
 describe is coming from, nor why inlining `mapM` will help.

 If you do have a clear idea, can you ''construct'' an example?  Switch off
 Call Arity if you like.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10034#comment:3>
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