Mesa (master): nir: Add nir_lower_multiview pass
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Tue Sep 29 10:48:47 UTC 2020
Module: Mesa
Branch: master
Commit: ffe946d7e82ca95a59851ea65fc725f0f1ebf85d
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=ffe946d7e82ca95a59851ea65fc725f0f1ebf85d
Author: Connor Abbott <cwabbott0 at gmail.com>
Date: Mon Jul 6 15:25:03 2020 +0200
nir: Add nir_lower_multiview pass
Taken mostly directly from the anv pass. A few anv-specific things that
I could leave in anv aren't included. Specifically on turnip we don't
need to set gl_Layer to 0, and we can handle the case where the FS reads
gl_ViewIndex, so that check is moved into anv.
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6514>
---
src/compiler/Makefile.sources | 1 +
src/compiler/nir/meson.build | 1 +
src/compiler/nir/nir.h | 4 +
src/compiler/nir/nir_lower_multiview.c | 348 +++++++++++++++++++++++++++++++++
4 files changed, 354 insertions(+)
diff --git a/src/compiler/Makefile.sources b/src/compiler/Makefile.sources
index 706a181c7ab..82a69e6c8af 100644
--- a/src/compiler/Makefile.sources
+++ b/src/compiler/Makefile.sources
@@ -274,6 +274,7 @@ NIR_FILES = \
nir/nir_lower_io_to_temporaries.c \
nir/nir_lower_io_to_scalar.c \
nir/nir_lower_io_to_vector.c \
+ nir/nir_lower_multiview.c \
nir/nir_lower_mediump_outputs.c \
nir/nir_lower_memcpy.c \
nir/nir_lower_memory_model.c \
diff --git a/src/compiler/nir/meson.build b/src/compiler/nir/meson.build
index af633d87061..1600a02b159 100644
--- a/src/compiler/nir/meson.build
+++ b/src/compiler/nir/meson.build
@@ -154,6 +154,7 @@ files_libnir = files(
'nir_lower_io_to_temporaries.c',
'nir_lower_io_to_scalar.c',
'nir_lower_io_to_vector.c',
+ 'nir_lower_multiview.c',
'nir_lower_mediump_outputs.c',
'nir_lower_memcpy.c',
'nir_lower_memory_model.c',
diff --git a/src/compiler/nir/nir.h b/src/compiler/nir/nir.h
index 0af5caef49d..054edf5dae3 100644
--- a/src/compiler/nir/nir.h
+++ b/src/compiler/nir/nir.h
@@ -4708,6 +4708,10 @@ bool nir_lower_memory_model(nir_shader *shader);
bool nir_lower_goto_ifs(nir_shader *shader);
+bool nir_shader_uses_view_index(nir_shader *shader);
+bool nir_can_lower_multiview(nir_shader *shader);
+bool nir_lower_multiview(nir_shader *shader, uint32_t view_mask);
+
bool nir_normalize_cubemap_coords(nir_shader *shader);
void nir_live_ssa_defs_impl(nir_function_impl *impl);
diff --git a/src/compiler/nir/nir_lower_multiview.c b/src/compiler/nir/nir_lower_multiview.c
new file mode 100644
index 00000000000..ce273dc8c5e
--- /dev/null
+++ b/src/compiler/nir/nir_lower_multiview.c
@@ -0,0 +1,348 @@
+/*
+ * Copyright © 2016 Intel Corporation
+ * Copyright © 2020 Valve 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 "nir_control_flow.h"
+#include "nir_builder.h"
+
+/**
+ * This file implements an optimization for multiview. Some GPU's have a
+ * special mode which allows the vertex shader (or last stage in the geometry
+ * pipeline) to create multiple primitives in different layers of the
+ * framebuffer at once by writing multiple copies of gl_Position. The
+ * assumption is that in most uses of multiview, the only use of gl_ViewIndex
+ * is to change the position to implement the parallax effect, and other
+ * varyings will be the same between the different views. We put the body of
+ * the original vertex shader in a loop, writing to a different copy of
+ * gl_Position each loop iteration, and then let other optimizations clean up
+ * the mess.
+ */
+
+static bool
+shader_writes_to_memory(nir_shader *shader)
+{
+ /* With multiview, we would need to ensure that memory writes happen either
+ * once or once per view. Since combination of multiview and memory writes
+ * is not expected, we'll just skip this optimization in this case.
+ */
+
+ nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
+
+ nir_foreach_block(block, entrypoint) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+ nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+ switch (intrin->intrinsic) {
+ case nir_intrinsic_deref_atomic_add:
+ case nir_intrinsic_deref_atomic_imin:
+ case nir_intrinsic_deref_atomic_umin:
+ case nir_intrinsic_deref_atomic_imax:
+ case nir_intrinsic_deref_atomic_umax:
+ case nir_intrinsic_deref_atomic_and:
+ case nir_intrinsic_deref_atomic_or:
+ case nir_intrinsic_deref_atomic_xor:
+ case nir_intrinsic_deref_atomic_exchange:
+ case nir_intrinsic_deref_atomic_comp_swap:
+ case nir_intrinsic_store_ssbo:
+ case nir_intrinsic_ssbo_atomic_add:
+ case nir_intrinsic_ssbo_atomic_imin:
+ case nir_intrinsic_ssbo_atomic_umin:
+ case nir_intrinsic_ssbo_atomic_imax:
+ case nir_intrinsic_ssbo_atomic_umax:
+ case nir_intrinsic_ssbo_atomic_and:
+ case nir_intrinsic_ssbo_atomic_or:
+ case nir_intrinsic_ssbo_atomic_xor:
+ case nir_intrinsic_ssbo_atomic_exchange:
+ case nir_intrinsic_ssbo_atomic_comp_swap:
+ case nir_intrinsic_store_shared:
+ case nir_intrinsic_shared_atomic_add:
+ case nir_intrinsic_shared_atomic_imin:
+ case nir_intrinsic_shared_atomic_umin:
+ case nir_intrinsic_shared_atomic_imax:
+ case nir_intrinsic_shared_atomic_umax:
+ case nir_intrinsic_shared_atomic_and:
+ case nir_intrinsic_shared_atomic_or:
+ case nir_intrinsic_shared_atomic_xor:
+ case nir_intrinsic_shared_atomic_exchange:
+ case nir_intrinsic_shared_atomic_comp_swap:
+ case nir_intrinsic_image_deref_store:
+ case nir_intrinsic_image_deref_atomic_add:
+ case nir_intrinsic_image_deref_atomic_umin:
+ case nir_intrinsic_image_deref_atomic_umax:
+ case nir_intrinsic_image_deref_atomic_imin:
+ case nir_intrinsic_image_deref_atomic_imax:
+ case nir_intrinsic_image_deref_atomic_and:
+ case nir_intrinsic_image_deref_atomic_or:
+ case nir_intrinsic_image_deref_atomic_xor:
+ case nir_intrinsic_image_deref_atomic_exchange:
+ case nir_intrinsic_image_deref_atomic_comp_swap:
+ return true;
+
+ default:
+ /* Keep walking. */
+ break;
+ }
+ }
+ }
+
+ return false;
+}
+
+bool
+nir_shader_uses_view_index(nir_shader *shader)
+{
+ nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
+
+ nir_foreach_block(block, entrypoint) {
+ nir_foreach_instr(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+ if (intrin->intrinsic == nir_intrinsic_load_view_index)
+ return true;
+ }
+ }
+
+ return false;
+}
+
+static bool
+shader_only_position_uses_view_index(nir_shader *shader)
+{
+ nir_shader *shader_no_position = nir_shader_clone(NULL, shader);
+ nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader_no_position);
+
+ /* Remove the store position from a cloned shader. */
+ nir_foreach_block(block, entrypoint) {
+ nir_foreach_instr_safe(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *store = nir_instr_as_intrinsic(instr);
+ if (store->intrinsic != nir_intrinsic_store_deref)
+ continue;
+
+ nir_variable *var = nir_intrinsic_get_var(store, 0);
+ if (var->data.location != VARYING_SLOT_POS)
+ continue;
+
+ nir_instr_remove(&store->instr);
+ }
+ }
+
+ /* Clean up shader so unused load_view_index intrinsics are removed. */
+ bool progress;
+ do {
+ progress = false;
+ progress |= nir_opt_dead_cf(shader_no_position);
+
+ /* Peephole select will drop if-blocks that have then and else empty,
+ * which will remove the usage of an SSA in the condition.
+ */
+ progress |= nir_opt_peephole_select(shader_no_position, 0, false, false);
+
+ progress |= nir_opt_dce(shader_no_position);
+ } while (progress);
+
+ bool uses_view_index = nir_shader_uses_view_index(shader_no_position);
+
+ ralloc_free(shader_no_position);
+ return !uses_view_index;
+}
+
+/* Return true if it's safe to call nir_lower_multiview() on this vertex
+ * shader. Note that this only handles driver-agnostic checks, i.e. things
+ * which would make nir_lower_multiview() incorrect. Any driver-specific
+ * checks, e.g. for sufficient varying space or performance considerations,
+ * should be handled in the driver.
+ *
+ * Note that we don't handle the more complex checks needed for lowering
+ * pipelines with geometry or tessellation shaders.
+ */
+
+bool
+nir_can_lower_multiview(nir_shader *shader)
+{
+ bool writes_position = false;
+ nir_foreach_shader_out_variable(var, shader) {
+ if (var->data.location == VARYING_SLOT_POS) {
+ writes_position = true;
+ break;
+ }
+ }
+
+ /* Don't bother handling this edge case. */
+ if (!writes_position)
+ return false;
+
+ return !shader_writes_to_memory(shader) &&
+ shader_only_position_uses_view_index(shader);
+}
+
+/**
+ * The lowering. Call with the last active geometry stage.
+ */
+
+bool
+nir_lower_multiview(nir_shader *shader, uint32_t view_mask)
+{
+ assert(shader->info.stage != MESA_SHADER_FRAGMENT);
+ int view_count = util_bitcount(view_mask);
+
+ nir_function_impl *entrypoint = nir_shader_get_entrypoint(shader);
+
+ /* Update position to refer to an array. */
+ nir_variable *pos_var = NULL;
+ nir_foreach_shader_out_variable(var, shader) {
+ if (var->data.location == VARYING_SLOT_POS) {
+ assert(var->type == glsl_vec4_type());
+ var->type = glsl_array_type(glsl_vec4_type(), view_count, 0);
+ var->data.per_view = true;
+ pos_var = var;
+ break;
+ }
+ }
+
+ assert(pos_var);
+
+ nir_cf_list body;
+ nir_cf_list_extract(&body, &entrypoint->body);
+
+ nir_builder b;
+ nir_builder_init(&b, entrypoint);
+ b.cursor = nir_after_cf_list(&entrypoint->body);
+
+ /* Loop Index will go from 0 to view_count. */
+ nir_variable *loop_index_var =
+ nir_local_variable_create(entrypoint, glsl_uint_type(), "loop_index");
+ nir_deref_instr *loop_index_deref = nir_build_deref_var(&b, loop_index_var);
+ nir_store_deref(&b, loop_index_deref, nir_imm_int(&b, 0), 1);
+
+ /* Array of view index values that are active in the loop. Note that the
+ * loop index only matches the view index if there are no gaps in the
+ * view_mask.
+ */
+ nir_variable *view_index_var = nir_local_variable_create(
+ entrypoint, glsl_array_type(glsl_uint_type(), view_count, 0), "view_index");
+ nir_deref_instr *view_index_deref = nir_build_deref_var(&b, view_index_var);
+ {
+ int array_position = 0;
+ uint32_t view_mask_temp = view_mask;
+ while (view_mask_temp) {
+ uint32_t view_index = u_bit_scan(&view_mask_temp);
+ nir_store_deref(&b, nir_build_deref_array_imm(&b, view_index_deref, array_position),
+ nir_imm_int(&b, view_index), 1);
+ array_position++;
+ }
+ }
+
+ /* Create the equivalent of
+ *
+ * while (true):
+ * if (loop_index >= view_count):
+ * break
+ *
+ * view_index = active_indices[loop_index]
+ * pos_deref = &pos[loop_index]
+ *
+ * # Placeholder for the body to be reinserted.
+ *
+ * loop_index += 1
+ *
+ * Later both `view_index` and `pos_deref` will be used to rewrite the
+ * original shader body.
+ */
+
+ nir_loop* loop = nir_push_loop(&b);
+
+ nir_ssa_def *loop_index = nir_load_deref(&b, loop_index_deref);
+ nir_ssa_def *cmp = nir_ige(&b, loop_index, nir_imm_int(&b, view_count));
+ nir_if *loop_check = nir_push_if(&b, cmp);
+ nir_jump(&b, nir_jump_break);
+ nir_pop_if(&b, loop_check);
+
+ nir_ssa_def *view_index =
+ nir_load_deref(&b, nir_build_deref_array(&b, view_index_deref, loop_index));
+ nir_deref_instr *pos_deref =
+ nir_build_deref_array(&b, nir_build_deref_var(&b, pos_var), loop_index);
+
+ nir_store_deref(&b, loop_index_deref, nir_iadd_imm(&b, loop_index, 1), 1);
+ nir_pop_loop(&b, loop);
+
+ /* Reinsert the body. */
+ b.cursor = nir_after_instr(&pos_deref->instr);
+ nir_cf_reinsert(&body, b.cursor);
+
+ nir_foreach_block(block, entrypoint) {
+ nir_foreach_instr_safe(instr, block) {
+ if (instr->type != nir_instr_type_intrinsic)
+ continue;
+
+ nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+
+ switch (intrin->intrinsic) {
+ case nir_intrinsic_load_view_index: {
+ assert(intrin->dest.is_ssa);
+ nir_ssa_def_rewrite_uses(&intrin->dest.ssa, nir_src_for_ssa(view_index));
+ break;
+ }
+
+ case nir_intrinsic_store_deref: {
+ nir_variable *var = nir_intrinsic_get_var(intrin, 0);
+ if (var == pos_var) {
+ nir_deref_instr *old_deref = nir_src_as_deref(intrin->src[0]);
+
+ nir_instr_rewrite_src(instr, &intrin->src[0],
+ nir_src_for_ssa(&pos_deref->dest.ssa));
+
+ /* Remove old deref since it has the wrong type. */
+ nir_deref_instr_remove_if_unused(old_deref);
+ }
+ break;
+ }
+
+ case nir_intrinsic_load_deref:
+ if (nir_intrinsic_get_var(intrin, 0) == pos_var) {
+ unreachable("Should have lowered I/O to temporaries "
+ "so no load_deref on position output is expected.");
+ }
+ break;
+
+ case nir_intrinsic_copy_deref:
+ unreachable("Should have lowered copy_derefs at this point");
+ break;
+
+ default:
+ /* Do nothing. */
+ break;
+ }
+ }
+ }
+
+ nir_metadata_preserve(entrypoint, nir_metadata_none);
+ return true;
+}
+
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