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Viewing changes to src/gallium/drivers/vc4/vc4_opt_dead_code.c

  • Committer: mmach
  • Date: 2022-09-22 19:56:13 UTC
  • Revision ID: netbit73@gmail.com-20220922195613-wtik9mmy20tmor0i
2022-09-22 21:17:09

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src/gallium/drivers/vc4/vc4_opt_dead_code.c
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/*
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 * Copyright © 2014 Broadcom
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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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/**
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 * @file vc4_opt_dead_code.c
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 *
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 * This is a simple dead code eliminator for SSA values in QIR.
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 *
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 * It walks all the instructions finding what temps are used, then walks again
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 * to remove instructions writing unused temps.
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 *
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 * This is an inefficient implementation if you have long chains of
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 * instructions where the entire chain is dead, but we expect those to have
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 * been eliminated at the NIR level, and here we're just cleaning up small
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 * problems produced by NIR->QIR.
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 */
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#include "vc4_qir.h"
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static bool debug;
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static void
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dce(struct vc4_compile *c, struct qinst *inst)
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{
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        if (debug) {
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                fprintf(stderr, "Removing: ");
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                qir_dump_inst(c, inst);
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                fprintf(stderr, "\n");
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        }
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        assert(!inst->sf);
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        qir_remove_instruction(c, inst);
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}
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static bool
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has_nonremovable_reads(struct vc4_compile *c, struct qinst *inst)
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{
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        for (int i = 0; i < qir_get_nsrc(inst); i++) {
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                if (inst->src[i].file == QFILE_VPM) {
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                        uint32_t attr = inst->src[i].index / 4;
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                        uint32_t offset = (inst->src[i].index % 4) * 4;
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                        if (c->vattr_sizes[attr] != offset + 4)
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                                return true;
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                        /* Can't get rid of the last VPM read, or the
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                         * simulator (at least) throws an error.
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                         */
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                        uint32_t total_size = 0;
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                        for (uint32_t i = 0; i < ARRAY_SIZE(c->vattr_sizes); i++)
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                                total_size += c->vattr_sizes[i];
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                        if (total_size == 4)
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                                return true;
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                }
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                if (inst->src[i].file == QFILE_VARY &&
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                    c->input_slots[inst->src[i].index].slot == 0xff) {
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                        return true;
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                }
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        }
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        return false;
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}
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bool
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qir_opt_dead_code(struct vc4_compile *c)
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{
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        bool progress = false;
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        bool *used = calloc(c->num_temps, sizeof(bool));
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        qir_for_each_inst_inorder(inst, c) {
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                for (int i = 0; i < qir_get_nsrc(inst); i++) {
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                        if (inst->src[i].file == QFILE_TEMP)
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                                used[inst->src[i].index] = true;
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                }
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        }
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        qir_for_each_block(block, c) {
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                qir_for_each_inst_safe(inst, block) {
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                        if (inst->dst.file != QFILE_NULL &&
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                            !(inst->dst.file == QFILE_TEMP &&
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                              !used[inst->dst.index])) {
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                                continue;
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                        }
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                        if (qir_has_side_effects(c, inst))
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                                continue;
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                        if (inst->sf ||
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                            has_nonremovable_reads(c, inst)) {
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                                /* If we can't remove the instruction, but we
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                                 * don't need its destination value, just
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                                 * remove the destination.  The register
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                                 * allocator would trivially color it and it
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                                 * wouldn't cause any register pressure, but
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                                 * it's nicer to read the QIR code without
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                                 * unused destination regs.
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                                 */
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                                if (inst->dst.file == QFILE_TEMP) {
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                                        if (debug) {
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                                                fprintf(stderr,
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                                                        "Removing dst from: ");
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                                                qir_dump_inst(c, inst);
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                                                fprintf(stderr, "\n");
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                                        }
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                                        c->defs[inst->dst.index] = NULL;
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                                        inst->dst.file = QFILE_NULL;
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                                        progress = true;
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                                }
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                                continue;
130
 
                        }
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                        for (int i = 0; i < qir_get_nsrc(inst); i++) {
133
 
                                if (inst->src[i].file != QFILE_VPM)
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                                        continue;
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                                uint32_t attr = inst->src[i].index / 4;
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                                uint32_t offset = (inst->src[i].index % 4) * 4;
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138
 
                                if (c->vattr_sizes[attr] == offset + 4) {
139
 
                                        c->num_inputs--;
140
 
                                        c->vattr_sizes[attr] -= 4;
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                                }
142
 
                        }
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144
 
                        dce(c, inst);
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                        progress = true;
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                        continue;
147
 
                }
148
 
        }
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150
 
        free(used);
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152
 
        return progress;
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}