i965: Fix variable indexing of UBO arrays under non-uniform control flow.

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

Reviewed-by: Matt Turner <mattst88@gmail.com>

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 523e56d..4c968f0 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -1407,13 +1407,13 @@ 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 fc05e77..2128795 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
@@ -1207,13 +1207,13 @@ 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 7e405ab..f0416be 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
@@ -1831,12 +1831,13 @@ 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.