nir/opt_peephole_select: Don't count some unary operations

In many cases, fsat, fneg, fabs, ineg, and iabs will get folded into
another instruction as either source or destination modifiers.
Counting them as instructions means that some if-statements won't get
converted to selects.  For example,

        vec1 32 ssa_25 = flt32 ssa_0, ssa_23.x
        /* succs: block_1 block_2 */
        if ssa_25 {
                block block_1:
                /* preds: block_0 */
                vec1 32 ssa_26 = fabs ssa_24
                vec1 32 ssa_27 = fneg ssa_26
                vec1 32 ssa_28 = fabs ssa_20
                vec1 32 ssa_29 = fneg ssa_28
                vec1 32 ssa_30 = fmul ssa_27, ssa_29
                vec1 32 ssa_31 = fsat ssa_30
                /* succs: block_3 */
        } else {
                block block_2:
                /* preds: block_0 */
                /* succs: block_3 */
        }
        block block_3:
        /* preds: block_1 block_2 */

block_1 isn't really 6 instructions, but it will be counted that way.

Most callers of the peephole_select pass use either 1 or 8.  It's very
easy to blow way past either of these limits with things that are really
only one or two actual instructions.

I also tried some fancier things like making sure the fsat was of
another SSA def from the same block, but the simple test was actually
better.

The i965 back-end SEL peephole pass still helps ~700 shaders in
shader-db with this change.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
All Gen6+ platforms had similar results. (Ice Lake shown)
total instructions in shared programs: 14743694 -> 14738910 (-0.03%)
instructions in affected programs: 156575 -> 151791 (-3.06%)
helped: 1204
HURT: 0
helped stats (abs) min: 1 max: 27 x̄: 3.97 x̃: 3
helped stats (rel) min: 0.15% max: 19.57% x̄: 5.15% x̃: 4.55%
95% mean confidence interval for instructions value: -4.12 -3.82
95% mean confidence interval for instructions %-change: -5.35% -4.95%
Instructions are helped.

total cycles in shared programs: 231749141 -> 231602916 (-0.06%)
cycles in affected programs: 2818975 -> 2672750 (-5.19%)
helped: 876
HURT: 322
helped stats (abs) min: 2 max: 788 x̄: 180.99 x̃: 220
helped stats (rel) min: <.01% max: 43.82% x̄: 20.75% x̃: 19.44%
HURT stats (abs)   min: 1 max: 1188 x̄: 38.27 x̃: 20
HURT stats (rel)   min: 0.09% max: 102.67% x̄: 5.17% x̃: 1.70%
95% mean confidence interval for cycles value: -130.47 -113.64
95% mean confidence interval for cycles %-change: -14.85% -12.72%
Cycles are helped.

total sends in shared programs: 730495 -> 730491 (<.01%)
sends in affected programs: 46 -> 42 (-8.70%)
helped: 2
HURT: 0

Iron Lake and GM45 had similar results. (Iron Lake shown)
total instructions in shared programs: 8122757 -> 8122617 (<.01%)
instructions in affected programs: 14716 -> 14576 (-0.95%)
helped: 46
HURT: 1
helped stats (abs) min: 1 max: 8 x̄: 3.07 x̃: 3
helped stats (rel) min: 0.36% max: 10.00% x̄: 2.54% x̃: 1.06%
HURT stats (abs)   min: 1 max: 1 x̄: 1.00 x̃: 1
HURT stats (rel)   min: 1.59% max: 1.59% x̄: 1.59% x̃: 1.59%
95% mean confidence interval for instructions value: -3.42 -2.54
95% mean confidence interval for instructions %-change: -3.28% -1.62%
Instructions are helped.

total cycles in shared programs: 188510100 -> 188509780 (<.01%)
cycles in affected programs: 58994 -> 58674 (-0.54%)
helped: 32
HURT: 1
helped stats (abs) min: 2 max: 96 x̄: 10.06 x̃: 6
helped stats (rel) min: 0.05% max: 15.29% x̄: 1.37% x̃: 0.31%
HURT stats (abs)   min: 2 max: 2 x̄: 2.00 x̃: 2
HURT stats (rel)   min: 0.68% max: 0.68% x̄: 0.68% x̃: 0.68%
95% mean confidence interval for cycles value: -16.34 -3.06
95% mean confidence interval for cycles %-change: -2.46% -0.15%
Cycles are helped.

diff --git a/src/compiler/nir/nir_opt_peephole_select.c b/src/compiler/nir/nir_opt_peephole_select.c
index 14f36e7..869f663 100644 (file)
--- a/src/compiler/nir/nir_opt_peephole_select.c
+++ b/src/compiler/nir/nir_opt_peephole_select.c
@@ -27,6 +27,7 @@
 
 #include "nir.h"
 #include "nir_control_flow.h"
+#include "nir_search_helpers.h"
 
 /*
  * Implements a small peephole optimization that looks for
@@ -107,6 +108,8 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
 
       case nir_instr_type_alu: {
          nir_alu_instr *mov = nir_instr_as_alu(instr);
+         bool movelike = false;
+
          switch (mov->op) {
          case nir_op_mov:
          case nir_op_fneg:
@@ -116,6 +119,7 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
          case nir_op_vec2:
          case nir_op_vec3:
          case nir_op_vec4:
+            movelike = true;
             break;
 
          case nir_op_fcos:
@@ -148,8 +152,18 @@ block_check_for_allowed_instrs(nir_block *block, unsigned *count,
          if (!mov->dest.dest.is_ssa)
             return false;
 
+         const struct nir_block *const expected_block = mov->instr.block;
+         const nir_alu_type expected_type =
+            nir_alu_type_get_base_type(nir_op_infos[mov->op].output_type);
+
          if (alu_ok) {
-            (*count)++;
+            /* If the ALU operation is an fsat or a move-like operation, do
+             * not count it.  The expectation is that it will eventually be
+             * merged as a destination modifier or source modifier on some
+             * other instruction.
+             */
+            if (mov->op != nir_op_fsat && !movelike)
+               (*count)++;
          } else {
             /* Can't handle saturate */
             if (mov->dest.saturate)