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/*
* Copyright © 2014 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 "brw_fs.h"
#include "brw_fs_live_variables.h"
#include "brw_cfg.h"
/** @file brw_fs_dead_code_eliminate.cpp
*
* Dataflow-aware dead code elimination.
*
* Walks the instruction list from the bottom, removing instructions that
* have results that both aren't used in later blocks and haven't been read
* yet in the tail end of this block.
*/
bool
fs_visitor::dead_code_eliminate()
{
bool progress = false;
cfg_t cfg(&instructions);
calculate_live_intervals();
int num_vars = live_intervals->num_vars;
BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
for (int b = 0; b < cfg.num_blocks; b++) {
bblock_t *block = cfg.blocks[b];
memcpy(live, live_intervals->bd[b].liveout,
sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
foreach_inst_in_block_reverse(fs_inst, inst, block) {
if (inst->dst.file == GRF &&
!inst->has_side_effects() &&
!inst->writes_flag()) {
bool result_live = false;
if (inst->regs_written == 1) {
int var = live_intervals->var_from_reg(&inst->dst);
result_live = BITSET_TEST(live, var);
} else {
int var = live_intervals->var_from_vgrf[inst->dst.reg];
for (int i = 0; i < inst->regs_written; i++) {
result_live = result_live || BITSET_TEST(live, var + i);
}
}
if (!result_live) {
progress = true;
if (inst->writes_accumulator) {
inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
continue;
}
}
}
if (inst->dst.file == GRF) {
if (!inst->is_partial_write()) {
int var = live_intervals->var_from_vgrf[inst->dst.reg];
for (int i = 0; i < inst->regs_written; i++) {
BITSET_CLEAR(live, var + inst->dst.reg_offset + i);
}
}
}
for (int i = 0; i < inst->sources; i++) {
if (inst->src[i].file == GRF) {
int var = live_intervals->var_from_vgrf[inst->src[i].reg];
for (int j = 0; j < inst->regs_read(this, i); j++) {
BITSET_SET(live, var + inst->src[i].reg_offset + j);
}
}
}
}
}
ralloc_free(live);
if (progress) {
foreach_list_safe(node, &this->instructions) {
fs_inst *inst = (fs_inst *)node;
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove();
}
}
invalidate_live_intervals();
}
return progress;
}
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