[GHC] #10137: Rewrite switch code generation

[GHC]

#10137: Rewrite switch code generation
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        Reporter:  nomeata           |                   Owner:
            Type:  task              |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.9
  (CodeGen)                          |                Keywords:
      Resolution:                    |            Architecture:
Operating System:  Unknown/Multiple  |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:  #9157, #8326,     |  Differential Revisions:
  #8317                              |
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Comment (by nomeata):

 All very well, but can we please keep this particular ticket for the
 discussion of better code generation from STG onwards :-)  #10124  is more
 suitable for what we can do in Core, I think.

 My rewrite will not only fix the issue of branchless cases, but also other
 (small) deficiencies in the current code (jump tables also for integer
 types; a better choice for if-then-else branching that leads to larger
 jump tables).

 Anyway, I started on wip/T10137, but already my refactoring broke
 something and I get segfaults :-)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10137#comment:3>
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