i965/vec4/nir: implement nir_intrinsic_get_buffer_size

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>

src/mesa/drivers/dri/i965/brw_vec4_nir.cpp

@@ -538,6 +538,32 @@ vec4_visitor::nir_emit_intrinsic(nir_intrinsic_instr *instr)
       break;
    }
 
+   case nir_intrinsic_get_buffer_size: {
+      nir_const_value *const_uniform_block = nir_src_as_const_value(instr->src[0]);
+      unsigned ubo_index = const_uniform_block ? const_uniform_block->u[0] : 0;
+
+      assert(shader->base.UniformBlocks[ubo_index].IsShaderStorage);
+
+      src_reg surf_index = src_reg(prog_data->base.binding_table.ubo_start +
+                                   ubo_index);
+      dst_reg result_dst = get_nir_dest(instr->dest);
+      vec4_instruction *inst = new(mem_ctx)
+         vec4_instruction(VS_OPCODE_GET_BUFFER_SIZE, result_dst);
+
+      inst->base_mrf = 2;
+      inst->mlen = 1; /* always at least one */
+      inst->src[1] = src_reg(surf_index);
+
+      /* MRF for the first parameter */
+      src_reg lod = src_reg(0);
+      int param_base = inst->base_mrf;
+      int writemask = WRITEMASK_X;
+      emit(MOV(dst_reg(MRF, param_base, glsl_type::int_type, writemask), lod));
+
+      emit(inst);
+      break;
+   }
+
    case nir_intrinsic_load_vertex_id:
       unreachable("should be lowered by lower_vertex_id()");