nir: Simplify 0 >= b2f(a)

This also prevented some regressions with other patches in my local
tree.

Broadwell / Skylake
total instructions in shared programs: 8980835 -> 8980833 (-0.00%)
instructions in affected programs: 45 -> 43 (-4.44%)
helped: 1
HURT: 0

total cycles in shared programs: 70077904 -> 70077900 (-0.00%)
cycles in affected programs: 122 -> 118 (-3.28%)
helped: 1
HURT: 0

No changes on earlier platforms.

v2: Modify the comments to look more like a proof.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 5b3694e1933d713e204a961c29c1f86b1f6982db..facc33b4e0ad55c88be974e97fd4b2d413950639 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -101,6 +101,13 @@ optimizations = [
    (('inot', ('ige', a, b)), ('ilt', a, b)),
    (('inot', ('ieq', a, b)), ('ine', a, b)),
    (('inot', ('ine', a, b)), ('ieq', a, b)),
+
+   # 0.0 >= b2f(a)
+   # b2f(a) <= 0.0
+   # b2f(a) == 0.0 because b2f(a) can only be 0 or 1
+   # inot(a)
+   (('fge', 0.0, ('b2f', a)), ('inot', a)),
+
    (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)),
    (('bcsel', ('flt', a, b), a, b), ('fmin', a, b)),
    (('bcsel', ('flt', a, b), b, a), ('fmax', a, b)),