[GHC] #15304: Huge increase of compile time and memory use from 8.0.2 to 8.2.2 or 8.4.2

[GHC]

#15304: Huge increase of compile time and memory use from 8.0.2 to 8.2.2 or 8.4.2
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        Reporter:  NathanWaivio      |                Owner:  tdammers
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.4.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:  x86_64
 Type of failure:  Compile-time      |  (amd64)
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by NathanWaivio):

 I have found an undocumented flag: "-fno-worker-wrapper". When enabled the
 original code compiles in 43.20 seconds (37x improvement in time), and
 uses 660MB max (48x improvement in space) with GHC 8.4.2.  All of the
 tests pass for the library and the benchmark still performs at the
 improved speed.  It seems like the Worker/Wrapper Transformation is
 causing issues with this code.  Why is that?  Perhaps Worker/Wrapper
 shouldn't be run in certain circumstances.  What do you think?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15304#comment:16>
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