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