[Mesa-dev] [PATCH 6/6] nir: Don't condition 'a-b < 0' -> 'a < b' on is_not_used_by_conditional

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

Now that i965 recognizes that a-b generates the same conditions as 'a <
b', there is no reason to condition this transformation on 'is not used
by conditional.'

Since this was the only user of the is_not_used_by_conditional function,
delete it.

All Gen6+ platforms had similar results. (Skylake shown)
total instructions in shared programs: 14400775 -> 14400595 (<.01%)
instructions in affected programs: 36712 -> 36532 (-0.49%)
helped: 182
HURT: 26
helped stats (abs) min: 1 max: 2 x̄: 1.13 x̃: 1
helped stats (rel) min: 0.15% max: 1.82% x̄: 0.70% x̃: 0.62%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 0.24% max: 1.02% x̄: 0.82% x̃: 0.90%
95% mean confidence interval for instructions value: -0.97 -0.76
95% mean confidence interval for instructions %-change: -0.59% -0.43%
Instructions are helped.

total cycles in shared programs: 532929592 -> 532926345 (<.01%)
cycles in affected programs: 478660 -> 475413 (-0.68%)
helped: 187
HURT: 22
helped stats (abs) min: 2 max: 200 x̄: 20.99 x̃: 18
helped stats (rel) min: 0.23% max: 24.10% x̄: 1.48% x̃: 1.03%
HURT stats (abs)   min: 1 max: 214 x̄: 30.86 x̃: 11
HURT stats (rel)   min: 0.01% max: 23.06% x̄: 3.12% x̃: 0.86%
95% mean confidence interval for cycles value: -19.50 -11.57
95% mean confidence interval for cycles %-change: -1.42% -0.58%
Cycles are helped.

GM45 and Iron Lake had similar results. (Iron Lake shown)
total cycles in shared programs: 177851578 -> 177851810 (<.01%)
cycles in affected programs: 24408 -> 24640 (0.95%)
helped: 2
HURT: 4
helped stats (abs) min: 4 max: 4 x̄: 4.00 x̃: 4
helped stats (rel) min: 0.42% max: 0.47% x̄: 0.44% x̃: 0.44%
HURT stats (abs)   min: 24 max: 108 x̄: 60.00 x̃: 54
HURT stats (rel)   min: 0.52% max: 1.62% x̄: 1.04% x̃: 1.02%
95% mean confidence interval for cycles value: -7.75 85.08
95% mean confidence interval for cycles %-change: -0.39% 1.49%
Inconclusive result (value mean confidence interval includes 0).

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/compiler/nir/nir_opt_algebraic.py |  4 +---
 src/compiler/nir/nir_search_helpers.h | 15 ---------------
 2 files changed, 1 insertion(+), 18 deletions(-)

diff --git a/src/compiler/nir/nir_opt_algebraic.py b/src/compiler/nir/nir_opt_algebraic.py
index b9565ce..96232f0 100644
--- a/src/compiler/nir/nir_opt_algebraic.py
+++ b/src/compiler/nir/nir_opt_algebraic.py
@@ -208,9 +208,7 @@ optimizations = [
    # fmax.  If b is > 1.0, the bcsel will be replaced with a b2f.
    (('fmin', ('b2f', a), '#b'), ('bcsel', a, ('fmin', b, 1.0), ('fmin', b, 0.0))),
 
-   # ignore this opt when the result is used by a bcsel or if so we can make
-   # use of conditional modifiers on supported hardware.
-   (('flt(is_not_used_by_conditional)', ('fadd(is_used_once)', a, ('fneg', b)), 0.0), ('flt', a, b)),
+   (('flt', ('fadd(is_used_once)', a, ('fneg', b)), 0.0), ('flt', a, b)),
 
    (('fge', ('fneg', ('fabs', a)), 0.0), ('feq', a, 0.0)),
    (('~bcsel', ('flt', b, a), b, a), ('fmin', a, b)),
diff --git a/src/compiler/nir/nir_search_helpers.h b/src/compiler/nir/nir_search_helpers.h
index 2e3bd13..2d399bd 100644
--- a/src/compiler/nir/nir_search_helpers.h
+++ b/src/compiler/nir/nir_search_helpers.h
@@ -170,19 +170,4 @@ is_not_used_by_if(nir_alu_instr *instr)
    return list_empty(&instr->dest.dest.ssa.if_uses);
 }
 
-static inline bool
-is_not_used_by_conditional(nir_alu_instr *instr)
-{
-   if (!is_not_used_by_if(instr))
-      return false;
-
-   nir_foreach_use(use, &instr->dest.dest.ssa) {
-      if (use->parent_instr->type == nir_instr_type_alu &&
-          nir_instr_as_alu(use->parent_instr)->op == nir_op_bcsel)
-         return false;
-   }
-
-   return true;
-}
-
 #endif /* _NIR_SEARCH_ */
-- 
2.9.5