[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:
       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 tdammers):

 Replying to [comment:53 simonpj]:
 > Let me urge you to try it with an explicit accumulator, exactly as I
 wrote it.
 >
 > I recall that this made a very big difference for Bartosz.

 Can you remember whether that situation involved raw `VarSet`s, or `FV`s?
 From what I see in the code, `FV` could, under the right circumstances,
 avoid hitting the underlying `IntSet` entirely, while after this patch,
 we're using `VarSet` directly, so maybe that's why those set operations
 are being hit harder now?

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:57>
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