[GHC] #14899: Significant compilation time regression between 8.4 and HEAD due to coverage checking

[GHC]

#14899: Significant compilation time regression between 8.4 and HEAD due to
coverage checking
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.5
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 > Does this sound plausible?

 Yes, something like that looks plausible, except that I think the last
 line should be more like
 {{{
     Δ' = Δ ∪ u_0 ≈ (y |> co)
 }}}
 (patterns `p` don't appear in expressions).

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14899#comment:5>
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