--- /dev/null
+/*
+ * Copyright © 2018 Intel 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.h"
+#include "nir_builder.h"
+#include "nir_control_flow.h"
+#include "nir_worklist.h"
+
+static bool
+nir_op_is_derivative(nir_op op)
+{
+ return op == nir_op_fddx ||
+ op == nir_op_fddy ||
+ op == nir_op_fddx_fine ||
+ op == nir_op_fddy_fine ||
+ op == nir_op_fddx_coarse ||
+ op == nir_op_fddy_coarse;
+}
+
+static bool
+nir_texop_implies_derivative(nir_texop op)
+{
+ return op == nir_texop_tex ||
+ op == nir_texop_txb ||
+ op == nir_texop_lod;
+}
+#define MOVE_INSTR_FLAG 1
+#define STOP_PROCESSING_INSTR_FLAG 2
+
+/** Check recursively if the source can be moved to the top of the shader.
+ * Sets instr->pass_flags to MOVE_INSTR_FLAG and adds the instr
+ * to the given worklist
+ */
+static bool
+can_move_src(nir_src *src, void *worklist)
+{
+ if (!src->is_ssa)
+ return false;
+
+ nir_instr *instr = src->ssa->parent_instr;
+ if (instr->pass_flags)
+ return true;
+
+ /* Phi instructions can't be moved at all. Also, if we're dependent on
+ * a phi then we are dependent on some other bit of control flow and
+ * it's hard to figure out the proper condition.
+ */
+ if (instr->type == nir_instr_type_phi)
+ return false;
+
+ if (instr->type == nir_instr_type_intrinsic) {
+ nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+ if (intrin->intrinsic == nir_intrinsic_load_deref) {
+ nir_deref_instr *deref = nir_src_as_deref(intrin->src[0]);
+ if (!nir_deref_mode_is_one_of(deref, nir_var_read_only_modes))
+ return false;
+ } else if (!(nir_intrinsic_infos[intrin->intrinsic].flags &
+ NIR_INTRINSIC_CAN_REORDER)) {
+ return false;
+ }
+ }
+
+ /* set pass_flags and remember the instruction for potential cleanup */
+ instr->pass_flags = MOVE_INSTR_FLAG;
+ nir_instr_worklist_push_tail(worklist, instr);
+
+ if (!nir_foreach_src(instr, can_move_src, worklist)) {
+ return false;
+ }
+ return true;
+}
+
+/** Try to mark a discard or demote instruction for moving
+ *
+ * This function does two things. One is that it searches through the
+ * dependency chain to see if this discard is an instruction that we can move
+ * up to the top. Second, if the discard is one we can move, it tags the
+ * discard and its dependencies (using pass_flags = 1).
+ * Demote are handled the same way, except that they can still be moved up
+ * when implicit derivatives are used.
+ */
+static bool
+try_move_discard(nir_intrinsic_instr *discard)
+{
+ /* We require the discard to be in the top level of control flow. We
+ * could, in theory, move discards that are inside ifs or loops but that
+ * would be a lot more work.
+ */
+ if (discard->instr.block->cf_node.parent->type != nir_cf_node_function)
+ return false;
+
+ /* Build the set of all instructions discard depends on to be able to
+ * clear the flags in case the discard cannot be moved.
+ */
+ nir_instr_worklist *work = nir_instr_worklist_create();
+ if (!work)
+ return false;
+ discard->instr.pass_flags = MOVE_INSTR_FLAG;
+
+ bool can_move_discard = can_move_src(&discard->src[0], work);
+ if (!can_move_discard) {
+ /* Moving the discard is impossible: clear the flags */
+ discard->instr.pass_flags = 0;
+ nir_foreach_instr_in_worklist(instr, work)
+ instr->pass_flags = 0;
+ }
+
+ nir_instr_worklist_destroy(work);
+
+ return can_move_discard;
+}
+
+static bool
+opt_move_discards_to_top_impl(nir_function_impl *impl)
+{
+ bool progress = false;
+ bool consider_discards = true;
+ bool moved = false;
+
+ /* Walk through the instructions and look for a discard that we can move
+ * to the top of the program. If we hit any operation along the way that
+ * we cannot safely move a discard above, break out of the loop and stop
+ * trying to move any more discards.
+ */
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr_safe(instr, block) {
+ instr->pass_flags = 0;
+
+ switch (instr->type) {
+ case nir_instr_type_alu: {
+ nir_alu_instr *alu = nir_instr_as_alu(instr);
+ if (nir_op_is_derivative(alu->op))
+ consider_discards = false;
+ continue;
+ }
+
+ case nir_instr_type_deref:
+ case nir_instr_type_load_const:
+ case nir_instr_type_ssa_undef:
+ case nir_instr_type_phi:
+ /* These are all safe */
+ continue;
+
+ case nir_instr_type_call:
+ instr->pass_flags = STOP_PROCESSING_INSTR_FLAG;
+ /* We don't know what the function will do */
+ goto break_all;
+
+ case nir_instr_type_tex: {
+ nir_tex_instr *tex = nir_instr_as_tex(instr);
+ if (nir_texop_implies_derivative(tex->op))
+ consider_discards = false;
+ continue;
+ }
+
+ case nir_instr_type_intrinsic: {
+ nir_intrinsic_instr *intrin = nir_instr_as_intrinsic(instr);
+ if (nir_intrinsic_writes_external_memory(intrin)) {
+ instr->pass_flags = STOP_PROCESSING_INSTR_FLAG;
+ goto break_all;
+ }
+
+ if ((intrin->intrinsic == nir_intrinsic_discard_if && consider_discards) ||
+ intrin->intrinsic == nir_intrinsic_demote_if)
+ moved = moved || try_move_discard(intrin);
+ continue;
+ }
+
+ case nir_instr_type_jump: {
+ nir_jump_instr *jump = nir_instr_as_jump(instr);
+ /* A return would cause the discard to not get executed */
+ if (jump->type == nir_jump_return) {
+ instr->pass_flags = STOP_PROCESSING_INSTR_FLAG;
+ goto break_all;
+ }
+ continue;
+ }
+
+ case nir_instr_type_parallel_copy:
+ unreachable("Unhanded instruction type");
+ }
+ }
+ }
+break_all:
+
+ if (moved) {
+ /* Walk the list of instructions and move the discard/demote and
+ * everything it depends on to the top. We walk the instruction list
+ * here because it ensures that everything stays in its original order.
+ * This provides stability for the algorithm and ensures that we don't
+ * accidentally get dependencies out-of-order.
+ */
+ nir_cursor cursor = nir_before_block(nir_start_block(impl));
+ nir_foreach_block(block, impl) {
+ nir_foreach_instr_safe(instr, block) {
+ if (instr->pass_flags == STOP_PROCESSING_INSTR_FLAG)
+ return progress;
+ if (instr->pass_flags == MOVE_INSTR_FLAG) {
+ progress |= nir_instr_move(cursor, instr);
+ cursor = nir_after_instr(instr);
+ }
+ }
+ }
+ }
+
+ return progress;
+}
+
+/* This optimization only operates on discard_if/demoe_if so
+ * nir_opt_conditional_discard and nir_lower_discard_or_demote
+ * should have been called before.
+ */
+bool
+nir_opt_move_discards_to_top(nir_shader *shader)
+{
+ assert(shader->info.stage == MESA_SHADER_FRAGMENT);
+
+ bool progress = false;
+
+ if (!shader->info.fs.uses_discard)
+ return false;
+
+ nir_foreach_function(function, shader) {
+ if (function->impl && opt_move_discards_to_top_impl(function->impl)) {
+ nir_metadata_preserve(function->impl, nir_metadata_block_index |
+ nir_metadata_dominance);
+ progress = true;
+ }
+ }
+
+ return progress;
+}
projects / platform / upstream / mesa.git / commitdiff