[GHC] #9159: cmm case, binary search instead of jump table

[GHC]

#9159: cmm case, binary search instead of jump table
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        Reporter:  wojteknar                |            Owner:
            Type:  feature request          |           Status:  new
        Priority:  low                      |        Milestone:
       Component:  Compiler                 |          Version:  7.8.2
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Changes (by rwbarton):

 * type:  bug => feature request


Comment:

 Presumably the case on an `Int#` uses a binary search because there's no
 reason the cases need to be consecutive integers: imagine you change the
 last case to `1000000# -> Chunk08 w#`. Now a jump table is not a good
 idea. The case on a `Nat` knows that the tag integer identifying the
 constructor will be in the range from 0 to 8.

 We would need some heuristic for when to use binary search vs. a jump
 table (or perhaps both, if the cases to be matched consist of multiple
 ranges of consecutive integers). Maybe worth looking into what C compilers
 do.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9159#comment:3>
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