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r600g/sb: use simple heuristic to limit register pressure 

It's not a complete register pressure tracking, yet it helps to prevent
register allocation problems in some cases where they were observed.

The problems are uncovered by false dependencies between fetch instructions
introduced by some recent changes in TGSI and/or default backend.
Sometimes we have code like this:

...
SAMPLE R5.xyzw, R5.xyzw
... store R5.xyzw somewhere
MOV R5.x, <next x coord>
MOV R5.y, <next y coord>
SAMPLE R5.xyzw, R5.xyzw
... <may be repeated a lot of times>

With 2D resources, z and w in SAMPLE src reg aren't used and can be simply
masked, but shader backend doesn't have this information, so it's
considered as data dependency by optimization algorithms.
This commit is contained in:
Vadim Girlin 2013-04-27 12:03:39 +04:00
parent 6d6c8c88a3
commit 3e476c311f
2 changed files with 33 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
src/gallium/drivers/r600/sb/sb_gcm.cpp
View File

@ -368,7 +368,7 @@ void gcm::bu_sched_bb(bb_node* bb) {
cnt_ready[sq] = bu_ready[sq].size();
if ((sq == SQ_TEX || sq == SQ_VTX) &&
if ((sq == SQ_TEX || sq == SQ_VTX) && live_count <= rp_threshold &&
cnt_ready[sq] < ctx.max_fetch/2 &&
!bu_ready_next[SQ_ALU].empty()) {
sq = SQ_ALU;
@ -384,6 +384,16 @@ void gcm::bu_sched_bb(bb_node* bb) {
last_inst_type = sq;
}
// simple heuristic to limit register pressure,
if (sq == SQ_ALU && live_count > rp_threshold &&
(!bu_ready[SQ_TEX].empty() ||
!bu_ready[SQ_VTX].empty() ||
!bu_ready_next[SQ_TEX].empty() ||
!bu_ready_next[SQ_VTX].empty())) {
GCM_DUMP( cerr << "switching to fetch (regpressure)\n"; );
break;
}
n = bu_ready[sq].front();
// real count (e.g. SAMPLE_G will be expanded to 3 instructions,
@ -442,6 +452,11 @@ void gcm::bu_release_defs(vvec& v, bool src) {
bu_release_defs(v->muse, true);
} else if (src)
bu_release_val(v);
else {
if (live.remove_val(v)) {
--live_count;
}
}
}
}
@ -586,6 +601,8 @@ void gcm::add_ready(node *n) {
sched_queue_id sq = sh.get_queue_id(n);
if (n->flags & NF_SCHEDULE_EARLY)
bu_ready_early[sq].push_back(n);
else if (sq == SQ_ALU && n->is_copy_mov())
bu_ready[sq].push_front(n);
else
bu_ready_next[sq].push_back(n);
}
@ -665,9 +682,15 @@ void gcm::bu_release_val(value* v) {
node *n = v->any_def();
if (n && n->parent == &pending) {
unsigned uc = ++nuc_stk[ucs_level][n];
nuc_map &m = nuc_stk[ucs_level];
unsigned uc = ++m[n];
unsigned uc2 = uses[n];
if (live.add_val(v)) {
++live_count;
GCM_DUMP ( cerr << "live_count: " << live_count << "\n"; );
}
GCM_DUMP(
cerr << "release val ";
dump::dump_val(v);

9
src/gallium/drivers/r600/sb/sb_pass.h
View File

@ -246,12 +246,19 @@ class gcm : public pass {
unsigned cur_sq;
// for register pressure tracking in bottom-up pass
val_set live;
int live_count;
static const int rp_threshold = 100;
public:
gcm(shader &sh) : pass(sh),
bu_ready(), bu_ready_next(), bu_ready_early(),
ready(), op_map(), uses(), nuc_stk(1), ucs_level(),
bu_bb(), pending_defs(), pending_nodes() {}
bu_bb(), pending_defs(), pending_nodes(), cur_sq(),
live(), live_count() {}
virtual int run();