[GHC] #13014: Seemingly unnecessary marking of a SpecConstr specialization as a loopbreaker

[GHC]

#13014: Seemingly unnecessary marking of a SpecConstr specialization as a
loopbreaker
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        Reporter:  nfrisby           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  SpecConstr
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Runtime           |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nfrisby):

 I've attached three `hs` files as `T13014.tar.gz`. They demonstrate the
 issue when they're all compiled with `-O`. (The second module specifies
 `OPTIONS_GHC -fspec-constr`.)

 The characteristic of this ticket is that the `-ddump-simpl` for the
 `GADTSpecConstr3.hs` module does not define `test` as simply `3`.

 Embarassingly and frustratingly, I've lost the `VLZ` rule with my interim
 edits and I can't get it back. Thankfully, it's not actually necessary for
 this ticket.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13014#comment:3>
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