mesa/src/compiler/nir/nir_lower_passthrough_edgeflags.c

/*
 * Copyright © 2015 Red Hat
 *
 * 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 "nir.h"
#include "nir_builder.h"

static void
lower_impl(nir_function_impl *impl)
{
   nir_shader *shader = impl->function->shader;
   nir_builder b = nir_builder_at(nir_before_impl(impl));

   /* The edge flag is the last input in st/mesa.  This code is also called by
    * i965 which calls it before any input locations are assigned.
    */
   assert(shader->num_inputs == 0 ||
          shader->num_inputs == util_bitcount64(shader->info.inputs_read));

   assert(shader->num_outputs ==
          util_bitcount64(shader->info.outputs_written));

   /* Load an edge flag. */
   nir_def *load = nir_load_input(&b, 1, 32, nir_imm_int(&b, 0),
                                  .base = shader->num_inputs++,
                                  .io_semantics.location = VERT_ATTRIB_EDGEFLAG);

   /* Store an edge flag. */
   nir_store_output(&b, load, nir_imm_int(&b, 0),
                    .base = shader->num_outputs++,
                    .io_semantics.location = VARYING_SLOT_EDGE);

   nir_progress(true, impl, nir_metadata_control_flow);
}

bool
nir_lower_passthrough_edgeflags(nir_shader *shader)
{
   assert(shader->info.stage == MESA_SHADER_VERTEX);
   assert(shader->info.io_lowered);

   shader->info.vs.needs_edge_flag = true;

   lower_impl(nir_shader_get_entrypoint(shader));
   return true;
}