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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;
calculate_live_intervals();
int num_vars = live_intervals->num_vars;
BITSET_WORD *live = ralloc_array(NULL, BITSET_WORD, BITSET_WORDS(num_vars));
BITSET_WORD *flag_live = ralloc_array(NULL, BITSET_WORD, 1);
foreach_block_reverse_safe(block, cfg) {
memcpy(live, live_intervals->block_data[block->num].liveout,
sizeof(BITSET_WORD) * BITSET_WORDS(num_vars));
memcpy(flag_live, live_intervals->block_data[block->num].flag_liveout,
sizeof(BITSET_WORD));
foreach_inst_in_block_reverse_safe(fs_inst, inst, block) {
if (inst->dst.file == VGRF && !inst->has_side_effects()) {
const unsigned var = live_intervals->var_from_reg(inst->dst);
bool result_live = false;
for (unsigned i = 0; i < regs_written(inst); i++)
result_live |= BITSET_TEST(live, var + i);
if (!result_live) {
progress = true;
if (inst->writes_accumulator || inst->flags_written()) {
inst->dst = fs_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
}
}
}
if (inst->dst.is_null() && inst->flags_written()) {
if (!(flag_live[0] & inst->flags_written())) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
}
}
if ((inst->opcode != BRW_OPCODE_IF &&
inst->opcode != BRW_OPCODE_WHILE) &&
inst->dst.is_null() &&
!inst->has_side_effects() &&
!inst->flags_written() &&
!inst->writes_accumulator) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
}
if (inst->dst.file == VGRF) {
if (!inst->is_partial_write()) {
int var = live_intervals->var_from_reg(inst->dst);
for (unsigned i = 0; i < regs_written(inst); i++) {
BITSET_CLEAR(live, var + i);
}
}
}
if (!inst->predicate && inst->exec_size >= 8)
flag_live[0] &= ~inst->flags_written();
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
continue;
}
for (int i = 0; i < inst->sources; i++) {
if (inst->src[i].file == VGRF) {
int var = live_intervals->var_from_reg(inst->src[i]);
for (unsigned j = 0; j < regs_read(inst, i); j++) {
BITSET_SET(live, var + j);
}
}
}
flag_live[0] |= inst->flags_read(devinfo);
}
}
ralloc_free(live);
ralloc_free(flag_live);
if (progress)
invalidate_live_intervals();
return progress;
}
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