nir/algebraic: Simplify a contradiction that can occur in __flt64_nonnan

The pattern is added to opt_algebraic because, for example, comparisons
with constant 0.0 will produce (a1 < 0).

Even with a pass that optimized Boolean expressions, I think this would
be very difficult to automatically recognize and optimize.

Results on the 308 shaders extracted from the fp64 portion of the OpenGL
CTS:

Tiger Lake and Ice Lake had similar results. (Tiger Lake shown)
total instructions in shared programs: 933054 -> 929619 (-0.37%)
instructions in affected programs: 784041 -> 780606 (-0.44%)
helped: 59
HURT: 0
helped stats (abs) min: 2 max: 213 x̄: 58.22 x̃: 44
helped stats (rel) min: 0.02% max: 2.51% x̄: 0.72% x̃: 0.46%
95% mean confidence interval for instructions value: -70.80 -45.64
95% mean confidence interval for instructions %-change: -0.92% -0.53%
Instructions are helped.

total cycles in shared programs: 7304712 -> 7280180 (-0.34%)
cycles in affected programs: 7176260 -> 7151728 (-0.34%)
helped: 92
HURT: 0
helped stats (abs) min: 8 max: 1414 x̄: 266.65 x̃: 166
helped stats (rel) min: 0.04% max: 2.34% x̄: 0.43% x̃: 0.22%
95% mean confidence interval for cycles value: -333.05 -200.26
95% mean confidence interval for cycles %-change: -0.54% -0.31%
Cycles are helped.

Regular shader-db changes:

No changes on any Intel platform.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4142>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 5cbb9e7c3c2c69886f483b3b3f5b4b7954c26f30..7d9775950a4d596d519df681ce6f86e605583173 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -942,6 +942,7 @@ optimizations.extend([
    (('ilt', 'a(is_lt_zero)',      'b(is_not_negative)'), True),
 
    (('ult', 0, 'a(is_gt_zero)'), True),
+   (('ult', a, 0), False),
 
    # Packing and then unpacking does nothing
    (('unpack_64_2x32_split_x', ('pack_64_2x32_split', a, b)), a),