/*
* Copyright © 2012 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.
*
* Authors:
* Eric Anholt <eric@anholt.net>
*
*/
#include "brw_cfg.h"
#include "brw_vec4_live_variables.h"
using namespace brw;
/** @file brw_vec4_live_variables.cpp
*
* Support for computing at the basic block level which variables
* (virtual GRFs in our case) are live at entry and exit.
*
* See Muchnick's Advanced Compiler Design and Implementation, section
* 14.1 (p444).
*/
/**
* Sets up the use[] and def[] arrays.
*
* The basic-block-level live variable analysis needs to know which
* variables get used before they're completely defined, and which
* variables are completely defined before they're used.
*
* We independently track each channel of a vec4. This is because we need to
* be able to recognize a sequence like:
*
* ...
* DP4 tmp.x a b;
* DP4 tmp.y c d;
* MUL result.xy tmp.xy e.xy
* ...
*
* as having tmp live only across that sequence (assuming it's used nowhere
* else), because it's a common pattern. A more conservative approach that
* doesn't get tmp marked a deffed in this block will tend to result in
* spilling.
*/
void
vec4_live_variables::setup_def_use()
{
int ip = 0;
foreach_block (block, cfg) {
assert(ip == block->start_ip);
if (block->num > 0)
assert(cfg->blocks[block->num - 1]->end_ip == ip - 1);
foreach_inst_in_block(vec4_instruction, inst, block) {
struct block_data *bd = &block_data[block->num];
/* Set use[] for this instruction */
for (unsigned 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++) {
const unsigned v =
var_from_reg(alloc, offset(inst->src[i], j), c);
if (!BITSET_TEST(bd->def, v))
BITSET_SET(bd->use, v);
}
}
}
}
if (inst->reads_flag()) {
if (!BITSET_TEST(bd->flag_def, 0)) {
BITSET_SET(bd->flag_use, 0);
}
}
/* Check for unconditional writes to whole registers. These
* are the things that screen off preceding definitions of a
* variable, and thus qualify for being in def[].
*/
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)) {
const unsigned v =
var_from_reg(alloc, offset(inst->dst, i), c);
if (!BITSET_TEST(bd->use, v))
BITSET_SET(bd->def, v);
}
}
}
}
if (inst->writes_flag()) {
if (!BITSET_TEST(bd->flag_use, 0)) {
BITSET_SET(bd->flag_def, 0);
}
}
ip++;
}
}
}
/**
* The algorithm incrementally sets bits in liveout and livein,
* propagating it through control flow. It will eventually terminate
* because it only ever adds bits, and stops when no bits are added in
* a pass.
*/
void
vec4_live_variables::compute_live_variables()
{
bool cont = true;
while (cont) {
cont = false;
foreach_block (block, cfg) {
struct block_data *bd = &block_data[block->num];
/* Update livein */
for (int i = 0; i < bitset_words; i++) {
BITSET_WORD new_livein = (bd->use[i] |
(bd->liveout[i] &
~bd->def[i]));
if (new_livein & ~bd->livein[i]) {
bd->livein[i] |= new_livein;
cont = true;
}
}
BITSET_WORD new_livein = (bd->flag_use[0] |
(bd->flag_liveout[0] &
~bd->flag_def[0]));
if (new_livein & ~bd->flag_livein[0]) {
bd->flag_livein[0] |= new_livein;
cont = true;
}
/* Update liveout */
foreach_list_typed(bblock_link, child_link, link, &block->children) {
struct block_data *child_bd = &block_data[child_link->block->num];
for (int i = 0; i < bitset_words; i++) {
BITSET_WORD new_liveout = (child_bd->livein[i] &
~bd->liveout[i]);
if (new_liveout) {
bd->liveout[i] |= new_liveout;
cont = true;
}
}
BITSET_WORD new_liveout = (child_bd->flag_livein[0] &
~bd->flag_liveout[0]);
if (new_liveout) {
bd->flag_liveout[0] |= new_liveout;
cont = true;
}
}
}
}
}
vec4_live_variables::vec4_live_variables(const simple_allocator &alloc,
cfg_t *cfg)
: alloc(alloc), cfg(cfg)
{
mem_ctx = ralloc_context(NULL);
num_vars = alloc.total_size * 4;
block_data = rzalloc_array(mem_ctx, struct block_data, cfg->num_blocks);
bitset_words = BITSET_WORDS(num_vars);
for (int i = 0; i < cfg->num_blocks; i++) {
block_data[i].def = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
block_data[i].use = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
block_data[i].livein = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
block_data[i].liveout = rzalloc_array(mem_ctx, BITSET_WORD, bitset_words);
block_data[i].flag_def[0] = 0;
block_data[i].flag_use[0] = 0;
block_data[i].flag_livein[0] = 0;
block_data[i].flag_liveout[0] = 0;
}
setup_def_use();
compute_live_variables();
}
vec4_live_variables::~vec4_live_variables()
{
ralloc_free(mem_ctx);
}
#define MAX_INSTRUCTION (1 << 30)
/**
* Computes a conservative start/end of the live intervals for each virtual GRF.
*
* We could expose per-channel live intervals to the consumer based on the
* information we computed in vec4_live_variables, except that our only
* current user is virtual_grf_interferes(). So we instead union the
* per-channel ranges into a per-vgrf range for virtual_grf_start[] and
* virtual_grf_end[].
*
* We could potentially have virtual_grf_interferes() do the test per-channel,
* which would let some interesting register allocation occur (particularly on
* code-generated GLSL sequences from the Cg compiler which does register
* allocation at the GLSL level and thus reuses components of the variable
* with distinct lifetimes). But right now the complexity of doing so doesn't
* seem worth it, since having virtual_grf_interferes() be cheap is important
* for register allocation performance.
*/
void
vec4_visitor::calculate_live_intervals()
{
if (this->live_intervals)
return;
int *start = ralloc_array(mem_ctx, int, this->alloc.total_size * 4);
int *end = ralloc_array(mem_ctx, int, this->alloc.total_size * 4);
ralloc_free(this->virtual_grf_start);
ralloc_free(this->virtual_grf_end);
this->virtual_grf_start = start;
this->virtual_grf_end = end;
for (unsigned i = 0; i < this->alloc.total_size * 4; i++) {
start[i] = MAX_INSTRUCTION;
end[i] = -1;
}
/* Start by setting up the intervals with no knowledge of control
* flow.
*/
int ip = 0;
foreach_block_and_inst(block, vec4_instruction, inst, cfg) {
for (unsigned 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++) {
const unsigned v =
var_from_reg(alloc, offset(inst->src[i], j), c);
start[v] = MIN2(start[v], ip);
end[v] = ip;
}
}
}
}
if (inst->dst.file == GRF) {
for (unsigned i = 0; i < inst->regs_written; i++) {
for (int c = 0; c < 4; c++) {
if (inst->dst.writemask & (1 << c)) {
const unsigned v =
var_from_reg(alloc, offset(inst->dst, i), c);
start[v] = MIN2(start[v], ip);
end[v] = ip;
}
}
}
}
ip++;
}
/* Now, extend those intervals using our analysis of control flow.
*
* The control flow-aware analysis was done at a channel level, while at
* this point we're distilling it down to vgrfs.
*/
this->live_intervals = new(mem_ctx) vec4_live_variables(alloc, cfg);
foreach_block (block, cfg) {
struct block_data *bd = &live_intervals->block_data[block->num];
for (int i = 0; i < live_intervals->num_vars; i++) {
if (BITSET_TEST(bd->livein, i)) {
start[i] = MIN2(start[i], block->start_ip);
end[i] = MAX2(end[i], block->start_ip);
}
if (BITSET_TEST(bd->liveout, i)) {
start[i] = MIN2(start[i], block->end_ip);
end[i] = MAX2(end[i], block->end_ip);
}
}
}
}
void
vec4_visitor::invalidate_live_intervals()
{
ralloc_free(live_intervals);
live_intervals = NULL;
}
int
vec4_visitor::var_range_start(unsigned v, unsigned n) const
{
int start = INT_MAX;
for (unsigned i = 0; i < n; i++)
start = MIN2(start, virtual_grf_start[v + i]);
return start;
}
int
vec4_visitor::var_range_end(unsigned v, unsigned n) const
{
int end = INT_MIN;
for (unsigned i = 0; i < n; i++)
end = MAX2(end, virtual_grf_end[v + i]);
return end;
}
bool
vec4_visitor::virtual_grf_interferes(int a, int b)
{
return !((var_range_end(4 * alloc.offsets[a], 4 * alloc.sizes[a]) <=
var_range_start(4 * alloc.offsets[b], 4 * alloc.sizes[b])) ||
(var_range_end(4 * alloc.offsets[b], 4 * alloc.sizes[b]) <=
var_range_start(4 * alloc.offsets[a], 4 * alloc.sizes[a])));
}