Mesa (main): nir/algebraic: reassociate add chains for more MAD/FMA-friendly code

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Module: Mesa
Branch: main
Commit: f95a16be722a1ec3f101263af99d9408e6265f57
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=f95a16be722a1ec3f101263af99d9408e6265f57

Author: Rhys Perry <pendingchaos02 at gmail.com>
Date:   Wed Mar 17 19:54:38 2021 +0000

nir/algebraic: reassociate add chains for more MAD/FMA-friendly code

fossil-db (GFX10.3):
Totals from 25866 (17.68% of 146267) affected shaders:
VGPRs: 1625456 -> 1644936 (+1.20%); split: -0.05%, +1.24%
SpillSGPRs: 11729 -> 11725 (-0.03%); split: -0.07%, +0.03%
CodeSize: 161604460 -> 161458052 (-0.09%); split: -0.11%, +0.02%
MaxWaves: 454842 -> 452160 (-0.59%); split: +0.04%, -0.63%
Instrs: 30652596 -> 30456446 (-0.64%); split: -0.65%, +0.01%
Latency: 723098749 -> 722084247 (-0.14%); split: -0.21%, +0.07%
InvThroughput: 166023468 -> 165506875 (-0.31%); split: -0.36%, +0.05%

fossil-db (GFX10):
Totals from 25866 (17.68% of 146267) affected shaders:
VGPRs: 1593576 -> 1611976 (+1.15%); split: -0.09%, +1.25%
SpillSGPRs: 11729 -> 11725 (-0.03%); split: -0.07%, +0.03%
CodeSize: 162294468 -> 162154456 (-0.09%); split: -0.11%, +0.02%
MaxWaves: 477448 -> 474166 (-0.69%); split: +0.10%, -0.79%
Instrs: 30820164 -> 30625805 (-0.63%); split: -0.65%, +0.02%
Latency: 723190249 -> 722273445 (-0.13%); split: -0.20%, +0.08%
InvThroughput: 163114872 -> 162582966 (-0.33%); split: -0.37%, +0.04%

fossil-db (GFX9):
Totals from 25866 (17.67% of 146401) affected shaders:
SGPRs: 2167808 -> 2169920 (+0.10%); split: -0.09%, +0.19%
VGPRs: 1649404 -> 1667592 (+1.10%); split: -0.43%, +1.53%
CodeSize: 161273556 -> 161281996 (+0.01%); split: -0.07%, +0.08%
MaxWaves: 114910 -> 113519 (-1.21%); split: +0.10%, -1.31%
Instrs: 31557180 -> 31403708 (-0.49%); split: -0.50%, +0.02%
Latency: 899594793 -> 898786283 (-0.09%); split: -0.19%, +0.10%
InvThroughput: 412265691 -> 411551698 (-0.17%); split: -0.28%, +0.11%

Signed-off-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig at collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8056>

---

 src/compiler/nir/nir_opt_algebraic.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index c3ee63c83cd..4a9a72cc7f8 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -1376,6 +1376,9 @@ optimizations.extend([
    (('ior',  '#a', ('ior',  'b(is_not_const)', '#c')), ('ior',  ('ior',  a, c), b)),
    (('ixor', '#a', ('ixor', 'b(is_not_const)', '#c')), ('ixor', ('ixor', a, c), b)),
 
+   # Reassociate add chains for more MAD/FMA-friendly code
+   (('~fadd', ('fadd(is_used_once)', 'a(is_fmul)', 'b(is_fmul)'), 'c(is_not_fmul)'), ('fadd', ('fadd', a, c), b)),
+
    # Drop mul-div by the same value when there's no wrapping.
    (('idiv', ('imul(no_signed_wrap)', a, b), b), a),