[GHC] #15164: Slowdown in ghc compile times from GHC 8.0.2 to GHC 8.2.1 when doing Called arity analysis

[GHC]

#15164: Slowdown in ghc compile times from GHC 8.0.2 to GHC 8.2.1 when doing Called
arity analysis
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        Reporter:  flip101           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Linux             |         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 nomeata):

 Ha, the code still compiles, and does so quickly with all versions, if I
 simply remove the contexts from the instance declarations, e.g.
 {{{
 -instance (Rule f Expression, Rule f Name) => Rule f ActualDesignator
 where
 +instance Rule f ActualDesignator where
 }}}
 This also lets me remove `UndecidableInstances`. See this commit:
 https://github.com/nomeata/parser-
 calledarityanalysis/commit/cb2e23b081d1016278feaa1397ad62a1672a52cf

 @flip101, I understand that this is minimized code. Can you check your
 real code if you really need the contexts in the instance declarations,
 and if the problem goes away when you remove them?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15164#comment:15>
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