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* Copyright © 2016 Intel Corporation
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* Permission is hereby granted, free of charge, to any person obtaining a
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* copy of this software and associated documentation files (the "Software"),
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* to deal in the Software without restriction, including without limitation
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* the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the
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* Software is furnished to do so, subject to the following conditions:
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* The above copyright notice and this permission notice (including the next
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* paragraph) shall be included in all copies or substantial portions of the
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
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* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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#include "nir/nir_builder.h"
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#include "util/debug.h"
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* This file implements the lowering required for VK_KHR_multiview.
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* When possible, Primitive Replication is used and the shader is modified to
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* make gl_Position an array and fill it with values for each view.
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* Otherwise we implement multiview using instanced rendering. The number of
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* instances in each draw call is multiplied by the number of views in the
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* subpass. Then, in the shader, we divide gl_InstanceId by the number of
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* views and use gl_InstanceId % view_count to compute the actual ViewIndex.
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struct lower_multiview_state {
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nir_ssa_def *instance_id;
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nir_ssa_def *view_index;
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build_instance_id(struct lower_multiview_state *state)
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assert(state->builder.shader->info.stage == MESA_SHADER_VERTEX);
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if (state->instance_id == NULL) {
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nir_builder *b = &state->builder;
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b->cursor = nir_before_block(nir_start_block(b->impl));
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/* We use instancing for implementing multiview. The actual instance id
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* is given by dividing instance_id by the number of views in this
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nir_idiv(b, nir_load_instance_id(b),
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nir_imm_int(b, util_bitcount(state->view_mask)));
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return state->instance_id;
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build_view_index(struct lower_multiview_state *state)
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if (state->view_index == NULL) {
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nir_builder *b = &state->builder;
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b->cursor = nir_before_block(nir_start_block(b->impl));
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assert(state->view_mask != 0);
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if (util_bitcount(state->view_mask) == 1) {
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/* Set the view index directly. */
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state->view_index = nir_imm_int(b, ffs(state->view_mask) - 1);
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} else if (state->builder.shader->info.stage == MESA_SHADER_VERTEX) {
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/* We only support 16 viewports */
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assert((state->view_mask & 0xffff0000) == 0);
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/* We use instancing for implementing multiview. The compacted view
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* id is given by instance_id % view_count. We then have to convert
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* that to an actual view id.
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nir_ssa_def *compacted =
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nir_umod(b, nir_load_instance_id(b),
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nir_imm_int(b, util_bitcount(state->view_mask)));
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if (util_is_power_of_two_or_zero(state->view_mask + 1)) {
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/* If we have a full view mask, then compacted is what we want */
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state->view_index = compacted;
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/* Now we define a map from compacted view index to the actual
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* view index that's based on the view_mask. The map is given by
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* 16 nibbles, each of which is a value from 0 to 15.
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u_foreach_bit(bit, state->view_mask) {
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remap |= (uint64_t)bit << (i++ * 4);
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nir_ssa_def *shift = nir_imul(b, compacted, nir_imm_int(b, 4));
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/* One of these days, when we have int64 everywhere, this will be
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nir_ssa_def *shifted;
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if (remap <= UINT32_MAX) {
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shifted = nir_ushr(b, nir_imm_int(b, remap), shift);
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nir_ssa_def *shifted_low =
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nir_ushr(b, nir_imm_int(b, remap), shift);
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nir_ssa_def *shifted_high =
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nir_ushr(b, nir_imm_int(b, remap >> 32),
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nir_isub(b, shift, nir_imm_int(b, 32)));
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shifted = nir_bcsel(b, nir_ilt(b, shift, nir_imm_int(b, 32)),
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shifted_low, shifted_high);
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state->view_index = nir_iand(b, shifted, nir_imm_int(b, 0xf));
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const struct glsl_type *type = glsl_int_type();
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if (b->shader->info.stage == MESA_SHADER_TESS_CTRL ||
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b->shader->info.stage == MESA_SHADER_GEOMETRY)
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type = glsl_array_type(type, 1, 0);
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nir_variable *idx_var =
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nir_variable_create(b->shader, nir_var_shader_in,
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idx_var->data.location = VARYING_SLOT_VIEW_INDEX;
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if (b->shader->info.stage == MESA_SHADER_FRAGMENT)
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idx_var->data.interpolation = INTERP_MODE_FLAT;
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nir_deref_instr *deref = nir_build_deref_var(b, idx_var);
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if (glsl_type_is_array(type))
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deref = nir_build_deref_array_imm(b, deref, 0);
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state->view_index = nir_load_deref(b, deref);
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return state->view_index;
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is_load_view_index(const nir_instr *instr, const void *data)
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return instr->type == nir_instr_type_intrinsic &&
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nir_instr_as_intrinsic(instr)->intrinsic == nir_intrinsic_load_view_index;
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replace_load_view_index_with_zero(struct nir_builder *b,
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nir_instr *instr, void *data)
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assert(is_load_view_index(instr, data));
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return nir_imm_zero(b, 1, 32);
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anv_nir_lower_multiview(nir_shader *shader,
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struct anv_graphics_pipeline *pipeline)
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assert(shader->info.stage != MESA_SHADER_COMPUTE);
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uint32_t view_mask = pipeline->view_mask;
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/* If multiview isn't enabled, just lower the ViewIndex builtin to zero. */
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if (view_mask == 0) {
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return nir_shader_lower_instructions(shader, is_load_view_index,
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replace_load_view_index_with_zero, NULL);
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/* This pass assumes a single entrypoint */
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nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
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/* Primitive Replication allows a shader to write different positions for
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* each view in the same execution. If only the position depends on the
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* view, then it is possible to use the feature instead of instancing to
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* implement multiview.
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if (pipeline->use_primitive_replication) {
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if (shader->info.stage == MESA_SHADER_FRAGMENT)
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bool progress = nir_lower_multiview(shader, pipeline->view_mask);
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nir_builder_init(&b, entrypoint);
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b.cursor = nir_before_cf_list(&entrypoint->body);
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/* Fill Layer ID with zero. Replication will use that as base to
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* apply the RTAI offsets.
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nir_variable *layer_id_out =
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nir_variable_create(shader, nir_var_shader_out,
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glsl_int_type(), "layer ID");
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layer_id_out->data.location = VARYING_SLOT_LAYER;
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nir_store_var(&b, layer_id_out, nir_imm_zero(&b, 1, 32), 0x1);
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struct lower_multiview_state state = {
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.view_mask = view_mask,
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nir_builder_init(&state.builder, entrypoint);
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bool progress = false;
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nir_foreach_block(block, entrypoint) {
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nir_foreach_instr_safe(instr, block) {
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if (instr->type != nir_instr_type_intrinsic)
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nir_intrinsic_instr *load = nir_instr_as_intrinsic(instr);
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if (load->intrinsic != nir_intrinsic_load_instance_id &&
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load->intrinsic != nir_intrinsic_load_view_index)
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assert(load->dest.is_ssa);
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if (load->intrinsic == nir_intrinsic_load_instance_id) {
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value = build_instance_id(&state);
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assert(load->intrinsic == nir_intrinsic_load_view_index);
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value = build_view_index(&state);
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nir_ssa_def_rewrite_uses(&load->dest.ssa, value);
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nir_instr_remove(&load->instr);
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/* The view index is available in all stages but the instance id is only
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* available in the VS. If it's not a fragment shader, we need to pass
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* the view index on to the next stage.
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if (shader->info.stage != MESA_SHADER_FRAGMENT) {
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nir_ssa_def *view_index = build_view_index(&state);
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nir_builder *b = &state.builder;
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assert(view_index->parent_instr->block == nir_start_block(entrypoint));
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b->cursor = nir_after_instr(view_index->parent_instr);
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/* Unless there is only one possible view index (that would be set
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* directly), pass it to the next stage. */
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if (util_bitcount(state.view_mask) != 1) {
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nir_variable *view_index_out =
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nir_variable_create(shader, nir_var_shader_out,
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glsl_int_type(), "view index");
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view_index_out->data.location = VARYING_SLOT_VIEW_INDEX;
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nir_store_var(b, view_index_out, view_index, 0x1);
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nir_variable *layer_id_out =
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nir_variable_create(shader, nir_var_shader_out,
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glsl_int_type(), "layer ID");
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layer_id_out->data.location = VARYING_SLOT_LAYER;
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nir_store_var(b, layer_id_out, view_index, 0x1);
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nir_metadata_preserve(entrypoint, nir_metadata_block_index |
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nir_metadata_dominance);
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nir_metadata_preserve(entrypoint, nir_metadata_all);
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anv_check_for_primitive_replication(nir_shader **shaders,
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struct anv_graphics_pipeline *pipeline)
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assert(pipeline->base.device->info.ver >= 12);
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static int primitive_replication_max_views = -1;
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if (primitive_replication_max_views < 0) {
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/* TODO: Figure out why we are not getting same benefits for larger than
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* 2 views. For now use Primitive Replication just for the 2-view case
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const unsigned default_max_views = 2;
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primitive_replication_max_views =
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MIN2(MAX_VIEWS_FOR_PRIMITIVE_REPLICATION,
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env_var_as_unsigned("ANV_PRIMITIVE_REPLICATION_MAX_VIEWS",
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/* TODO: We should be able to support replication at 'geometry' stages
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* later than Vertex. In that case only the last stage can refer to
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if (pipeline->active_stages != (VK_SHADER_STAGE_VERTEX_BIT |
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VK_SHADER_STAGE_FRAGMENT_BIT)) {
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uint32_t view_mask = pipeline->view_mask;
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int view_count = util_bitcount(view_mask);
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if (view_count == 1 || view_count > primitive_replication_max_views)
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/* We can't access the view index in the fragment shader. */
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if (nir_shader_uses_view_index(shaders[MESA_SHADER_FRAGMENT]))
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return nir_can_lower_multiview(shaders[MESA_SHADER_VERTEX]);