dxil_signature.c

/*
 * Copyright © Microsoft Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#include "dxil_enums.h"
#include "dxil_module.h"
#include "dxil_signature.h"

#include "nir_to_dxil.h"
#include "glsl_types.h"
#include "util/u_debug.h"

#include <string.h>


struct semantic_info {
   enum dxil_semantic_kind kind;
   char name[64];
   int index;
   enum dxil_prog_sig_comp_type comp_type;
   uint8_t sig_comp_type;
   int32_t start_row;
   int32_t rows;
   uint8_t start_col;
   uint8_t cols;
   uint8_t interpolation;
   const char *sysvalue_name;
};


static bool
is_depth_output(enum dxil_semantic_kind kind)
{
   return kind == DXIL_SEM_DEPTH ||
         kind == DXIL_SEM_STENCIL_REF;
}

static uint8_t
get_interpolation(nir_variable *var)
{
   if (unlikely(var->data.centroid)) {
      switch (var->data.interpolation) {
      case INTERP_MODE_NONE: return DXIL_INTERP_LINEAR_CENTROID;
      case INTERP_MODE_FLAT: return DXIL_INTERP_CONSTANT;
      case INTERP_MODE_NOPERSPECTIVE: return DXIL_INTERP_LINEAR_NOPERSPECTIVE_CENTROID;
      case INTERP_MODE_SMOOTH: return DXIL_INTERP_LINEAR_CENTROID;

      }
   } else {
      switch (var->data.interpolation) {
      case INTERP_MODE_NONE: return DXIL_INTERP_LINEAR;
      case INTERP_MODE_FLAT: return DXIL_INTERP_CONSTANT;
      case INTERP_MODE_NOPERSPECTIVE: return DXIL_INTERP_LINEAR_NOPERSPECTIVE;
      case INTERP_MODE_SMOOTH: return DXIL_INTERP_LINEAR;
      }
   }

   return DXIL_INTERP_LINEAR;
}

static const char *
in_sysvalue_name(nir_variable *var)
{
   switch (var->data.location) {
   case VARYING_SLOT_POS:
      return "POS";
   case VARYING_SLOT_FACE:
      return "FACE";
   default:
      return "NONE";
   }
}

/*
 * The signatures are written into the stream in two pieces:
 * DxilProgramSignatureElement is a fixes size structure that gets dumped
 * to the stream in order of the registers and each contains an offset
 * to the semantic name string. Then these strings are dumped into the stream.
 */
static unsigned
get_additional_semantic_info(nir_shader *s, nir_variable *var, struct semantic_info *info,
                             unsigned next_row, bool is_gs_shader)
{
   const struct glsl_type *type = var->type;

   info->comp_type =
      dxil_get_prog_sig_comp_type(var->type);

   bool is_depth = is_depth_output(info->kind);
   info->sig_comp_type = dxil_get_comp_type(var->type);

   info->rows = 1;
   if (info->kind == DXIL_SEM_TARGET) {
      info->start_row = info->index;
   } else if (is_depth || (info->kind == DXIL_SEM_PRIMITIVE_ID && is_gs_shader)) {
      info->start_row = -1;
   } else if (var->data.compact) {
      if (var->data.location_frac) {
         info->start_row = next_row - 1;
      } else {
         info->start_row = next_row;
         next_row++;
      }

      assert(glsl_type_is_array(type) && info->kind == DXIL_SEM_CLIP_DISTANCE);
      unsigned num_floats = glsl_get_aoa_size(type);
      unsigned start_offset = (var->data.location - VARYING_SLOT_CLIP_DIST0) * 4 +
         var->data.location_frac;

      if (start_offset >= s->info.clip_distance_array_size) {
         info->kind = DXIL_SEM_CULL_DISTANCE;
         snprintf(info->name, 64, "SV_CullDistance");
      }
      info->cols = num_floats;
   } else {
      info->start_row = next_row;
      if (glsl_type_is_array(type) && is_gs_shader)
         type = glsl_without_array(type);

      if (glsl_type_is_array(type)) {
         info->rows = glsl_get_aoa_size(type);
         type = glsl_get_array_element(type);
         assert(info->rows);
      }
      next_row += info->rows;
   }
   info->start_col = (uint8_t)var->data.location_frac;
   if (!info->cols) {
      if (glsl_type_is_array(type))
         type = glsl_get_array_element(type);
      info->cols = (uint8_t)glsl_get_components(type);
   }

   return next_row;
}

typedef void (*semantic_info_proc)(nir_variable *var, struct semantic_info *info, bool vulkan);

static void
get_semantic_vs_in_name(nir_variable *var, struct semantic_info *info, bool vulkan)
{
   strcpy(info->name, "TEXCOORD");
   if (vulkan) {
      info->index = var->data.location >= VERT_ATTRIB_GENERIC0 ?
         var->data.location - VERT_ATTRIB_GENERIC0 :
         var->data.location;
   } else {
      info->index = var->data.driver_location;
   }
   info->kind = DXIL_SEM_ARBITRARY;
}

static void
get_semantic_sv_name(nir_variable *var, struct semantic_info *info, bool _vulkan)
{
   switch (var->data.location) {
   case SYSTEM_VALUE_VERTEX_ID_ZERO_BASE:
      info->kind = DXIL_SEM_VERTEX_ID;
      break;
   case SYSTEM_VALUE_FRONT_FACE:
      info->kind = DXIL_SEM_IS_FRONT_FACE;
      break;
   case SYSTEM_VALUE_INSTANCE_ID:
      info->kind = DXIL_SEM_INSTANCE_ID;
      break;
   case SYSTEM_VALUE_PRIMITIVE_ID:
      info->kind = DXIL_SEM_PRIMITIVE_ID;
      break;
   default:
      unreachable("unsupported system value");
   }
   strncpy(info->name, var->name, ARRAY_SIZE(info->name) - 1);
}

static void
get_semantic_ps_outname(nir_variable *var, struct semantic_info *info)
{
   info->kind = DXIL_SEM_INVALID;
   switch (var->data.location) {
   case FRAG_RESULT_COLOR:
      snprintf(info->name, 64, "%s", "SV_Target");
      info->index = var->data.index;
      info->kind = DXIL_SEM_TARGET;
      break;
   case FRAG_RESULT_DATA0:
   case FRAG_RESULT_DATA1:
   case FRAG_RESULT_DATA2:
   case FRAG_RESULT_DATA3:
   case FRAG_RESULT_DATA4:
   case FRAG_RESULT_DATA5:
   case FRAG_RESULT_DATA6:
   case FRAG_RESULT_DATA7:
      snprintf(info->name, 64, "%s", "SV_Target");
      info->index = var->data.location - FRAG_RESULT_DATA0;
      if (var->data.location == FRAG_RESULT_DATA0 &&
          var->data.index > 0)
         info->index = var->data.index;
      info->kind = DXIL_SEM_TARGET;
      break;
   case FRAG_RESULT_DEPTH:
      snprintf(info->name, 64, "%s", "SV_Depth");
      info->kind = DXIL_SEM_DEPTH;
      break;
   case FRAG_RESULT_STENCIL:
      snprintf(info->name, 64, "%s", "SV_StencilRef");
      info->kind = DXIL_SEM_STENCIL_REF; //??
      break;
   case FRAG_RESULT_SAMPLE_MASK:
      snprintf(info->name, 64, "%s", "SV_Coverage");
      info->kind = DXIL_SEM_COVERAGE; //??
      break;
   default:
      snprintf(info->name, 64, "%s", "UNDEFINED");
      break;
   }
}

static void
get_semantic_name(nir_variable *var, struct semantic_info *info,
                  const struct glsl_type *type, bool vulkan)
{
   info->kind = DXIL_SEM_INVALID;
   info->interpolation = get_interpolation(var);
   switch (var->data.location) {

   case VARYING_SLOT_POS:
      assert(glsl_get_components(type) == 4);
      snprintf(info->name, 64, "%s", "SV_Position");
      info->kind = DXIL_SEM_POSITION;
      break;

    case VARYING_SLOT_FACE:
      assert(glsl_get_components(var->type) == 1);
      snprintf(info->name, 64, "%s", "SV_IsFrontFace");
      info->kind = DXIL_SEM_IS_FRONT_FACE;
      break;

   case VARYING_SLOT_PRIMITIVE_ID:
     assert(glsl_get_components(var->type) == 1);
     snprintf(info->name, 64, "%s", "SV_PrimitiveID");
     info->kind = DXIL_SEM_PRIMITIVE_ID;
     break;

   case VARYING_SLOT_CLIP_DIST1:
      info->index = 1;
      FALLTHROUGH;
   case VARYING_SLOT_CLIP_DIST0:
      assert(var->data.location == VARYING_SLOT_CLIP_DIST1 || info->index == 0);
      snprintf(info->name, 64, "%s", "SV_ClipDistance");
      info->kind = DXIL_SEM_CLIP_DISTANCE;
      break;

   default: {
         info->index = var->data.location -
            (vulkan ? VARYING_SLOT_VAR0 : VARYING_SLOT_POS);
         strcpy(info->name, "TEXCOORD");
         info->kind = DXIL_SEM_ARBITRARY;
      }
   }
}

static void
get_semantic_in_name(nir_variable *var, struct semantic_info *info, bool vulkan)
{
   get_semantic_name(var, info, var->type, vulkan);
   info->sysvalue_name = in_sysvalue_name(var);
}

static void
get_semantic_gs_in_name(nir_variable *var, struct semantic_info *info, bool vulkan)
{
   /* geometry shader input varyings come as arrays, but we want to use
    * the element type */
   const struct glsl_type *type =
         glsl_type_is_array(var->type) ? glsl_without_array(var->type) : var->type;

   get_semantic_name(var, info, type, vulkan);
   info->sysvalue_name = in_sysvalue_name(var);
}


static enum dxil_prog_sig_semantic
prog_semantic_from_kind(enum dxil_semantic_kind kind)
{
   switch (kind) {
   case DXIL_SEM_ARBITRARY: return DXIL_PROG_SEM_UNDEFINED;
   case DXIL_SEM_VERTEX_ID: return DXIL_PROG_SEM_VERTEX_ID;
   case DXIL_SEM_INSTANCE_ID: return DXIL_PROG_SEM_INSTANCE_ID;
   case DXIL_SEM_POSITION: return DXIL_PROG_SEM_POSITION;
   case DXIL_SEM_COVERAGE: return DXIL_PROG_SEM_COVERAGE;
   case DXIL_SEM_INNER_COVERAGE: return DXIL_PROG_SEM_INNER_COVERAGE;
   case DXIL_SEM_PRIMITIVE_ID: return DXIL_PROG_SEM_PRIMITIVE_ID;
   case DXIL_SEM_SAMPLE_INDEX: return DXIL_PROG_SEM_SAMPLE_INDEX;
   case DXIL_SEM_IS_FRONT_FACE: return DXIL_PROG_SEM_IS_FRONTFACE;
   case DXIL_SEM_RENDERTARGET_ARRAY_INDEX: return DXIL_PROG_SEM_RENDERTARGET_ARRAY_INDEX;
   case DXIL_SEM_VIEWPORT_ARRAY_INDEX: return DXIL_PROG_SEM_VIEWPORT_ARRAY_INDEX;
   case DXIL_SEM_CLIP_DISTANCE: return DXIL_PROG_SEM_CLIP_DISTANCE;
   case DXIL_SEM_CULL_DISTANCE: return DXIL_PROG_SEM_CULL_DISTANCE;
   case DXIL_SEM_BARYCENTRICS: return DXIL_PROG_SEM_BARYCENTRICS;
   case DXIL_SEM_SHADING_RATE: return DXIL_PROG_SEM_SHADING_RATE;
   case DXIL_SEM_CULL_PRIMITIVE: return DXIL_PROG_SEM_CULL_PRIMITIVE;
   case DXIL_SEM_TARGET: return DXIL_PROG_SEM_TARGET;
   case DXIL_SEM_DEPTH: return DXIL_PROG_SEM_DEPTH;
   case DXIL_SEM_DEPTH_LE: return DXIL_PROG_SEM_DEPTH_LE;
   case DXIL_SEM_DEPTH_GE: return DXIL_PROG_SEM_DEPTH_GE;
   case DXIL_SEM_STENCIL_REF: return DXIL_PROG_SEM_STENCIL_REF;
   default:
       return DXIL_PROG_SEM_UNDEFINED;
   }
}

static
uint32_t
copy_semantic_name_to_string(struct _mesa_string_buffer *string_out, const char *name)
{
   /*  copy the semantic name */
   uint32_t retval = string_out->length;
   size_t name_len = strlen(name) + 1;
   _mesa_string_buffer_append_len(string_out, name, name_len);
   return retval;
}

static
uint32_t
append_semantic_index_to_table(struct dxil_psv_sem_index_table *table, uint32_t index,
                               uint32_t num_rows)
{
   if (num_rows == 1) {
      for (unsigned i = 0; i < table->size; ++i) {
         if (table->data[i] == index)
            return i;
      }
   }
   uint32_t retval = table->size;
   assert(table->size + num_rows <= 80);
   for (unsigned i = 0; i < num_rows; ++i)
      table->data[table->size++] = index + i;
   return retval;
}

static const struct dxil_mdnode *
fill_SV_param_nodes(struct dxil_module *mod, unsigned record_id,
                    struct semantic_info *semantic) {

   const struct dxil_mdnode *SV_params_nodes[11];
   /* For this to always work we should use vectorize_io, but for FS out and VS in
    * this is not implemented globally */
   const struct dxil_mdnode *flattened_semantics[256];

   for (unsigned i = 0; i < semantic->rows; ++i)
      flattened_semantics[i] = dxil_get_metadata_int32(mod, semantic->index + i);

   SV_params_nodes[0] = dxil_get_metadata_int32(mod, (int)record_id); // Unique element ID
   SV_params_nodes[1] = dxil_get_metadata_string(mod, semantic->name); // Element name
   SV_params_nodes[2] = dxil_get_metadata_int8(mod, semantic->sig_comp_type); // Element type
   SV_params_nodes[3] = dxil_get_metadata_int8(mod, (int8_t)semantic->kind); // Effective system value
   SV_params_nodes[4] = dxil_get_metadata_node(mod, flattened_semantics,
                                               semantic->rows); // Semantic index vector
   SV_params_nodes[5] = dxil_get_metadata_int8(mod, semantic->interpolation); // Interpolation mode
   SV_params_nodes[6] = dxil_get_metadata_int32(mod, semantic->rows); // Number of rows
   SV_params_nodes[7] = dxil_get_metadata_int8(mod, semantic->cols); // Number of columns
   SV_params_nodes[8] = dxil_get_metadata_int32(mod, semantic->start_row); // Element packing start row
   SV_params_nodes[9] = dxil_get_metadata_int8(mod, semantic->start_col); // Element packing start column
   SV_params_nodes[10] = 0; // optional Metadata

   return dxil_get_metadata_node(mod, SV_params_nodes, ARRAY_SIZE(SV_params_nodes));
}

static void
fill_signature_element(struct dxil_signature_element *elm,
                       struct semantic_info *semantic,
                       unsigned row)
{
   memset(elm, 0, sizeof(struct dxil_signature_element));
   // elm->stream = 0;
   // elm->semantic_name_offset = 0;  // Offset needs to be filled out when writing
   elm->semantic_index = semantic->index + row;
   elm->system_value = (uint32_t) prog_semantic_from_kind(semantic->kind);
   elm->comp_type = (uint32_t) semantic->comp_type;
   elm->reg = semantic->start_row + row;

   assert(semantic->cols + semantic->start_col <= 4);
   elm->mask = (uint8_t) (((1 << semantic->cols) - 1) << semantic->start_col);
   // elm->never_writes_mask = 0;
   elm->min_precision = DXIL_MIN_PREC_DEFAULT;
}

static bool
fill_psv_signature_element(struct dxil_psv_signature_element *psv_elm,
                           struct semantic_info *semantic, struct dxil_module *mod)
{
   memset(psv_elm, 0, sizeof(struct dxil_psv_signature_element));
   psv_elm->rows = semantic->rows;
   if (semantic->start_row >= 0) {
      assert(semantic->start_row < 256);
      psv_elm->start_row = semantic->start_row;
      psv_elm->cols_and_start = (1u << 6) | (semantic->start_col << 4) | semantic->cols;
   } else {
      /* The validation expects that the the start row is not egative
       * and apparently the extra bit in the cols_and_start indicates that the
       * row is meant literally, so don't set it in this case.
       * (Source of information: Comparing with the validation structures
       * created by dxcompiler)
       */
      psv_elm->start_row = 0;
      psv_elm->cols_and_start = (semantic->start_col << 4) | semantic->cols;
   }
   psv_elm->semantic_kind = (uint8_t)semantic->kind;
   psv_elm->component_type = semantic->comp_type; //`??
   psv_elm->interpolation_mode = semantic->interpolation;
   /* to be filled later
     psv_elm->dynamic_mask_and_stream = 0;
   */
   if (semantic->kind == DXIL_SEM_ARBITRARY && strlen(semantic->name)) {
      psv_elm->semantic_name_offset =
            copy_semantic_name_to_string(mod->sem_string_table, semantic->name);

      /* TODO: clean up memory */
      if (psv_elm->semantic_name_offset == (uint32_t)-1)
         return false;
   }

   psv_elm->semantic_indexes_offset =
         append_semantic_index_to_table(&mod->sem_index_table, semantic->index, semantic->rows);

   return true;
}

static bool
fill_io_signature(struct dxil_module *mod, int id,
                  struct semantic_info *semantic,
                  const struct dxil_mdnode **io,
                  struct dxil_signature_element *elm,
                  struct dxil_psv_signature_element *psv_elm)
{

   *io = fill_SV_param_nodes(mod, id, semantic);
   for (unsigned i = 0; i < semantic->rows; ++i)
      fill_signature_element(&elm[i], semantic, i);
   return fill_psv_signature_element(psv_elm, semantic, mod);
}

static unsigned
get_input_signature_group(struct dxil_module *mod, const struct dxil_mdnode **inputs,
                          unsigned num_inputs,
                          nir_shader *s, nir_variable_mode modes,
                          semantic_info_proc get_semantics, unsigned *row_iter,
                          bool is_gs_shader, bool vulkan)
{
   nir_foreach_variable_with_modes(var, s, modes) {
      struct semantic_info semantic = {0};
      get_semantics(var, &semantic, vulkan);
      mod->inputs[num_inputs].sysvalue = semantic.sysvalue_name;
      *row_iter = get_additional_semantic_info(s, var, &semantic, *row_iter, is_gs_shader);

      mod->inputs[num_inputs].name = ralloc_strdup(mod->ralloc_ctx,
                                                   semantic.name);
      mod->inputs[num_inputs].num_elements = semantic.rows;
      struct dxil_signature_element *elm = mod->inputs[num_inputs].elements;
      struct dxil_psv_signature_element *psv_elm = &mod->psv_inputs[num_inputs];

      if (!fill_io_signature(mod, num_inputs, &semantic,
                             &inputs[num_inputs], elm, psv_elm))
         return 0;

      ++num_inputs;
      assert(num_inputs < VARYING_SLOT_MAX);
   }
   return num_inputs;
}

static const struct dxil_mdnode *
get_input_signature(struct dxil_module *mod, nir_shader *s, bool vulkan)
{
   if (s->info.stage == MESA_SHADER_KERNEL)
      return NULL;

   const struct dxil_mdnode *inputs[VARYING_SLOT_MAX];
   unsigned next_row = 0;
   bool is_gs_shader = s->info.stage == MESA_SHADER_GEOMETRY;

   mod->num_sig_inputs = get_input_signature_group(mod, inputs, 0,
                                                   s, nir_var_shader_in,
                                                   s->info.stage == MESA_SHADER_VERTEX ?
                                                      get_semantic_vs_in_name :
                                                      (s->info.stage == MESA_SHADER_GEOMETRY ?
                                                         get_semantic_gs_in_name : get_semantic_in_name),
                                                   &next_row, is_gs_shader,
                                                   vulkan);

   mod->num_sig_inputs = get_input_signature_group(mod, inputs, mod->num_sig_inputs,
                                                   s, nir_var_system_value,
                                                   get_semantic_sv_name,
                                                   &next_row, is_gs_shader,
                                                   vulkan);

   if (!mod->num_sig_inputs && !mod->num_sig_inputs)
      return NULL;

   mod->num_psv_inputs = next_row;

   const struct dxil_mdnode *retval = mod->num_sig_inputs ?
         dxil_get_metadata_node(mod, inputs, mod->num_sig_inputs) : NULL;

   return retval;
}

static const char *out_sysvalue_name(nir_variable *var)
{
   switch (var->data.location) {
   case VARYING_SLOT_FACE:
      return "FACE";
   case VARYING_SLOT_POS:
      return "POS";
   case VARYING_SLOT_CLIP_DIST0:
   case VARYING_SLOT_CLIP_DIST1:
      return "CLIPDST";
   case VARYING_SLOT_PRIMITIVE_ID:
      return "PRIMID";
   default:
      return "NO";
   }
}

static const struct dxil_mdnode *
get_output_signature(struct dxil_module *mod, nir_shader *s, bool vulkan)
{
   const struct dxil_mdnode *outputs[VARYING_SLOT_MAX];
   unsigned num_outputs = 0;
   unsigned next_row = 0;
   nir_foreach_variable_with_modes(var, s, nir_var_shader_out) {
      struct semantic_info semantic = {0};

      if (s->info.stage == MESA_SHADER_FRAGMENT) {
         get_semantic_ps_outname(var, &semantic);
         mod->outputs[num_outputs].sysvalue = "TARGET";
      } else {
         get_semantic_name(var, &semantic, var->type, vulkan);
         mod->outputs[num_outputs].sysvalue = out_sysvalue_name(var);
      }
      next_row = get_additional_semantic_info(s, var, &semantic, next_row, false);

      mod->info.has_out_position |= semantic.kind== DXIL_SEM_POSITION;
      mod->info.has_out_depth |= semantic.kind == DXIL_SEM_DEPTH;

      mod->outputs[num_outputs].name = ralloc_strdup(mod->ralloc_ctx,
                                                     semantic.name);
      mod->outputs[num_outputs].num_elements = semantic.rows;
      struct dxil_signature_element *elm = mod->outputs[num_outputs].elements;

      struct dxil_psv_signature_element *psv_elm = &mod->psv_outputs[num_outputs];

      if (!fill_io_signature(mod, num_outputs, &semantic,
                             &outputs[num_outputs], elm, psv_elm))
         return NULL;

      /* This is fishy, logic suggests that the LHS should be 0xf, but from the
       * validation it needs to be 0xff */
      elm->never_writes_mask = 0xff & ~elm->mask;

      ++num_outputs;

      if (!is_depth_output(semantic.kind))
         ++mod->num_psv_outputs;

      assert(num_outputs < ARRAY_SIZE(outputs));
   }

   if (!num_outputs)
      return NULL;

   const struct dxil_mdnode *retval = dxil_get_metadata_node(mod, outputs, num_outputs);
   mod->num_sig_outputs = num_outputs;
   return retval;
}

const struct dxil_mdnode *
get_signatures(struct dxil_module *mod, nir_shader *s, bool vulkan)
{
   /* DXC does the same: Add an empty string before everything else */
   mod->sem_string_table = _mesa_string_buffer_create(mod->ralloc_ctx, 1024);
   copy_semantic_name_to_string(mod->sem_string_table, "");

   const struct dxil_mdnode *input_signature = get_input_signature(mod, s, vulkan);
   const struct dxil_mdnode *output_signature = get_output_signature(mod, s, vulkan);

   const struct dxil_mdnode *SV_nodes[3] = {
      input_signature,
      output_signature,
      NULL
   };
   if (output_signature || input_signature)
      return dxil_get_metadata_node(mod, SV_nodes, ARRAY_SIZE(SV_nodes));
   else
      return NULL;
}