[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):

 Call Arity does a fixed-point iteration for mutual recursive groups; if
 there is one giant, then I am not surprised to see that it explodes there.
 We could detect absurdly large groups and do some conservative
 approximation.

 But as Sebastian finds, there is *another*, independent regression that
 inflates the Core and compilation time (and blows it up in a way that
 completely chokes Call Arity)…

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15164#comment:8>
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