[Mesa-dev] [PATCH 3/6] i965/vec4: Optimize OR with 0 into a MOV

[Ian Romanick]

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

All of the affected shaders are geometry shaders... the same ones from
the similar fs changes.

The "No changes on any other platforms" comment below is not quite
right.  Without the previous change to register coalescing, this
optimization caused quite a few regressions in tests that either used
gl_ClipVertex or used different interpolation modes.  I observed that
with both patches applied,
glsl-1.10/execution/interpolation/interpolation-none-gl_BackSecondaryColor-smooth-vertex.shader_test
was one instruction shorter.  I suspect other shaders would be similarly
affected.  Since this is all based on NOS, shader-db does not reflect
it.

Haswell
total instructions in shared programs: 12954955 -> 12954918 (<.01%)
instructions in affected programs: 3603 -> 3566 (-1.03%)
helped: 37
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 0.21% max: 2.50% x̄: 1.99% x̃: 2.50%
95% mean confidence interval for instructions value: -1.00 -1.00
95% mean confidence interval for instructions %-change: -2.30% -1.69%
Instructions are helped.

total cycles in shared programs: 410012108 -> 410012098 (<.01%)
cycles in affected programs: 3540 -> 3530 (-0.28%)
helped: 5
HURT: 0
helped stats (abs) min: 2 max: 2 x̄: 2.00 x̃: 2
helped stats (rel) min: 0.28% max: 0.28% x̄: 0.28% x̃: 0.28%
95% mean confidence interval for cycles value: -2.00 -2.00
95% mean confidence interval for cycles %-change: -0.28% -0.28%
Cycles are helped.

Ivy Bridge
total instructions in shared programs: 11679387 -> 11679351 (<.01%)
instructions in affected programs: 3292 -> 3256 (-1.09%)
helped: 36
HURT: 0
helped stats (abs) min: 1 max: 1 x̄: 1.00 x̃: 1
helped stats (rel) min: 0.21% max: 2.50% x̄: 2.04% x̃: 2.50%
95% mean confidence interval for instructions value: -1.00 -1.00
95% mean confidence interval for instructions %-change: -2.34% -1.74%
Instructions are helped.

No changes on any other platforms.

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
---
 src/intel/compiler/brw_vec4.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/intel/compiler/brw_vec4.cpp b/src/intel/compiler/brw_vec4.cpp
index e67d7802550..d1c46d610d9 100644
--- a/src/intel/compiler/brw_vec4.cpp
+++ b/src/intel/compiler/brw_vec4.cpp
@@ -810,6 +810,14 @@ vec4_visitor::opt_algebraic()
          }
          break;
 
+      case BRW_OPCODE_OR:
+         if (inst->src[1].is_zero()) {
+            inst->opcode = BRW_OPCODE_MOV;
+            inst->src[1] = src_reg();
+            progress = true;
+         }
+         break;
+
       case VEC4_OPCODE_UNPACK_UNIFORM:
          if (inst->src[0].file != UNIFORM) {
             inst->opcode = BRW_OPCODE_MOV;
-- 
2.14.4