[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
-------------------------------------+-------------------------------------
        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):

 We already go from
 {{{
 ==================== Desugar (after optimization) ====================
 Result size of Desugar (after optimization)
   = {terms: 3,189, types: 4,403, coercions: 132}
 }}}
 to
 {{{
 ==================== Desugar (after optimization) ====================
 Result size of Desugar (after optimization)
   = {terms: 82,881, types: 86,775, coercions: 132, joins: 0/20,633}
 }}}

 Maybe the use of `UndecidableInstances` is the problem here?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15164#comment:13>
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