Mesa (main): pan/va: Lower MUX to CSEL where possible

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Module: Mesa
Branch: main
Commit: 677a66b3eb5e2059d29004039367366a3217936b
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=677a66b3eb5e2059d29004039367366a3217936b

Author: Alyssa Rosenzweig <alyssa at collabora.com>
Date:   Fri May  6 17:10:56 2022 -0400

pan/va: Lower MUX to CSEL where possible

CSEL executes on the conversion unit (CVT), while MUX executes on the special
function unit (SFU). Throughput on CVT is 4x higher than SFU, so this is
(almost) always an optimization.

The "real" MUX is still used for unusual cases, like 8-bit and bitselect.

Note that it's easier for us to use MUX everywhere for the IR. This is an easy
fixup to get better codegen on Valhall without touching the core Bifrost code.

shader-db is a bit of a toss up: register pressure and instruction count are
hurt in some cases due to restrictions on FAU access. In particular, a shader
that muxes between two uniforms needs an extra move due to extra constant
(zero). However, in terms of throughput this is still a win: 2 CVT instructions
(MOV + CSEL) have 2x throughput to 1 SFU instruction (MUX). The MOV has
opportunities for CSE, but that can hurt pressure in turn. Overall, cycles are
helped substantially.

total instructions in shared programs: 2728438 -> 2731597 (0.12%)
instructions in affected programs: 414391 -> 417550 (0.76%)
helped: 87
HURT: 1063
helped stats (abs) min: 1.0 max: 6.0 x̄: 5.17 x̃: 6
helped stats (rel) min: 0.19% max: 15.79% x̄: 4.12% x̃: 4.11%
HURT stats (abs)   min: 1.0 max: 56.0 x̄: 3.40 x̃: 2
HURT stats (rel)   min: 0.11% max: 23.43% x̄: 1.15% x̃: 0.63%
95% mean confidence interval for instructions value: 2.47 3.03
95% mean confidence interval for instructions %-change: 0.61% 0.90%
Instructions are HURT.

total cycles in shared programs: 142103 -> 142015.75 (-0.06%)
cycles in affected programs: 1263.45 -> 1176.20 (-6.91%)
helped: 281
HURT: 176
helped stats (abs) min: 0.015625 max: 2.234375 x̄: 0.50 x̃: 0
helped stats (rel) min: 0.71% max: 54.17% x̄: 16.93% x̃: 15.31%
HURT stats (abs)   min: 0.015625 max: 30.0 x̄: 0.30 x̃: 0
HURT stats (rel)   min: 0.84% max: 120.00% x̄: 7.16% x̃: 5.00%
95% mean confidence interval for cycles value: -0.33 -0.05
95% mean confidence interval for cycles %-change: -9.08% -6.22%
Cycles are helped.

total cvt in shared programs: 13983.34 -> 14891.70 (6.50%)
cvt in affected programs: 7498.36 -> 8406.72 (12.11%)
helped: 71
HURT: 4711
helped stats (abs) min: 0.0625 max: 0.0625 x̄: 0.06 x̃: 0
helped stats (rel) min: 5.41% max: 40.00% x̄: 10.23% x̃: 9.30%
HURT stats (abs)   min: 0.015625 max: 2.640625 x̄: 0.19 x̃: 0
HURT stats (rel)   min: 0.18% max: 141.18% x̄: 16.21% x̃: 9.52%
95% mean confidence interval for cvt value: 0.18 0.20
95% mean confidence interval for cvt %-change: 15.21% 16.42%
Cvt are HURT.

total sfu in shared programs: 11320.44 -> 7882.56 (-30.37%)
sfu in affected programs: 7618.50 -> 4180.62 (-45.13%)
helped: 4782
HURT: 0
helped stats (abs) min: 0.0625 max: 10.5625 x̄: 0.72 x̃: 0
helped stats (rel) min: 1.34% max: 100.00% x̄: 41.91% x̃: 37.50%
95% mean confidence interval for sfu value: -0.75 -0.68
95% mean confidence interval for sfu %-change: -42.68% -41.14%
Sfu are helped.

total ls in shared programs: 129660 -> 129690 (0.02%)
ls in affected programs: 25 -> 55 (120.00%)
helped: 0
HURT: 1

total quadwords in shared programs: 1482728 -> 1484128 (0.09%)
quadwords in affected programs: 58624 -> 60024 (2.39%)
helped: 24
HURT: 195
helped stats (abs) min: 8.0 max: 8.0 x̄: 8.00 x̃: 8
helped stats (rel) min: 3.70% max: 20.00% x̄: 10.34% x̃: 10.00%
HURT stats (abs)   min: 8.0 max: 24.0 x̄: 8.16 x̃: 8
HURT stats (rel)   min: 1.41% max: 50.00% x̄: 4.84% x̃: 2.56%
95% mean confidence interval for quadwords value: 5.70 7.09
95% mean confidence interval for quadwords %-change: 2.22% 4.14%
Quadwords are HURT.

total spills in shared programs: 125 -> 127 (1.60%)
spills in affected programs: 0 -> 2
helped: 0
HURT: 1

total fills in shared programs: 800 -> 828 (3.50%)
fills in affected programs: 0 -> 28
helped: 0
HURT: 1

Signed-off-by: Alyssa Rosenzweig <alyssa at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16857>

---

 src/panfrost/bifrost/valhall/va_lower_isel.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/panfrost/bifrost/valhall/va_lower_isel.c b/src/panfrost/bifrost/valhall/va_lower_isel.c
index 2be3df67a32..ad54a9352ba 100644
--- a/src/panfrost/bifrost/valhall/va_lower_isel.c
+++ b/src/panfrost/bifrost/valhall/va_lower_isel.c
@@ -104,6 +104,13 @@ va_lower_isel(bi_instr *I)
 
       break;
 
+   case BI_OPCODE_MUX_I32:
+   case BI_OPCODE_MUX_V2I16:
+      if (bi_can_replace_with_csel(I))
+         bi_replace_mux_with_csel(I, true);
+
+      break;
+
    default:
       break;
    }