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

[GHC]

#15019: Fix performance regressions from #14737
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        Reporter:  tdammers          |                Owner:  (none)
            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:D4635
       Wiki Page:                    |
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Comment (by tdammers):

 T12425 at least does not look like it could possibly have become marginal.
 We went from 141952368 after #14747 (non-marginally up) to 130646336 in
 #15019 (non-marginally down), and now back up to 150743648 in this patch,
 which is even higher than the original value post-#14747. So this is
 somewhat curious IMO.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15019#comment:26>
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