i965/gen6/gs: implement transform feedback support in gen6_gs_visitor

This takes care of generating code required to handle transform feedback.
Notice that transform feedback isn't enabled yet, since that requires
additional setups in other parts of the code that will come in later patches.

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

1 files changed, 306 insertions, 3 deletions

diff --git a/src/mesa/drivers/dri/i965/gen6_gs_visitor.cpp b/src/mesa/drivers/dri/i965/gen6_gs_visitor.cpp
index 7a832ca..c9e8e66 100644
--- a/src/mesa/drivers/dri/i965/gen6_gs_visitor.cpp
+++ b/src/mesa/drivers/dri/i965/gen6_gs_visitor.cpp
@@ -97,6 +97,43 @@ gen6_gs_visitor::emit_prolog()
    this->prim_count = src_reg(this, glsl_type::uint_type);
    emit(MOV(dst_reg(this->prim_count), 0u));
 
+   if (c->prog_data.gen6_xfb_enabled) {
+      const struct gl_transform_feedback_info *linked_xfb_info =
+         &this->shader_prog->LinkedTransformFeedback;
+
+      /* Gen6 geometry shaders are required to ask for Streamed Vertex Buffer
+       * Indices values via FF_SYNC message, when Transform Feedback is
+       * enabled.
+       *
+       * To achieve this we buffer the Transform feedback outputs for each
+       * emitted vertex in xfb_output during operation. Then, when we have
+       * processed the last vertex (that is, at thread end time), we know all
+       * the required data for the FF_SYNC message header in order to receive
+       * the SVBI in the writeback.
+       *
+       * For each emitted vertex, xfb_output will hold
+       * num_transform_feedback_bindings data items plus one, which will
+       * indicate the end of the primitive. Next vertex's data comes right
+       * after.
+       */
+      this->xfb_output = src_reg(this,
+                                 glsl_type::uint_type,
+                                 linked_xfb_info->NumOutputs *
+                                 c->gp->program.VerticesOut);
+      this->xfb_output_offset = src_reg(this, glsl_type::uint_type);
+      emit(MOV(dst_reg(this->xfb_output_offset), src_reg(0u)));
+      /* Create a virtual register to hold destination indices in SOL */
+      this->destination_indices = src_reg(this, glsl_type::uvec4_type);
+      /* Create a virtual register to hold number of written primitives */
+      this->sol_prim_written = src_reg(this, glsl_type::uint_type);
+      /* Create a virtual register to hold Streamed Vertex Buffer Indices */
+      this->svbi = src_reg(this, glsl_type::uvec4_type);
+      /* Create a virtual register to hold max values of SVBI */
+      this->max_svbi = src_reg(this, glsl_type::uvec4_type);
+      emit(MOV(dst_reg(this->max_svbi),
+               src_reg(retype(brw_vec1_grf(1, 4), BRW_REGISTER_TYPE_UD))));
+   }
+
    /* PrimitveID is delivered in r0.1 of the thread payload. If the program
     * needs it we have to move it to a separate register where we can map
     * the atttribute.
@@ -134,6 +171,9 @@ gen6_gs_visitor::visit(ir_emit_vertex *)
             BRW_CONDITIONAL_L));
    emit(IF(BRW_PREDICATE_NORMAL));
    {
+      if (c->prog_data.gen6_xfb_enabled)
+         xfb_buffer_output();
+
       /* Buffer all output slots for this vertex in vertex_output */
       for (int slot = 0; slot < prog_data->vue_map.num_slots; ++slot) {
          /* We will handle PSIZ for each vertex at thread end time since it
@@ -330,9 +370,21 @@ gen6_gs_visitor::emit_thread_end()
    emit(IF(BRW_PREDICATE_NORMAL));
    {
       this->current_annotation = "gen6 thread end: ff_sync";
-      vec4_instruction *inst =
-         emit(GS_OPCODE_FF_SYNC, dst_reg(this->temp), this->prim_count,
-              brw_imm_ud(0u));
+
+      vec4_instruction *inst;
+      if (c->prog_data.gen6_xfb_enabled) {
+         src_reg sol_temp(this, glsl_type::uvec4_type);
+         emit(GS_OPCODE_FF_SYNC_SET_PRIMITIVES,
+              dst_reg(this->svbi),
+              this->vertex_count,
+              this->prim_count,
+              sol_temp);
+         inst = emit(GS_OPCODE_FF_SYNC,
+                     dst_reg(this->temp), this->prim_count, this->svbi);
+      } else {
+         inst = emit(GS_OPCODE_FF_SYNC,
+                     dst_reg(this->temp), this->prim_count, brw_imm_ud(0u));
+      }
       inst->base_mrf = base_mrf;
 
       /* Loop over all buffered vertices and emit URB write messages */
@@ -413,6 +465,9 @@ gen6_gs_visitor::emit_thread_end()
          emit(ADD(dst_reg(vertex), vertex, 1u));
       }
       emit(BRW_OPCODE_WHILE);
+
+      if (c->prog_data.gen6_xfb_enabled)
+         xfb_write();
    }
    emit(BRW_OPCODE_ENDIF);
 
@@ -432,6 +487,15 @@ gen6_gs_visitor::emit_thread_end()
     * the EOT message.
     */
    this->current_annotation = "gen6 thread end: EOT";
+
+   if (c->prog_data.gen6_xfb_enabled) {
+      /* When emitting EOT, set SONumPrimsWritten Increment Value. */
+      src_reg data(this, glsl_type::uint_type);
+      emit(AND(dst_reg(data), this->sol_prim_written, brw_imm_ud(0xffffu)));
+      emit(SHL(dst_reg(data), data, brw_imm_ud(16u)));
+      emit(GS_OPCODE_SET_DWORD_2, dst_reg(MRF, base_mrf), data);
+   }
+
    vec4_instruction *inst = emit(GS_OPCODE_THREAD_END);
    inst->urb_write_flags = BRW_URB_WRITE_COMPLETE | BRW_URB_WRITE_UNUSED;
    inst->base_mrf = base_mrf;
@@ -479,4 +543,243 @@ gen6_gs_visitor::setup_payload()
    this->first_non_payload_grf = reg;
 }
 
+void
+gen6_gs_visitor::xfb_buffer_output()
+{
+   static const unsigned swizzle_for_offset[4] = {
+      BRW_SWIZZLE4(0, 1, 2, 3),
+      BRW_SWIZZLE4(1, 2, 3, 3),
+      BRW_SWIZZLE4(2, 3, 3, 3),
+      BRW_SWIZZLE4(3, 3, 3, 3)
+   };
+
+   struct brw_gs_prog_data *prog_data =
+      (struct brw_gs_prog_data *) &c->prog_data;
+
+   if (!prog_data->num_transform_feedback_bindings) {
+      const struct gl_transform_feedback_info *linked_xfb_info =
+         &this->shader_prog->LinkedTransformFeedback;
+      int i;
+
+      /* Make sure that the VUE slots won't overflow the unsigned chars in
+       * prog_data->transform_feedback_bindings[].
+       */
+      STATIC_ASSERT(BRW_VARYING_SLOT_COUNT <= 256);
+
+      /* Make sure that we don't need more binding table entries than we've
+       * set aside for use in transform feedback.  (We shouldn't, since we
+       * set aside enough binding table entries to have one per component).
+       */
+      assert(linked_xfb_info->NumOutputs <= BRW_MAX_SOL_BINDINGS);
+
+      prog_data->num_transform_feedback_bindings = linked_xfb_info->NumOutputs;
+      for (i = 0; i < prog_data->num_transform_feedback_bindings; i++) {
+         prog_data->transform_feedback_bindings[i] =
+            linked_xfb_info->Outputs[i].OutputRegister;
+         prog_data->transform_feedback_swizzles[i] =
+            swizzle_for_offset[linked_xfb_info->Outputs[i].ComponentOffset];
+      }
+   }
+
+   /* Buffer all TF outputs for this vertex in xfb_output */
+   for (int binding = 0; binding < prog_data->num_transform_feedback_bindings;
+        binding++) {
+      /* We will handle PSIZ for each vertex at thread end time since it
+       * is not computed by the GS algorithm and requires specific handling.
+       */
+      unsigned varying =
+         prog_data->transform_feedback_bindings[binding];
+      if (varying != VARYING_SLOT_PSIZ) {
+         dst_reg dst(this->xfb_output);
+         dst.reladdr = ralloc(mem_ctx, src_reg);
+         memcpy(dst.reladdr, &this->xfb_output_offset, sizeof(src_reg));
+         dst.type = output_reg[varying].type;
+
+         this->current_annotation = output_reg_annotation[varying];
+         src_reg out_reg = src_reg(output_reg[varying]);
+         out_reg.swizzle = prog_data->transform_feedback_swizzles[binding];
+         emit(MOV(dst, out_reg));
+      }
+      emit(ADD(dst_reg(this->xfb_output_offset), this->xfb_output_offset, 1u));
+   }
+}
+
+void
+gen6_gs_visitor::xfb_write()
+{
+   unsigned num_verts;
+   struct brw_gs_prog_data *prog_data =
+      (struct brw_gs_prog_data *) &c->prog_data;
+
+   if (!prog_data->num_transform_feedback_bindings)
+      return;
+
+   switch (c->prog_data.output_topology) {
+   case _3DPRIM_POINTLIST:
+      num_verts = 1;
+      break;
+   case _3DPRIM_LINELIST:
+   case _3DPRIM_LINESTRIP:
+   case _3DPRIM_LINELOOP:
+      num_verts = 2;
+      break;
+   case _3DPRIM_TRILIST:
+   case _3DPRIM_TRIFAN:
+   case _3DPRIM_TRISTRIP:
+   case _3DPRIM_RECTLIST:
+      num_verts = 3;
+      break;
+   case _3DPRIM_QUADLIST:
+   case _3DPRIM_QUADSTRIP:
+   case _3DPRIM_POLYGON:
+      num_verts = 3;
+      break;
+   default:
+      unreachable("Unexpected primitive type in Gen6 SOL program.");
+   }
+
+   this->current_annotation = "gen6 thread end: svb writes init";
+
+   emit(MOV(dst_reg(this->xfb_output_offset), 0u));
+   emit(MOV(dst_reg(this->sol_prim_written), 0u));
+
+   /* Check that at least one primitive can be written
+    *
+    * Note: since we use the binding table to keep track of buffer offsets
+    * and stride, the GS doesn't need to keep track of a separate pointer
+    * into each buffer; it uses a single pointer which increments by 1 for
+    * each vertex.  So we use SVBI0 for this pointer, regardless of whether
+    * transform feedback is in interleaved or separate attribs mode.
+    */
+   src_reg sol_temp(this, glsl_type::uvec4_type);
+   emit(ADD(dst_reg(sol_temp), this->svbi, brw_imm_ud(num_verts)));
+
+   /* Compare SVBI calculated number with the maximum value, which is
+    * in R1.4 (previously saved in this->max_svbi) for gen6.
+    */
+   emit(CMP(dst_null_d(), sol_temp, this->max_svbi, BRW_CONDITIONAL_LE));
+   emit(IF(BRW_PREDICATE_NORMAL));
+   {
+      struct src_reg destination_indices_uw =
+         retype(destination_indices, BRW_REGISTER_TYPE_UW);
+
+      vec4_instruction *inst = emit(MOV(dst_reg(destination_indices_uw),
+                                        brw_imm_v(0x00020100))); /* (0, 1, 2) */
+      inst->force_writemask_all = true;
+
+      emit(ADD(dst_reg(this->destination_indices),
+               this->destination_indices,
+               this->svbi));
+   }
+   emit(BRW_OPCODE_ENDIF);
+
+   this->current_vertex = 0;
+   /* Make sure we do not emit more transform feedback data than the amount
+    * we have buffered.
+    */
+   for (int i = 0; i < c->gp->program.VerticesOut; i++) {
+      emit(MOV(dst_reg(sol_temp), i));
+      emit(CMP(dst_null_d(), sol_temp, this->vertex_count,
+               BRW_CONDITIONAL_L));
+      emit(IF(BRW_PREDICATE_NORMAL));
+      {
+         xfb_program(num_verts);
+      }
+      emit(BRW_OPCODE_ENDIF);
+   }
+}
+
+void
+gen6_gs_visitor::xfb_program(unsigned num_verts)
+{
+   struct brw_gs_prog_data *prog_data =
+      (struct brw_gs_prog_data *) &c->prog_data;
+   unsigned binding;
+   unsigned num_bindings = prog_data->num_transform_feedback_bindings;
+   src_reg sol_temp(this, glsl_type::uvec4_type);
+
+   /* Check if we can write one primitive more */
+   emit(ADD(dst_reg(sol_temp), this->sol_prim_written, 1u));
+   emit(MUL(dst_reg(sol_temp), sol_temp, brw_imm_ud(num_verts)));
+   emit(ADD(dst_reg(sol_temp), sol_temp, this->svbi));
+   emit(CMP(dst_null_d(), sol_temp, this->max_svbi, BRW_CONDITIONAL_LE));
+   emit(IF(BRW_PREDICATE_NORMAL));
+   {
+      if (this->current_vertex >= num_verts)
+         this->current_vertex = 0;
+
+      /* Avoid overwriting MRF 1 as it is used as URB write message header */
+      dst_reg mrf_reg(MRF, 2);
+
+      this->current_annotation = "gen6: emit SOL vertex data";
+      /* For each vertex, generate code to output each varying using the
+       * appropriate binding table entry.
+       */
+      for (binding = 0; binding < num_bindings; ++binding) {
+         /* Set up the correct destination index for this vertex */
+         vec4_instruction *inst = emit(GS_OPCODE_SVB_SET_DST_INDEX,
+                                       mrf_reg,
+                                       this->destination_indices);
+         inst->sol_vertex = this->current_vertex;
+
+         unsigned char varying =
+            prog_data->transform_feedback_bindings[binding];
+
+         /* From the Sandybridge PRM, Volume 2, Part 1, Section 4.5.1:
+          *
+          *   "Prior to End of Thread with a URB_WRITE, the kernel must
+          *   ensure that all writes are complete by sending the final
+          *   write as a committed write."
+          */
+         bool final_write = binding == (unsigned) num_bindings - 1 &&
+                            this->current_vertex == num_verts - 1;
+
+         /* Compute offset of this varying for the current vertex
+          * in xfb_output
+          */
+         src_reg data(this->xfb_output);
+         data.reladdr = ralloc(mem_ctx, src_reg);
+         memcpy(data.reladdr, &this->xfb_output_offset, sizeof(src_reg));
+         src_reg out_reg;
+         this->current_annotation = output_reg_annotation[varying];
+
+         if (varying == VARYING_SLOT_PSIZ) {
+            /* We did not buffer PSIZ, emit it directly here */
+            out_reg = src_reg(output_reg[varying]);
+            out_reg.swizzle = BRW_SWIZZLE_WWWW;
+         } else {
+            /* Copy this varying to the appropriate message register */
+            out_reg = src_reg(this, glsl_type::uvec4_type);
+            out_reg.type = output_reg[varying].type;
+
+            data.type = output_reg[varying].type;
+            emit(MOV(dst_reg(out_reg), data));
+         }
+
+         /* Write data and send SVB Write */
+         inst = emit(GS_OPCODE_SVB_WRITE, mrf_reg, out_reg, sol_temp);
+         inst->sol_binding = binding;
+         inst->sol_final_write = final_write;
+
+         emit(ADD(dst_reg(this->xfb_output_offset),
+                  this->xfb_output_offset, 1u));
+
+         if (final_write) {
+            /* This is the last vertex of the primitive, then increment
+             * SO num primitive counter and destination indices.
+             */
+            emit(ADD(dst_reg(this->destination_indices),
+                     this->destination_indices,
+                     brw_imm_ud(num_verts)));
+            emit(ADD(dst_reg(this->sol_prim_written),
+                     this->sol_prim_written, 1u));
+         }
+
+      }
+      this->current_vertex++;
+      this->current_annotation = NULL;
+   }
+   emit(BRW_OPCODE_ENDIF);
+}
+
 } /* namespace brw */