nir/algebraic: optimize bitfield_select(a, b, 0) to iand(a, b)
(src0 & src1) | (~src0 & src2) to (src0 & src1).
fossils-db (Polaris10):
Totals from 873 (0.63% of 138014) affected shaders:
SGPRs: 33781 -> 33733 (-0.14%)
VGPRs: 37704 -> 37520 (-0.49%); split: -0.51%, +0.02%
CodeSize: 3861460 -> 3853424 (-0.21%); split: -0.21%, +0.00%
MaxWaves: 5306 -> 5305 (-0.02%)
Instrs: 743798 -> 743486 (-0.04%); split: -0.04%, +0.00%
Cycles: 10962244 -> 10960936 (-0.01%); split: -0.01%, +0.00%
VMEM: 128309 -> 128350 (+0.03%); split: +0.33%, -0.30%
SMEM: 44797 -> 44113 (-1.53%); split: +0.02%, -1.54%
Copies: 71875 -> 71674 (-0.28%); split: -0.31%, +0.03%
PreSGPRs: 23484 -> 23479 (-0.02%)
PreVGPRs: 34582 -> 34529 (-0.15%)
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7479>
diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 987965d..3112623 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -1399,6 +1399,9 @@
('ubfe', 'value', 'offset', 'bits')),
'options->lower_bitfield_extract'),
+ # (src0 & src1) | (~src0 & src2). Constant fold if src2 is 0.
+ (('bitfield_select', a, b, 0), ('iand', a, b)),
+
# Note that these opcodes are defined to only use the five least significant bits of 'offset' and 'bits'
(('ubfe', 'value', 'offset', ('iand', 31, 'bits')), ('ubfe', 'value', 'offset', 'bits')),
(('ubfe', 'value', ('iand', 31, 'offset'), 'bits'), ('ubfe', 'value', 'offset', 'bits')),