Mesa (main): nir/opt_algebraic: Optimize Doom Eternal's word extract by LSB.

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Module: Mesa
Branch: main
Commit: bc5c68fc08fb40026fff9775c221860885c2aacc
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=bc5c68fc08fb40026fff9775c221860885c2aacc

Author: Georg Lehmann <dadschoorse at gmail.com>
Date:   Tue May 10 17:26:42 2022 +0200

nir/opt_algebraic: Optimize Doom Eternal's word extract by LSB.

Foz-db GFX10_3:
Totals from 419 (0.31% of 134913) affected shaders:
CodeSize: 4126032 -> 4121756 (-0.10%)
Instrs: 783608 -> 782541 (-0.14%)
Latency: 7889664 -> 7888521 (-0.01%); split: -0.02%, +0.00%
InvThroughput: 1315690 -> 1314863 (-0.06%); split: -0.06%, +0.00%
VClause: 11826 -> 11830 (+0.03%)
SClause: 27736 -> 27734 (-0.01%)
Copies: 50493 -> 50428 (-0.13%); split: -0.13%, +0.01%
PreSGPRs: 23264 -> 23265 (+0.00%)

Signed-off-by: Georg Lehmann <dadschoorse at gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16436>

---

 src/compiler/nir/nir_opt_algebraic.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 9f73c336beb..e7f21ad0b7f 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -30,6 +30,7 @@ from nir_opcodes import type_sizes
 import itertools
 import struct
 from math import pi
+import math
 
 # Convenience variables
 a = 'a'
@@ -1012,6 +1013,8 @@ for op in ['iand', 'ior', 'ixor']:
 
 # Integer sizes
 for s in [8, 16, 32, 64]:
+    last_shift_bit = int(math.log2(s)) - 1
+
     optimizations.extend([
        (('iand', ('ieq', 'a@{}'.format(s), 0), ('ieq', 'b@{}'.format(s), 0)), ('ieq', ('ior', a, b), 0), 'options->lower_umax'),
        (('ior',  ('ine', 'a@{}'.format(s), 0), ('ine', 'b@{}'.format(s), 0)), ('ine', ('ior', a, b), 0), 'options->lower_umin'),
@@ -1027,6 +1030,7 @@ for s in [8, 16, 32, 64]:
        (('ishl', 'a@{}'.format(s), ('iand', s - 1, b)), ('ishl', a, b)),
        (('ishr', 'a@{}'.format(s), ('iand', s - 1, b)), ('ishr', a, b)),
        (('ushr', 'a@{}'.format(s), ('iand', s - 1, b)), ('ushr', a, b)),
+       (('ushr', 'a@{}'.format(s), ('ishl(is_used_once)', ('iand', b, 1), last_shift_bit)), ('ushr', a, ('ishl', b, last_shift_bit))),
     ])
 
 optimizations.extend([