1 /*
2 * Copyright (c) 1999, 2011, 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.hpp"
30 #include "c1/c1_ValueStack.hpp"
31 #include "utilities/bitMap.inline.hpp"
32
33 define_array(ValueSetArray, ValueSet*);
34 define_stack(ValueSetList, ValueSetArray);
35
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) : _cee_count(0), _ifop_count(0), _hir(hir) {
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 int cee_count() const { return _cee_count; }
59 int ifop_count() const { return _ifop_count; }
60
61 void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
62 int e = sux->number_of_exception_handlers();
63 for (int i = 0; i < e; i++) {
64 BlockBegin* xhandler = sux->exception_handler_at(i);
65 block->add_exception_handler(xhandler);
66
67 assert(xhandler->is_predecessor(sux), "missing predecessor");
68 if (sux->number_of_preds() == 0) {
69 // sux is disconnected from graph so disconnect from exception handlers
70 xhandler->remove_predecessor(sux);
71 }
72 if (!xhandler->is_predecessor(block)) {
73 xhandler->add_predecessor(block);
74 }
75 }
76 }
77
78 virtual void block_do(BlockBegin* block);
79
80 private:
81 Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
82 };
83
84 void CE_Eliminator::block_do(BlockBegin* block) {
85 // 1) find conditional expression
86 // check if block ends with an If
87 If* if_ = block->end()->as_If();
88 if (if_ == NULL) return;
89
90 // check if If works on int or object types
91 // (we cannot handle If's working on long, float or doubles yet,
92 // since IfOp doesn't support them - these If's show up if cmp
93 // operations followed by If's are eliminated)
94 ValueType* if_type = if_->x()->type();
95 if (!if_type->is_int() && !if_type->is_object()) return;
96
97 BlockBegin* t_block = if_->tsux();
98 BlockBegin* f_block = if_->fsux();
99 Instruction* t_cur = t_block->next();
100 Instruction* f_cur = f_block->next();
101
102 // one Constant may be present between BlockBegin and BlockEnd
103 Value t_const = NULL;
104 Value f_const = NULL;
105 if (t_cur->as_Constant() != NULL && !t_cur->can_trap()) {
106 t_const = t_cur;
107 t_cur = t_cur->next();
108 }
109 if (f_cur->as_Constant() != NULL && !f_cur->can_trap()) {
110 f_const = f_cur;
111 f_cur = f_cur->next();
112 }
113
114 // check if both branches end with a goto
115 Goto* t_goto = t_cur->as_Goto();
116 if (t_goto == NULL) return;
117 Goto* f_goto = f_cur->as_Goto();
118 if (f_goto == NULL) return;
119
120 // check if both gotos merge into the same block
121 BlockBegin* sux = t_goto->default_sux();
122 if (sux != f_goto->default_sux()) return;
123
124 // check if at least one word was pushed on sux_state
125 // inlining depths must match
126 ValueStack* if_state = if_->state();
127 ValueStack* sux_state = sux->state();
128 if (if_state->scope()->level() > sux_state->scope()->level()) {
129 while (sux_state->scope() != if_state->scope()) {
130 if_state = if_state->caller_state();
131 assert(if_state != NULL, "states do not match up");
132 }
133 } else if (if_state->scope()->level() < sux_state->scope()->level()) {
134 while (sux_state->scope() != if_state->scope()) {
135 sux_state = sux_state->caller_state();
136 assert(sux_state != NULL, "states do not match up");
137 }
138 }
139
140 if (sux_state->stack_size() <= if_state->stack_size()) return;
141
142 // check if phi function is present at end of successor stack and that
143 // only this phi was pushed on the stack
144 Value sux_phi = sux_state->stack_at(if_state->stack_size());
145 if (sux_phi == NULL || sux_phi->as_Phi() == NULL || sux_phi->as_Phi()->block() != sux) return;
146 if (sux_phi->type()->size() != sux_state->stack_size() - if_state->stack_size()) return;
147
148 // get the values that were pushed in the true- and false-branch
149 Value t_value = t_goto->state()->stack_at(if_state->stack_size());
150 Value f_value = f_goto->state()->stack_at(if_state->stack_size());
151
152 // backend does not support floats
153 assert(t_value->type()->base() == f_value->type()->base(), "incompatible types");
154 if (t_value->type()->is_float_kind()) return;
155
156 // check that successor has no other phi functions but sux_phi
157 // this can happen when t_block or f_block contained additonal stores to local variables
158 // that are no longer represented by explicit instructions
159 for_each_phi_fun(sux, phi,
160 if (phi != sux_phi) return;
161 );
162 // true and false blocks can't have phis
163 for_each_phi_fun(t_block, phi, return; );
164 for_each_phi_fun(f_block, phi, return; );
165
166 // 2) substitute conditional expression
167 // with an IfOp followed by a Goto
168 // cut if_ away and get node before
169 Instruction* cur_end = if_->prev(block);
170
171 // append constants of true- and false-block if necessary
172 // clone constants because original block must not be destroyed
173 assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
174 if (t_value == t_const) {
175 t_value = new Constant(t_const->type());
176 NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
177 cur_end = cur_end->set_next(t_value);
178 }
179 if (f_value == f_const) {
180 f_value = new Constant(f_const->type());
181 NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
182 cur_end = cur_end->set_next(f_value);
183 }
184
185 Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
186 assert(result != NULL, "make_ifop must return a non-null instruction");
187 if (!result->is_linked() && result->can_be_linked()) {
188 NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
189 cur_end = cur_end->set_next(result);
190 }
191
192 // append Goto to successor
193 ValueStack* state_before = if_->is_safepoint() ? if_->state_before() : NULL;
194 Goto* goto_ = new Goto(sux, state_before, if_->is_safepoint() || t_goto->is_safepoint() || f_goto->is_safepoint());
195
196 // prepare state for Goto
197 ValueStack* goto_state = if_state;
198 goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
199 goto_state->push(result->type(), result);
200 assert(goto_state->is_same(sux_state), "states must match now");
201 goto_->set_state(goto_state);
202
203 cur_end = cur_end->set_next(goto_, goto_state->bci());
204
205 // Adjust control flow graph
206 BlockBegin::disconnect_edge(block, t_block);
207 BlockBegin::disconnect_edge(block, f_block);
208 if (t_block->number_of_preds() == 0) {
209 BlockBegin::disconnect_edge(t_block, sux);
210 }
211 adjust_exception_edges(block, t_block);
212 if (f_block->number_of_preds() == 0) {
213 BlockBegin::disconnect_edge(f_block, sux);
214 }
215 adjust_exception_edges(block, f_block);
216
217 // update block end
218 block->set_end(goto_);
219
220 // substitute the phi if possible
221 if (sux_phi->as_Phi()->operand_count() == 1) {
222 assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
223 sux_phi->set_subst(result);
224 _has_substitution = true;
225 }
226
227 // 3) successfully eliminated a conditional expression
228 _cee_count++;
229 if (PrintCEE) {
230 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());
231 tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
232 }
233
234 _hir->verify();
235 }
236
237 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
238 if (!OptimizeIfOps) {
239 return new IfOp(x, cond, y, tval, fval);
240 }
241
242 tval = tval->subst();
243 fval = fval->subst();
244 if (tval == fval) {
245 _ifop_count++;
246 return tval;
247 }
248
249 x = x->subst();
250 y = y->subst();
251
252 Constant* y_const = y->as_Constant();
253 if (y_const != NULL) {
254 IfOp* x_ifop = x->as_IfOp();
255 if (x_ifop != NULL) { // x is an ifop, y is a constant
256 Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
257 Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
258
259 if (x_tval_const != NULL && x_fval_const != NULL) {
260 Instruction::Condition x_ifop_cond = x_ifop->cond();
261
262 Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
263 Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
264
265 // not_comparable here is a valid return in case we're comparing unloaded oop constants
266 if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
267 Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
268 Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
269
270 _ifop_count++;
271 if (new_tval == new_fval) {
272 return new_tval;
273 } else {
274 return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
275 }
276 }
277 }
278 } else {
279 Constant* x_const = x->as_Constant();
280 if (x_const != NULL) { // x and y are constants
281 Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
282 // not_comparable here is a valid return in case we're comparing unloaded oop constants
283 if (x_compare_res != Constant::not_comparable) {
284 _ifop_count++;
285 return x_compare_res == Constant::cond_true ? tval : fval;
286 }
287 }
288 }
289 }
290 return new IfOp(x, cond, y, tval, fval);
291 }
292
293 void Optimizer::eliminate_conditional_expressions() {
294 // find conditional expressions & replace them with IfOps
295 CE_Eliminator ce(ir());
296 }
297
298 class BlockMerger: public BlockClosure {
299 private:
300 IR* _hir;
301 int _merge_count; // the number of block pairs successfully merged
302
303 public:
304 BlockMerger(IR* hir)
305 : _hir(hir)
306 , _merge_count(0)
307 {
308 _hir->iterate_preorder(this);
309 }
310
311 bool try_merge(BlockBegin* block) {
312 BlockEnd* end = block->end();
313 if (end->as_Goto() != NULL) {
314 assert(end->number_of_sux() == 1, "end must have exactly one successor");
315 // Note: It would be sufficient to check for the number of successors (= 1)
316 // in order to decide if this block can be merged potentially. That
317 // would then also include switch statements w/ only a default case.
318 // However, in that case we would need to make sure the switch tag
319 // expression is executed if it can produce observable side effects.
320 // We should probably have the canonicalizer simplifying such switch
321 // statements and then we are sure we don't miss these merge opportunities
322 // here (was bug - gri 7/7/99).
323 BlockBegin* sux = end->default_sux();
324 if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {
325 // merge the two blocks
326
327 #ifdef ASSERT
328 // verify that state at the end of block and at the beginning of sux are equal
329 // no phi functions must be present at beginning of sux
330 ValueStack* sux_state = sux->state();
331 ValueStack* end_state = end->state();
332
333 assert(end_state->scope() == sux_state->scope(), "scopes must match");
334 assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
335 assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
336
337 int index;
338 Value sux_value;
339 for_each_stack_value(sux_state, index, sux_value) {
340 assert(sux_value == end_state->stack_at(index), "stack not equal");
341 }
342 for_each_local_value(sux_state, index, sux_value) {
343 assert(sux_value == end_state->local_at(index), "locals not equal");
344 }
345 assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
346 #endif
347
348 // find instruction before end & append first instruction of sux block
349 Instruction* prev = end->prev(block);
350 Instruction* next = sux->next();
351 assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
352 prev->set_next(next);
353 sux->disconnect_from_graph();
354 block->set_end(sux->end());
355 // add exception handlers of deleted block, if any
356 for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
357 BlockBegin* xhandler = sux->exception_handler_at(k);
358 block->add_exception_handler(xhandler);
359
360 // also substitute predecessor of exception handler
361 assert(xhandler->is_predecessor(sux), "missing predecessor");
362 xhandler->remove_predecessor(sux);
363 if (!xhandler->is_predecessor(block)) {
364 xhandler->add_predecessor(block);
365 }
366 }
367
368 // debugging output
369 _merge_count++;
370 if (PrintBlockElimination) {
371 tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
372 _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
373 }
374
375 _hir->verify();
376
377 If* if_ = block->end()->as_If();
378 if (if_) {
379 IfOp* ifop = if_->x()->as_IfOp();
380 Constant* con = if_->y()->as_Constant();
381 bool swapped = false;
382 if (!con || !ifop) {
383 ifop = if_->y()->as_IfOp();
384 con = if_->x()->as_Constant();
385 swapped = true;
386 }
387 if (con && ifop) {
388 Constant* tval = ifop->tval()->as_Constant();
389 Constant* fval = ifop->fval()->as_Constant();
390 if (tval && fval) {
391 // Find the instruction before if_, starting with ifop.
392 // When if_ and ifop are not in the same block, prev
393 // becomes NULL In such (rare) cases it is not
394 // profitable to perform the optimization.
395 Value prev = ifop;
396 while (prev != NULL && prev->next() != if_) {
397 prev = prev->next();
398 }
399
400 if (prev != NULL) {
401 Instruction::Condition cond = if_->cond();
402 BlockBegin* tsux = if_->tsux();
403 BlockBegin* fsux = if_->fsux();
404 if (swapped) {
405 cond = Instruction::mirror(cond);
406 }
407
408 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
409 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
410 if (tblock != fblock && !if_->is_safepoint()) {
411 If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
412 tblock, fblock, if_->state_before(), if_->is_safepoint());
413 newif->set_state(if_->state()->copy());
414
415 assert(prev->next() == if_, "must be guaranteed by above search");
416 NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
417 prev->set_next(newif);
418 block->set_end(newif);
419
420 _merge_count++;
421 if (PrintBlockElimination) {
422 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
423 }
424
425 _hir->verify();
426 }
427 }
428 }
429 }
430 }
431
432 return true;
433 }
434 }
435 return false;
436 }
437
438 virtual void block_do(BlockBegin* block) {
439 _hir->verify();
440 // repeat since the same block may merge again
441 while (try_merge(block)) {
442 _hir->verify();
443 }
444 }
445 };
446
447
448 void Optimizer::eliminate_blocks() {
449 // merge blocks if possible
450 BlockMerger bm(ir());
451 }
452
453
454 class NullCheckEliminator;
455 class NullCheckVisitor: public InstructionVisitor {
456 private:
457 NullCheckEliminator* _nce;
458 NullCheckEliminator* nce() { return _nce; }
459
460 public:
461 NullCheckVisitor() {}
462
463 void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
464
465 void do_Phi (Phi* x);
466 void do_Local (Local* x);
467 void do_Constant (Constant* x);
468 void do_LoadField (LoadField* x);
469 void do_StoreField (StoreField* x);
470 void do_ArrayLength (ArrayLength* x);
471 void do_LoadIndexed (LoadIndexed* x);
472 void do_StoreIndexed (StoreIndexed* x);
473 void do_NegateOp (NegateOp* x);
474 void do_ArithmeticOp (ArithmeticOp* x);
475 void do_ShiftOp (ShiftOp* x);
476 void do_LogicOp (LogicOp* x);
477 void do_CompareOp (CompareOp* x);
478 void do_IfOp (IfOp* x);
479 void do_Convert (Convert* x);
480 void do_NullCheck (NullCheck* x);
481 void do_Invoke (Invoke* x);
482 void do_NewInstance (NewInstance* x);
483 void do_NewTypeArray (NewTypeArray* x);
484 void do_NewObjectArray (NewObjectArray* x);
485 void do_NewMultiArray (NewMultiArray* x);
486 void do_CheckCast (CheckCast* x);
487 void do_InstanceOf (InstanceOf* x);
488 void do_MonitorEnter (MonitorEnter* x);
489 void do_MonitorExit (MonitorExit* x);
490 void do_Intrinsic (Intrinsic* x);
491 void do_BlockBegin (BlockBegin* x);
492 void do_Goto (Goto* x);
493 void do_If (If* x);
494 void do_IfInstanceOf (IfInstanceOf* x);
495 void do_TableSwitch (TableSwitch* x);
496 void do_LookupSwitch (LookupSwitch* x);
497 void do_Return (Return* x);
498 void do_Throw (Throw* x);
499 void do_Base (Base* x);
500 void do_OsrEntry (OsrEntry* x);
501 void do_ExceptionObject(ExceptionObject* x);
502 void do_RoundFP (RoundFP* x);
503 void do_UnsafeGetRaw (UnsafeGetRaw* x);
504 void do_UnsafePutRaw (UnsafePutRaw* x);
505 void do_UnsafeGetObject(UnsafeGetObject* x);
506 void do_UnsafePutObject(UnsafePutObject* x);
507 void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
508 void do_UnsafePrefetchRead (UnsafePrefetchRead* x);
509 void do_UnsafePrefetchWrite(UnsafePrefetchWrite* x);
510 void do_ProfileCall (ProfileCall* x);
511 void do_ProfileInvoke (ProfileInvoke* x);
512 void do_RuntimeCall (RuntimeCall* x);
513 void do_MemBar (MemBar* x);
514 };
515
516
517 // Because of a static contained within (for the purpose of iteration
518 // over instructions), it is only valid to have one of these active at
519 // a time
520 class NullCheckEliminator: public ValueVisitor {
521 private:
522 Optimizer* _opt;
523
524 ValueSet* _visitable_instructions; // Visit each instruction only once per basic block
525 BlockList* _work_list; // Basic blocks to visit
526
527 bool visitable(Value x) {
528 assert(_visitable_instructions != NULL, "check");
529 return _visitable_instructions->contains(x);
530 }
531 void mark_visited(Value x) {
532 assert(_visitable_instructions != NULL, "check");
533 _visitable_instructions->remove(x);
534 }
535 void mark_visitable(Value x) {
536 assert(_visitable_instructions != NULL, "check");
537 _visitable_instructions->put(x);
538 }
539 void clear_visitable_state() {
540 assert(_visitable_instructions != NULL, "check");
541 _visitable_instructions->clear();
542 }
543
544 ValueSet* _set; // current state, propagated to subsequent BlockBegins
545 ValueSetList _block_states; // BlockBegin null-check states for all processed blocks
546 NullCheckVisitor _visitor;
547 NullCheck* _last_explicit_null_check;
548
549 bool set_contains(Value x) { assert(_set != NULL, "check"); return _set->contains(x); }
550 void set_put (Value x) { assert(_set != NULL, "check"); _set->put(x); }
551 void set_remove (Value x) { assert(_set != NULL, "check"); _set->remove(x); }
552
553 BlockList* work_list() { return _work_list; }
554
555 void iterate_all();
556 void iterate_one(BlockBegin* block);
557
558 ValueSet* state() { return _set; }
559 void set_state_from (ValueSet* state) { _set->set_from(state); }
560 ValueSet* state_for (BlockBegin* block) { return _block_states[block->block_id()]; }
561 void set_state_for (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }
562 // Returns true if caused a change in the block's state.
563 bool merge_state_for(BlockBegin* block,
564 ValueSet* incoming_state);
565
566 public:
567 // constructor
568 NullCheckEliminator(Optimizer* opt)
569 : _opt(opt)
570 , _set(new ValueSet())
571 , _last_explicit_null_check(NULL)
572 , _block_states(BlockBegin::number_of_blocks(), NULL)
573 , _work_list(new BlockList()) {
574 _visitable_instructions = new ValueSet();
575 _visitor.set_eliminator(this);
576 }
577
578 Optimizer* opt() { return _opt; }
579 IR* ir () { return opt()->ir(); }
580
581 // Process a graph
582 void iterate(BlockBegin* root);
583
584 void visit(Value* f);
585
586 // In some situations (like NullCheck(x); getfield(x)) the debug
587 // information from the explicit NullCheck can be used to populate
588 // the getfield, even if the two instructions are in different
589 // scopes; this allows implicit null checks to be used but the
590 // correct exception information to be generated. We must clear the
591 // last-traversed NullCheck when we reach a potentially-exception-
592 // throwing instruction, as well as in some other cases.
593 void set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
594 NullCheck* last_explicit_null_check() { return _last_explicit_null_check; }
595 Value last_explicit_null_check_obj() { return (_last_explicit_null_check
596 ? _last_explicit_null_check->obj()
597 : NULL); }
598 NullCheck* consume_last_explicit_null_check() {
599 _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
600 _last_explicit_null_check->set_can_trap(false);
601 return _last_explicit_null_check;
602 }
603 void clear_last_explicit_null_check() { _last_explicit_null_check = NULL; }
604
605 // Handlers for relevant instructions
606 // (separated out from NullCheckVisitor for clarity)
607
608 // The basic contract is that these must leave the instruction in
609 // the desired state; must not assume anything about the state of
610 // the instruction. We make multiple passes over some basic blocks
611 // and the last pass is the only one whose result is valid.
612 void handle_AccessField (AccessField* x);
613 void handle_ArrayLength (ArrayLength* x);
614 void handle_LoadIndexed (LoadIndexed* x);
615 void handle_StoreIndexed (StoreIndexed* x);
616 void handle_NullCheck (NullCheck* x);
617 void handle_Invoke (Invoke* x);
618 void handle_NewInstance (NewInstance* x);
619 void handle_NewArray (NewArray* x);
620 void handle_AccessMonitor (AccessMonitor* x);
621 void handle_Intrinsic (Intrinsic* x);
622 void handle_ExceptionObject (ExceptionObject* x);
623 void handle_Phi (Phi* x);
624 };
625
626
627 // NEEDS_CLEANUP
628 // There may be other instructions which need to clear the last
629 // explicit null check. Anything across which we can not hoist the
630 // debug information for a NullCheck instruction must clear it. It
631 // might be safer to pattern match "NullCheck ; {AccessField,
632 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
633 // Should test to see performance hit of clearing it for all handlers
634 // with empty bodies below. If it is negligible then we should leave
635 // that in for safety, otherwise should think more about it.
636 void NullCheckVisitor::do_Phi (Phi* x) { nce()->handle_Phi(x); }
637 void NullCheckVisitor::do_Local (Local* x) {}
638 void NullCheckVisitor::do_Constant (Constant* x) { /* FIXME: handle object constants */ }
639 void NullCheckVisitor::do_LoadField (LoadField* x) { nce()->handle_AccessField(x); }
640 void NullCheckVisitor::do_StoreField (StoreField* x) { nce()->handle_AccessField(x); }
641 void NullCheckVisitor::do_ArrayLength (ArrayLength* x) { nce()->handle_ArrayLength(x); }
642 void NullCheckVisitor::do_LoadIndexed (LoadIndexed* x) { nce()->handle_LoadIndexed(x); }
643 void NullCheckVisitor::do_StoreIndexed (StoreIndexed* x) { nce()->handle_StoreIndexed(x); }
644 void NullCheckVisitor::do_NegateOp (NegateOp* x) {}
645 void NullCheckVisitor::do_ArithmeticOp (ArithmeticOp* x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
646 void NullCheckVisitor::do_ShiftOp (ShiftOp* x) {}
647 void NullCheckVisitor::do_LogicOp (LogicOp* x) {}
648 void NullCheckVisitor::do_CompareOp (CompareOp* x) {}
649 void NullCheckVisitor::do_IfOp (IfOp* x) {}
650 void NullCheckVisitor::do_Convert (Convert* x) {}
651 void NullCheckVisitor::do_NullCheck (NullCheck* x) { nce()->handle_NullCheck(x); }
652 void NullCheckVisitor::do_Invoke (Invoke* x) { nce()->handle_Invoke(x); }
653 void NullCheckVisitor::do_NewInstance (NewInstance* x) { nce()->handle_NewInstance(x); }
654 void NullCheckVisitor::do_NewTypeArray (NewTypeArray* x) { nce()->handle_NewArray(x); }
655 void NullCheckVisitor::do_NewObjectArray (NewObjectArray* x) { nce()->handle_NewArray(x); }
656 void NullCheckVisitor::do_NewMultiArray (NewMultiArray* x) { nce()->handle_NewArray(x); }
657 void NullCheckVisitor::do_CheckCast (CheckCast* x) { nce()->clear_last_explicit_null_check(); }
658 void NullCheckVisitor::do_InstanceOf (InstanceOf* x) {}
659 void NullCheckVisitor::do_MonitorEnter (MonitorEnter* x) { nce()->handle_AccessMonitor(x); }
660 void NullCheckVisitor::do_MonitorExit (MonitorExit* x) { nce()->handle_AccessMonitor(x); }
661 void NullCheckVisitor::do_Intrinsic (Intrinsic* x) { nce()->handle_Intrinsic(x); }
662 void NullCheckVisitor::do_BlockBegin (BlockBegin* x) {}
663 void NullCheckVisitor::do_Goto (Goto* x) {}
664 void NullCheckVisitor::do_If (If* x) {}
665 void NullCheckVisitor::do_IfInstanceOf (IfInstanceOf* x) {}
666 void NullCheckVisitor::do_TableSwitch (TableSwitch* x) {}
667 void NullCheckVisitor::do_LookupSwitch (LookupSwitch* x) {}
668 void NullCheckVisitor::do_Return (Return* x) {}
669 void NullCheckVisitor::do_Throw (Throw* x) { nce()->clear_last_explicit_null_check(); }
670 void NullCheckVisitor::do_Base (Base* x) {}
671 void NullCheckVisitor::do_OsrEntry (OsrEntry* x) {}
672 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
673 void NullCheckVisitor::do_RoundFP (RoundFP* x) {}
674 void NullCheckVisitor::do_UnsafeGetRaw (UnsafeGetRaw* x) {}
675 void NullCheckVisitor::do_UnsafePutRaw (UnsafePutRaw* x) {}
676 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
677 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
678 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
679 void NullCheckVisitor::do_UnsafePrefetchRead (UnsafePrefetchRead* x) {}
680 void NullCheckVisitor::do_UnsafePrefetchWrite(UnsafePrefetchWrite* x) {}
681 void NullCheckVisitor::do_ProfileCall (ProfileCall* x) { nce()->clear_last_explicit_null_check(); }
682 void NullCheckVisitor::do_ProfileInvoke (ProfileInvoke* x) {}
683 void NullCheckVisitor::do_RuntimeCall (RuntimeCall* x) {}
684 void NullCheckVisitor::do_MemBar (MemBar* x) {}
685
686
687 void NullCheckEliminator::visit(Value* p) {
688 assert(*p != NULL, "should not find NULL instructions");
689 if (visitable(*p)) {
690 mark_visited(*p);
691 (*p)->visit(&_visitor);
692 }
693 }
694
695 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
696 ValueSet* state = state_for(block);
697 if (state == NULL) {
698 state = incoming_state->copy();
699 set_state_for(block, state);
700 return true;
701 } else {
702 bool changed = state->set_intersect(incoming_state);
703 if (PrintNullCheckElimination && changed) {
704 tty->print_cr("Block %d's null check state changed", block->block_id());
705 }
706 return changed;
707 }
708 }
709
710
711 void NullCheckEliminator::iterate_all() {
712 while (work_list()->length() > 0) {
713 iterate_one(work_list()->pop());
714 }
715 }
716
717
718 void NullCheckEliminator::iterate_one(BlockBegin* block) {
719 clear_visitable_state();
720 // clear out an old explicit null checks
721 set_last_explicit_null_check(NULL);
722
723 if (PrintNullCheckElimination) {
724 tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
725 block->block_id(),
726 ir()->method()->holder()->name()->as_utf8(),
727 ir()->method()->name()->as_utf8(),
728 ir()->method()->signature()->as_symbol()->as_utf8());
729 }
730
731 // Create new state if none present (only happens at root)
732 if (state_for(block) == NULL) {
733 ValueSet* tmp_state = new ValueSet();
734 set_state_for(block, tmp_state);
735 // Initial state is that local 0 (receiver) is non-null for
736 // non-static methods
737 ValueStack* stack = block->state();
738 IRScope* scope = stack->scope();
739 ciMethod* method = scope->method();
740 if (!method->is_static()) {
741 Local* local0 = stack->local_at(0)->as_Local();
742 assert(local0 != NULL, "must be");
743 assert(local0->type() == objectType, "invalid type of receiver");
744
745 if (local0 != NULL) {
746 // Local 0 is used in this scope
747 tmp_state->put(local0);
748 if (PrintNullCheckElimination) {
749 tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
750 }
751 }
752 }
753 }
754
755 // Must copy block's state to avoid mutating it during iteration
756 // through the block -- otherwise "not-null" states can accidentally
757 // propagate "up" through the block during processing of backward
758 // branches and algorithm is incorrect (and does not converge)
759 set_state_from(state_for(block));
760
761 // allow visiting of Phis belonging to this block
762 for_each_phi_fun(block, phi,
763 mark_visitable(phi);
764 );
765
766 BlockEnd* e = block->end();
767 assert(e != NULL, "incomplete graph");
768 int i;
769
770 // Propagate the state before this block into the exception
771 // handlers. They aren't true successors since we aren't guaranteed
772 // to execute the whole block before executing them. Also putting
773 // them on first seems to help reduce the amount of iteration to
774 // reach a fixed point.
775 for (i = 0; i < block->number_of_exception_handlers(); i++) {
776 BlockBegin* next = block->exception_handler_at(i);
777 if (merge_state_for(next, state())) {
778 if (!work_list()->contains(next)) {
779 work_list()->push(next);
780 }
781 }
782 }
783
784 // Iterate through block, updating state.
785 for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
786 // Mark instructions in this block as visitable as they are seen
787 // in the instruction list. This keeps the iteration from
788 // visiting instructions which are references in other blocks or
789 // visiting instructions more than once.
790 mark_visitable(instr);
791 if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
792 mark_visited(instr);
793 instr->input_values_do(this);
794 instr->visit(&_visitor);
795 }
796 }
797
798 // Propagate state to successors if necessary
799 for (i = 0; i < e->number_of_sux(); i++) {
800 BlockBegin* next = e->sux_at(i);
801 if (merge_state_for(next, state())) {
802 if (!work_list()->contains(next)) {
803 work_list()->push(next);
804 }
805 }
806 }
807 }
808
809
810 void NullCheckEliminator::iterate(BlockBegin* block) {
811 work_list()->push(block);
812 iterate_all();
813 }
814
815 void NullCheckEliminator::handle_AccessField(AccessField* x) {
816 if (x->is_static()) {
817 if (x->as_LoadField() != NULL) {
818 // If the field is a non-null static final object field (as is
819 // often the case for sun.misc.Unsafe), put this LoadField into
820 // the non-null map
821 ciField* field = x->field();
822 if (field->is_constant()) {
823 ciConstant field_val = field->constant_value();
824 BasicType field_type = field_val.basic_type();
825 if (field_type == T_OBJECT || field_type == T_ARRAY) {
826 ciObject* obj_val = field_val.as_object();
827 if (!obj_val->is_null_object()) {
828 if (PrintNullCheckElimination) {
829 tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
830 x->id());
831 }
832 set_put(x);
833 }
834 }
835 }
836 }
837 // Be conservative
838 clear_last_explicit_null_check();
839 return;
840 }
841
842 Value obj = x->obj();
843 if (set_contains(obj)) {
844 // Value is non-null => update AccessField
845 if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
846 x->set_explicit_null_check(consume_last_explicit_null_check());
847 x->set_needs_null_check(true);
848 if (PrintNullCheckElimination) {
849 tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
850 x->explicit_null_check()->id(), x->id(), obj->id());
851 }
852 } else {
853 x->set_explicit_null_check(NULL);
854 x->set_needs_null_check(false);
855 if (PrintNullCheckElimination) {
856 tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
857 }
858 }
859 } else {
860 set_put(obj);
861 if (PrintNullCheckElimination) {
862 tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
863 }
864 // Ensure previous passes do not cause wrong state
865 x->set_needs_null_check(true);
866 x->set_explicit_null_check(NULL);
867 }
868 clear_last_explicit_null_check();
869 }
870
871
872 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
873 Value array = x->array();
874 if (set_contains(array)) {
875 // Value is non-null => update AccessArray
876 if (last_explicit_null_check_obj() == array) {
877 x->set_explicit_null_check(consume_last_explicit_null_check());
878 x->set_needs_null_check(true);
879 if (PrintNullCheckElimination) {
880 tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
881 x->explicit_null_check()->id(), x->id(), array->id());
882 }
883 } else {
884 x->set_explicit_null_check(NULL);
885 x->set_needs_null_check(false);
886 if (PrintNullCheckElimination) {
887 tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
888 }
889 }
890 } else {
891 set_put(array);
892 if (PrintNullCheckElimination) {
893 tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
894 }
895 // Ensure previous passes do not cause wrong state
896 x->set_needs_null_check(true);
897 x->set_explicit_null_check(NULL);
898 }
899 clear_last_explicit_null_check();
900 }
901
902
903 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
904 Value array = x->array();
905 if (set_contains(array)) {
906 // Value is non-null => update AccessArray
907 if (last_explicit_null_check_obj() == array) {
908 x->set_explicit_null_check(consume_last_explicit_null_check());
909 x->set_needs_null_check(true);
910 if (PrintNullCheckElimination) {
911 tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
912 x->explicit_null_check()->id(), x->id(), array->id());
913 }
914 } else {
915 x->set_explicit_null_check(NULL);
916 x->set_needs_null_check(false);
917 if (PrintNullCheckElimination) {
918 tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
919 }
920 }
921 } else {
922 set_put(array);
923 if (PrintNullCheckElimination) {
924 tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
925 }
926 // Ensure previous passes do not cause wrong state
927 x->set_needs_null_check(true);
928 x->set_explicit_null_check(NULL);
929 }
930 clear_last_explicit_null_check();
931 }
932
933
934 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
935 Value array = x->array();
936 if (set_contains(array)) {
937 // Value is non-null => update AccessArray
938 if (PrintNullCheckElimination) {
939 tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
940 }
941 x->set_needs_null_check(false);
942 } else {
943 set_put(array);
944 if (PrintNullCheckElimination) {
945 tty->print_cr("StoreIndexed %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 }
950 clear_last_explicit_null_check();
951 }
952
953
954 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
955 Value obj = x->obj();
956 if (set_contains(obj)) {
957 // Already proven to be non-null => this NullCheck is useless
958 if (PrintNullCheckElimination) {
959 tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
960 }
961 // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
962 // The code generator won't emit LIR for a NullCheck that cannot trap.
963 x->set_can_trap(false);
964 } else {
965 // May be null => add to map and set last explicit NullCheck
966 x->set_can_trap(true);
967 // make sure it's pinned if it can trap
968 x->pin(Instruction::PinExplicitNullCheck);
969 set_put(obj);
970 set_last_explicit_null_check(x);
971 if (PrintNullCheckElimination) {
972 tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
973 }
974 }
975 }
976
977
978 void NullCheckEliminator::handle_Invoke(Invoke* x) {
979 if (!x->has_receiver()) {
980 // Be conservative
981 clear_last_explicit_null_check();
982 return;
983 }
984
985 Value recv = x->receiver();
986 if (!set_contains(recv)) {
987 set_put(recv);
988 if (PrintNullCheckElimination) {
989 tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
990 }
991 }
992 clear_last_explicit_null_check();
993 }
994
995
996 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
997 set_put(x);
998 if (PrintNullCheckElimination) {
999 tty->print_cr("NewInstance %d is non-null", x->id());
1000 }
1001 }
1002
1003
1004 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1005 set_put(x);
1006 if (PrintNullCheckElimination) {
1007 tty->print_cr("NewArray %d is non-null", x->id());
1008 }
1009 }
1010
1011
1012 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1013 set_put(x);
1014 if (PrintNullCheckElimination) {
1015 tty->print_cr("ExceptionObject %d is non-null", x->id());
1016 }
1017 }
1018
1019
1020 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1021 Value obj = x->obj();
1022 if (set_contains(obj)) {
1023 // Value is non-null => update AccessMonitor
1024 if (PrintNullCheckElimination) {
1025 tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1026 }
1027 x->set_needs_null_check(false);
1028 } else {
1029 set_put(obj);
1030 if (PrintNullCheckElimination) {
1031 tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1032 }
1033 // Ensure previous passes do not cause wrong state
1034 x->set_needs_null_check(true);
1035 }
1036 clear_last_explicit_null_check();
1037 }
1038
1039
1040 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1041 if (!x->has_receiver()) {
1042 if (x->id() == vmIntrinsics::_arraycopy) {
1043 for (int i = 0; i < x->number_of_arguments(); i++) {
1044 x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1045 }
1046 }
1047
1048 // Be conservative
1049 clear_last_explicit_null_check();
1050 return;
1051 }
1052
1053 Value recv = x->receiver();
1054 if (set_contains(recv)) {
1055 // Value is non-null => update Intrinsic
1056 if (PrintNullCheckElimination) {
1057 tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1058 }
1059 x->set_needs_null_check(false);
1060 } else {
1061 set_put(recv);
1062 if (PrintNullCheckElimination) {
1063 tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1064 }
1065 // Ensure previous passes do not cause wrong state
1066 x->set_needs_null_check(true);
1067 }
1068 clear_last_explicit_null_check();
1069 }
1070
1071
1072 void NullCheckEliminator::handle_Phi(Phi* x) {
1073 int i;
1074 bool all_non_null = true;
1075 if (x->is_illegal()) {
1076 all_non_null = false;
1077 } else {
1078 for (i = 0; i < x->operand_count(); i++) {
1079 Value input = x->operand_at(i);
1080 if (!set_contains(input)) {
1081 all_non_null = false;
1082 }
1083 }
1084 }
1085
1086 if (all_non_null) {
1087 // Value is non-null => update Phi
1088 if (PrintNullCheckElimination) {
1089 tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1090 }
1091 x->set_needs_null_check(false);
1092 } else if (set_contains(x)) {
1093 set_remove(x);
1094 }
1095 }
1096
1097
1098 void Optimizer::eliminate_null_checks() {
1099 ResourceMark rm;
1100
1101 NullCheckEliminator nce(this);
1102
1103 if (PrintNullCheckElimination) {
1104 tty->print_cr("Starting null check elimination for method %s::%s%s",
1105 ir()->method()->holder()->name()->as_utf8(),
1106 ir()->method()->name()->as_utf8(),
1107 ir()->method()->signature()->as_symbol()->as_utf8());
1108 }
1109
1110 // Apply to graph
1111 nce.iterate(ir()->start());
1112
1113 // walk over the graph looking for exception
1114 // handlers and iterate over them as well
1115 int nblocks = BlockBegin::number_of_blocks();
1116 BlockList blocks(nblocks);
1117 boolArray visited_block(nblocks, false);
1118
1119 blocks.push(ir()->start());
1120 visited_block[ir()->start()->block_id()] = true;
1121 for (int i = 0; i < blocks.length(); i++) {
1122 BlockBegin* b = blocks[i];
1123 // exception handlers need to be treated as additional roots
1124 for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1125 BlockBegin* excp = b->exception_handler_at(e);
1126 int id = excp->block_id();
1127 if (!visited_block[id]) {
1128 blocks.push(excp);
1129 visited_block[id] = true;
1130 nce.iterate(excp);
1131 }
1132 }
1133 // traverse successors
1134 BlockEnd *end = b->end();
1135 for (int s = end->number_of_sux(); s-- > 0; ) {
1136 BlockBegin* next = end->sux_at(s);
1137 int id = next->block_id();
1138 if (!visited_block[id]) {
1139 blocks.push(next);
1140 visited_block[id] = true;
1141 }
1142 }
1143 }
1144
1145
1146 if (PrintNullCheckElimination) {
1147 tty->print_cr("Done with null check elimination for method %s::%s%s",
1148 ir()->method()->holder()->name()->as_utf8(),
1149 ir()->method()->name()->as_utf8(),
1150 ir()->method()->signature()->as_symbol()->as_utf8());
1151 }
1152 }