[GHC] #9646: Simplifer non-determinism leading to 8 fold difference in run time performance

[GHC]

#9646: Simplifer non-determinism leading to 8 fold difference in run time
performance
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              Reporter:  erikd       |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.8.3
            Resolution:              |         Keywords:
      Operating System:  Linux       |     Architecture:  x86_64 (amd64)
       Type of failure:  Runtime     |       Difficulty:  Unknown
  performance bug                    |       Blocked By:
             Test Case:              |  Related Tickets:
              Blocking:              |
Differential Revisions:              |
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Comment (by simonpj):

 I spent a few minutes earlier today, and indeed I'm sure that difference
 in eta expansion is the cause of the trouble. What I do not understand is
 why it happens.

 Would you be prepared to cut down the example still more?  Dump the
 Criterion wrapping.  Just leave enough to reproduce the strange difference
 in Core generated in the wot different ways.  Strip away everything else;
 eg we don't actually need to run the program any more.

 Thanks

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9646#comment:10>
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