[GHC] #10293: CallArity taking 20% of compile time

[GHC]

#10293: CallArity taking 20% of compile time
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        Reporter:  simonpj           |                   Owner:  nomeata
            Type:  bug               |                  Status:  new
        Priority:  high              |               Milestone:  7.12.1
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by nomeata):

 The culprit is `callArityRecEnv` , which analyzes recursive groups and
 calls `calledWith` with quadratic complexity.

 I might have an idea for way to shortcut this. Or maybe the code should
 revert to a quick and conservative conversation when analyzing a very
 large recursive group – the largest here is has 754 mutually recursive
 definitions.

 I’ll need to ponder this some more.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10293#comment:4>
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