[GHC] #13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC 8.2

[GHC]

#13426: compile-time memory-usage regression for DynFlags between GHC 8.0 and GHC
8.2
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        Reporter:  hvr               |                Owner:  rwbarton
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Well done!  Yes, use `simplType`!  Can you add a Note to `simplType`
 explaining why it is so important to use it rather than naked `substTy`
 calls; and pointing to this ticket?

 I suspect that it has been a problem for a long time; just that no one has
 noticed.

 It's very uncomfortable that this is so delicate; and even when recognised
 is so hard to find.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13426#comment:13>
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