[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):

 Wow! It never occurred to me that the incidental change around ordering
 (which was entirely unforced -- done just so that users would more often
 see variables reported in an order similar to what was written) could have
 such an impact on performance. I suppose it's because `mapUnionFV` can get
 inlined but `f` can't? Happily, the solution is dead simple: just don't
 make that change! (We still can, I imagine, make the changes in UniqDFM.
 I'd be even more flabbergasted if those changes affected performance.)

 Thanks!

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:116>
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