154 lines
6.0 KiB
C
154 lines
6.0 KiB
C
/*
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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;
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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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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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if (c->vattr_sizes[attr] == offset + 4) {
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c->num_inputs--;
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c->vattr_sizes[attr] -= 4;
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}
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}
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dce(c, inst);
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progress = true;
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continue;
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}
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}
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free(used);
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return progress;
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}
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