1 /*
2 * Copyright (c) 1999, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "c1/c1_Canonicalizer.hpp"
27 #include "c1/c1_Optimizer.hpp"
28 #include "c1/c1_ValueMap.hpp"
29 #include "c1/c1_ValueSet.inline.hpp"
30 #include "c1/c1_ValueStack.hpp"
31 #include "memory/resourceArea.hpp"
32 #include "utilities/bitMap.inline.hpp"
33 #include "compiler/compileLog.hpp"
34
35 typedef GrowableArray<ValueSet*> ValueSetList;
36
37 Optimizer::Optimizer(IR* ir) {
38 assert(ir->is_valid(), "IR must be valid");
39 _ir = ir;
40 }
41
42 class CE_Eliminator: public BlockClosure {
43 private:
44 IR* _hir;
45 int _cee_count; // the number of CEs successfully eliminated
46 int _ifop_count; // the number of IfOps successfully simplified
47 int _has_substitution;
48
49 public:
50 CE_Eliminator(IR* hir) : _hir(hir), _cee_count(0), _ifop_count(0) {
51 _has_substitution = false;
52 _hir->iterate_preorder(this);
53 if (_has_substitution) {
54 // substituted some ifops/phis, so resolve the substitution
55 SubstitutionResolver sr(_hir);
56 }
57
58 CompileLog* log = _hir->compilation()->log();
59 if (log != NULL)
60 log->set_context("optimize name='cee'");
61 }
62
63 ~CE_Eliminator() {
64 CompileLog* log = _hir->compilation()->log();
65 if (log != NULL)
66 log->clear_context(); // skip marker if nothing was printed
67 }
68
69 int cee_count() const { return _cee_count; }
70 int ifop_count() const { return _ifop_count; }
71
72 void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
73 int e = sux->number_of_exception_handlers();
74 for (int i = 0; i < e; i++) {
75 BlockBegin* xhandler = sux->exception_handler_at(i);
76 block->add_exception_handler(xhandler);
77
78 assert(xhandler->is_predecessor(sux), "missing predecessor");
79 if (sux->number_of_preds() == 0) {
80 // sux is disconnected from graph so disconnect from exception handlers
81 xhandler->remove_predecessor(sux);
82 }
83 if (!xhandler->is_predecessor(block)) {
84 xhandler->add_predecessor(block);
85 }
86 }
87 }
88
89 virtual void block_do(BlockBegin* block);
90
91 private:
92 Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval,
93 ValueStack* state_before, bool substitutability_check);
94 };
95
96 void CE_Eliminator::block_do(BlockBegin* block) {
97 // 1) find conditional expression
98 // check if block ends with an If
99 If* if_ = block->end()->as_If();
100 if (if_ == NULL) return;
101
102 // check if If works on int or object types
103 // (we cannot handle If's working on long, float or doubles yet,
104 // since IfOp doesn't support them - these If's show up if cmp
105 // operations followed by If's are eliminated)
106 ValueType* if_type = if_->x()->type();
107 if (!if_type->is_int() && !if_type->is_object()) return;
108
109 BlockBegin* t_block = if_->tsux();
110 BlockBegin* f_block = if_->fsux();
111 Instruction* t_cur = t_block->next();
112 Instruction* f_cur = f_block->next();
113
114 // one Constant may be present between BlockBegin and BlockEnd
115 Value t_const = NULL;
116 Value f_const = NULL;
117 if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {
118 t_const = t_cur;
119 t_cur = t_cur->next();
120 }
121 if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {
122 f_const = f_cur;
123 f_cur = f_cur->next();
124 }
125
126 // check if both branches end with a goto
127 Goto* t_goto = t_cur->as_Goto();
128 if (t_goto == NULL) return;
129 Goto* f_goto = f_cur->as_Goto();
130 if (f_goto == NULL) return;
131
132 // check if both gotos merge into the same block
133 BlockBegin* sux = t_goto->default_sux();
134 if (sux != f_goto->default_sux()) return;
135
136 // check if at least one word was pushed on sux_state
137 // inlining depths must match
138 ValueStack* if_state = if_->state();
139 ValueStack* sux_state = sux->state();
140 if (if_state->scope()->level() > sux_state->scope()->level()) {
141 while (sux_state->scope() != if_state->scope()) {
142 if_state = if_state->caller_state();
143 assert(if_state != NULL, "states do not match up");
144 }
145 } else if (if_state->scope()->level() < sux_state->scope()->level()) {
146 while (sux_state->scope() != if_state->scope()) {
147 sux_state = sux_state->caller_state();
148 assert(sux_state != NULL, "states do not match up");
149 }
150 }
151
152 if (sux_state->stack_size() <= if_state->stack_size()) return;
153
154 // check if phi function is present at end of successor stack and that
155 // only this phi was pushed on the stack
156 Value sux_phi = sux_state->stack_at(if_state->stack_size());
157 if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;
158 if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
159
160 // get the values that were pushed in the true- and false-branch
161 Value t_value = t_goto->state()->stack_at(if_state->stack_size());
162 Value f_value = f_goto->state()->stack_at(if_state->stack_size());
163
164 // backend does not support floats
165 assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
166 if (t_value->type()->is_float_kind()) return;
167
168 // check that successor has no other phi functions but sux_phi
169 // this can happen when t_block or f_block contained additonal stores to local variables
170 // that are no longer represented by explicit instructions
171 for_each_phi_fun(sux, phi,
172 if (phi != sux_phi) return;
173 );
174 // true and false blocks can't have phis
175 for_each_phi_fun(t_block, phi, return; );
176 for_each_phi_fun(f_block, phi, return; );
177
178 // Only replace safepoint gotos if state_before information is available (if is a safepoint)
179 bool is_safepoint = if_->is_safepoint();
180 if (!is_safepoint && (t_goto->is_safepoint() || f_goto->is_safepoint())) {
181 return;
182 }
183
184 // 2) substitute conditional expression
185 // with an IfOp followed by a Goto
186 // cut if_ away and get node before
187 Instruction* cur_end = if_->prev();
188
189 // append constants of true- and false-block if necessary
190 // clone constants because original block must not be destroyed
191 assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
192 if (t_value == t_const) {
193 t_value = new Constant(t_const->type());
194 NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
195 cur_end = cur_end->set_next(t_value);
196 }
197 if (f_value == f_const) {
198 f_value = new Constant(f_const->type());
199 NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
200 cur_end = cur_end->set_next(f_value);
201 }
202
203 Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value,
204 if_->state_before(), if_->substitutability_check());
205 assert(result != NULL, "make_ifop must return a non-null instruction");
206 if (!result->is_linked() && result->can_be_linked()) {
207 NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
208 cur_end = cur_end->set_next(result);
209 }
210
211 // append Goto to successor
212 ValueStack* state_before = if_->state_before();
213 Goto* goto_ = new Goto(sux, state_before, is_safepoint);
214
215 // prepare state for Goto
216 ValueStack* goto_state = if_state;
217 goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
218 goto_state->push(result->type(), result);
219 assert(goto_state->is_same(sux_state), "states must match now");
220 goto_->set_state(goto_state);
221
222 cur_end = cur_end->set_next(goto_, goto_state->bci());
223
224 // Adjust control flow graph
225 BlockBegin::disconnect_edge(block, t_block);
226 BlockBegin::disconnect_edge(block, f_block);
227 if (t_block->number_of_preds() == 0) {
228 BlockBegin::disconnect_edge(t_block, sux);
229 }
230 adjust_exception_edges(block, t_block);
231 if (f_block->number_of_preds() == 0) {
232 BlockBegin::disconnect_edge(f_block, sux);
233 }
234 adjust_exception_edges(block, f_block);
235
236 // update block end
237 block->set_end(goto_);
238
239 // substitute the phi if possible
240 if (sux_phi->as_Phi()->operand_count() == 1) {
241 assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
242 sux_phi->set_subst(result);
243 _has_substitution = true;
244 }
245
246 // 3) successfully eliminated a conditional expression
247 _cee_count++;
248 if (PrintCEE) {
249 tty->print_cr("%d. CEE in B%d (B%d B%d)", cee_count(), block->block_id(), t_block->block_id(), f_block->block_id());
250 tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
251 }
252
253 _hir->verify();
254 }
255
256 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval,
257 ValueStack* state_before, bool substitutability_check) {
258 if (!OptimizeIfOps) {
259 return new IfOp(x, cond, y, tval, fval, state_before, substitutability_check);
260 }
261
262 tval = tval->subst();
263 fval = fval->subst();
264 if (tval == fval) {
265 _ifop_count++;
266 return tval;
267 }
268
269 x = x->subst();
270 y = y->subst();
271
272 Constant* y_const = y->as_Constant();
273 if (y_const != NULL) {
274 IfOp* x_ifop = x->as_IfOp();
275 if (x_ifop != NULL) { // x is an ifop, y is a constant
276 Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
277 Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
278
279 if (x_tval_const != NULL && x_fval_const != NULL) {
280 Instruction::Condition x_ifop_cond = x_ifop->cond();
281
282 Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
283 Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
284
285 // not_comparable here is a valid return in case we're comparing unloaded oop constants
286 if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
287 Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
288 Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
289
290 _ifop_count++;
291 if (new_tval == new_fval) {
292 return new_tval;
293 } else {
294 return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval, state_before, substitutability_check);
295 }
296 }
297 }
298 } else {
299 Constant* x_const = x->as_Constant();
300 if (x_const != NULL) { // x and y are constants
301 Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
302 // not_comparable here is a valid return in case we're comparing unloaded oop constants
303 if (x_compare_res != Constant::not_comparable) {
304 _ifop_count++;
305 return x_compare_res == Constant::cond_true ? tval : fval;
306 }
307 }
308 }
309 }
310 return new IfOp(x, cond, y, tval, fval, state_before, substitutability_check);
311 }
312
313 void Optimizer::eliminate_conditional_expressions() {
314 // find conditional expressions & replace them with IfOps
315 CE_Eliminator ce(ir());
316 }
317
318 class BlockMerger: public BlockClosure {
319 private:
320 IR* _hir;
321 int _merge_count; // the number of block pairs successfully merged
322
323 public:
324 BlockMerger(IR* hir)
325 : _hir(hir)
326 , _merge_count(0)
327 {
328 _hir->iterate_preorder(this);
329 CompileLog* log = _hir->compilation()->log();
330 if (log != NULL)
331 log->set_context("optimize name='eliminate_blocks'");
332 }
333
334 ~BlockMerger() {
335 CompileLog* log = _hir->compilation()->log();
336 if (log != NULL)
337 log->clear_context(); // skip marker if nothing was printed
338 }
339
340 bool try_merge(BlockBegin* block) {
341 BlockEnd* end = block->end();
342 if (end->as_Goto() != NULL) {
343 assert(end->number_of_sux() == 1, "end must have exactly one successor");
344 // Note: It would be sufficient to check for the number of successors (= 1)
345 // in order to decide if this block can be merged potentially. That
346 // would then also include switch statements w/ only a default case.
347 // However, in that case we would need to make sure the switch tag
348 // expression is executed if it can produce observable side effects.
349 // We should probably have the canonicalizer simplifying such switch
350 // statements and then we are sure we don't miss these merge opportunities
351 // here (was bug - gri 7/7/99).
352 BlockBegin* sux = end->default_sux();
353 if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {
354 // merge the two blocks
355
356 #ifdef ASSERT
357 // verify that state at the end of block and at the beginning of sux are equal
358 // no phi functions must be present at beginning of sux
359 ValueStack* sux_state = sux->state();
360 ValueStack* end_state = end->state();
361
362 assert(end_state->scope() == sux_state->scope(), "scopes must match");
363 assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
364 assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
365
366 int index;
367 Value sux_value;
368 for_each_stack_value(sux_state, index, sux_value) {
369 assert(sux_value == end_state->stack_at(index), "stack not equal");
370 }
371 for_each_local_value(sux_state, index, sux_value) {
372 assert(sux_value == end_state->local_at(index), "locals not equal");
373 }
374 assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
375 #endif
376
377 // find instruction before end & append first instruction of sux block
378 Instruction* prev = end->prev();
379 Instruction* next = sux->next();
380 assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
381 prev->set_next(next);
382 prev->fixup_block_pointers();
383 sux->disconnect_from_graph();
384 block->set_end(sux->end());
385 // add exception handlers of deleted block, if any
386 for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
387 BlockBegin* xhandler = sux->exception_handler_at(k);
388 block->add_exception_handler(xhandler);
389
390 // also substitute predecessor of exception handler
391 assert(xhandler->is_predecessor(sux), "missing predecessor");
392 xhandler->remove_predecessor(sux);
393 if (!xhandler->is_predecessor(block)) {
394 xhandler->add_predecessor(block);
395 }
396 }
397
398 // debugging output
399 _merge_count++;
400 if (PrintBlockElimination) {
401 tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
402 _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
403 }
404
405 _hir->verify();
406
407 If* if_ = block->end()->as_If();
408 if (if_) {
409 IfOp* ifop = if_->x()->as_IfOp();
410 Constant* con = if_->y()->as_Constant();
411 bool swapped = false;
412 if (!con || !ifop) {
413 ifop = if_->y()->as_IfOp();
414 con = if_->x()->as_Constant();
415 swapped = true;
416 }
417 if (con && ifop) {
418 Constant* tval = ifop->tval()->as_Constant();
419 Constant* fval = ifop->fval()->as_Constant();
420 if (tval && fval) {
421 // Find the instruction before if_, starting with ifop.
422 // When if_ and ifop are not in the same block, prev
423 // becomes NULL In such (rare) cases it is not
424 // profitable to perform the optimization.
425 Value prev = ifop;
426 while (prev != NULL && prev->next() != if_) {
427 prev = prev->next();
428 }
429
430 if (prev != NULL) {
431 Instruction::Condition cond = if_->cond();
432 BlockBegin* tsux = if_->tsux();
433 BlockBegin* fsux = if_->fsux();
434 if (swapped) {
435 cond = Instruction::mirror(cond);
436 }
437
438 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
439 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
440 if (tblock != fblock && !if_->is_safepoint()) {
441 If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
442 tblock, fblock, if_->state_before(), if_->is_safepoint(), if_->substitutability_check());
443 newif->set_state(if_->state()->copy());
444
445 assert(prev->next() == if_, "must be guaranteed by above search");
446 NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
447 prev->set_next(newif);
448 block->set_end(newif);
449
450 _merge_count++;
451 if (PrintBlockElimination) {
452 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
453 }
454
455 _hir->verify();
456 }
457 }
458 }
459 }
460 }
461
462 return true;
463 }
464 }
465 return false;
466 }
467
468 virtual void block_do(BlockBegin* block) {
469 _hir->verify();
470 // repeat since the same block may merge again
471 while (try_merge(block)) {
472 _hir->verify();
473 }
474 }
475 };
476
477
478 void Optimizer::eliminate_blocks() {
479 // merge blocks if possible
480 BlockMerger bm(ir());
481 }
482
483
484 class NullCheckEliminator;
485 class NullCheckVisitor: public InstructionVisitor {
486 private:
487 NullCheckEliminator* _nce;
488 NullCheckEliminator* nce() { return _nce; }
489
490 public:
491 NullCheckVisitor() {}
492
493 void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
494
495 void do_Phi (Phi* x);
496 void do_Local (Local* x);
497 void do_Constant (Constant* x);
498 void do_LoadField (LoadField* x);
499 void do_StoreField (StoreField* x);
500 void do_ArrayLength (ArrayLength* x);
501 void do_LoadIndexed (LoadIndexed* x);
502 void do_StoreIndexed (StoreIndexed* x);
503 void do_NegateOp (NegateOp* x);
504 void do_ArithmeticOp (ArithmeticOp* x);
505 void do_ShiftOp (ShiftOp* x);
506 void do_LogicOp (LogicOp* x);
507 void do_CompareOp (CompareOp* x);
508 void do_IfOp (IfOp* x);
509 void do_Convert (Convert* x);
510 void do_NullCheck (NullCheck* x);
511 void do_TypeCast (TypeCast* x);
512 void do_Invoke (Invoke* x);
513 void do_NewInstance (NewInstance* x);
514 void do_NewValueTypeInstance(NewValueTypeInstance* x);
515 void do_NewTypeArray (NewTypeArray* x);
516 void do_NewObjectArray (NewObjectArray* x);
517 void do_NewMultiArray (NewMultiArray* x);
518 void do_CheckCast (CheckCast* x);
519 void do_InstanceOf (InstanceOf* x);
520 void do_MonitorEnter (MonitorEnter* x);
521 void do_MonitorExit (MonitorExit* x);
522 void do_Intrinsic (Intrinsic* x);
523 void do_BlockBegin (BlockBegin* x);
524 void do_Goto (Goto* x);
525 void do_If (If* x);
526 void do_IfInstanceOf (IfInstanceOf* x);
527 void do_TableSwitch (TableSwitch* x);
528 void do_LookupSwitch (LookupSwitch* x);
529 void do_Return (Return* x);
530 void do_Throw (Throw* x);
531 void do_Base (Base* x);
532 void do_OsrEntry (OsrEntry* x);
533 void do_ExceptionObject(ExceptionObject* x);
534 void do_RoundFP (RoundFP* x);
535 void do_UnsafeGetRaw (UnsafeGetRaw* x);
536 void do_UnsafePutRaw (UnsafePutRaw* x);
537 void do_UnsafeGetObject(UnsafeGetObject* x);
538 void do_UnsafePutObject(UnsafePutObject* x);
539 void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
540 void do_ProfileCall (ProfileCall* x);
541 void do_ProfileReturnType (ProfileReturnType* x);
542 void do_ProfileInvoke (ProfileInvoke* x);
543 void do_RuntimeCall (RuntimeCall* x);
544 void do_MemBar (MemBar* x);
545 void do_RangeCheckPredicate(RangeCheckPredicate* x);
546 #ifdef ASSERT
547 void do_Assert (Assert* x);
548 #endif
549 };
550
551
552 // Because of a static contained within (for the purpose of iteration
553 // over instructions), it is only valid to have one of these active at
554 // a time
555 class NullCheckEliminator: public ValueVisitor {
556 private:
557 Optimizer* _opt;
558
559 ValueSet* _visitable_instructions; // Visit each instruction only once per basic block
560 BlockList* _work_list; // Basic blocks to visit
561
562 bool visitable(Value x) {
563 assert(_visitable_instructions != NULL, "check");
564 return _visitable_instructions->contains(x);
565 }
566 void mark_visited(Value x) {
567 assert(_visitable_instructions != NULL, "check");
568 _visitable_instructions->remove(x);
569 }
570 void mark_visitable(Value x) {
571 assert(_visitable_instructions != NULL, "check");
572 _visitable_instructions->put(x);
573 }
574 void clear_visitable_state() {
575 assert(_visitable_instructions != NULL, "check");
576 _visitable_instructions->clear();
577 }
578
579 ValueSet* _set; // current state, propagated to subsequent BlockBegins
580 ValueSetList _block_states; // BlockBegin null-check states for all processed blocks
581 NullCheckVisitor _visitor;
582 NullCheck* _last_explicit_null_check;
583
584 bool set_contains(Value x) { assert(_set != NULL, "check"); return _set->contains(x); }
585 void set_put (Value x) { assert(_set != NULL, "check"); _set->put(x); }
586 void set_remove (Value x) { assert(_set != NULL, "check"); _set->remove(x); }
587
588 BlockList* work_list() { return _work_list; }
589
590 void iterate_all();
591 void iterate_one(BlockBegin* block);
592
593 ValueSet* state() { return _set; }
594 void set_state_from (ValueSet* state) { _set->set_from(state); }
595 ValueSet* state_for (BlockBegin* block) { return _block_states.at(block->block_id()); }
596 void set_state_for (BlockBegin* block, ValueSet* stack) { _block_states.at_put(block->block_id(), stack); }
597 // Returns true if caused a change in the block's state.
598 bool merge_state_for(BlockBegin* block,
599 ValueSet* incoming_state);
600
601 public:
602 // constructor
603 NullCheckEliminator(Optimizer* opt)
604 : _opt(opt)
605 , _work_list(new BlockList())
606 , _set(new ValueSet())
607 , _block_states(BlockBegin::number_of_blocks(), BlockBegin::number_of_blocks(), NULL)
608 , _last_explicit_null_check(NULL) {
609 _visitable_instructions = new ValueSet();
610 _visitor.set_eliminator(this);
611 CompileLog* log = _opt->ir()->compilation()->log();
612 if (log != NULL)
613 log->set_context("optimize name='null_check_elimination'");
614 }
615
616 ~NullCheckEliminator() {
617 CompileLog* log = _opt->ir()->compilation()->log();
618 if (log != NULL)
619 log->clear_context(); // skip marker if nothing was printed
620 }
621
622 Optimizer* opt() { return _opt; }
623 IR* ir () { return opt()->ir(); }
624
625 // Process a graph
626 void iterate(BlockBegin* root);
627
628 void visit(Value* f);
629
630 // In some situations (like NullCheck(x); getfield(x)) the debug
631 // information from the explicit NullCheck can be used to populate
632 // the getfield, even if the two instructions are in different
633 // scopes; this allows implicit null checks to be used but the
634 // correct exception information to be generated. We must clear the
635 // last-traversed NullCheck when we reach a potentially-exception-
636 // throwing instruction, as well as in some other cases.
637 void set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
638 NullCheck* last_explicit_null_check() { return _last_explicit_null_check; }
639 Value last_explicit_null_check_obj() { return (_last_explicit_null_check
640 ? _last_explicit_null_check->obj()
641 : NULL); }
642 NullCheck* consume_last_explicit_null_check() {
643 _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
644 _last_explicit_null_check->set_can_trap(false);
645 return _last_explicit_null_check;
646 }
647 void clear_last_explicit_null_check() { _last_explicit_null_check = NULL; }
648
649 // Handlers for relevant instructions
650 // (separated out from NullCheckVisitor for clarity)
651
652 // The basic contract is that these must leave the instruction in
653 // the desired state; must not assume anything about the state of
654 // the instruction. We make multiple passes over some basic blocks
655 // and the last pass is the only one whose result is valid.
656 void handle_AccessField (AccessField* x);
657 void handle_ArrayLength (ArrayLength* x);
658 void handle_LoadIndexed (LoadIndexed* x);
659 void handle_StoreIndexed (StoreIndexed* x);
660 void handle_NullCheck (NullCheck* x);
661 void handle_Invoke (Invoke* x);
662 void handle_NewInstance (NewInstance* x);
663 void handle_NewValueTypeInstance(NewValueTypeInstance* x);
664 void handle_NewArray (NewArray* x);
665 void handle_AccessMonitor (AccessMonitor* x);
666 void handle_Intrinsic (Intrinsic* x);
667 void handle_ExceptionObject (ExceptionObject* x);
668 void handle_Phi (Phi* x);
669 void handle_ProfileCall (ProfileCall* x);
670 void handle_ProfileReturnType (ProfileReturnType* x);
671 };
672
673
674 // NEEDS_CLEANUP
675 // There may be other instructions which need to clear the last
676 // explicit null check. Anything across which we can not hoist the
677 // debug information for a NullCheck instruction must clear it. It
678 // might be safer to pattern match "NullCheck ; {AccessField,
679 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
680 // Should test to see performance hit of clearing it for all handlers
681 // with empty bodies below. If it is negligible then we should leave
682 // that in for safety, otherwise should think more about it.
683 void NullCheckVisitor::do_Phi (Phi* x) { nce()->handle_Phi(x); }
684 void NullCheckVisitor::do_Local (Local* x) {}
685 void NullCheckVisitor::do_Constant (Constant* x) { /* FIXME: handle object constants */ }
686 void NullCheckVisitor::do_LoadField (LoadField* x) { nce()->handle_AccessField(x); }
687 void NullCheckVisitor::do_StoreField (StoreField* x) { nce()->handle_AccessField(x); }
688 void NullCheckVisitor::do_ArrayLength (ArrayLength* x) { nce()->handle_ArrayLength(x); }
689 void NullCheckVisitor::do_LoadIndexed (LoadIndexed* x) { nce()->handle_LoadIndexed(x); }
690 void NullCheckVisitor::do_StoreIndexed (StoreIndexed* x) { nce()->handle_StoreIndexed(x); }
691 void NullCheckVisitor::do_NegateOp (NegateOp* x) {}
692 void NullCheckVisitor::do_ArithmeticOp (ArithmeticOp* x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
693 void NullCheckVisitor::do_ShiftOp (ShiftOp* x) {}
694 void NullCheckVisitor::do_LogicOp (LogicOp* x) {}
695 void NullCheckVisitor::do_CompareOp (CompareOp* x) {}
696 void NullCheckVisitor::do_IfOp (IfOp* x) {}
697 void NullCheckVisitor::do_Convert (Convert* x) {}
698 void NullCheckVisitor::do_NullCheck (NullCheck* x) { nce()->handle_NullCheck(x); }
699 void NullCheckVisitor::do_TypeCast (TypeCast* x) {}
700 void NullCheckVisitor::do_Invoke (Invoke* x) { nce()->handle_Invoke(x); }
701 void NullCheckVisitor::do_NewInstance (NewInstance* x) { nce()->handle_NewInstance(x); }
702 void NullCheckVisitor::do_NewValueTypeInstance(NewValueTypeInstance* x) { nce()->handle_NewValueTypeInstance(x); }
703 void NullCheckVisitor::do_NewTypeArray (NewTypeArray* x) { nce()->handle_NewArray(x); }
704 void NullCheckVisitor::do_NewObjectArray (NewObjectArray* x) { nce()->handle_NewArray(x); }
705 void NullCheckVisitor::do_NewMultiArray (NewMultiArray* x) { nce()->handle_NewArray(x); }
706 void NullCheckVisitor::do_CheckCast (CheckCast* x) { nce()->clear_last_explicit_null_check(); }
707 void NullCheckVisitor::do_InstanceOf (InstanceOf* x) {}
708 void NullCheckVisitor::do_MonitorEnter (MonitorEnter* x) { nce()->handle_AccessMonitor(x); }
709 void NullCheckVisitor::do_MonitorExit (MonitorExit* x) { nce()->handle_AccessMonitor(x); }
710 void NullCheckVisitor::do_Intrinsic (Intrinsic* x) { nce()->handle_Intrinsic(x); }
711 void NullCheckVisitor::do_BlockBegin (BlockBegin* x) {}
712 void NullCheckVisitor::do_Goto (Goto* x) {}
713 void NullCheckVisitor::do_If (If* x) {}
714 void NullCheckVisitor::do_IfInstanceOf (IfInstanceOf* x) {}
715 void NullCheckVisitor::do_TableSwitch (TableSwitch* x) {}
716 void NullCheckVisitor::do_LookupSwitch (LookupSwitch* x) {}
717 void NullCheckVisitor::do_Return (Return* x) {}
718 void NullCheckVisitor::do_Throw (Throw* x) { nce()->clear_last_explicit_null_check(); }
719 void NullCheckVisitor::do_Base (Base* x) {}
720 void NullCheckVisitor::do_OsrEntry (OsrEntry* x) {}
721 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
722 void NullCheckVisitor::do_RoundFP (RoundFP* x) {}
723 void NullCheckVisitor::do_UnsafeGetRaw (UnsafeGetRaw* x) {}
724 void NullCheckVisitor::do_UnsafePutRaw (UnsafePutRaw* x) {}
725 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
726 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
727 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
728 void NullCheckVisitor::do_ProfileCall (ProfileCall* x) { nce()->clear_last_explicit_null_check();
729 nce()->handle_ProfileCall(x); }
730 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
731 void NullCheckVisitor::do_ProfileInvoke (ProfileInvoke* x) {}
732 void NullCheckVisitor::do_RuntimeCall (RuntimeCall* x) {}
733 void NullCheckVisitor::do_MemBar (MemBar* x) {}
734 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
735 #ifdef ASSERT
736 void NullCheckVisitor::do_Assert (Assert* x) {}
737 #endif
738
739 void NullCheckEliminator::visit(Value* p) {
740 assert(*p != NULL, "should not find NULL instructions");
741 if (visitable(*p)) {
742 mark_visited(*p);
743 (*p)->visit(&_visitor);
744 }
745 }
746
747 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
748 ValueSet* state = state_for(block);
749 if (state == NULL) {
750 state = incoming_state->copy();
751 set_state_for(block, state);
752 return true;
753 } else {
754 bool changed = state->set_intersect(incoming_state);
755 if (PrintNullCheckElimination && changed) {
756 tty->print_cr("Block %d's null check state changed", block->block_id());
757 }
758 return changed;
759 }
760 }
761
762
763 void NullCheckEliminator::iterate_all() {
764 while (work_list()->length() > 0) {
765 iterate_one(work_list()->pop());
766 }
767 }
768
769
770 void NullCheckEliminator::iterate_one(BlockBegin* block) {
771 clear_visitable_state();
772 // clear out an old explicit null checks
773 set_last_explicit_null_check(NULL);
774
775 if (PrintNullCheckElimination) {
776 tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
777 block->block_id(),
778 ir()->method()->holder()->name()->as_utf8(),
779 ir()->method()->name()->as_utf8(),
780 ir()->method()->signature()->as_symbol()->as_utf8());
781 }
782
783 // Create new state if none present (only happens at root)
784 if (state_for(block) == NULL) {
785 ValueSet* tmp_state = new ValueSet();
786 set_state_for(block, tmp_state);
787 // Initial state is that local 0 (receiver) is non-null for
788 // non-static methods
789 ValueStack* stack = block->state();
790 IRScope* scope = stack->scope();
791 ciMethod* method = scope->method();
792 if (!method->is_static()) {
793 Local* local0 = stack->local_at(0)->as_Local();
794 assert(local0 != NULL, "must be");
795 assert(local0->type() == objectType, "invalid type of receiver");
796
797 if (local0 != NULL) {
798 // Local 0 is used in this scope
799 tmp_state->put(local0);
800 if (PrintNullCheckElimination) {
801 tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
802 }
803 }
804 }
805 }
806
807 // Must copy block's state to avoid mutating it during iteration
808 // through the block -- otherwise "not-null" states can accidentally
809 // propagate "up" through the block during processing of backward
810 // branches and algorithm is incorrect (and does not converge)
811 set_state_from(state_for(block));
812
813 // allow visiting of Phis belonging to this block
814 for_each_phi_fun(block, phi,
815 mark_visitable(phi);
816 );
817
818 BlockEnd* e = block->end();
819 assert(e != NULL, "incomplete graph");
820 int i;
821
822 // Propagate the state before this block into the exception
823 // handlers. They aren't true successors since we aren't guaranteed
824 // to execute the whole block before executing them. Also putting
825 // them on first seems to help reduce the amount of iteration to
826 // reach a fixed point.
827 for (i = 0; i < block->number_of_exception_handlers(); i++) {
828 BlockBegin* next = block->exception_handler_at(i);
829 if (merge_state_for(next, state())) {
830 if (!work_list()->contains(next)) {
831 work_list()->push(next);
832 }
833 }
834 }
835
836 // Iterate through block, updating state.
837 for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
838 // Mark instructions in this block as visitable as they are seen
839 // in the instruction list. This keeps the iteration from
840 // visiting instructions which are references in other blocks or
841 // visiting instructions more than once.
842 mark_visitable(instr);
843 if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
844 mark_visited(instr);
845 instr->input_values_do(this);
846 instr->visit(&_visitor);
847 }
848 }
849
850 // Propagate state to successors if necessary
851 for (i = 0; i < e->number_of_sux(); i++) {
852 BlockBegin* next = e->sux_at(i);
853 if (merge_state_for(next, state())) {
854 if (!work_list()->contains(next)) {
855 work_list()->push(next);
856 }
857 }
858 }
859 }
860
861
862 void NullCheckEliminator::iterate(BlockBegin* block) {
863 work_list()->push(block);
864 iterate_all();
865 }
866
867 void NullCheckEliminator::handle_AccessField(AccessField* x) {
868 if (x->is_static()) {
869 if (x->as_LoadField() != NULL) {
870 // If the field is a non-null static final object field (as is
871 // often the case for sun.misc.Unsafe), put this LoadField into
872 // the non-null map
873 ciField* field = x->field();
874 if (field->is_constant()) {
875 ciConstant field_val = field->constant_value();
876 BasicType field_type = field_val.basic_type();
877 if (field_type == T_OBJECT || field_type == T_ARRAY || field_type == T_VALUETYPE) {
878 ciObject* obj_val = field_val.as_object();
879 if (!obj_val->is_null_object()) {
880 if (PrintNullCheckElimination) {
881 tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
882 x->id());
883 }
884 set_put(x);
885 }
886 }
887 }
888 }
889 // Be conservative
890 clear_last_explicit_null_check();
891 return;
892 }
893
894 Value obj = x->obj();
895 if (set_contains(obj)) {
896 // Value is non-null => update AccessField
897 if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
898 x->set_explicit_null_check(consume_last_explicit_null_check());
899 x->set_needs_null_check(true);
900 if (PrintNullCheckElimination) {
901 tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
902 x->explicit_null_check()->id(), x->id(), obj->id());
903 }
904 } else {
905 x->set_explicit_null_check(NULL);
906 x->set_needs_null_check(false);
907 if (PrintNullCheckElimination) {
908 tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
909 }
910 }
911 } else {
912 set_put(obj);
913 if (PrintNullCheckElimination) {
914 tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
915 }
916 // Ensure previous passes do not cause wrong state
917 x->set_needs_null_check(true);
918 x->set_explicit_null_check(NULL);
919 }
920 clear_last_explicit_null_check();
921 }
922
923
924 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
925 Value array = x->array();
926 if (set_contains(array)) {
927 // Value is non-null => update AccessArray
928 if (last_explicit_null_check_obj() == array) {
929 x->set_explicit_null_check(consume_last_explicit_null_check());
930 x->set_needs_null_check(true);
931 if (PrintNullCheckElimination) {
932 tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
933 x->explicit_null_check()->id(), x->id(), array->id());
934 }
935 } else {
936 x->set_explicit_null_check(NULL);
937 x->set_needs_null_check(false);
938 if (PrintNullCheckElimination) {
939 tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
940 }
941 }
942 } else {
943 set_put(array);
944 if (PrintNullCheckElimination) {
945 tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
946 }
947 // Ensure previous passes do not cause wrong state
948 x->set_needs_null_check(true);
949 x->set_explicit_null_check(NULL);
950 }
951 clear_last_explicit_null_check();
952 }
953
954
955 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
956 Value array = x->array();
957 if (set_contains(array)) {
958 // Value is non-null => update AccessArray
959 if (last_explicit_null_check_obj() == array) {
960 x->set_explicit_null_check(consume_last_explicit_null_check());
961 x->set_needs_null_check(true);
962 if (PrintNullCheckElimination) {
963 tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
964 x->explicit_null_check()->id(), x->id(), array->id());
965 }
966 } else {
967 x->set_explicit_null_check(NULL);
968 x->set_needs_null_check(false);
969 if (PrintNullCheckElimination) {
970 tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
971 }
972 }
973 } else {
974 set_put(array);
975 if (PrintNullCheckElimination) {
976 tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
977 }
978 // Ensure previous passes do not cause wrong state
979 x->set_needs_null_check(true);
980 x->set_explicit_null_check(NULL);
981 }
982 clear_last_explicit_null_check();
983 }
984
985
986 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
987 Value array = x->array();
988 if (set_contains(array)) {
989 // Value is non-null => update AccessArray
990 if (PrintNullCheckElimination) {
991 tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
992 }
993 x->set_needs_null_check(false);
994 } else {
995 set_put(array);
996 if (PrintNullCheckElimination) {
997 tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
998 }
999 // Ensure previous passes do not cause wrong state
1000 x->set_needs_null_check(true);
1001 }
1002 clear_last_explicit_null_check();
1003 }
1004
1005
1006 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
1007 Value obj = x->obj();
1008 if (set_contains(obj)) {
1009 // Already proven to be non-null => this NullCheck is useless
1010 if (PrintNullCheckElimination) {
1011 tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
1012 }
1013 // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
1014 // The code generator won't emit LIR for a NullCheck that cannot trap.
1015 x->set_can_trap(false);
1016 } else {
1017 // May be null => add to map and set last explicit NullCheck
1018 x->set_can_trap(true);
1019 // make sure it's pinned if it can trap
1020 x->pin(Instruction::PinExplicitNullCheck);
1021 set_put(obj);
1022 set_last_explicit_null_check(x);
1023 if (PrintNullCheckElimination) {
1024 tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1025 }
1026 }
1027 }
1028
1029
1030 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1031 if (!x->has_receiver()) {
1032 // Be conservative
1033 clear_last_explicit_null_check();
1034 return;
1035 }
1036
1037 Value recv = x->receiver();
1038 if (!set_contains(recv)) {
1039 set_put(recv);
1040 if (PrintNullCheckElimination) {
1041 tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1042 }
1043 }
1044 clear_last_explicit_null_check();
1045 }
1046
1047
1048 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1049 set_put(x);
1050 if (PrintNullCheckElimination) {
1051 tty->print_cr("NewInstance %d is non-null", x->id());
1052 }
1053 }
1054
1055 void NullCheckEliminator::handle_NewValueTypeInstance(NewValueTypeInstance* x) {
1056 set_put(x);
1057 if (PrintNullCheckElimination) {
1058 tty->print_cr("NewValueTypeInstance %d is non-null", x->id());
1059 }
1060 }
1061
1062
1063 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1064 set_put(x);
1065 if (PrintNullCheckElimination) {
1066 tty->print_cr("NewArray %d is non-null", x->id());
1067 }
1068 }
1069
1070
1071 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1072 set_put(x);
1073 if (PrintNullCheckElimination) {
1074 tty->print_cr("ExceptionObject %d is non-null", x->id());
1075 }
1076 }
1077
1078
1079 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1080 Value obj = x->obj();
1081 if (set_contains(obj)) {
1082 // Value is non-null => update AccessMonitor
1083 if (PrintNullCheckElimination) {
1084 tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1085 }
1086 x->set_needs_null_check(false);
1087 } else {
1088 set_put(obj);
1089 if (PrintNullCheckElimination) {
1090 tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1091 }
1092 // Ensure previous passes do not cause wrong state
1093 x->set_needs_null_check(true);
1094 }
1095 clear_last_explicit_null_check();
1096 }
1097
1098
1099 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1100 if (!x->has_receiver()) {
1101 if (x->id() == vmIntrinsics::_arraycopy) {
1102 for (int i = 0; i < x->number_of_arguments(); i++) {
1103 x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1104 }
1105 }
1106
1107 // Be conservative
1108 clear_last_explicit_null_check();
1109 return;
1110 }
1111
1112 Value recv = x->receiver();
1113 if (set_contains(recv)) {
1114 // Value is non-null => update Intrinsic
1115 if (PrintNullCheckElimination) {
1116 tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1117 }
1118 x->set_needs_null_check(false);
1119 } else {
1120 set_put(recv);
1121 if (PrintNullCheckElimination) {
1122 tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1123 }
1124 // Ensure previous passes do not cause wrong state
1125 x->set_needs_null_check(true);
1126 }
1127 clear_last_explicit_null_check();
1128 }
1129
1130
1131 void NullCheckEliminator::handle_Phi(Phi* x) {
1132 int i;
1133 bool all_non_null = true;
1134 if (x->is_illegal()) {
1135 all_non_null = false;
1136 } else {
1137 for (i = 0; i < x->operand_count(); i++) {
1138 Value input = x->operand_at(i);
1139 if (!set_contains(input)) {
1140 all_non_null = false;
1141 }
1142 }
1143 }
1144
1145 if (all_non_null) {
1146 // Value is non-null => update Phi
1147 if (PrintNullCheckElimination) {
1148 tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1149 }
1150 x->set_needs_null_check(false);
1151 } else if (set_contains(x)) {
1152 set_remove(x);
1153 }
1154 }
1155
1156 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1157 for (int i = 0; i < x->nb_profiled_args(); i++) {
1158 x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1159 }
1160 }
1161
1162 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1163 x->set_needs_null_check(!set_contains(x->ret()));
1164 }
1165
1166 void Optimizer::eliminate_null_checks() {
1167 ResourceMark rm;
1168
1169 NullCheckEliminator nce(this);
1170
1171 if (PrintNullCheckElimination) {
1172 tty->print_cr("Starting null check elimination for method %s::%s%s",
1173 ir()->method()->holder()->name()->as_utf8(),
1174 ir()->method()->name()->as_utf8(),
1175 ir()->method()->signature()->as_symbol()->as_utf8());
1176 }
1177
1178 // Apply to graph
1179 nce.iterate(ir()->start());
1180
1181 // walk over the graph looking for exception
1182 // handlers and iterate over them as well
1183 int nblocks = BlockBegin::number_of_blocks();
1184 BlockList blocks(nblocks);
1185 boolArray visited_block(nblocks, nblocks, false);
1186
1187 blocks.push(ir()->start());
1188 visited_block.at_put(ir()->start()->block_id(), true);
1189 for (int i = 0; i < blocks.length(); i++) {
1190 BlockBegin* b = blocks.at(i);
1191 // exception handlers need to be treated as additional roots
1192 for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1193 BlockBegin* excp = b->exception_handler_at(e);
1194 int id = excp->block_id();
1195 if (!visited_block.at(id)) {
1196 blocks.push(excp);
1197 visited_block.at_put(id, true);
1198 nce.iterate(excp);
1199 }
1200 }
1201 // traverse successors
1202 BlockEnd *end = b->end();
1203 for (int s = end->number_of_sux(); s-- > 0; ) {
1204 BlockBegin* next = end->sux_at(s);
1205 int id = next->block_id();
1206 if (!visited_block.at(id)) {
1207 blocks.push(next);
1208 visited_block.at_put(id, true);
1209 }
1210 }
1211 }
1212
1213
1214 if (PrintNullCheckElimination) {
1215 tty->print_cr("Done with null check elimination for method %s::%s%s",
1216 ir()->method()->holder()->name()->as_utf8(),
1217 ir()->method()->name()->as_utf8(),
1218 ir()->method()->signature()->as_symbol()->as_utf8());
1219 }
1220 }