[GHC] #14295: tagToEnum# leads to some silly closures

[GHC]

#14295: tagToEnum# leads to some silly closures
-------------------------------------+-------------------------------------
        Reporter:  dfeuer            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.4.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  datacon-tags
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 dfeuer):

 Specifically, any time CorePrep is tempted to produce

 {{{#!hs
 let x = tagToEnum# @KnownType y
 in e
 }}}

 it should pause a moment and instead produce

 {{{#!hs
 case leWord# (int2Word# y) limit of
   DEFAULT -> error "blah"
   1# -> case tagToEnum# @KnownType y of x
           DEFAULT -> e
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14295#comment:3>
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