bool ShortLoopOptimizer::process(BlockBegin* loop_header) {
TRACE_VALUE_NUMBERING(tty->print_cr("** loop header block"));
_too_complicated_loop = false;
_loop_blocks.clear();
_loop_blocks.append(loop_header);
for (int i = 0; i < _loop_blocks.length(); i++) {
BlockBegin* block = _loop_blocks.at(i);
TRACE_VALUE_NUMBERING(tty->print_cr("processing loop block B%d", block->block_id()));
if (block->is_set(BlockBegin::exception_entry_flag)) {
// this would be too complicated
return false;
}
// add predecessors to worklist
for (int j = block->number_of_preds() - 1; j >= 0; j--) {
BlockBegin* pred = block->pred_at(j);
if (pred->is_set(BlockBegin::osr_entry_flag)) {
return false;
}
ValueMap* pred_map = value_map_of(pred);
if (pred_map != NULL) {
current_map()->kill_map(pred_map);
} else if (!_loop_blocks.contains(pred)) {
if (_loop_blocks.length() >= ValueMapMaxLoopSize) {
return false;
}
_loop_blocks.append(pred);
}
}
// use the instruction visitor for killing values
for (Value instr = block->next(); instr != NULL; instr = instr->next()) {
instr->visit(this);
if (_too_complicated_loop) {
return false;
}
}
}
bool optimistic = this->_gvn->compilation()->is_optimistic();
if (UseLoopInvariantCodeMotion && optimistic) {
LoopInvariantCodeMotion code_motion(this, _gvn, loop_header, &_loop_blocks);
}
TRACE_VALUE_NUMBERING(tty->print_cr("** loop successfully optimized"));
return true;
}
void set_value_map_of(BlockBegin* block, ValueMap* map) {
assert(value_map_of(block) == NULL, "");
_value_maps.at_put(block->linear_scan_number(), map);
}
GlobalValueNumbering::GlobalValueNumbering(IR* ir)
: _current_map(NULL)
, _value_maps(ir->linear_scan_order()->length(), NULL)
{
TRACE_VALUE_NUMBERING(tty->print_cr("****** start of global value numbering"));
ShortLoopOptimizer short_loop_optimizer(this);
int subst_count = 0;
BlockList* blocks = ir->linear_scan_order();
int num_blocks = blocks->length();
BlockBegin* start_block = blocks->at(0);
assert(start_block == ir->start() && start_block->number_of_preds() == 0 && start_block->dominator() == NULL, "must be start block");
assert(start_block->next()->as_Base() != NULL && start_block->next()->next() == NULL, "start block must not have instructions");
// initial, empty value map with nesting 0
set_value_map_of(start_block, new ValueMap());
for (int i = 1; i < num_blocks; i++) {
BlockBegin* block = blocks->at(i);
TRACE_VALUE_NUMBERING(tty->print_cr("**** processing block B%d", block->block_id()));
int num_preds = block->number_of_preds();
assert(num_preds > 0, "block must have predecessors");
BlockBegin* dominator = block->dominator();
assert(dominator != NULL, "dominator must exist");
assert(value_map_of(dominator) != NULL, "value map of dominator must exist");
// create new value map with increased nesting
_current_map = new ValueMap(value_map_of(dominator));
if (num_preds == 1) {
assert(dominator == block->pred_at(0), "dominator must be equal to predecessor");
// nothing to do here
} else if (block->is_set(BlockBegin::linear_scan_loop_header_flag)) {
// block has incoming backward branches -> try to optimize short loops
if (!short_loop_optimizer.process(block)) {
// loop is too complicated, so kill all memory loads because there might be
// stores to them in the loop
current_map()->kill_memory();
}
} else {
// only incoming forward branches that are already processed
for (int j = 0; j < num_preds; j++) {
BlockBegin* pred = block->pred_at(j);
ValueMap* pred_map = value_map_of(pred);
if (pred_map != NULL) {
// propagate killed values of the predecessor to this block
current_map()->kill_map(value_map_of(pred));
} else {
// kill all memory loads because predecessor not yet processed
// (this can happen with non-natural loops and OSR-compiles)
current_map()->kill_memory();
}
}
}
if (block->is_set(BlockBegin::exception_entry_flag)) {
current_map()->kill_exception();
}
TRACE_VALUE_NUMBERING(tty->print("value map before processing block: "); current_map()->print());
// visit all instructions of this block
for (Value instr = block->next(); instr != NULL; instr = instr->next()) {
assert(!instr->has_subst(), "substitution already set");
// check if instruction kills any values
instr->visit(this);
if (instr->hash() != 0) {
Value f = current_map()->find_insert(instr);
if (f != instr) {
assert(!f->has_subst(), "can't have a substitution");
instr->set_subst(f);
subst_count++;
}
}
}
// remember value map for successors
set_value_map_of(block, current_map());
}
if (subst_count != 0) {
SubstitutionResolver resolver(ir);
}
TRACE_VALUE_NUMBERING(tty->print("****** end of global value numbering. "); ValueMap::print_statistics());
}
