[Mesa-dev] [PATCH 6/7] i965: Fix variable indexing of UBO arrays under non-uniform control flow.

[Francisco Jerez]

ARB_gpu_shader5 requires UBO array indexing expressions to be
dynamically uniform, this however doesn't have any implications on the
control flow that leads to the evaluation of that expression being
uniform.  Use emit_uniformize() to obtain an arbitrary live value from
the binding table index calculation instead of assuming that the first
channel is always live.

Fixes the following Piglit tests:
  arb_gpu_shader5/execution/ubo_array_indexing/fs-nonuniform-control-flow.shader_test
  arb_gpu_shader5/execution/ubo_array_indexing/vs-nonuniform-control-flow.shader_test

part of the series:
  http://lists.freedesktop.org/archives/piglit/2015-February/014616.html
---
 src/mesa/drivers/dri/i965/brw_fs_nir.cpp       | 8 ++++----
 src/mesa/drivers/dri/i965/brw_fs_visitor.cpp   | 8 ++++----
 src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp | 5 +++--
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 90eecae..ad77752 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -1263,13 +1263,13 @@ fs_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
                              const_index->u[0]);
       } else {
          /* The block index is not a constant. Evaluate the index expression
-          * per-channel and add the base UBO index; the generator will select
-          * a value from any live channel.
+          * per-channel and add the base UBO index; we have to select a value
+          * from any live channel.
           */
          surf_index = vgrf(glsl_type::uint_type);
          emit(ADD(surf_index, get_nir_src(instr->src[0]),
-                  fs_reg(stage_prog_data->binding_table.ubo_start)))
-            ->force_writemask_all = true;
+                  fs_reg(stage_prog_data->binding_table.ubo_start)));
+         emit_uniformize(surf_index, surf_index);
 
          /* Assume this may touch any UBO. It would be nice to provide
           * a tighter bound, but the array information is already lowered away.
diff --git a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
index 6f1ff20..dee6a6d 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -1127,13 +1127,13 @@ fs_visitor::visit(ir_expression *ir)
                                  const_uniform_block->value.u[0]);
       } else {
          /* The block index is not a constant. Evaluate the index expression
-          * per-channel and add the base UBO index; the generator will select
-          * a value from any live channel.
+          * per-channel and add the base UBO index; we have to select a value
+          * from any live channel.
           */
          surf_index = vgrf(glsl_type::uint_type);
          emit(ADD(surf_index, op[0],
-                  fs_reg(stage_prog_data->binding_table.ubo_start)))
-            ->force_writemask_all = true;
+                  fs_reg(stage_prog_data->binding_table.ubo_start)));
+         emit_uniformize(surf_index, surf_index);
 
          /* Assume this may touch any UBO. It would be nice to provide
           * a tighter bound, but the array information is already lowered away.
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
index 4515fc7..d5848d2 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -1750,12 +1750,13 @@ vec4_visitor::visit(ir_expression *ir)
                               const_uniform_block->value.u[0]);
       } else {
          /* The block index is not a constant. Evaluate the index expression
-          * per-channel and add the base UBO index; the generator will select
-          * a value from any live channel.
+          * per-channel and add the base UBO index; we have to select a value
+          * from any live channel.
           */
          surf_index = src_reg(this, glsl_type::uint_type);
          emit(ADD(dst_reg(surf_index), op[0],
                   src_reg(prog_data->base.binding_table.ubo_start)));
+         emit_uniformize(dst_reg(surf_index), surf_index);
 
          /* Assume this may touch any UBO. It would be nice to provide
           * a tighter bound, but the array information is already lowered away.
-- 
2.1.3