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intel/fs/live_variables: Do compute_start_end in BITSET_WORD chunks 

For a block with a contiguous chunk of 32 vars that don't need updating,
this lets us skip 32 vars at a time. Also, by using bitscan, we only
iterate for each set bit rather than testing them all one at a time.
Looking at perf (with -O0 which is unfortunately necessary to get
reasonable back-traces), this seems to cuts about 50-60% of the time
spent in compute_start_end() which is, itself about 4-6% of the
run-time. In the real world, with a release driver build, this cuts
1.34% off a full shader-db run. (I ran shader-db 5 times in each
configuration).

Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Jason Ekstrand 2019-05-15 12:06:38 -05:00
parent b2d274c677
commit fce0214e94
1 changed files with 15 additions and 9 deletions
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24
src/intel/compiler/brw_fs_live_variables.cpp
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@ -235,15 +235,21 @@ fs_live_variables::compute_start_end()
foreach_block (block, cfg) {
struct block_data *bd = &block_data[block->num];
for (int i = 0; i < num_vars; i++) {
if (BITSET_TEST(bd->livein, i) && BITSET_TEST(bd->defin, i)) {
start[i] = MIN2(start[i], block->start_ip);
end[i] = MAX2(end[i], block->start_ip);
}
if (BITSET_TEST(bd->liveout, i) && BITSET_TEST(bd->defout, i)) {
start[i] = MIN2(start[i], block->end_ip);
end[i] = MAX2(end[i], block->end_ip);
for (int w = 0; w < bitset_words; w++) {
BITSET_WORD livedefin = bd->livein[w] & bd->defin[w];
BITSET_WORD livedefout = bd->liveout[w] & bd->defout[w];
BITSET_WORD livedefinout = livedefin | livedefout;
while (livedefinout) {
unsigned b = u_bit_scan(&livedefinout);
unsigned i = w * BITSET_WORDBITS + b;
if (livedefin & (1u << b)) {
start[i] = MIN2(start[i], block->start_ip);
end[i] = MAX2(end[i], block->start_ip);
}
if (livedefout & (1u << b)) {
start[i] = MIN2(start[i], block->end_ip);
end[i] = MAX2(end[i], block->end_ip);
}
}
}
}