[GHC] #11677: Dramatic de-optimization with "-O", "-O1", "-O2" options

[GHC]

#11677: Dramatic de-optimization with "-O", "-O1", "-O2" options
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        Reporter:  malphunction      |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:  optimization
                                     |  deoptimization
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Runtime           |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by malphunction):

 Update: if disable `-fenable-rewrite-rule` (i.e. `-O2 -fno-enable-rewrite-
 rule`), then compiled program runs fast!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11677#comment:3>
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