nir/algebraic: Use value range analysis to eliminate tautological compares not used by if-statements

This just eliminates tautological / contradictory compares that are used
for bcsel and other non-if-statement cases.  If-statements are not
affected because removing flow control can cause the i965 instrution
scheduler to create some very long live ranges resulting in unncessary
spilling.  This causes some shaders to fall of a performance cliff.

Since many small if-statements are already flattened to bcsel, this
optimization covers more than 68% of the possible cases (2417 shaders
helped for instructions on Skylake vs. 3554).

v2: Reorder and add whitespace to make the relationship between the
patterns more obvious.  Suggested by Caio.

All Gen7+ platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 16333474 -> 16322028 (-0.07%)
instructions in affected programs: 438559 -> 427113 (-2.61%)
helped: 1765
HURT: 0
helped stats (abs) min: 1 max: 275 x̄: 6.48 x̃: 4
helped stats (rel) min: 0.20% max: 36.36% x̄: 4.07% x̃: 1.82%
95% mean confidence interval for instructions value: -6.87 -6.10
95% mean confidence interval for instructions %-change: -4.30% -3.84%
Instructions are helped.

total cycles in shared programs: 367608554 -> 367511103 (-0.03%)
cycles in affected programs: 8368829 -> 8271378 (-1.16%)
helped: 1541
HURT: 129
helped stats (abs) min: 1 max: 4468 x̄: 66.78 x̃: 39
helped stats (rel) min: 0.01% max: 45.69% x̄: 4.10% x̃: 2.17%
HURT stats (abs)   min: 1 max: 973 x̄: 42.25 x̃: 10
HURT stats (rel)   min: 0.02% max: 64.39% x̄: 2.15% x̃: 0.60%
95% mean confidence interval for cycles value: -64.90 -51.81
95% mean confidence interval for cycles %-change: -3.89% -3.36%
Cycles are helped.

total spills in shared programs: 8867 -> 8868 (0.01%)
spills in affected programs: 18 -> 19 (5.56%)
helped: 0
HURT: 1

total fills in shared programs: 21900 -> 21903 (0.01%)
fills in affected programs: 78 -> 81 (3.85%)
helped: 0
HURT: 1

All Gen6 and earlier platforms had similar results. (Sandy Bridge shown)
total instructions in shared programs: 10829877 -> 10829247 (<.01%)
instructions in affected programs: 30240 -> 29610 (-2.08%)
helped: 177
HURT: 0
helped stats (abs) min: 1 max: 15 x̄: 3.56 x̃: 3
helped stats (rel) min: 0.37% max: 17.39% x̄: 2.68% x̃: 1.94%
95% mean confidence interval for instructions value: -3.93 -3.18
95% mean confidence interval for instructions %-change: -3.04% -2.32%
Instructions are helped.

total cycles in shared programs: 154036580 -> 154035437 (<.01%)
cycles in affected programs: 352402 -> 351259 (-0.32%)
helped: 96
HURT: 28
helped stats (abs) min: 1 max: 128 x̄: 14.73 x̃: 6
helped stats (rel) min: 0.03% max: 24.00% x̄: 1.51% x̃: 0.46%
HURT stats (abs)   min: 1 max: 117 x̄: 9.68 x̃: 4
HURT stats (rel)   min: 0.03% max: 2.24% x̄: 0.43% x̃: 0.23%
95% mean confidence interval for cycles value: -13.40 -5.03
95% mean confidence interval for cycles %-change: -1.62% -0.53%
Cycles are helped.

Reviewed-by: Caio Marcelo de Oliveira Filho <[email protected]>

1 files changed, 28 insertions, 0 deletions

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index 29ef4eb13bf..d3f6c196e3b 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -798,6 +798,34 @@ optimizations = [
    (('fmax', ('fadd', ('fmul', ('fsat', a), ('fneg', ('fsat', a))), 1.0), 0.0), ('fadd', ('fmul', ('fsat', a), ('fneg', ('fsat', a))), 1.0)),
    (('fmax', ('fadd', ('fneg', ('fmul', ('fsat', a), ('fsat', a))), 1.0), 0.0), ('fadd', ('fneg', ('fmul', ('fsat', a), ('fsat', a))), 1.0)),
 
+   (('fne(is_not_used_by_if)', 'a(is_not_zero)', 0.0), True),
+   (('feq(is_not_used_by_if)', 'a(is_not_zero)', 0.0), False),
+
+   (('fge(is_not_used_by_if)', 'a(is_not_negative)', 'b(is_not_positive)'), True),
+   (('fge(is_not_used_by_if)', 'b(is_not_positive)', 'a(is_gt_zero)'),      False),
+   (('fge(is_not_used_by_if)', 'a(is_lt_zero)',      'b(is_not_negative)'), False),
+   (('fge(is_not_used_by_if)', 'b(is_not_negative)', 'a(is_not_positive)'), True),
+
+   (('flt(is_not_used_by_if)', 'a(is_not_negative)', 'b(is_not_positive)'), False),
+   (('flt(is_not_used_by_if)', 'b(is_not_positive)', 'a(is_gt_zero)'),      True),
+   (('flt(is_not_used_by_if)', 'a(is_lt_zero)',      'b(is_not_negative)'), True),
+   (('flt(is_not_used_by_if)', 'b(is_not_negative)', 'a(is_not_positive)'), False),
+
+   (('ine(is_not_used_by_if)', 'a(is_not_zero)', 0), True),
+   (('ieq(is_not_used_by_if)', 'a(is_not_zero)', 0), False),
+
+   (('ige(is_not_used_by_if)', 'a(is_not_negative)', 'b(is_not_positive)'), True),
+   (('ige(is_not_used_by_if)', 'b(is_not_positive)', 'a(is_gt_zero)'),      False),
+   (('ige(is_not_used_by_if)', 'a(is_lt_zero)',      'b(is_not_negative)'), False),
+   (('ige(is_not_used_by_if)', 'b(is_not_negative)', 'a(is_not_positive)'), True),
+
+   (('ilt(is_not_used_by_if)', 'a(is_not_negative)', 'b(is_not_positive)'), False),
+   (('ilt(is_not_used_by_if)', 'b(is_not_positive)', 'a(is_gt_zero)'),      True),
+   (('ilt(is_not_used_by_if)', 'a(is_lt_zero)',      'b(is_not_negative)'), True),
+   (('ilt(is_not_used_by_if)', 'b(is_not_negative)', 'a(is_not_positive)'), False),
+
+   (('ult(is_not_used_by_if)', 0, 'a(is_gt_zero)'), True),
+
    # Packing and then unpacking does nothing
    (('unpack_64_2x32_split_x', ('pack_64_2x32_split', a, b)), a),
    (('unpack_64_2x32_split_y', ('pack_64_2x32_split', a, b)), b),