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nir/opt_algebraic: optimize signed pow in Control

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used in a post-processing shader which goes 896 instrs -> 749 instrs.

In my Control fossil:

   Totals from 2 (0.63% of 319) affected shaders:
   Instrs: 2078 -> 1841 (-11.41%)
   CodeSize: 14540 -> 12800 (-11.97%)
   ALU: 1779 -> 1626 (-8.60%)
   FSCIB: 1779 -> 1626 (-8.60%)
   Uniforms: 370 -> 372 (+0.54%)

In radv_fossils, there are affected shaders in Dredge.

   Totals from 4 (0.01% of 54019) affected shaders:
   Instrs: 2306 -> 2294 (-0.52%)
   CodeSize: 16594 -> 16534 (-0.36%)
   ALU: 2010 -> 2004 (-0.30%)
   FSCIB: 2010 -> 2004 (-0.30%)
   Uniforms: 1138 -> 1146 (+0.70%)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35989>
This commit is contained in:
Alyssa Rosenzweig
2025-07-07 13:01:31 -04:00
committed by Marge Bot
parent 2765017553
commit 042adf3cc5
1 changed files with 12 additions and 0 deletions
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src/compiler/nir/nir_opt_algebraic.py
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@@ -1146,6 +1146,18 @@ for s in [16, 32, 64]:
(('bcsel@{}'.format(s), ('feq', a, 0.0), 1.0, ('i2f{}'.format(s), ('iadd', ('b2i{}'.format(s), ('flt', 0.0, 'a@{}'.format(s))), ('ineg', ('b2i{}'.format(s), ('flt', 'a@{}'.format(s), 0.0)))))),
('i2f{}'.format(s), ('iadd', ('b2i32', ('!fge', a, 0.0)), ('ineg', ('b2i32', ('!flt', a, 0.0)))))),
# Signed pow() used in Control. It's not enough to match just the
# copysign piece because we would require extra instructions to handle
# the various floating point special cases. Specializing to the pow
# sequence lets us collapse all the sign fixup code.
(('fmul', ('fexp2', ('fmul', ('flog2', ('fabs', a)), b)),
('i2f', ('iadd', ('b2i', ('flt', 0.0, a)),
('ineg', ('b2i', ('flt', a, 0.0)))))),
('bcsel', ('!flt', a, 0.0),
('fneg', ('fexp2', ('fmul', ('flog2', ('fabs', a)), b))),
('fexp2', ('fmul', ('flog2', ('fabs', a)), b)))),
(('bcsel', a, ('b2f(is_used_once)', 'b@{}'.format(s)), ('b2f', 'c@{}'.format(s))), ('b2f', ('bcsel', a, b, c))),
# The C spec says, "If the value of the integral part cannot be represented