Mesa (master): nir/algebraic: sign(x)*x*x is abs(x)*x

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Module: Mesa
Branch: master
Commit: 1546204cdd45476a2cc4ff4adcc742505366398f
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=1546204cdd45476a2cc4ff4adcc742505366398f

Author: Ian Romanick <ian.d.romanick at intel.com>
Date:   Mon Sep 10 10:39:42 2018 -0700

nir/algebraic: sign(x)*x*x is abs(x)*x

shader-db results:

All Gen7+ platforms had similar results. (Skylake shown)
total instructions in shared programs: 15106023 -> 15105981 (<.01%)
instructions in affected programs: 300 -> 258 (-14.00%)
helped: 6
HURT: 0
helped stats (abs) min: 7 max: 7 x̄: 7.00 x̃: 7
helped stats (rel) min: 14.00% max: 14.00% x̄: 14.00% x̃: 14.00%
95% mean confidence interval for instructions value: -7.00 -7.00
95% mean confidence interval for instructions %-change: -14.00% -14.00%
Instructions are helped.

total cycles in shared programs: 566050327 -> 566050075 (<.01%)
cycles in affected programs: 2826 -> 2574 (-8.92%)
helped: 6
HURT: 0
helped stats (abs) min: 40 max: 44 x̄: 42.00 x̃: 42
helped stats (rel) min: 8.89% max: 8.94% x̄: 8.92% x̃: 8.92%
95% mean confidence interval for cycles value: -44.30 -39.70
95% mean confidence interval for cycles %-change: -8.95% -8.88%
Cycles are helped.

No changes on Gen6 or earlier.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Reviewed-by: Thomas Helland <thomashelland90 at gmail.com>

---

 src/compiler/nir/nir_opt_algebraic.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index ae1261f874..3267e93a58 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -105,6 +105,11 @@ optimizations = [
    (('imul', a, 1), a),
    (('fmul', a, -1.0), ('fneg', a)),
    (('imul', a, -1), ('ineg', a)),
+   # If a < 0: fsign(a)*a*a => -1*a*a => -a*a => abs(a)*a
+   # If a > 0: fsign(a)*a*a => 1*a*a => a*a => abs(a)*a
+   # If a == 0: fsign(a)*a*a => 0*0*0 => abs(0)*0
+   (('fmul', ('fsign', a), ('fmul', a, a)), ('fmul', ('fabs', a), a)),
+   (('fmul', ('fmul', ('fsign', a), a), a), ('fmul', ('fabs', a), a)),
    (('~ffma', 0.0, a, b), b),
    (('~ffma', a, 0.0, b), b),
    (('~ffma', a, b, 0.0), ('fmul', a, b)),