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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_vec4.h"
#include "brw_vec4_live_variables.h"
#include "brw_cfg.h"
/** @file brw_vec4_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.
*/
using namespace brw;
static bool
can_do_writemask(const struct brw_context *brw,
const vec4_instruction *inst)
{
switch (inst->opcode) {
case SHADER_OPCODE_GEN4_SCRATCH_READ:
case VS_OPCODE_PULL_CONSTANT_LOAD:
case VS_OPCODE_PULL_CONSTANT_LOAD_GEN7:
return false;
default:
/* The MATH instruction on Gen6 only executes in align1 mode, which does
* not support writemasking.
*/
if (brw->gen == 6 && inst->is_math())
return false;
if (inst->is_tex())
return false;
return true;
}
}
bool
vec4_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(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(vec4_instruction, inst, block) {
if (inst->dst.file == GRF && !inst->has_side_effects()) {
bool result_live[4] = { false };
for (unsigned i = 0; i < inst->regs_written; i++) {
for (int c = 0; c < 4; c++)
result_live[c] |= BITSET_TEST(
live, var_from_reg(alloc, offset(inst->dst, i), c));
}
/* If the instruction can't do writemasking, then it's all or
* nothing.
*/
if (!can_do_writemask(brw, inst)) {
bool result = result_live[0] | result_live[1] |
result_live[2] | result_live[3];
result_live[0] = result;
result_live[1] = result;
result_live[2] = result;
result_live[3] = result;
}
for (int c = 0; c < 4; c++) {
if (!result_live[c] && inst->dst.writemask & (1 << c)) {
inst->dst.writemask &= ~(1 << c);
progress = true;
if (inst->dst.writemask == 0) {
if (inst->writes_accumulator || inst->writes_flag()) {
inst->dst = dst_reg(retype(brw_null_reg(), inst->dst.type));
} else {
inst->opcode = BRW_OPCODE_NOP;
continue;
}
}
}
}
}
if (inst->dst.is_null() && inst->writes_flag()) {
if (!BITSET_TEST(flag_live, 0)) {
inst->opcode = BRW_OPCODE_NOP;
progress = true;
continue;
}
}
if (inst->dst.file == GRF && !inst->predicate) {
for (unsigned i = 0; i < inst->regs_written; i++) {
for (int c = 0; c < 4; c++) {
if (inst->dst.writemask & (1 << c)) {
BITSET_CLEAR(live, var_from_reg(alloc,
offset(inst->dst, i), c));
}
}
}
}
if (inst->writes_flag()) {
BITSET_CLEAR(flag_live, 0);
}
for (int i = 0; i < 3; i++) {
if (inst->src[i].file == GRF) {
for (unsigned j = 0; j < inst->regs_read(i); j++) {
for (int c = 0; c < 4; c++) {
BITSET_SET(live, var_from_reg(alloc,
offset(inst->src[i], j), c));
}
}
}
}
if (inst->reads_flag()) {
BITSET_SET(flag_live, 0);
}
}
}
ralloc_free(live);
ralloc_free(flag_live);
if (progress) {
foreach_block_and_inst_safe(block, backend_instruction, inst, cfg) {
if (inst->opcode == BRW_OPCODE_NOP) {
inst->remove(block);
}
}
invalidate_live_intervals();
}
return progress;
}
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