The original comment was a little terse and a little incorrect. The
rearrangements are fine w.r.t. NaN. However, they produce incorrect
results if one operand is +Inf and the other is -Inf.
A later commit, "nir/algebraic: Add some compare-with-zero optimizations
that are exact", will add some more patterns here. It may be reasonable
to squash this commit (forward) into that commit.
v2: Fix some incorrect comparisons operators in the comment (<= vs >=).
Add commentary that subtraction works like addition w.r.t. NaN. Both
noticed / suggested by Caio.
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6358>
Ian Romanick
aec0547838