[GHC] #9251: ghc does not expose branchless max/min operations as primops

[GHC]

#9251: ghc does not expose branchless max/min operations as primops
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        Reporter:  carter            |            Owner:  carter
            Type:  task              |           Status:  new
        Priority:  normal            |        Milestone:  7.10.1
       Component:  Compiler          |          Version:  7.8.2
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:  #9246
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Comment (by carter):

 actually, importantly, in section 5.11 of the 2008 standard they say

    Four mutually exclusive relations are possible: **less than** ,
 **equal**, **greater than**, and **unordered**. The last case arises when
 at least one    operand is NaN. Every NaN shall compare unordered with
 everything, including itself. Comparisons shall ignore the sign of zero
 (so +0 = −0). Infinite operands of the same sign shall compare equal.


 thus the Ord compare based instance should actually perhaps throw an
 exception or otherwise fail when either  argument is Nan? I'll need read a
 bit more.

 ANYWAY, theres several *distinct* semantics that can be chosen, and adding
 suitable support to ghc for the different semantics that aren't
 interexpressible is something I'll spend some time thinking about.

 don't worry, you'll have the version you want, but there will be an IEEE
 compliant one that also satisfies the corresponding haskell standard
 (BOTH, if they disagree theres a serious problem i'll have to have some
 discussion about)

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9251#comment:4>
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