[GHC] #13523: Be more explicit in generated case alternatives

4 Apr 2017

      #13523: Be more explicit in generated case alternatives
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           Reporter:  bgamari        |             Owner:  (none)
               Type:  feature        |            Status:  new
  request                            |
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This came up during the GHC call while discussing #13397 and I thought it
 would be good to record.

 Often in the compiler we end up with a case analysis with a number of
 alternatives and a `DEFAULT` case in place of the remaining alternative,
 {{{!#hs
 case x of
   True -> a
   DEFAULT -> b
 }}}
 Arguably we should instead generate,
 {{{
 case x of
   True -> a
   False -> b
 }}}
 instead as this may allow the code generator may be able to emit better
 code when it knows the finite bounds of the switch (e.g. using a jump
 table).

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13523
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