Andreas Klebinger authored Sep 18, 2018 and Krzysztof Gogolewski committed Sep 18, 2018

Summary:
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.

By reversing comparisons we can avoid testing the parity
for < and <= as well. This works since:
* If any of the arguments is an NaN CF gets set. Resulting in a false result.
* Since this allows us to rule out NaN we can exchange the arguments and invert the
  direction of the arrows.

Test Plan: ci/nofib

Reviewers: carter, bgamari, alpmestan

Reviewed By: alpmestan

Subscribers: alpmestan, simonpj, jmct, rwbarton, thomie

GHC Trac Issues: #15196

Differential Revision: https://phabricator.haskell.org/D4990