[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:  lowest                   |        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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Comment (by arotenberg):

 For comparison: The Java Virtual Machine has two instructions called
 `tableswitch` and `lookupswitch`, which are normally implemented as a
 lookup table and a binary search, respectively.
 [http://cr.openjdk.java.net/~forax/lambda/src/share/classes/com/sun/tools/javac/jvm/Gen.java.html
 Here] is the code javac uses to decide whether to generate a `tableswitch`
 or `lookupswitch` for a `switch` statement:
 {{{
 // Determine whether to issue a tableswitch or a lookupswitch
 // instruction.
 long table_space_cost = 4 + ((long) hi - lo + 1); // words
 long table_time_cost = 3; // comparisons
 long lookup_space_cost = 3 + 2 * (long) nlabels;
 long lookup_time_cost = nlabels;
 int opcode =
         nlabels > 0 &&
         table_space_cost + 3 * table_time_cost <=
         lookup_space_cost + 3 * lookup_time_cost
         ?
         tableswitch : lookupswitch;
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9159#comment:5>
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