[GHC] #13397: Optimise calls to tagToEnum#

[GHC]

#13397: Optimise calls to tagToEnum#
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 I found another reason to do this: `tagToEnum# (x ># y)` is floated out by
 full laziness, creating a new thunk and a free variable of the function
 closure.  But plain `(x ># y)` is not: it's too cheap to be worth it.

 We could make `tagToEnum# (x ># y)` look cheaper, but if we eliminate it
 we don't have to bother.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13397#comment:5>
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