[GHC] #12765: Don't optimize coercions with -O0

[GHC]

#12765: Don't optimize coercions with -O0
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        Reporter:  bgamari           |                Owner:
            Type:  task              |               Status:  new
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by bgamari):

 I'm dropping a ticket here since I'm no longer convinced that this is
 worthwhile. Unfortunately this would require a significant amount of
 plumbing of the optimization level through a bunch of pure simplification
 functions to make this happen. Moreover, even if we forego the coercion
 simplification pass in `simpleOptPgm`, we still do run the simplifier even
 with `-O0`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12765#comment:1>
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