1 /*
2 * Copyright (c) 1999, 2025, 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 "c1/c1_Optimizer.hpp"
26 #include "c1/c1_ValueSet.hpp"
27 #include "c1/c1_ValueStack.hpp"
28 #include "compiler/compileLog.hpp"
29 #include "memory/resourceArea.hpp"
30 #include "utilities/bitMap.inline.hpp"
31
32 typedef GrowableArray<ValueSet*> ValueSetList;
33
34 Optimizer::Optimizer(IR* ir) {
35 assert(ir->is_valid(), "IR must be valid");
36 _ir = ir;
37 }
38
39 class CE_Eliminator: public BlockClosure {
40 private:
41 IR* _hir;
42 int _cee_count; // the number of CEs successfully eliminated
43 int _ifop_count; // the number of IfOps successfully simplified
44 int _has_substitution;
45
46 public:
47 CE_Eliminator(IR* hir) : _hir(hir), _cee_count(0), _ifop_count(0) {
48 _has_substitution = false;
49 _hir->iterate_preorder(this);
50 if (_has_substitution) {
51 // substituted some ifops/phis, so resolve the substitution
52 SubstitutionResolver sr(_hir);
53 }
54
55 CompileLog* log = _hir->compilation()->log();
56 if (log != nullptr)
57 log->set_context("optimize name='cee'");
58 }
59
60 ~CE_Eliminator() {
61 CompileLog* log = _hir->compilation()->log();
62 if (log != nullptr)
63 log->clear_context(); // skip marker if nothing was printed
64 }
65
66 int cee_count() const { return _cee_count; }
67 int ifop_count() const { return _ifop_count; }
68
69 void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
70 int e = sux->number_of_exception_handlers();
71 for (int i = 0; i < e; i++) {
72 BlockBegin* xhandler = sux->exception_handler_at(i);
73 block->add_exception_handler(xhandler);
74
75 assert(xhandler->is_predecessor(sux), "missing predecessor");
76 if (sux->number_of_preds() == 0) {
77 // sux is disconnected from graph so disconnect from exception handlers
78 xhandler->remove_predecessor(sux);
79 }
80 if (!xhandler->is_predecessor(block)) {
81 xhandler->add_predecessor(block);
82 }
83 }
84 }
85
86 virtual void block_do(BlockBegin* block);
87
88 private:
89 Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
90 };
91
92 void CE_Eliminator::block_do(BlockBegin* block) {
93 // 1) find conditional expression
94 // check if block ends with an If
95 If* if_ = block->end()->as_If();
96 if (if_ == nullptr) return;
97
98 // check if If works on int or object types
99 // (we cannot handle If's working on long, float or doubles yet,
100 // since IfOp doesn't support them - these If's show up if cmp
101 // operations followed by If's are eliminated)
102 ValueType* if_type = if_->x()->type();
103 if (!if_type->is_int() && !if_type->is_object()) return;
104
105 BlockBegin* t_block = if_->tsux();
106 BlockBegin* f_block = if_->fsux();
107 Instruction* t_cur = t_block->next();
108 Instruction* f_cur = f_block->next();
109
110 // one Constant may be present between BlockBegin and BlockEnd
111 Value t_const = nullptr;
112 Value f_const = nullptr;
113 if (t_cur->as_Constant() != nullptr && !t_cur->can_trap()) {
114 t_const = t_cur;
115 t_cur = t_cur->next();
116 }
117 if (f_cur->as_Constant() != nullptr && !f_cur->can_trap()) {
118 f_const = f_cur;
119 f_cur = f_cur->next();
120 }
121
122 // check if both branches end with a goto
123 Goto* t_goto = t_cur->as_Goto();
124 if (t_goto == nullptr) return;
125 Goto* f_goto = f_cur->as_Goto();
126 if (f_goto == nullptr) return;
127
128 // check if both gotos merge into the same block
129 BlockBegin* sux = t_goto->default_sux();
130 if (sux != f_goto->default_sux()) return;
131
132 // check if at least one word was pushed on sux_state
133 // inlining depths must match
134 ValueStack* if_state = if_->state();
135 ValueStack* sux_state = sux->state();
136 if (if_state->scope()->level() > sux_state->scope()->level()) {
137 while (sux_state->scope() != if_state->scope()) {
138 if_state = if_state->caller_state();
139 assert(if_state != nullptr, "states do not match up");
140 }
141 } else if (if_state->scope()->level() < sux_state->scope()->level()) {
142 while (sux_state->scope() != if_state->scope()) {
143 sux_state = sux_state->caller_state();
144 assert(sux_state != nullptr, "states do not match up");
145 }
146 }
147
148 if (sux_state->stack_size() <= if_state->stack_size()) return;
149
150 // check if phi function is present at end of successor stack and that
151 // only this phi was pushed on the stack
152 Value sux_phi = sux_state->stack_at(if_state->stack_size());
153 if (sux_phi == nullptr || sux_phi->as_Phi() == nullptr || sux_phi->as_Phi()->block() != sux) return;
154 if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
155
156 // get the values that were pushed in the true- and false-branch
157 Value t_value = t_goto->state()->stack_at(if_state->stack_size());
158 Value f_value = f_goto->state()->stack_at(if_state->stack_size());
159
160 // backend does not support floats
161 assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
162 if (t_value->type()->is_float_kind()) return;
163
164 // check that successor has no other phi functions but sux_phi
165 // this can happen when t_block or f_block contained additional stores to local variables
166 // that are no longer represented by explicit instructions
167 for_each_phi_fun(sux, phi,
168 if (phi != sux_phi) return;
169 );
170 // true and false blocks can't have phis
171 for_each_phi_fun(t_block, phi, return; );
172 for_each_phi_fun(f_block, phi, return; );
173
174 // Only replace safepoint gotos if state_before information is available (if is a safepoint)
175 bool is_safepoint = if_->is_safepoint();
176 if (!is_safepoint && (t_goto->is_safepoint() || f_goto->is_safepoint())) {
177 return;
178 }
179
180 #ifdef ASSERT
181 #define DO_DELAYED_VERIFICATION
182 /*
183 * We need to verify the internal representation after modifying it.
184 * Verifying only the blocks that have been tampered with is cheaper than verifying the whole graph, but we must
185 * capture blocks_to_verify_later before making the changes, since they might not be reachable afterwards.
186 * DO_DELAYED_VERIFICATION ensures that the code for this is either enabled in full, or not at all.
187 */
188 #endif // ASSERT
189
190 #ifdef DO_DELAYED_VERIFICATION
191 BlockList blocks_to_verify_later;
192 blocks_to_verify_later.append(block);
193 blocks_to_verify_later.append(t_block);
194 blocks_to_verify_later.append(f_block);
195 blocks_to_verify_later.append(sux);
196 _hir->expand_with_neighborhood(blocks_to_verify_later);
197 #endif // DO_DELAYED_VERIFICATION
198
199 // 2) substitute conditional expression
200 // with an IfOp followed by a Goto
201 // cut if_ away and get node before
202 Instruction* cur_end = if_->prev();
203
204 // append constants of true- and false-block if necessary
205 // clone constants because original block must not be destroyed
206 assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
207 if (t_value == t_const) {
208 t_value = new Constant(t_const->type());
209 NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
210 cur_end = cur_end->set_next(t_value);
211 }
212 if (f_value == f_const) {
213 f_value = new Constant(f_const->type());
214 NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
215 cur_end = cur_end->set_next(f_value);
216 }
217
218 Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
219 assert(result != nullptr, "make_ifop must return a non-null instruction");
220 if (!result->is_linked() && result->can_be_linked()) {
221 NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
222 cur_end = cur_end->set_next(result);
223 }
224
225 // append Goto to successor
226 ValueStack* state_before = if_->state_before();
227 Goto* goto_ = new Goto(sux, state_before, is_safepoint);
228
229 // prepare state for Goto
230 ValueStack* goto_state = if_state;
231 goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
232 goto_state->push(result->type(), result);
233 assert(goto_state->is_same(sux_state), "states must match now");
234 goto_->set_state(goto_state);
235
236 cur_end = cur_end->set_next(goto_, goto_state->bci());
237
238 // Adjust control flow graph
239 BlockBegin::disconnect_edge(block, t_block);
240 BlockBegin::disconnect_edge(block, f_block);
241 if (t_block->number_of_preds() == 0) {
242 BlockBegin::disconnect_edge(t_block, sux);
243 }
244 adjust_exception_edges(block, t_block);
245 if (f_block->number_of_preds() == 0) {
246 BlockBegin::disconnect_edge(f_block, sux);
247 }
248 adjust_exception_edges(block, f_block);
249
250 // update block end
251 block->set_end(goto_);
252
253 // substitute the phi if possible
254 if (sux_phi->as_Phi()->operand_count() == 1) {
255 assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
256 sux_phi->set_subst(result);
257 _has_substitution = true;
258 }
259
260 // 3) successfully eliminated a conditional expression
261 _cee_count++;
262 if (PrintCEE) {
263 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());
264 tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
265 }
266
267 #ifdef DO_DELAYED_VERIFICATION
268 _hir->verify_local(blocks_to_verify_later);
269 #endif // DO_DELAYED_VERIFICATION
270
271 }
272
273 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
274 if (!OptimizeIfOps) {
275 return new IfOp(x, cond, y, tval, fval);
276 }
277
278 tval = tval->subst();
279 fval = fval->subst();
280 if (tval == fval) {
281 _ifop_count++;
282 return tval;
283 }
284
285 x = x->subst();
286 y = y->subst();
287
288 Constant* y_const = y->as_Constant();
289 if (y_const != nullptr) {
290 IfOp* x_ifop = x->as_IfOp();
291 if (x_ifop != nullptr) { // x is an ifop, y is a constant
292 Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
293 Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
294
295 if (x_tval_const != nullptr && x_fval_const != nullptr) {
296 Instruction::Condition x_ifop_cond = x_ifop->cond();
297
298 Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
299 Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
300
301 // not_comparable here is a valid return in case we're comparing unloaded oop constants
302 if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
303 Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
304 Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
305
306 _ifop_count++;
307 if (new_tval == new_fval) {
308 return new_tval;
309 } else {
310 return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
311 }
312 }
313 }
314 } else {
315 Constant* x_const = x->as_Constant();
316 if (x_const != nullptr) { // x and y are constants
317 Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
318 // not_comparable here is a valid return in case we're comparing unloaded oop constants
319 if (x_compare_res != Constant::not_comparable) {
320 _ifop_count++;
321 return x_compare_res == Constant::cond_true ? tval : fval;
322 }
323 }
324 }
325 }
326 return new IfOp(x, cond, y, tval, fval);
327 }
328
329 void Optimizer::eliminate_conditional_expressions() {
330 // find conditional expressions & replace them with IfOps
331 CE_Eliminator ce(ir());
332 }
333
334 // This removes others' relation to block, but doesn't empty block's lists
335 static void disconnect_from_graph(BlockBegin* block) {
336 for (int p = 0; p < block->number_of_preds(); p++) {
337 BlockBegin* pred = block->pred_at(p);
338 int idx;
339 while ((idx = pred->end()->find_sux(block)) >= 0) {
340 pred->end()->remove_sux_at(idx);
341 }
342 }
343 for (int s = 0; s < block->number_of_sux(); s++) {
344 block->sux_at(s)->remove_predecessor(block);
345 }
346 }
347
348 class BlockMerger: public BlockClosure {
349 private:
350 IR* _hir;
351 int _merge_count; // the number of block pairs successfully merged
352
353 public:
354 BlockMerger(IR* hir)
355 : _hir(hir)
356 , _merge_count(0)
357 {
358 _hir->iterate_preorder(this);
359 CompileLog* log = _hir->compilation()->log();
360 if (log != nullptr)
361 log->set_context("optimize name='eliminate_blocks'");
362 }
363
364 ~BlockMerger() {
365 CompileLog* log = _hir->compilation()->log();
366 if (log != nullptr)
367 log->clear_context(); // skip marker if nothing was printed
368 }
369
370 bool try_merge(BlockBegin* block) {
371 BlockEnd* end = block->end();
372 if (end->as_Goto() == nullptr) return false;
373
374 assert(end->number_of_sux() == 1, "end must have exactly one successor");
375 // Note: It would be sufficient to check for the number of successors (= 1)
376 // in order to decide if this block can be merged potentially. That
377 // would then also include switch statements w/ only a default case.
378 // However, in that case we would need to make sure the switch tag
379 // expression is executed if it can produce observable side effects.
380 // We should probably have the canonicalizer simplifying such switch
381 // statements and then we are sure we don't miss these merge opportunities
382 // here (was bug - gri 7/7/99).
383 BlockBegin* sux = end->default_sux();
384 if (sux->number_of_preds() != 1 || sux->is_entry_block() || end->is_safepoint()) return false;
385 // merge the two blocks
386
387 #ifdef ASSERT
388 // verify that state at the end of block and at the beginning of sux are equal
389 // no phi functions must be present at beginning of sux
390 ValueStack* sux_state = sux->state();
391 ValueStack* end_state = end->state();
392
393 assert(end_state->scope() == sux_state->scope(), "scopes must match");
394 assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
395 assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
396
397 int index;
398 Value sux_value;
399 for_each_stack_value(sux_state, index, sux_value) {
400 assert(sux_value == end_state->stack_at(index), "stack not equal");
401 }
402 for_each_local_value(sux_state, index, sux_value) {
403 Phi* sux_phi = sux_value->as_Phi();
404 if (sux_phi != nullptr && sux_phi->is_illegal()) continue;
405 assert(sux_value == end_state->local_at(index), "locals not equal");
406 }
407 assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
408 #endif
409
410 #ifdef DO_DELAYED_VERIFICATION
411 BlockList blocks_to_verify_later;
412 blocks_to_verify_later.append(block);
413 _hir->expand_with_neighborhood(blocks_to_verify_later);
414 #endif // DO_DELAYED_VERIFICATION
415
416 // find instruction before end & append first instruction of sux block
417 Instruction* prev = end->prev();
418 Instruction* next = sux->next();
419 assert(prev->as_BlockEnd() == nullptr, "must not be a BlockEnd");
420 prev->set_next(next);
421 prev->fixup_block_pointers();
422
423 // disconnect this block from all other blocks
424 disconnect_from_graph(sux);
425 #ifdef DO_DELAYED_VERIFICATION
426 blocks_to_verify_later.remove(sux); // Sux is not part of graph anymore
427 #endif // DO_DELAYED_VERIFICATION
428 block->set_end(sux->end());
429
430 // TODO Should this be done in set_end universally?
431 // add exception handlers of deleted block, if any
432 for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
433 BlockBegin* xhandler = sux->exception_handler_at(k);
434 block->add_exception_handler(xhandler);
435
436 // TODO This should be in disconnect from graph...
437 // also substitute predecessor of exception handler
438 assert(xhandler->is_predecessor(sux), "missing predecessor");
439 xhandler->remove_predecessor(sux);
440 if (!xhandler->is_predecessor(block)) {
441 xhandler->add_predecessor(block);
442 }
443 }
444
445 // debugging output
446 _merge_count++;
447 if (PrintBlockElimination) {
448 tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
449 _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
450 }
451
452 #ifdef DO_DELAYED_VERIFICATION
453 _hir->verify_local(blocks_to_verify_later);
454 #endif // DO_DELAYED_VERIFICATION
455
456 If* if_ = block->end()->as_If();
457 if (if_) {
458 IfOp* ifop = if_->x()->as_IfOp();
459 Constant* con = if_->y()->as_Constant();
460 bool swapped = false;
461 if (!con || !ifop) {
462 ifop = if_->y()->as_IfOp();
463 con = if_->x()->as_Constant();
464 swapped = true;
465 }
466 if (con && ifop) {
467 Constant* tval = ifop->tval()->as_Constant();
468 Constant* fval = ifop->fval()->as_Constant();
469 if (tval && fval) {
470 // Find the instruction before if_, starting with ifop.
471 // When if_ and ifop are not in the same block, prev
472 // becomes null In such (rare) cases it is not
473 // profitable to perform the optimization.
474 Value prev = ifop;
475 while (prev != nullptr && prev->next() != if_) {
476 prev = prev->next();
477 }
478
479 if (prev != nullptr) {
480 Instruction::Condition cond = if_->cond();
481 BlockBegin* tsux = if_->tsux();
482 BlockBegin* fsux = if_->fsux();
483 if (swapped) {
484 cond = Instruction::mirror(cond);
485 }
486
487 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
488 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
489 if (tblock != fblock && !if_->is_safepoint()) {
490 If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
491 tblock, fblock, if_->state_before(), if_->is_safepoint());
492 newif->set_state(if_->state()->copy());
493
494 assert(prev->next() == if_, "must be guaranteed by above search");
495 NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
496 prev->set_next(newif);
497 block->set_end(newif);
498
499 _merge_count++;
500 if (PrintBlockElimination) {
501 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
502 }
503
504 #ifdef DO_DELAYED_VERIFICATION
505 _hir->verify_local(blocks_to_verify_later);
506 #endif // DO_DELAYED_VERIFICATION
507 }
508 }
509 }
510 }
511 }
512
513 return true;
514 }
515
516 virtual void block_do(BlockBegin* block) {
517 // repeat since the same block may merge again
518 while (try_merge(block)) ;
519 }
520 };
521
522 #ifdef ASSERT
523 #undef DO_DELAYED_VERIFICATION
524 #endif // ASSERT
525
526 void Optimizer::eliminate_blocks() {
527 // merge blocks if possible
528 BlockMerger bm(ir());
529 }
530
531
532 class NullCheckEliminator;
533 class NullCheckVisitor: public InstructionVisitor {
534 private:
535 NullCheckEliminator* _nce;
536 NullCheckEliminator* nce() { return _nce; }
537
538 public:
539 NullCheckVisitor() {}
540
541 void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
542
543 void do_Phi (Phi* x);
544 void do_Local (Local* x);
545 void do_Constant (Constant* x);
546 void do_LoadField (LoadField* x);
547 void do_StoreField (StoreField* x);
548 void do_ArrayLength (ArrayLength* x);
549 void do_LoadIndexed (LoadIndexed* x);
550 void do_StoreIndexed (StoreIndexed* x);
551 void do_NegateOp (NegateOp* x);
552 void do_ArithmeticOp (ArithmeticOp* x);
553 void do_ShiftOp (ShiftOp* x);
554 void do_LogicOp (LogicOp* x);
555 void do_CompareOp (CompareOp* x);
556 void do_IfOp (IfOp* x);
557 void do_Convert (Convert* x);
558 void do_NullCheck (NullCheck* x);
559 void do_TypeCast (TypeCast* x);
560 void do_Invoke (Invoke* x);
561 void do_NewInstance (NewInstance* x);
562 void do_NewTypeArray (NewTypeArray* x);
563 void do_NewObjectArray (NewObjectArray* x);
564 void do_NewMultiArray (NewMultiArray* x);
565 void do_CheckCast (CheckCast* x);
566 void do_InstanceOf (InstanceOf* x);
567 void do_MonitorEnter (MonitorEnter* x);
568 void do_MonitorExit (MonitorExit* x);
569 void do_Intrinsic (Intrinsic* x);
570 void do_BlockBegin (BlockBegin* x);
571 void do_Goto (Goto* x);
572 void do_If (If* x);
573 void do_TableSwitch (TableSwitch* x);
574 void do_LookupSwitch (LookupSwitch* x);
575 void do_Return (Return* x);
576 void do_Throw (Throw* x);
577 void do_Base (Base* x);
578 void do_OsrEntry (OsrEntry* x);
579 void do_ExceptionObject(ExceptionObject* x);
580 void do_UnsafeGet (UnsafeGet* x);
581 void do_UnsafePut (UnsafePut* x);
582 void do_UnsafeGetAndSet(UnsafeGetAndSet* x);
583 void do_ProfileCall (ProfileCall* x);
584 void do_ProfileReturnType (ProfileReturnType* x);
585 void do_ProfileInvoke (ProfileInvoke* x);
586 void do_RuntimeCall (RuntimeCall* x);
587 void do_MemBar (MemBar* x);
588 void do_RangeCheckPredicate(RangeCheckPredicate* x);
589 #ifdef ASSERT
590 void do_Assert (Assert* x);
591 #endif
592 };
593
594
595 // Because of a static contained within (for the purpose of iteration
596 // over instructions), it is only valid to have one of these active at
597 // a time
598 class NullCheckEliminator: public ValueVisitor {
599 private:
600 Optimizer* _opt;
601
602 ValueSet* _visitable_instructions; // Visit each instruction only once per basic block
603 BlockList* _work_list; // Basic blocks to visit
604
605 bool visitable(Value x) {
606 assert(_visitable_instructions != nullptr, "check");
607 return _visitable_instructions->contains(x);
608 }
609 void mark_visited(Value x) {
610 assert(_visitable_instructions != nullptr, "check");
611 _visitable_instructions->remove(x);
612 }
613 void mark_visitable(Value x) {
614 assert(_visitable_instructions != nullptr, "check");
615 _visitable_instructions->put(x);
616 }
617 void clear_visitable_state() {
618 assert(_visitable_instructions != nullptr, "check");
619 _visitable_instructions->clear();
620 }
621
622 ValueSet* _set; // current state, propagated to subsequent BlockBegins
623 ValueSetList _block_states; // BlockBegin null-check states for all processed blocks
624 NullCheckVisitor _visitor;
625 NullCheck* _last_explicit_null_check;
626
627 bool set_contains(Value x) { assert(_set != nullptr, "check"); return _set->contains(x); }
628 void set_put (Value x) { assert(_set != nullptr, "check"); _set->put(x); }
629 void set_remove (Value x) { assert(_set != nullptr, "check"); _set->remove(x); }
630
631 BlockList* work_list() { return _work_list; }
632
633 void iterate_all();
634 void iterate_one(BlockBegin* block);
635
636 ValueSet* state() { return _set; }
637 void set_state_from (ValueSet* state) { _set->set_from(state); }
638 ValueSet* state_for (BlockBegin* block) { return _block_states.at(block->block_id()); }
639 void set_state_for (BlockBegin* block, ValueSet* stack) { _block_states.at_put(block->block_id(), stack); }
640 // Returns true if caused a change in the block's state.
641 bool merge_state_for(BlockBegin* block,
642 ValueSet* incoming_state);
643
644 public:
645 // constructor
646 NullCheckEliminator(Optimizer* opt)
647 : _opt(opt)
648 , _work_list(new BlockList())
649 , _set(new ValueSet())
650 , _block_states(BlockBegin::number_of_blocks(), BlockBegin::number_of_blocks(), nullptr)
651 , _last_explicit_null_check(nullptr) {
652 _visitable_instructions = new ValueSet();
653 _visitor.set_eliminator(this);
654 CompileLog* log = _opt->ir()->compilation()->log();
655 if (log != nullptr)
656 log->set_context("optimize name='null_check_elimination'");
657 }
658
659 ~NullCheckEliminator() {
660 CompileLog* log = _opt->ir()->compilation()->log();
661 if (log != nullptr)
662 log->clear_context(); // skip marker if nothing was printed
663 }
664
665 Optimizer* opt() { return _opt; }
666 IR* ir () { return opt()->ir(); }
667
668 // Process a graph
669 void iterate(BlockBegin* root);
670
671 void visit(Value* f);
672
673 // In some situations (like NullCheck(x); getfield(x)) the debug
674 // information from the explicit NullCheck can be used to populate
675 // the getfield, even if the two instructions are in different
676 // scopes; this allows implicit null checks to be used but the
677 // correct exception information to be generated. We must clear the
678 // last-traversed NullCheck when we reach a potentially-exception-
679 // throwing instruction, as well as in some other cases.
680 void set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
681 NullCheck* last_explicit_null_check() { return _last_explicit_null_check; }
682 Value last_explicit_null_check_obj() { return (_last_explicit_null_check
683 ? _last_explicit_null_check->obj()
684 : nullptr); }
685 NullCheck* consume_last_explicit_null_check() {
686 _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
687 _last_explicit_null_check->set_can_trap(false);
688 return _last_explicit_null_check;
689 }
690 void clear_last_explicit_null_check() { _last_explicit_null_check = nullptr; }
691
692 // Handlers for relevant instructions
693 // (separated out from NullCheckVisitor for clarity)
694
695 // The basic contract is that these must leave the instruction in
696 // the desired state; must not assume anything about the state of
697 // the instruction. We make multiple passes over some basic blocks
698 // and the last pass is the only one whose result is valid.
699 void handle_AccessField (AccessField* x);
700 void handle_ArrayLength (ArrayLength* x);
701 void handle_LoadIndexed (LoadIndexed* x);
702 void handle_StoreIndexed (StoreIndexed* x);
703 void handle_NullCheck (NullCheck* x);
704 void handle_Invoke (Invoke* x);
705 void handle_NewInstance (NewInstance* x);
706 void handle_NewArray (NewArray* x);
707 void handle_AccessMonitor (AccessMonitor* x);
708 void handle_Intrinsic (Intrinsic* x);
709 void handle_ExceptionObject (ExceptionObject* x);
710 void handle_Phi (Phi* x);
711 void handle_ProfileCall (ProfileCall* x);
712 void handle_ProfileReturnType (ProfileReturnType* x);
713 void handle_Constant (Constant* x);
714 void handle_IfOp (IfOp* x);
715 };
716
717
718 // NEEDS_CLEANUP
719 // There may be other instructions which need to clear the last
720 // explicit null check. Anything across which we can not hoist the
721 // debug information for a NullCheck instruction must clear it. It
722 // might be safer to pattern match "NullCheck ; {AccessField,
723 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
724 // Should test to see performance hit of clearing it for all handlers
725 // with empty bodies below. If it is negligible then we should leave
726 // that in for safety, otherwise should think more about it.
727 void NullCheckVisitor::do_Phi (Phi* x) { nce()->handle_Phi(x); }
728 void NullCheckVisitor::do_Local (Local* x) {}
729 void NullCheckVisitor::do_Constant (Constant* x) { nce()->handle_Constant(x); }
730 void NullCheckVisitor::do_LoadField (LoadField* x) { nce()->handle_AccessField(x); }
731 void NullCheckVisitor::do_StoreField (StoreField* x) { nce()->handle_AccessField(x); }
732 void NullCheckVisitor::do_ArrayLength (ArrayLength* x) { nce()->handle_ArrayLength(x); }
733 void NullCheckVisitor::do_LoadIndexed (LoadIndexed* x) { nce()->handle_LoadIndexed(x); }
734 void NullCheckVisitor::do_StoreIndexed (StoreIndexed* x) { nce()->handle_StoreIndexed(x); }
735 void NullCheckVisitor::do_NegateOp (NegateOp* x) {}
736 void NullCheckVisitor::do_ArithmeticOp (ArithmeticOp* x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
737 void NullCheckVisitor::do_ShiftOp (ShiftOp* x) {}
738 void NullCheckVisitor::do_LogicOp (LogicOp* x) {}
739 void NullCheckVisitor::do_CompareOp (CompareOp* x) {}
740 void NullCheckVisitor::do_IfOp (IfOp* x) { nce()->handle_IfOp(x); }
741 void NullCheckVisitor::do_Convert (Convert* x) {}
742 void NullCheckVisitor::do_NullCheck (NullCheck* x) { nce()->handle_NullCheck(x); }
743 void NullCheckVisitor::do_TypeCast (TypeCast* x) {}
744 void NullCheckVisitor::do_Invoke (Invoke* x) { nce()->handle_Invoke(x); }
745 void NullCheckVisitor::do_NewInstance (NewInstance* x) { nce()->handle_NewInstance(x); }
746 void NullCheckVisitor::do_NewTypeArray (NewTypeArray* x) { nce()->handle_NewArray(x); }
747 void NullCheckVisitor::do_NewObjectArray (NewObjectArray* x) { nce()->handle_NewArray(x); }
748 void NullCheckVisitor::do_NewMultiArray (NewMultiArray* x) { nce()->handle_NewArray(x); }
749 void NullCheckVisitor::do_CheckCast (CheckCast* x) { nce()->clear_last_explicit_null_check(); }
750 void NullCheckVisitor::do_InstanceOf (InstanceOf* x) {}
751 void NullCheckVisitor::do_MonitorEnter (MonitorEnter* x) { nce()->handle_AccessMonitor(x); }
752 void NullCheckVisitor::do_MonitorExit (MonitorExit* x) { nce()->handle_AccessMonitor(x); }
753 void NullCheckVisitor::do_Intrinsic (Intrinsic* x) { nce()->handle_Intrinsic(x); }
754 void NullCheckVisitor::do_BlockBegin (BlockBegin* x) {}
755 void NullCheckVisitor::do_Goto (Goto* x) {}
756 void NullCheckVisitor::do_If (If* x) {}
757 void NullCheckVisitor::do_TableSwitch (TableSwitch* x) {}
758 void NullCheckVisitor::do_LookupSwitch (LookupSwitch* x) {}
759 void NullCheckVisitor::do_Return (Return* x) {}
760 void NullCheckVisitor::do_Throw (Throw* x) { nce()->clear_last_explicit_null_check(); }
761 void NullCheckVisitor::do_Base (Base* x) {}
762 void NullCheckVisitor::do_OsrEntry (OsrEntry* x) {}
763 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
764 void NullCheckVisitor::do_UnsafeGet (UnsafeGet* x) {}
765 void NullCheckVisitor::do_UnsafePut (UnsafePut* x) {}
766 void NullCheckVisitor::do_UnsafeGetAndSet(UnsafeGetAndSet* x) {}
767 void NullCheckVisitor::do_ProfileCall (ProfileCall* x) { nce()->clear_last_explicit_null_check();
768 nce()->handle_ProfileCall(x); }
769 void NullCheckVisitor::do_ProfileReturnType (ProfileReturnType* x) { nce()->handle_ProfileReturnType(x); }
770 void NullCheckVisitor::do_ProfileInvoke (ProfileInvoke* x) {}
771 void NullCheckVisitor::do_RuntimeCall (RuntimeCall* x) {}
772 void NullCheckVisitor::do_MemBar (MemBar* x) {}
773 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
774 #ifdef ASSERT
775 void NullCheckVisitor::do_Assert (Assert* x) {}
776 #endif
777
778 void NullCheckEliminator::visit(Value* p) {
779 assert(*p != nullptr, "should not find null instructions");
780 if (visitable(*p)) {
781 mark_visited(*p);
782 (*p)->visit(&_visitor);
783 }
784 }
785
786 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
787 ValueSet* state = state_for(block);
788 if (state == nullptr) {
789 state = incoming_state->copy();
790 set_state_for(block, state);
791 return true;
792 } else {
793 bool changed = state->set_intersect(incoming_state);
794 if (PrintNullCheckElimination && changed) {
795 tty->print_cr("Block %d's null check state changed", block->block_id());
796 }
797 return changed;
798 }
799 }
800
801
802 void NullCheckEliminator::iterate_all() {
803 while (work_list()->length() > 0) {
804 iterate_one(work_list()->pop());
805 }
806 }
807
808
809 void NullCheckEliminator::iterate_one(BlockBegin* block) {
810 clear_visitable_state();
811 // clear out an old explicit null checks
812 set_last_explicit_null_check(nullptr);
813
814 if (PrintNullCheckElimination) {
815 tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
816 block->block_id(),
817 ir()->method()->holder()->name()->as_utf8(),
818 ir()->method()->name()->as_utf8(),
819 ir()->method()->signature()->as_symbol()->as_utf8());
820 }
821
822 // Create new state if none present (only happens at root)
823 if (state_for(block) == nullptr) {
824 ValueSet* tmp_state = new ValueSet();
825 set_state_for(block, tmp_state);
826 // Initial state is that local 0 (receiver) is non-null for
827 // non-static methods
828 ValueStack* stack = block->state();
829 IRScope* scope = stack->scope();
830 ciMethod* method = scope->method();
831 if (!method->is_static()) {
832 Local* local0 = stack->local_at(0)->as_Local();
833 assert(local0 != nullptr, "must be");
834 assert(local0->type() == objectType, "invalid type of receiver");
835
836 if (local0 != nullptr) {
837 // Local 0 is used in this scope
838 tmp_state->put(local0);
839 if (PrintNullCheckElimination) {
840 tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
841 }
842 }
843 }
844 }
845
846 // Must copy block's state to avoid mutating it during iteration
847 // through the block -- otherwise "not-null" states can accidentally
848 // propagate "up" through the block during processing of backward
849 // branches and algorithm is incorrect (and does not converge)
850 set_state_from(state_for(block));
851
852 // allow visiting of Phis belonging to this block
853 for_each_phi_fun(block, phi,
854 mark_visitable(phi);
855 );
856
857 BlockEnd* e = block->end();
858 assert(e != nullptr, "incomplete graph");
859 int i;
860
861 // Propagate the state before this block into the exception
862 // handlers. They aren't true successors since we aren't guaranteed
863 // to execute the whole block before executing them. Also putting
864 // them on first seems to help reduce the amount of iteration to
865 // reach a fixed point.
866 for (i = 0; i < block->number_of_exception_handlers(); i++) {
867 BlockBegin* next = block->exception_handler_at(i);
868 if (merge_state_for(next, state())) {
869 if (!work_list()->contains(next)) {
870 work_list()->push(next);
871 }
872 }
873 }
874
875 // Iterate through block, updating state.
876 for (Instruction* instr = block; instr != nullptr; instr = instr->next()) {
877 // Mark instructions in this block as visitable as they are seen
878 // in the instruction list. This keeps the iteration from
879 // visiting instructions which are references in other blocks or
880 // visiting instructions more than once.
881 mark_visitable(instr);
882 if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != nullptr)
883 || (instr->as_Constant() != nullptr && instr->as_Constant()->type()->is_object())
884 || (instr->as_IfOp() != nullptr)) {
885 mark_visited(instr);
886 instr->input_values_do(this);
887 instr->visit(&_visitor);
888 }
889 }
890
891 // Propagate state to successors if necessary
892 for (i = 0; i < e->number_of_sux(); i++) {
893 BlockBegin* next = e->sux_at(i);
894 if (merge_state_for(next, state())) {
895 if (!work_list()->contains(next)) {
896 work_list()->push(next);
897 }
898 }
899 }
900 }
901
902
903 void NullCheckEliminator::iterate(BlockBegin* block) {
904 work_list()->push(block);
905 iterate_all();
906 }
907
908 void NullCheckEliminator::handle_AccessField(AccessField* x) {
909 if (x->is_static()) {
910 if (x->as_LoadField() != nullptr) {
911 // If the field is a non-null static final object field (as is
912 // often the case for sun.misc.Unsafe), put this LoadField into
913 // the non-null map
914 ciField* field = x->field();
915 if (field->is_constant()) {
916 ciConstant field_val = field->constant_value();
917 BasicType field_type = field_val.basic_type();
918 if (is_reference_type(field_type)) {
919 ciObject* obj_val = field_val.as_object();
920 if (!obj_val->is_null_object()) {
921 if (PrintNullCheckElimination) {
922 tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
923 x->id());
924 }
925 set_put(x);
926 }
927 }
928 }
929 }
930 // Be conservative
931 clear_last_explicit_null_check();
932 return;
933 }
934
935 Value obj = x->obj();
936 if (set_contains(obj)) {
937 // Value is non-null => update AccessField
938 if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
939 x->set_explicit_null_check(consume_last_explicit_null_check());
940 x->set_needs_null_check(true);
941 if (PrintNullCheckElimination) {
942 tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
943 x->explicit_null_check()->id(), x->id(), obj->id());
944 }
945 } else {
946 x->set_explicit_null_check(nullptr);
947 x->set_needs_null_check(false);
948 if (PrintNullCheckElimination) {
949 tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
950 }
951 }
952 } else {
953 set_put(obj);
954 if (PrintNullCheckElimination) {
955 tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
956 }
957 // Ensure previous passes do not cause wrong state
958 x->set_needs_null_check(true);
959 x->set_explicit_null_check(nullptr);
960 }
961 clear_last_explicit_null_check();
962 }
963
964
965 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
966 Value array = x->array();
967 if (set_contains(array)) {
968 // Value is non-null => update AccessArray
969 if (last_explicit_null_check_obj() == array) {
970 x->set_explicit_null_check(consume_last_explicit_null_check());
971 x->set_needs_null_check(true);
972 if (PrintNullCheckElimination) {
973 tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
974 x->explicit_null_check()->id(), x->id(), array->id());
975 }
976 } else {
977 x->set_explicit_null_check(nullptr);
978 x->set_needs_null_check(false);
979 if (PrintNullCheckElimination) {
980 tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
981 }
982 }
983 } else {
984 set_put(array);
985 if (PrintNullCheckElimination) {
986 tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
987 }
988 // Ensure previous passes do not cause wrong state
989 x->set_needs_null_check(true);
990 x->set_explicit_null_check(nullptr);
991 }
992 clear_last_explicit_null_check();
993 }
994
995
996 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
997 Value array = x->array();
998 if (set_contains(array)) {
999 // Value is non-null => update AccessArray
1000 if (last_explicit_null_check_obj() == array) {
1001 x->set_explicit_null_check(consume_last_explicit_null_check());
1002 x->set_needs_null_check(true);
1003 if (PrintNullCheckElimination) {
1004 tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
1005 x->explicit_null_check()->id(), x->id(), array->id());
1006 }
1007 } else {
1008 x->set_explicit_null_check(nullptr);
1009 x->set_needs_null_check(false);
1010 if (PrintNullCheckElimination) {
1011 tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
1012 }
1013 }
1014 } else {
1015 set_put(array);
1016 if (PrintNullCheckElimination) {
1017 tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
1018 }
1019 // Ensure previous passes do not cause wrong state
1020 x->set_needs_null_check(true);
1021 x->set_explicit_null_check(nullptr);
1022 }
1023 clear_last_explicit_null_check();
1024 }
1025
1026
1027 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
1028 Value array = x->array();
1029 if (set_contains(array)) {
1030 // Value is non-null => update AccessArray
1031 if (PrintNullCheckElimination) {
1032 tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
1033 }
1034 x->set_needs_null_check(false);
1035 } else {
1036 set_put(array);
1037 if (PrintNullCheckElimination) {
1038 tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
1039 }
1040 // Ensure previous passes do not cause wrong state
1041 x->set_needs_null_check(true);
1042 }
1043 clear_last_explicit_null_check();
1044 }
1045
1046
1047 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
1048 Value obj = x->obj();
1049 if (set_contains(obj)) {
1050 // Already proven to be non-null => this NullCheck is useless
1051 if (PrintNullCheckElimination) {
1052 tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
1053 }
1054 // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
1055 // The code generator won't emit LIR for a NullCheck that cannot trap.
1056 x->set_can_trap(false);
1057 } else {
1058 // May be null => add to map and set last explicit NullCheck
1059 x->set_can_trap(true);
1060 // make sure it's pinned if it can trap
1061 x->pin(Instruction::PinExplicitNullCheck);
1062 set_put(obj);
1063 set_last_explicit_null_check(x);
1064 if (PrintNullCheckElimination) {
1065 tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1066 }
1067 }
1068 }
1069
1070
1071 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1072 if (!x->has_receiver()) {
1073 // Be conservative
1074 clear_last_explicit_null_check();
1075 return;
1076 }
1077
1078 Value recv = x->receiver();
1079 if (!set_contains(recv)) {
1080 set_put(recv);
1081 if (PrintNullCheckElimination) {
1082 tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1083 }
1084 }
1085 clear_last_explicit_null_check();
1086 }
1087
1088
1089 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1090 set_put(x);
1091 if (PrintNullCheckElimination) {
1092 tty->print_cr("NewInstance %d is non-null", x->id());
1093 }
1094 }
1095
1096
1097 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1098 set_put(x);
1099 if (PrintNullCheckElimination) {
1100 tty->print_cr("NewArray %d is non-null", x->id());
1101 }
1102 }
1103
1104
1105 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1106 set_put(x);
1107 if (PrintNullCheckElimination) {
1108 tty->print_cr("ExceptionObject %d is non-null", x->id());
1109 }
1110 }
1111
1112
1113 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1114 Value obj = x->obj();
1115 if (set_contains(obj)) {
1116 // Value is non-null => update AccessMonitor
1117 if (PrintNullCheckElimination) {
1118 tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1119 }
1120 x->set_needs_null_check(false);
1121 } else {
1122 set_put(obj);
1123 if (PrintNullCheckElimination) {
1124 tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1125 }
1126 // Ensure previous passes do not cause wrong state
1127 x->set_needs_null_check(true);
1128 }
1129 clear_last_explicit_null_check();
1130 }
1131
1132
1133 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1134 if (!x->has_receiver()) {
1135 if (x->id() == vmIntrinsics::_arraycopy) {
1136 for (int i = 0; i < x->number_of_arguments(); i++) {
1137 x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1138 }
1139 }
1140
1141 // Be conservative
1142 clear_last_explicit_null_check();
1143 return;
1144 }
1145
1146 Value recv = x->receiver();
1147 if (set_contains(recv)) {
1148 // Value is non-null => update Intrinsic
1149 if (PrintNullCheckElimination) {
1150 tty->print_cr("Eliminated Intrinsic %d's null check for value %d", vmIntrinsics::as_int(x->id()), recv->id());
1151 }
1152 x->set_needs_null_check(false);
1153 } else {
1154 set_put(recv);
1155 if (PrintNullCheckElimination) {
1156 tty->print_cr("Intrinsic %d of value %d proves value to be non-null", vmIntrinsics::as_int(x->id()), recv->id());
1157 }
1158 // Ensure previous passes do not cause wrong state
1159 x->set_needs_null_check(true);
1160 }
1161 clear_last_explicit_null_check();
1162 }
1163
1164
1165 void NullCheckEliminator::handle_Phi(Phi* x) {
1166 int i;
1167 bool all_non_null = true;
1168 if (x->is_illegal()) {
1169 all_non_null = false;
1170 } else {
1171 for (i = 0; i < x->operand_count(); i++) {
1172 Value input = x->operand_at(i);
1173 if (!set_contains(input)) {
1174 all_non_null = false;
1175 }
1176 }
1177 }
1178
1179 if (all_non_null) {
1180 // Value is non-null => update Phi
1181 if (PrintNullCheckElimination) {
1182 tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1183 }
1184 x->set_needs_null_check(false);
1185 } else if (set_contains(x)) {
1186 set_remove(x);
1187 }
1188 }
1189
1190 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1191 for (int i = 0; i < x->nb_profiled_args(); i++) {
1192 x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1193 }
1194 }
1195
1196 void NullCheckEliminator::handle_ProfileReturnType(ProfileReturnType* x) {
1197 x->set_needs_null_check(!set_contains(x->ret()));
1198 }
1199
1200 void NullCheckEliminator::handle_Constant(Constant *x) {
1201 ObjectType* ot = x->type()->as_ObjectType();
1202 if (ot != nullptr && ot->is_loaded()) {
1203 ObjectConstant* oc = ot->as_ObjectConstant();
1204 if (oc == nullptr || !oc->value()->is_null_object()) {
1205 set_put(x);
1206 if (PrintNullCheckElimination) {
1207 tty->print_cr("Constant %d is non-null", x->id());
1208 }
1209 }
1210 }
1211 }
1212
1213 void NullCheckEliminator::handle_IfOp(IfOp *x) {
1214 if (x->type()->is_object() && set_contains(x->tval()) && set_contains(x->fval())) {
1215 set_put(x);
1216 if (PrintNullCheckElimination) {
1217 tty->print_cr("IfOp %d is non-null", x->id());
1218 }
1219 }
1220 }
1221
1222 void Optimizer::eliminate_null_checks() {
1223 ResourceMark rm;
1224
1225 NullCheckEliminator nce(this);
1226
1227 if (PrintNullCheckElimination) {
1228 tty->print_cr("Starting null check elimination for method %s::%s%s",
1229 ir()->method()->holder()->name()->as_utf8(),
1230 ir()->method()->name()->as_utf8(),
1231 ir()->method()->signature()->as_symbol()->as_utf8());
1232 }
1233
1234 // Apply to graph
1235 nce.iterate(ir()->start());
1236
1237 // walk over the graph looking for exception
1238 // handlers and iterate over them as well
1239 int nblocks = BlockBegin::number_of_blocks();
1240 BlockList blocks(nblocks);
1241 boolArray visited_block(nblocks, nblocks, false);
1242
1243 blocks.push(ir()->start());
1244 visited_block.at_put(ir()->start()->block_id(), true);
1245 for (int i = 0; i < blocks.length(); i++) {
1246 BlockBegin* b = blocks.at(i);
1247 // exception handlers need to be treated as additional roots
1248 for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1249 BlockBegin* excp = b->exception_handler_at(e);
1250 int id = excp->block_id();
1251 if (!visited_block.at(id)) {
1252 blocks.push(excp);
1253 visited_block.at_put(id, true);
1254 nce.iterate(excp);
1255 }
1256 }
1257 // traverse successors
1258 BlockEnd *end = b->end();
1259 for (int s = end->number_of_sux(); s-- > 0; ) {
1260 BlockBegin* next = end->sux_at(s);
1261 int id = next->block_id();
1262 if (!visited_block.at(id)) {
1263 blocks.push(next);
1264 visited_block.at_put(id, true);
1265 }
1266 }
1267 }
1268
1269
1270 if (PrintNullCheckElimination) {
1271 tty->print_cr("Done with null check elimination for method %s::%s%s",
1272 ir()->method()->holder()->name()->as_utf8(),
1273 ir()->method()->name()->as_utf8(),
1274 ir()->method()->signature()->as_symbol()->as_utf8());
1275 }
1276 }