[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 tdammers):

 Replying to [comment:71 simonpj]:
 > I was suspicious about comment:64 so I took a look.  Sure enough
 >
 > * The list `[1..n]` wasn't being fused away because it was shared
 between `insert` and `union`, while `balanced` worked differently and
 generated no intermediate list.

 Ah yes. Lesson learned once again: benchmarking is hard and subtle.

 > * More significantly, the integers were in ascending order which is
 fantastically good for balanced union: the tree that implements the set is
 always balanced and never needs to be transformed.

 Right. I probably had the wrong intuition about set performance
 characteristics here.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:72>
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