[GHC] #6135: Unboxed Booleans

[GHC]

#6135: Unboxed Booleans
-------------------------------+--------------------------------------------
  Reporter:  benl              |          Owner:  jstolarek       
      Type:  feature request   |         Status:  patch           
  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            
-------------------------------+--------------------------------------------

Comment(by simonpj):

 I think we should treat all Bool-returning primops identically.  I think
 it's just the `sameX` family of operators, and they can perfectly well
 return `Int#` in the same way that `eqInt#` now does.  Then you can
 eliminate those cases from the codegen path, which is great.

 One thing I'm puzzled about is this.  If `>#` yields an `Int#`, how does
 that `Int#` get into a register?  Do we get code like
 {{{
   cmp x,y
   bne L1
   ld R1, 1
   goto L2
 L1: ld R1, 0
 L2: ...now R1 has the Int#...
 }}}
 Getting the info from the status flags into a value, which we then compare
 with 0, would be silly.  How is this avoided?  Esp when there are several
 tests and you do logical operations on the `Int#`?

 I looked on the wiki page
 http://hackage.haskell.org/trac/ghc/wiki/PrimBool, but could not figure it
 out. Maybe worth adding a section to explain this?  Thanks

 Simon

 Simon

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6135#comment:69>
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