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nir/opt_algebraic: generalize fmax(fadd(a, b), 0.0) to fsat by not requiring fneg

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Not a large effect, but it's positive and makes the pattern simpler.

Foz-DB Navi21:
Totals from 1 (0.00% of 79789) affected shaders:
Instrs: 145 -> 138 (-4.83%)
CodeSize: 784 -> 756 (-3.57%)
Latency: 1495 -> 1487 (-0.54%)
InvThroughput: 210 -> 196 (-6.67%)
VALU: 103 -> 96 (-6.80%)

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34125>
This commit is contained in:
Georg Lehmann 2025-03-22 06:53:20 +01:00 • committed by Marge Bot
parent 1050c69833
commit f71fc26393
1 changed files with 5 additions and 5 deletions
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10
src/compiler/nir/nir_opt_algebraic.py
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@ -1022,14 +1022,14 @@ optimizations.extend([
(('fmax', ('fneg', ('fmin', b, a)), b), ('fmax', ('fabs', b), ('fneg', a))),
(('fmin', ('fneg', ('fmax', b, a)), b), ('fmin', ('fneg', ('fabs', b)), ('fneg', a))),
# If a in [0,b] then b-a is also in [0,b]. Since b in [0,1], max(b-a, 0) =
# fsat(b-a).
# If a in [-b,0] then a+b is in [0,b]. Since b in [0,1], max(a+b, 0) =
# fsat(a+b).
#
# If a > b, then b-a < 0 and max(b-a, 0) = fsat(b-a) = 0
# If a < -b, then a+b < 0 and max(a+b, 0) = fsat(a+b) = 0
#
# This should be NaN safe since max(NaN, 0) = fsat(NaN) = 0.
(('fmax', ('fadd(is_used_once)', ('fneg', 'a(is_not_negative)'), '#b(is_zero_to_one)'), 0.0),
('fsat', ('fadd', ('fneg', a), b)), '!options->lower_fsat'),
(('fmax', ('fadd(is_used_once)', 'a(is_not_positive)', '#b(is_zero_to_one)'), 0.0),
('fsat', ('fadd', a, b)), '!options->lower_fsat'),
(('extract_u8', ('imin', ('imax', a, 0), 0xff), 0), ('imin', ('imax', a, 0), 0xff)),