nir/algebraic: optimize fmul(x, bcsel(c, -1.0, 1.0)) -> bcsel(c, -x, x)

Totals from affected shaders: (VEGA)
SGPRS: 545712 -> 545712 (0.00 %)
VGPRS: 413092 -> 413116 (0.01 %)
Spilled SGPRs: 10616 -> 10616 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 37031684 -> 36984248 (-0.13 %) bytes
LDS: 427 -> 427 (0.00 %) blocks
Max Waves: 54350 -> 54340 (-0.02 %)

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4830>

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 6a94d4043094fb85917582c32cb1b8f4ba86e3c4..bd84966821acb8dfd8ec1d9e6447ed1be50f0746 100644 (file)
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -1134,6 +1134,9 @@ optimizations.extend([
 
    (('bcsel', ('ine', a, -1), ('ifind_msb', a), -1), ('ifind_msb', a)),
 
+   (('~fmul', ('bcsel(is_used_once)', c, -1.0, 1.0), b), ('bcsel', c, ('fneg', b), b)),
+   (('~fmul', ('bcsel(is_used_once)', c, 1.0, -1.0), b), ('bcsel', c, b, ('fneg', b))),
+
    (('fmin3@64', a, b, c), ('fmin@64', a, ('fmin@64', b, c))),
    (('fmax3@64', a, b, c), ('fmax@64', a, ('fmax@64', b, c))),
    (('fmed3@64', a, b, c), ('fmax@64', ('fmin@64', ('fmax@64', a, b), c), ('fmin@64', a, b))),