nir/algebraic: a & ~(a >> 31) -> imax(a, 0)

Found in some Doom shaders

Totals from affected shaders:
SGPRS: 30056 -> 30064 (0.03 %)
VGPRS: 28024 -> 28024 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Code Size: 4278648 -> 4270852 (-0.18 %) bytes
Max Waves: 1476 -> 1476 (0.00 %)
Instructions: 835287 -> 833338 (-0.23 %)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3089>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3089>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 633ee8792d9f5535c7b63691fe91254a50db4133..fbf0f6944309dc1d94aaacd6eb4f91baf4efc6f6 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -480,6 +480,7 @@ optimizations.extend([
    (('fmin', ('fmin', a, b), b), ('fmin', a, b)),
    (('umin', ('umin', a, b), b), ('umin', a, b)),
    (('imin', ('imin', a, b), b), ('imin', a, b)),
+   (('iand@32', a, ('inot', ('ishr', a, 31))), ('imax', a, 0)),
    (('fmax', a, ('fneg', a)), ('fabs', a)),
    (('imax', a, ('ineg', a)), ('iabs', a)),
    (('fmin', a, ('fneg', a)), ('fneg', ('fabs', a))),