[Mesa-dev] [PATCH 5/5] HACK: i965/ir: Test thread dispatch packing assumptions.

[Francisco Jerez]

Not intended for upstream.  Should cause a GPU hang if some thread is
executed with a non-contiguous dispatch mask breaking assumptions of
brw_stage_has_packed_dispatch().  Doesn't cause any CTS, DEQP or
Piglit regressions, while replacing brw_stage_has_packed_dispatch()
with a dummy implementation that unconditionally returns true on top
of this patch causes multiple GPU hangs.
---
 src/mesa/drivers/dri/i965/brw_fs_nir.cpp   | 17 +++++++++++++++++
 src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 21 +++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
index 042203d..b3eec49 100644
--- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp
@@ -33,6 +33,23 @@ using namespace brw::surface_access;
 void
 fs_visitor::emit_nir_code()
 {
+   if (brw_stage_has_packed_dispatch(stage, prog_data)) {
+      const fs_builder ubld = bld.exec_all().group(1, 0);
+      const fs_reg tmp = component(bld.vgrf(BRW_REGISTER_TYPE_UD), 0);
+      const fs_reg mask = (stage == MESA_SHADER_FRAGMENT ? brw_vmask_reg() :
+                           brw_dmask_reg());
+
+      ubld.ADD(tmp, mask, brw_imm_ud(1));
+      ubld.AND(tmp, mask, tmp);
+
+      /* This will loop forever if the dispatch mask doesn't have the expected
+       * form '2^n-1', in which case tmp will be non-zero.
+       */
+      bld.emit(BRW_OPCODE_DO);
+      bld.CMP(bld.null_reg_ud(), tmp, brw_imm_ud(0), BRW_CONDITIONAL_NZ);
+      set_predicate(BRW_PREDICATE_NORMAL, bld.emit(BRW_OPCODE_WHILE));
+   }
+
    /* emit the arrays used for inputs and outputs - load/store intrinsics will
     * be converted to reads/writes of these arrays
     */
diff --git a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
index ba3bbdf..9f7a1f0 100644
--- a/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
+++ b/src/mesa/drivers/dri/i965/brw_vec4_nir.cpp
@@ -35,6 +35,27 @@ namespace brw {
 void
 vec4_visitor::emit_nir_code()
 {
+   if (brw_stage_has_packed_dispatch(stage, &prog_data->base)) {
+      const dst_reg tmp = writemask(dst_reg(this, glsl_type::uint_type),
+                                    WRITEMASK_X);
+      const src_reg mask =
+         brw_swizzle(retype(stride(brw_vec4_reg(BRW_ARCHITECTURE_REGISTER_FILE, BRW_ARF_STATE, 0),
+                                   0, 4, 1),
+                            BRW_REGISTER_TYPE_UD),
+                     BRW_SWIZZLE_ZZZZ);
+
+      emit(ADD(tmp, mask, brw_imm_ud(1)));
+      emit(AND(tmp, mask, src_reg(tmp)));
+
+      /* This will loop forever if the dispatch mask doesn't have the expected
+       * form '2^n-1', in which case tmp will be non-zero.
+       */
+      emit(BRW_OPCODE_DO);
+      emit(CMP(dst_null_ud(), src_reg(tmp), brw_imm_ud(0),
+               BRW_CONDITIONAL_NZ));
+      emit(BRW_OPCODE_WHILE)->predicate = BRW_PREDICATE_NORMAL;
+   }
+
    if (nir->num_uniforms > 0)
       nir_setup_uniforms();
 
-- 
2.9.0