[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
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        Reporter:  RyanGlScott       |                Owner:  goldfire
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15076            |  Differential Rev(s):  Phab:D4769
       Wiki Page:                    |
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Comment (by goldfire):

 Before we continue drilling in that direction, are these results
 reproducible? Timing is notoriously fickle, and I think it would be wise
 to make sure we know what we're getting into here.

 Also, I do think it's worthwhile to still measure allocations, just as
 another data point.

 If the `FV`/`VarSet` change isn't the driving force here, then what is? I
 recommend removing the code that adds the fvs of a variable's kind
 (without replacing this logic with anything) and testing again. That
 should surely take less time. (Be careful, e.g., by comparing `-ddump-tc-
 trace`s, that GHC's overall behavior doesn't change by doing this.) Then,
 add the `closeOverKinds`. Maybe the algorithm in `closeOverKinds` (simple
 though it is) is somehow grossly inefficient.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:78>
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