[GHC] #14626: No need to enter a scrutinised value

[GHC]

#14626: No need to enter a scrutinised value
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        Reporter:  heisenbug         |                Owner:  heisenbug
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:  performance
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13861            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by heisenbug):

 @simonpj, thanks this is a good start. When restricting myself to `wild*`
 vars, I already get a nice performance diff on dynamic instruction counts:
 https://perf.haskell.org/ghc/#compare/7a25659efc4d22086a9e75dc90e3701c1706c625/9ad6982e4074c1fdeff967cafa51e436023d69bb

 Then I tried to add `ds*` variables too, and (some of) those made the
 stage-2 crash. It is checked in on the branch if you want to have a try...
 https://github.com/ghc/ghc/commit/b30d61f64772d744e06e2acbab21895cb20d9bf7

 Any hints appreciated!

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14626#comment:9>
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