[GHC] #6135: Unboxed Booleans

[GHC]

#6135: Unboxed Booleans
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  Reporter:  benl              |          Owner:                  
      Type:  feature request   |         Status:  new             
  Priority:  normal            |      Milestone:  7.8.1           
 Component:  Compiler          |        Version:  7.4.1           
Resolution:                    |       Keywords:                  
        Os:  Unknown/Multiple  |   Architecture:  Unknown/Multiple
   Failure:  None/Unknown      |     Difficulty:  Unknown         
  Testcase:                    |      Blockedby:                  
  Blocking:                    |        Related:  #605            
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Comment(by simonmar):

 Replying to [comment:69 simonpj]:
 >
 > One thing I'm puzzled about is this.  If `>#` yields an `Int#`, how does
 that `Int#` get into a register?

 If we branch directly on the result of the comparison, then the
 intermediate `Int#` is never manifested, the code generator just generates
 a conditional branch instruction.  The optimisations in `CmmSink` try to
 ensure that the comparison is pushed into the `CmmCondBranch` so the code
 generator can spot it.

 If the `Int#` value is really used (as in the example with logical ops on
 the wiki page), then on x86 there are instructions to generate it (e.g.
 `sete`, `setge`, etc.).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6135#comment:75>
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