[GHC] #9659: Offer branchless conditional (CMOV) primop

[GHC]

#9659: Offer branchless conditional (CMOV) primop
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              Reporter:  dfeuer      |            Owner:
                  Type:  feature     |           Status:  new
  request                            |        Milestone:
              Priority:  normal      |          Version:  7.8.3
             Component:  Compiler    |         Keywords:
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
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Description changed by dfeuer:

Old description:

> I'd like to see something similar to C's `?:`, like
>
> {{{#!hs
> ifInt#, boolInt# :: Int# -> Int# -> Int# -> Int#
> }}}
>
> We could then write things like
>
> {{{#!hs
> ifInt# (x <# y) 12# (x +# 17#)
> boolInt# potato cannon (y ># 2)
> }}}
>
> When the value of the test is difficult to predict, this would be better
> than the usual branching `if` or `case`.

New description:

 I'd like to see something similar to C's `?:`, like

 {{{#!hs
 ifI#, boolI# :: Int# -> Int# -> Int# -> Int#
 }}}

 We could then write things like

 {{{#!hs
 ifI# (x <# y) 12# (x +# 17#)
 boolI# potato cannon (y ># 2)
 }}}

 When the value of the test is difficult to predict, this would be better
 than the usual branching `if` or `case`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9659#comment:1>
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