Mesa (master): nir/algebraic: distribute imul(iadd(a, b), c) when b and c are constants

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Module: Mesa
Branch: master
Commit: 77d6fda0f50218c2a37f9229a210ca749f824255
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=77d6fda0f50218c2a37f9229a210ca749f824255

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Wed Nov  4 13:56:41 2020 +0100

nir/algebraic: distribute imul(iadd(a, b), c) when b and c are constants

This distributes imul(iadd(a, b), c) to iadd(imul(a, c), b * c)
when both b and c are constants. This might allow some compiler
backends to create more MADs.

For ACO, this allows to combine more DS additions.

fossilds-db (Vega10):
Totals from 673 (0.49% of 136546) affected shaders:
VGPRs: 44548 -> 44516 (-0.07%); split: -0.11%, +0.04%
CodeSize: 8301552 -> 8286220 (-0.18%); split: -0.19%, +0.01%
MaxWaves: 2731 -> 2735 (+0.15%); split: +0.26%, -0.11%
Instrs: 1642684 -> 1638725 (-0.24%); split: -0.24%, +0.00%
Cycles: 20846156 -> 20793444 (-0.25%); split: -0.25%, +0.00%
VMEM: 108870 -> 108106 (-0.70%); split: +0.03%, -0.73%
SMEM: 35718 -> 35674 (-0.12%); split: +0.22%, -0.34%
VClause: 20603 -> 20622 (+0.09%); split: -0.01%, +0.10%
SClause: 48527 -> 48539 (+0.02%)
Copies: 156735 -> 156742 (+0.00%); split: -0.05%, +0.05%
PreSGPRs: 43169 -> 43166 (-0.01%); split: -0.02%, +0.02%
PreVGPRs: 41369 -> 41330 (-0.09%)

shader-db results on Intel:
Ice Lake
total instructions in shared programs: 20027588 -> 20027446 (<.01%)
instructions in affected programs: 71766 -> 71624 (-0.20%)
helped: 70
HURT: 0
helped stats (abs) min: 1 max: 7 x̄: 2.03 x̃: 1
helped stats (rel) min: 0.10% max: 2.50% x̄: 0.29% x̃: 0.15%
95% mean confidence interval for instructions value: -2.42 -1.64
95% mean confidence interval for instructions %-change: -0.38% -0.20%
Instructions are helped.

total cycles in shared programs: 977525222 -> 977494323 (<.01%)
cycles in affected programs: 8884593 -> 8853694 (-0.35%)
helped: 56
HURT: 16
helped stats (abs) min: 2 max: 7852 x̄: 681.29 x̃: 400
helped stats (rel) min: <.01% max: 19.84% x̄: 2.79% x̃: 0.41%
HURT stats (abs)   min: 2 max: 1212 x̄: 453.31 x̃: 120
HURT stats (rel)   min: 0.05% max: 1.09% x̄: 0.32% x̃: 0.11%
95% mean confidence interval for cycles value: -802.75 -55.56
95% mean confidence interval for cycles %-change: -3.19% -1.01%
Cycles are helped.

total sends in shared programs: 1032273 -> 1032272 (<.01%)
sends in affected programs: 41 -> 40 (-2.44%)
helped: 1
HURT: 0

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Eric Anholt <eric at anholt.net>
Reviewed-by: Rhys Perry <pendingchaos02 at gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7445>

---

 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 d095591f37b..987965d23d6 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -302,6 +302,9 @@ optimizations.extend([
    # instruction or a constant offset field for in load / store instructions.
    (('ishl', ('iadd', a, '#b'), '#c'), ('iadd', ('ishl', a, c), ('ishl', b, c))),
 
+   # (a + #b) * #c
+   (('imul', ('iadd(is_used_once)', a, '#b'), '#c'), ('iadd', ('imul', a, c), ('imul', b, c))),
+
    # Comparison simplifications
    (('~inot', ('flt', a, b)), ('fge', a, b)),
    (('~inot', ('fge', a, b)), ('flt', a, b)),