[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):

 In principle yes.  But although +0.59% allocation in T783, say isn't
 important enough to prevent using is, it'd be good to know why it
 happened.  Maybe there's something simple going wrong that would be easily
 fixed?

 Or maybe it's one of those things like "with the change, f becomes small
 enough to inline into g, so g becomes too big to inline at its call sites
 and that makes the difference".  If so, fine.  But it'd be good to know.

 I find `-ticky` lets you nail the changes really fast.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13397#comment:8>
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