intel/compiler: More peephole select

Shader-db results:

The one shader hurt for instructions is a compute shader that had both
spills and fills hurt.

v2: Fix typo in comment noticed by Caio.

v3: Fix inverted condition in brw_nir.c.  Noticed by Lionel.

Skylake, Broadwell, and Haswell had similar results. (Skylake shown)
total instructions in shared programs: 15072761 -> 15047884 (-0.17%)
instructions in affected programs: 895539 -> 870662 (-2.78%)
helped: 3623
HURT: 1
helped stats (abs) min: 1 max: 181 x̄: 6.89 x̃: 4
helped stats (rel) min: 0.10% max: 25.00% x̄: 3.93% x̃: 3.20%
HURT stats (abs)   min: 92 max: 92 x̄: 92.00 x̃: 92
HURT stats (rel)   min: 1.92% max: 1.92% x̄: 1.92% x̃: 1.92%
95% mean confidence interval for instructions value: -7.10 -6.63
95% mean confidence interval for instructions %-change: -4.03% -3.82%
Instructions are helped.

total cycles in shared programs: 369738930 -> 369535732 (-0.05%)
cycles in affected programs: 68027851 -> 67824653 (-0.30%)
helped: 2609
HURT: 1035
helped stats (abs) min: 1 max: 4508 x̄: 181.44 x̃: 77
helped stats (rel) min: <.01% max: 71.31% x̄: 9.14% x̃: 5.47%
HURT stats (abs)   min: 1 max: 33336 x̄: 261.04 x̃: 20
HURT stats (rel)   min: <.01% max: 47.61% x̄: 2.93% x̃: 1.47%
95% mean confidence interval for cycles value: -96.43 -15.09
95% mean confidence interval for cycles %-change: -6.07% -5.36%
Cycles are helped.

total spills in shared programs: 10158 -> 10159 (<.01%)
spills in affected programs: 166 -> 167 (0.60%)
helped: 1
HURT: 1

total fills in shared programs: 22105 -> 22116 (0.05%)
fills in affected programs: 837 -> 848 (1.31%)
helped: 4
HURT: 1

Ivy Bridge
total instructions in shared programs: 12021190 -> 11990256 (-0.26%)
instructions in affected programs: 910561 -> 879627 (-3.40%)
helped: 3344
HURT: 18
helped stats (abs) min: 1 max: 99 x̄: 9.29 x̃: 6
helped stats (rel) min: 0.11% max: 31.18% x̄: 5.19% x̃: 3.31%
HURT stats (abs)   min: 2 max: 20 x̄: 7.89 x̃: 6
HURT stats (rel)   min: 0.70% max: 2.59% x̄: 1.63% x̃: 1.70%
95% mean confidence interval for instructions value: -9.49 -8.91
95% mean confidence interval for instructions %-change: -5.32% -4.98%
Instructions are helped.

total cycles in shared programs: 179077826 -> 178570196 (-0.28%)
cycles in affected programs: 63205667 -> 62698037 (-0.80%)
helped: 2767
HURT: 620
helped stats (abs) min: 1 max: 7531 x̄: 217.58 x̃: 88
helped stats (rel) min: <.01% max: 75.86% x̄: 9.59% x̃: 6.09%
HURT stats (abs)   min: 1 max: 31255 x̄: 152.27 x̃: 11
HURT stats (rel)   min: <.01% max: 36.36% x̄: 2.77% x̃: 0.58%
95% mean confidence interval for cycles value: -173.94 -125.81
95% mean confidence interval for cycles %-change: -7.68% -6.97%
Cycles are helped.

Sandy Bridge
total instructions in shared programs: 10852569 -> 10843758 (-0.08%)
instructions in affected programs: 235803 -> 226992 (-3.74%)
helped: 800
HURT: 0
helped stats (abs) min: 1 max: 88 x̄: 11.01 x̃: 8
helped stats (rel) min: 0.11% max: 23.08% x̄: 4.69% x̃: 3.36%
95% mean confidence interval for instructions value: -11.93 -10.10
95% mean confidence interval for instructions %-change: -4.99% -4.39%
Instructions are helped.

total cycles in shared programs: 154732047 -> 154608941 (-0.08%)
cycles in affected programs: 4063110 -> 3940004 (-3.03%)
helped: 606
HURT: 253
helped stats (abs) min: 1 max: 2524 x̄: 227.93 x̃: 62
helped stats (rel) min: 0.02% max: 39.24% x̄: 4.36% x̃: 1.81%
HURT stats (abs)   min: 1 max: 1966 x̄: 59.36 x̃: 11
HURT stats (rel)   min: 0.02% max: 67.10% x̄: 3.22% x̃: 0.67%
95% mean confidence interval for cycles value: -170.49 -116.13
95% mean confidence interval for cycles %-change: -2.61% -1.65%
Cycles are helped.

No change on Iron Lake or GM45.

Signed-off-by: Ian Romanick <[email protected]>
Reviewed-by: Lionel Landwerlin <[email protected]>

1 files changed, 14 insertions, 1 deletions

diff --git a/src/intel/compiler/brw_nir.c b/src/intel/compiler/brw_nir.c
index e0aa927f2f4..3e547daf78a 100644
--- a/src/intel/compiler/brw_nir.c
+++ b/src/intel/compiler/brw_nir.c
@@ -569,7 +569,18 @@ brw_nir_optimize(nir_shader *nir, const struct brw_compiler *compiler,
       OPT(nir_opt_dce);
       OPT(nir_opt_cse);
 
-      /* For indirect loads of uniforms (push constants), we assume that array
+      /* Passing 0 to the peephole select pass causes it to convert
+       * if-statements that contain only move instructions in the branches
+       * regardless of the count.
+       *
+       * Passing 1 to the peephole select pass causes it to convert
+       * if-statements that contain at most a single ALU instruction (total)
+       * in both branches.  Before Gen6, some math instructions were
+       * prohibitively expensive and the results of compare operations need an
+       * extra resolve step.  For these reasons, this pass is more harmful
+       * than good on those platforms.
+       *
+       * For indirect loads of uniforms (push constants), we assume that array
        * indices will nearly always be in bounds and the cost of the load is
        * low.  Therefore there shouldn't be a performance benefit to avoid it.
        * However, in vec4 tessellation shaders, these loads operate by
@@ -579,6 +590,8 @@ brw_nir_optimize(nir_shader *nir, const struct brw_compiler *compiler,
          (nir->info.stage == MESA_SHADER_TESS_CTRL ||
           nir->info.stage == MESA_SHADER_TESS_EVAL);
       OPT(nir_opt_peephole_select, 0, !is_vec4_tessellation);
+      if (compiler->devinfo->gen >= 6)
+         OPT(nir_opt_peephole_select, 1, !is_vec4_tessellation);
 
       OPT(nir_opt_intrinsics);
       OPT(nir_opt_idiv_const, 32);