[GHC] #14282: tagToEnum# . dataToTag# not optimized away

[GHC]

#14282: tagToEnum# . dataToTag# not optimized away
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        Reporter:  dfeuer            |                Owner:  dfeuer
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.6.1
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:  datacon-tags
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D4375
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"1d90f66095de9844c925211e5fb52b5c4d3f0674/ghc" 1d90f66/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="1d90f66095de9844c925211e5fb52b5c4d3f0674"
 Document missing dataToTag# . tagToEnum# rule

 Explain why we don't have a rule to optimize `dataToTag# (tagToEnum# x)`
 to `x`.

 [skip ci]

 Reviewers: bgamari

 Reviewed By: bgamari

 Subscribers: rwbarton, thomie, carter

 GHC Trac Issues: #14282

 Differential Revision: https://phabricator.haskell.org/D4375
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14282#comment:9>
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