[GHC] #9233: Compiler performance regression

[GHC]

#9233: Compiler performance regression
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              Reporter:  augustss    |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  low         |         Milestone:
             Component:  Compiler    |           Version:  7.8.2
            Resolution:              |          Keywords:
Differential Revisions:  Phab:D73    |  Operating System:  Windows
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |         Test Case:
            Difficulty:  Unknown     |          Blocking:
            Blocked By:              |
       Related Tickets:              |
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Comment (by simonpj):

 Some questions for Richard:

  * In the first commit "Rewrite coercionRole", there is a small change in
 `OptCoercion`, whicg does entirely un-commented.  What's it about?  Could
 you comment it?  A Note?

  * In the new `OptCoercion` (after both commits) I see that `opt_co1` is
 called only with `Nothing` as its third arg.  So can we get rid of that
 arg?

  * Ditto `opt_co2`.  (In contrast `opt_co3` does have non-Nothing calls.
 It's the only one that does.

  * Do those changes change something in `Note [Optimising coercion
 optimisation]`?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9233#comment:20>
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