[GHC] #15019: Fix performance regressions from #14737

[GHC]

#15019: Fix performance regressions from #14737
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        Reporter:  tdammers          |                Owner:  tdammers
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #14737            |  Differential Rev(s):  phab:D4568
       Wiki Page:                    |
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Comment (by tdammers):

 {{{
 Remove unnecessary check in simplCast

 The coercion optimizer will take care of it anyway, and the check is
 prohibitively expensive.

 See Trac Trac #14737.

 Reviewers: bgamari

 Subscribers: simonpj, thomie, carter

 Differential Revision: https://phabricator.haskell.org/D4568
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15019#comment:19>
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