[GHC] #15196: Invert floating point comparisons such that no extra parity check is required.

30 May 2018


      #15196: Invert floating point comparisons such that no extra parity check is
required.
-------------------------------------+-------------------------------------
           Reporter:  AndreasK       |             Owner:  (none)
               Type:  task           |            Status:  new
           Priority:  normal         |         Milestone:  8.6.1
          Component:  Compiler       |           Version:  8.4.3
  (NCG)                              |
           Keywords:  CodeGen        |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 This comment pretty much explains it already:

 {{{
         -- We have to worry about unordered operands (eg. comparisons
         -- against NaN).  If the operands are unordered, the comparison
         -- sets the parity flag, carry flag and zero flag.
         -- All comparisons are supposed to return false for unordered
         -- operands except for !=, which returns true.
         --
         -- Optimisation: we don't have to test the parity flag if we
         -- know the test has already excluded the unordered case: eg >
         -- and >= test for a zero carry flag, which can only occur for
         -- ordered operands.
         --
         -- ToDo: by reversing comparisons we could avoid testing the
         -- parity flag in more cases.
 }}}

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15196
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