1 /*
2 * Copyright (c) 1999, 2012, 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 #include "compiler/compileLog.hpp"
33
34 define_array(ValueSetArray, ValueSet*);
35 define_stack(ValueSetList, ValueSetArray);
36
37
38 Optimizer::Optimizer(IR* ir) {
39 assert(ir->is_valid(), "IR must be valid");
40 _ir = ir;
41 }
42
43 class CE_Eliminator: public BlockClosure {
44 private:
45 IR* _hir;
46 int _cee_count; // the number of CEs successfully eliminated
47 int _ifop_count; // the number of IfOps successfully simplified
48 int _has_substitution;
49
50 public:
51 CE_Eliminator(IR* hir) : _cee_count(0), _ifop_count(0), _hir(hir) {
52 _has_substitution = false;
53 _hir->iterate_preorder(this);
54 if (_has_substitution) {
55 // substituted some ifops/phis, so resolve the substitution
56 SubstitutionResolver sr(_hir);
57 }
58
59 CompileLog* log = _hir->compilation()->log();
60 if (log != NULL)
61 log->set_context("optimize name='cee'");
62 }
63
64 ~CE_Eliminator() {
65 CompileLog* log = _hir->compilation()->log();
66 if (log != NULL)
67 log->clear_context(); // skip marker if nothing was printed
68 }
69
70 int cee_count() const { return _cee_count; }
71 int ifop_count() const { return _ifop_count; }
72
73 void adjust_exception_edges(BlockBegin* block, BlockBegin* sux) {
74 int e = sux->number_of_exception_handlers();
75 for (int i = 0; i < e; i++) {
76 BlockBegin* xhandler = sux->exception_handler_at(i);
77 block->add_exception_handler(xhandler);
78
79 assert(xhandler->is_predecessor(sux), "missing predecessor");
80 if (sux->number_of_preds() == 0) {
81 // sux is disconnected from graph so disconnect from exception handlers
82 xhandler->remove_predecessor(sux);
83 }
84 if (!xhandler->is_predecessor(block)) {
85 xhandler->add_predecessor(block);
86 }
87 }
88 }
89
90 virtual void block_do(BlockBegin* block);
91
92 private:
93 Value make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval);
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 // 2) substitute conditional expression
179 // with an IfOp followed by a Goto
180 // cut if_ away and get node before
181 Instruction* cur_end = if_->prev();
182
183 // append constants of true- and false-block if necessary
184 // clone constants because original block must not be destroyed
185 assert((t_value != f_const && f_value != t_const) || t_const == f_const, "mismatch");
186 if (t_value == t_const) {
187 t_value = new Constant(t_const->type());
188 NOT_PRODUCT(t_value->set_printable_bci(if_->printable_bci()));
189 cur_end = cur_end->set_next(t_value);
190 }
191 if (f_value == f_const) {
192 f_value = new Constant(f_const->type());
193 NOT_PRODUCT(f_value->set_printable_bci(if_->printable_bci()));
194 cur_end = cur_end->set_next(f_value);
195 }
196
197 Value result = make_ifop(if_->x(), if_->cond(), if_->y(), t_value, f_value);
198 assert(result != NULL, "make_ifop must return a non-null instruction");
199 if (!result->is_linked() && result->can_be_linked()) {
200 NOT_PRODUCT(result->set_printable_bci(if_->printable_bci()));
201 cur_end = cur_end->set_next(result);
202 }
203
204 // append Goto to successor
205 ValueStack* state_before = if_->state_before();
206 Goto* goto_ = new Goto(sux, state_before, if_->is_safepoint() || t_goto->is_safepoint() || f_goto->is_safepoint());
207
208 // prepare state for Goto
209 ValueStack* goto_state = if_state;
210 goto_state = goto_state->copy(ValueStack::StateAfter, goto_state->bci());
211 goto_state->push(result->type(), result);
212 assert(goto_state->is_same(sux_state), "states must match now");
213 goto_->set_state(goto_state);
214
215 cur_end = cur_end->set_next(goto_, goto_state->bci());
216
217 // Adjust control flow graph
218 BlockBegin::disconnect_edge(block, t_block);
219 BlockBegin::disconnect_edge(block, f_block);
220 if (t_block->number_of_preds() == 0) {
221 BlockBegin::disconnect_edge(t_block, sux);
222 }
223 adjust_exception_edges(block, t_block);
224 if (f_block->number_of_preds() == 0) {
225 BlockBegin::disconnect_edge(f_block, sux);
226 }
227 adjust_exception_edges(block, f_block);
228
229 // update block end
230 block->set_end(goto_);
231
232 // substitute the phi if possible
233 if (sux_phi->as_Phi()->operand_count() == 1) {
234 assert(sux_phi->as_Phi()->operand_at(0) == result, "screwed up phi");
235 sux_phi->set_subst(result);
236 _has_substitution = true;
237 }
238
239 // 3) successfully eliminated a conditional expression
240 _cee_count++;
241 if (PrintCEE) {
242 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());
243 tty->print_cr("%d. IfOp in B%d", ifop_count(), block->block_id());
244 }
245
246 _hir->verify();
247 }
248
249 Value CE_Eliminator::make_ifop(Value x, Instruction::Condition cond, Value y, Value tval, Value fval) {
250 if (!OptimizeIfOps) {
251 return new IfOp(x, cond, y, tval, fval);
252 }
253
254 tval = tval->subst();
255 fval = fval->subst();
256 if (tval == fval) {
257 _ifop_count++;
258 return tval;
259 }
260
261 x = x->subst();
262 y = y->subst();
263
264 Constant* y_const = y->as_Constant();
265 if (y_const != NULL) {
266 IfOp* x_ifop = x->as_IfOp();
267 if (x_ifop != NULL) { // x is an ifop, y is a constant
268 Constant* x_tval_const = x_ifop->tval()->subst()->as_Constant();
269 Constant* x_fval_const = x_ifop->fval()->subst()->as_Constant();
270
271 if (x_tval_const != NULL && x_fval_const != NULL) {
272 Instruction::Condition x_ifop_cond = x_ifop->cond();
273
274 Constant::CompareResult t_compare_res = x_tval_const->compare(cond, y_const);
275 Constant::CompareResult f_compare_res = x_fval_const->compare(cond, y_const);
276
277 // not_comparable here is a valid return in case we're comparing unloaded oop constants
278 if (t_compare_res != Constant::not_comparable && f_compare_res != Constant::not_comparable) {
279 Value new_tval = t_compare_res == Constant::cond_true ? tval : fval;
280 Value new_fval = f_compare_res == Constant::cond_true ? tval : fval;
281
282 _ifop_count++;
283 if (new_tval == new_fval) {
284 return new_tval;
285 } else {
286 return new IfOp(x_ifop->x(), x_ifop_cond, x_ifop->y(), new_tval, new_fval);
287 }
288 }
289 }
290 } else {
291 Constant* x_const = x->as_Constant();
292 if (x_const != NULL) { // x and y are constants
293 Constant::CompareResult x_compare_res = x_const->compare(cond, y_const);
294 // not_comparable here is a valid return in case we're comparing unloaded oop constants
295 if (x_compare_res != Constant::not_comparable) {
296 _ifop_count++;
297 return x_compare_res == Constant::cond_true ? tval : fval;
298 }
299 }
300 }
301 }
302 return new IfOp(x, cond, y, tval, fval);
303 }
304
305 void Optimizer::eliminate_conditional_expressions() {
306 // find conditional expressions & replace them with IfOps
307 CE_Eliminator ce(ir());
308 }
309
310 class BlockMerger: public BlockClosure {
311 private:
312 IR* _hir;
313 int _merge_count; // the number of block pairs successfully merged
314
315 public:
316 BlockMerger(IR* hir)
317 : _hir(hir)
318 , _merge_count(0)
319 {
320 _hir->iterate_preorder(this);
321 CompileLog* log = _hir->compilation()->log();
322 if (log != NULL)
323 log->set_context("optimize name='eliminate_blocks'");
324 }
325
326 ~BlockMerger() {
327 CompileLog* log = _hir->compilation()->log();
328 if (log != NULL)
329 log->clear_context(); // skip marker if nothing was printed
330 }
331
332 bool try_merge(BlockBegin* block) {
333 BlockEnd* end = block->end();
334 if (end->as_Goto() != NULL) {
335 assert(end->number_of_sux() == 1, "end must have exactly one successor");
336 // Note: It would be sufficient to check for the number of successors (= 1)
337 // in order to decide if this block can be merged potentially. That
338 // would then also include switch statements w/ only a default case.
339 // However, in that case we would need to make sure the switch tag
340 // expression is executed if it can produce observable side effects.
341 // We should probably have the canonicalizer simplifying such switch
342 // statements and then we are sure we don't miss these merge opportunities
343 // here (was bug - gri 7/7/99).
344 BlockBegin* sux = end->default_sux();
345 if (sux->number_of_preds() == 1 && !sux->is_entry_block() && !end->is_safepoint()) {
346 // merge the two blocks
347
348 #ifdef ASSERT
349 // verify that state at the end of block and at the beginning of sux are equal
350 // no phi functions must be present at beginning of sux
351 ValueStack* sux_state = sux->state();
352 ValueStack* end_state = end->state();
353
354 assert(end_state->scope() == sux_state->scope(), "scopes must match");
355 assert(end_state->stack_size() == sux_state->stack_size(), "stack not equal");
356 assert(end_state->locals_size() == sux_state->locals_size(), "locals not equal");
357
358 int index;
359 Value sux_value;
360 for_each_stack_value(sux_state, index, sux_value) {
361 assert(sux_value == end_state->stack_at(index), "stack not equal");
362 }
363 for_each_local_value(sux_state, index, sux_value) {
364 assert(sux_value == end_state->local_at(index), "locals not equal");
365 }
366 assert(sux_state->caller_state() == end_state->caller_state(), "caller not equal");
367 #endif
368
369 // find instruction before end & append first instruction of sux block
370 Instruction* prev = end->prev();
371 Instruction* next = sux->next();
372 assert(prev->as_BlockEnd() == NULL, "must not be a BlockEnd");
373 prev->set_next(next);
374 prev->fixup_block_pointers();
375 sux->disconnect_from_graph();
376 block->set_end(sux->end());
377 // add exception handlers of deleted block, if any
378 for (int k = 0; k < sux->number_of_exception_handlers(); k++) {
379 BlockBegin* xhandler = sux->exception_handler_at(k);
380 block->add_exception_handler(xhandler);
381
382 // also substitute predecessor of exception handler
383 assert(xhandler->is_predecessor(sux), "missing predecessor");
384 xhandler->remove_predecessor(sux);
385 if (!xhandler->is_predecessor(block)) {
386 xhandler->add_predecessor(block);
387 }
388 }
389
390 // debugging output
391 _merge_count++;
392 if (PrintBlockElimination) {
393 tty->print_cr("%d. merged B%d & B%d (stack size = %d)",
394 _merge_count, block->block_id(), sux->block_id(), sux->state()->stack_size());
395 }
396
397 _hir->verify();
398
399 If* if_ = block->end()->as_If();
400 if (if_) {
401 IfOp* ifop = if_->x()->as_IfOp();
402 Constant* con = if_->y()->as_Constant();
403 bool swapped = false;
404 if (!con || !ifop) {
405 ifop = if_->y()->as_IfOp();
406 con = if_->x()->as_Constant();
407 swapped = true;
408 }
409 if (con && ifop) {
410 Constant* tval = ifop->tval()->as_Constant();
411 Constant* fval = ifop->fval()->as_Constant();
412 if (tval && fval) {
413 // Find the instruction before if_, starting with ifop.
414 // When if_ and ifop are not in the same block, prev
415 // becomes NULL In such (rare) cases it is not
416 // profitable to perform the optimization.
417 Value prev = ifop;
418 while (prev != NULL && prev->next() != if_) {
419 prev = prev->next();
420 }
421
422 if (prev != NULL) {
423 Instruction::Condition cond = if_->cond();
424 BlockBegin* tsux = if_->tsux();
425 BlockBegin* fsux = if_->fsux();
426 if (swapped) {
427 cond = Instruction::mirror(cond);
428 }
429
430 BlockBegin* tblock = tval->compare(cond, con, tsux, fsux);
431 BlockBegin* fblock = fval->compare(cond, con, tsux, fsux);
432 if (tblock != fblock && !if_->is_safepoint()) {
433 If* newif = new If(ifop->x(), ifop->cond(), false, ifop->y(),
434 tblock, fblock, if_->state_before(), if_->is_safepoint());
435 newif->set_state(if_->state()->copy());
436
437 assert(prev->next() == if_, "must be guaranteed by above search");
438 NOT_PRODUCT(newif->set_printable_bci(if_->printable_bci()));
439 prev->set_next(newif);
440 block->set_end(newif);
441
442 _merge_count++;
443 if (PrintBlockElimination) {
444 tty->print_cr("%d. replaced If and IfOp at end of B%d with single If", _merge_count, block->block_id());
445 }
446
447 _hir->verify();
448 }
449 }
450 }
451 }
452 }
453
454 return true;
455 }
456 }
457 return false;
458 }
459
460 virtual void block_do(BlockBegin* block) {
461 _hir->verify();
462 // repeat since the same block may merge again
463 while (try_merge(block)) {
464 _hir->verify();
465 }
466 }
467 };
468
469
470 void Optimizer::eliminate_blocks() {
471 // merge blocks if possible
472 BlockMerger bm(ir());
473 }
474
475
476 class NullCheckEliminator;
477 class NullCheckVisitor: public InstructionVisitor {
478 private:
479 NullCheckEliminator* _nce;
480 NullCheckEliminator* nce() { return _nce; }
481
482 public:
483 NullCheckVisitor() {}
484
485 void set_eliminator(NullCheckEliminator* nce) { _nce = nce; }
486
487 void do_Phi (Phi* x);
488 void do_Local (Local* x);
489 void do_Constant (Constant* x);
490 void do_LoadField (LoadField* x);
491 void do_StoreField (StoreField* x);
492 void do_ArrayLength (ArrayLength* x);
493 void do_LoadIndexed (LoadIndexed* x);
494 void do_StoreIndexed (StoreIndexed* x);
495 void do_NegateOp (NegateOp* x);
496 void do_ArithmeticOp (ArithmeticOp* x);
497 void do_ShiftOp (ShiftOp* x);
498 void do_LogicOp (LogicOp* x);
499 void do_CompareOp (CompareOp* x);
500 void do_IfOp (IfOp* x);
501 void do_Convert (Convert* x);
502 void do_NullCheck (NullCheck* x);
503 void do_TypeCast (TypeCast* x);
504 void do_Invoke (Invoke* x);
505 void do_NewInstance (NewInstance* x);
506 void do_NewTypeArray (NewTypeArray* x);
507 void do_NewObjectArray (NewObjectArray* x);
508 void do_NewMultiArray (NewMultiArray* x);
509 void do_CheckCast (CheckCast* x);
510 void do_InstanceOf (InstanceOf* x);
511 void do_MonitorEnter (MonitorEnter* x);
512 void do_MonitorExit (MonitorExit* x);
513 void do_Intrinsic (Intrinsic* x);
514 void do_BlockBegin (BlockBegin* x);
515 void do_Goto (Goto* x);
516 void do_If (If* x);
517 void do_IfInstanceOf (IfInstanceOf* x);
518 void do_TableSwitch (TableSwitch* x);
519 void do_LookupSwitch (LookupSwitch* x);
520 void do_Return (Return* x);
521 void do_Throw (Throw* x);
522 void do_Base (Base* x);
523 void do_OsrEntry (OsrEntry* x);
524 void do_ExceptionObject(ExceptionObject* x);
525 void do_RoundFP (RoundFP* x);
526 void do_UnsafeGetRaw (UnsafeGetRaw* x);
527 void do_UnsafePutRaw (UnsafePutRaw* x);
528 void do_UnsafeGetObject(UnsafeGetObject* x);
529 void do_UnsafePutObject(UnsafePutObject* x);
530 void do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x);
531 void do_UnsafePrefetchRead (UnsafePrefetchRead* x);
532 void do_UnsafePrefetchWrite(UnsafePrefetchWrite* x);
533 void do_ProfileCall (ProfileCall* x);
534 void do_ProfileInvoke (ProfileInvoke* x);
535 void do_RuntimeCall (RuntimeCall* x);
536 void do_MemBar (MemBar* x);
537 void do_RangeCheckPredicate(RangeCheckPredicate* x);
538 #ifdef ASSERT
539 void do_Assert (Assert* x);
540 #endif
541 };
542
543
544 // Because of a static contained within (for the purpose of iteration
545 // over instructions), it is only valid to have one of these active at
546 // a time
547 class NullCheckEliminator: public ValueVisitor {
548 private:
549 Optimizer* _opt;
550
551 ValueSet* _visitable_instructions; // Visit each instruction only once per basic block
552 BlockList* _work_list; // Basic blocks to visit
553
554 bool visitable(Value x) {
555 assert(_visitable_instructions != NULL, "check");
556 return _visitable_instructions->contains(x);
557 }
558 void mark_visited(Value x) {
559 assert(_visitable_instructions != NULL, "check");
560 _visitable_instructions->remove(x);
561 }
562 void mark_visitable(Value x) {
563 assert(_visitable_instructions != NULL, "check");
564 _visitable_instructions->put(x);
565 }
566 void clear_visitable_state() {
567 assert(_visitable_instructions != NULL, "check");
568 _visitable_instructions->clear();
569 }
570
571 ValueSet* _set; // current state, propagated to subsequent BlockBegins
572 ValueSetList _block_states; // BlockBegin null-check states for all processed blocks
573 NullCheckVisitor _visitor;
574 NullCheck* _last_explicit_null_check;
575
576 bool set_contains(Value x) { assert(_set != NULL, "check"); return _set->contains(x); }
577 void set_put (Value x) { assert(_set != NULL, "check"); _set->put(x); }
578 void set_remove (Value x) { assert(_set != NULL, "check"); _set->remove(x); }
579
580 BlockList* work_list() { return _work_list; }
581
582 void iterate_all();
583 void iterate_one(BlockBegin* block);
584
585 ValueSet* state() { return _set; }
586 void set_state_from (ValueSet* state) { _set->set_from(state); }
587 ValueSet* state_for (BlockBegin* block) { return _block_states[block->block_id()]; }
588 void set_state_for (BlockBegin* block, ValueSet* stack) { _block_states[block->block_id()] = stack; }
589 // Returns true if caused a change in the block's state.
590 bool merge_state_for(BlockBegin* block,
591 ValueSet* incoming_state);
592
593 public:
594 // constructor
595 NullCheckEliminator(Optimizer* opt)
596 : _opt(opt)
597 , _set(new ValueSet())
598 , _last_explicit_null_check(NULL)
599 , _block_states(BlockBegin::number_of_blocks(), NULL)
600 , _work_list(new BlockList()) {
601 _visitable_instructions = new ValueSet();
602 _visitor.set_eliminator(this);
603 CompileLog* log = _opt->ir()->compilation()->log();
604 if (log != NULL)
605 log->set_context("optimize name='null_check_elimination'");
606 }
607
608 ~NullCheckEliminator() {
609 CompileLog* log = _opt->ir()->compilation()->log();
610 if (log != NULL)
611 log->clear_context(); // skip marker if nothing was printed
612 }
613
614 Optimizer* opt() { return _opt; }
615 IR* ir () { return opt()->ir(); }
616
617 // Process a graph
618 void iterate(BlockBegin* root);
619
620 void visit(Value* f);
621
622 // In some situations (like NullCheck(x); getfield(x)) the debug
623 // information from the explicit NullCheck can be used to populate
624 // the getfield, even if the two instructions are in different
625 // scopes; this allows implicit null checks to be used but the
626 // correct exception information to be generated. We must clear the
627 // last-traversed NullCheck when we reach a potentially-exception-
628 // throwing instruction, as well as in some other cases.
629 void set_last_explicit_null_check(NullCheck* check) { _last_explicit_null_check = check; }
630 NullCheck* last_explicit_null_check() { return _last_explicit_null_check; }
631 Value last_explicit_null_check_obj() { return (_last_explicit_null_check
632 ? _last_explicit_null_check->obj()
633 : NULL); }
634 NullCheck* consume_last_explicit_null_check() {
635 _last_explicit_null_check->unpin(Instruction::PinExplicitNullCheck);
636 _last_explicit_null_check->set_can_trap(false);
637 return _last_explicit_null_check;
638 }
639 void clear_last_explicit_null_check() { _last_explicit_null_check = NULL; }
640
641 // Handlers for relevant instructions
642 // (separated out from NullCheckVisitor for clarity)
643
644 // The basic contract is that these must leave the instruction in
645 // the desired state; must not assume anything about the state of
646 // the instruction. We make multiple passes over some basic blocks
647 // and the last pass is the only one whose result is valid.
648 void handle_AccessField (AccessField* x);
649 void handle_ArrayLength (ArrayLength* x);
650 void handle_LoadIndexed (LoadIndexed* x);
651 void handle_StoreIndexed (StoreIndexed* x);
652 void handle_NullCheck (NullCheck* x);
653 void handle_Invoke (Invoke* x);
654 void handle_NewInstance (NewInstance* x);
655 void handle_NewArray (NewArray* x);
656 void handle_AccessMonitor (AccessMonitor* x);
657 void handle_Intrinsic (Intrinsic* x);
658 void handle_ExceptionObject (ExceptionObject* x);
659 void handle_Phi (Phi* x);
660 void handle_ProfileCall (ProfileCall* x);
661 };
662
663
664 // NEEDS_CLEANUP
665 // There may be other instructions which need to clear the last
666 // explicit null check. Anything across which we can not hoist the
667 // debug information for a NullCheck instruction must clear it. It
668 // might be safer to pattern match "NullCheck ; {AccessField,
669 // ArrayLength, LoadIndexed}" but it is more easily structured this way.
670 // Should test to see performance hit of clearing it for all handlers
671 // with empty bodies below. If it is negligible then we should leave
672 // that in for safety, otherwise should think more about it.
673 void NullCheckVisitor::do_Phi (Phi* x) { nce()->handle_Phi(x); }
674 void NullCheckVisitor::do_Local (Local* x) {}
675 void NullCheckVisitor::do_Constant (Constant* x) { /* FIXME: handle object constants */ }
676 void NullCheckVisitor::do_LoadField (LoadField* x) { nce()->handle_AccessField(x); }
677 void NullCheckVisitor::do_StoreField (StoreField* x) { nce()->handle_AccessField(x); }
678 void NullCheckVisitor::do_ArrayLength (ArrayLength* x) { nce()->handle_ArrayLength(x); }
679 void NullCheckVisitor::do_LoadIndexed (LoadIndexed* x) { nce()->handle_LoadIndexed(x); }
680 void NullCheckVisitor::do_StoreIndexed (StoreIndexed* x) { nce()->handle_StoreIndexed(x); }
681 void NullCheckVisitor::do_NegateOp (NegateOp* x) {}
682 void NullCheckVisitor::do_ArithmeticOp (ArithmeticOp* x) { if (x->can_trap()) nce()->clear_last_explicit_null_check(); }
683 void NullCheckVisitor::do_ShiftOp (ShiftOp* x) {}
684 void NullCheckVisitor::do_LogicOp (LogicOp* x) {}
685 void NullCheckVisitor::do_CompareOp (CompareOp* x) {}
686 void NullCheckVisitor::do_IfOp (IfOp* x) {}
687 void NullCheckVisitor::do_Convert (Convert* x) {}
688 void NullCheckVisitor::do_NullCheck (NullCheck* x) { nce()->handle_NullCheck(x); }
689 void NullCheckVisitor::do_TypeCast (TypeCast* x) {}
690 void NullCheckVisitor::do_Invoke (Invoke* x) { nce()->handle_Invoke(x); }
691 void NullCheckVisitor::do_NewInstance (NewInstance* x) { nce()->handle_NewInstance(x); }
692 void NullCheckVisitor::do_NewTypeArray (NewTypeArray* x) { nce()->handle_NewArray(x); }
693 void NullCheckVisitor::do_NewObjectArray (NewObjectArray* x) { nce()->handle_NewArray(x); }
694 void NullCheckVisitor::do_NewMultiArray (NewMultiArray* x) { nce()->handle_NewArray(x); }
695 void NullCheckVisitor::do_CheckCast (CheckCast* x) { nce()->clear_last_explicit_null_check(); }
696 void NullCheckVisitor::do_InstanceOf (InstanceOf* x) {}
697 void NullCheckVisitor::do_MonitorEnter (MonitorEnter* x) { nce()->handle_AccessMonitor(x); }
698 void NullCheckVisitor::do_MonitorExit (MonitorExit* x) { nce()->handle_AccessMonitor(x); }
699 void NullCheckVisitor::do_Intrinsic (Intrinsic* x) { nce()->handle_Intrinsic(x); }
700 void NullCheckVisitor::do_BlockBegin (BlockBegin* x) {}
701 void NullCheckVisitor::do_Goto (Goto* x) {}
702 void NullCheckVisitor::do_If (If* x) {}
703 void NullCheckVisitor::do_IfInstanceOf (IfInstanceOf* x) {}
704 void NullCheckVisitor::do_TableSwitch (TableSwitch* x) {}
705 void NullCheckVisitor::do_LookupSwitch (LookupSwitch* x) {}
706 void NullCheckVisitor::do_Return (Return* x) {}
707 void NullCheckVisitor::do_Throw (Throw* x) { nce()->clear_last_explicit_null_check(); }
708 void NullCheckVisitor::do_Base (Base* x) {}
709 void NullCheckVisitor::do_OsrEntry (OsrEntry* x) {}
710 void NullCheckVisitor::do_ExceptionObject(ExceptionObject* x) { nce()->handle_ExceptionObject(x); }
711 void NullCheckVisitor::do_RoundFP (RoundFP* x) {}
712 void NullCheckVisitor::do_UnsafeGetRaw (UnsafeGetRaw* x) {}
713 void NullCheckVisitor::do_UnsafePutRaw (UnsafePutRaw* x) {}
714 void NullCheckVisitor::do_UnsafeGetObject(UnsafeGetObject* x) {}
715 void NullCheckVisitor::do_UnsafePutObject(UnsafePutObject* x) {}
716 void NullCheckVisitor::do_UnsafeGetAndSetObject(UnsafeGetAndSetObject* x) {}
717 void NullCheckVisitor::do_UnsafePrefetchRead (UnsafePrefetchRead* x) {}
718 void NullCheckVisitor::do_UnsafePrefetchWrite(UnsafePrefetchWrite* x) {}
719 void NullCheckVisitor::do_ProfileCall (ProfileCall* x) { nce()->clear_last_explicit_null_check();
720 nce()->handle_ProfileCall(x); }
721 void NullCheckVisitor::do_ProfileInvoke (ProfileInvoke* x) {}
722 void NullCheckVisitor::do_RuntimeCall (RuntimeCall* x) {}
723 void NullCheckVisitor::do_MemBar (MemBar* x) {}
724 void NullCheckVisitor::do_RangeCheckPredicate(RangeCheckPredicate* x) {}
725 #ifdef ASSERT
726 void NullCheckVisitor::do_Assert (Assert* x) {}
727 #endif
728
729 void NullCheckEliminator::visit(Value* p) {
730 assert(*p != NULL, "should not find NULL instructions");
731 if (visitable(*p)) {
732 mark_visited(*p);
733 (*p)->visit(&_visitor);
734 }
735 }
736
737 bool NullCheckEliminator::merge_state_for(BlockBegin* block, ValueSet* incoming_state) {
738 ValueSet* state = state_for(block);
739 if (state == NULL) {
740 state = incoming_state->copy();
741 set_state_for(block, state);
742 return true;
743 } else {
744 bool changed = state->set_intersect(incoming_state);
745 if (PrintNullCheckElimination && changed) {
746 tty->print_cr("Block %d's null check state changed", block->block_id());
747 }
748 return changed;
749 }
750 }
751
752
753 void NullCheckEliminator::iterate_all() {
754 while (work_list()->length() > 0) {
755 iterate_one(work_list()->pop());
756 }
757 }
758
759
760 void NullCheckEliminator::iterate_one(BlockBegin* block) {
761 clear_visitable_state();
762 // clear out an old explicit null checks
763 set_last_explicit_null_check(NULL);
764
765 if (PrintNullCheckElimination) {
766 tty->print_cr(" ...iterating block %d in null check elimination for %s::%s%s",
767 block->block_id(),
768 ir()->method()->holder()->name()->as_utf8(),
769 ir()->method()->name()->as_utf8(),
770 ir()->method()->signature()->as_symbol()->as_utf8());
771 }
772
773 // Create new state if none present (only happens at root)
774 if (state_for(block) == NULL) {
775 ValueSet* tmp_state = new ValueSet();
776 set_state_for(block, tmp_state);
777 // Initial state is that local 0 (receiver) is non-null for
778 // non-static methods
779 ValueStack* stack = block->state();
780 IRScope* scope = stack->scope();
781 ciMethod* method = scope->method();
782 if (!method->is_static()) {
783 Local* local0 = stack->local_at(0)->as_Local();
784 assert(local0 != NULL, "must be");
785 assert(local0->type() == objectType, "invalid type of receiver");
786
787 if (local0 != NULL) {
788 // Local 0 is used in this scope
789 tmp_state->put(local0);
790 if (PrintNullCheckElimination) {
791 tty->print_cr("Local 0 (value %d) proven non-null upon entry", local0->id());
792 }
793 }
794 }
795 }
796
797 // Must copy block's state to avoid mutating it during iteration
798 // through the block -- otherwise "not-null" states can accidentally
799 // propagate "up" through the block during processing of backward
800 // branches and algorithm is incorrect (and does not converge)
801 set_state_from(state_for(block));
802
803 // allow visiting of Phis belonging to this block
804 for_each_phi_fun(block, phi,
805 mark_visitable(phi);
806 );
807
808 BlockEnd* e = block->end();
809 assert(e != NULL, "incomplete graph");
810 int i;
811
812 // Propagate the state before this block into the exception
813 // handlers. They aren't true successors since we aren't guaranteed
814 // to execute the whole block before executing them. Also putting
815 // them on first seems to help reduce the amount of iteration to
816 // reach a fixed point.
817 for (i = 0; i < block->number_of_exception_handlers(); i++) {
818 BlockBegin* next = block->exception_handler_at(i);
819 if (merge_state_for(next, state())) {
820 if (!work_list()->contains(next)) {
821 work_list()->push(next);
822 }
823 }
824 }
825
826 // Iterate through block, updating state.
827 for (Instruction* instr = block; instr != NULL; instr = instr->next()) {
828 // Mark instructions in this block as visitable as they are seen
829 // in the instruction list. This keeps the iteration from
830 // visiting instructions which are references in other blocks or
831 // visiting instructions more than once.
832 mark_visitable(instr);
833 if (instr->is_pinned() || instr->can_trap() || (instr->as_NullCheck() != NULL)) {
834 mark_visited(instr);
835 instr->input_values_do(this);
836 instr->visit(&_visitor);
837 }
838 }
839
840 // Propagate state to successors if necessary
841 for (i = 0; i < e->number_of_sux(); i++) {
842 BlockBegin* next = e->sux_at(i);
843 if (merge_state_for(next, state())) {
844 if (!work_list()->contains(next)) {
845 work_list()->push(next);
846 }
847 }
848 }
849 }
850
851
852 void NullCheckEliminator::iterate(BlockBegin* block) {
853 work_list()->push(block);
854 iterate_all();
855 }
856
857 void NullCheckEliminator::handle_AccessField(AccessField* x) {
858 if (x->is_static()) {
859 if (x->as_LoadField() != NULL) {
860 // If the field is a non-null static final object field (as is
861 // often the case for sun.misc.Unsafe), put this LoadField into
862 // the non-null map
863 ciField* field = x->field();
864 if (field->is_constant()) {
865 ciConstant field_val = field->constant_value();
866 BasicType field_type = field_val.basic_type();
867 if (field_type == T_OBJECT || field_type == T_ARRAY) {
868 ciObject* obj_val = field_val.as_object();
869 if (!obj_val->is_null_object()) {
870 if (PrintNullCheckElimination) {
871 tty->print_cr("AccessField %d proven non-null by static final non-null oop check",
872 x->id());
873 }
874 set_put(x);
875 }
876 }
877 }
878 }
879 // Be conservative
880 clear_last_explicit_null_check();
881 return;
882 }
883
884 Value obj = x->obj();
885 if (set_contains(obj)) {
886 // Value is non-null => update AccessField
887 if (last_explicit_null_check_obj() == obj && !x->needs_patching()) {
888 x->set_explicit_null_check(consume_last_explicit_null_check());
889 x->set_needs_null_check(true);
890 if (PrintNullCheckElimination) {
891 tty->print_cr("Folded NullCheck %d into AccessField %d's null check for value %d",
892 x->explicit_null_check()->id(), x->id(), obj->id());
893 }
894 } else {
895 x->set_explicit_null_check(NULL);
896 x->set_needs_null_check(false);
897 if (PrintNullCheckElimination) {
898 tty->print_cr("Eliminated AccessField %d's null check for value %d", x->id(), obj->id());
899 }
900 }
901 } else {
902 set_put(obj);
903 if (PrintNullCheckElimination) {
904 tty->print_cr("AccessField %d of value %d proves value to be non-null", x->id(), obj->id());
905 }
906 // Ensure previous passes do not cause wrong state
907 x->set_needs_null_check(true);
908 x->set_explicit_null_check(NULL);
909 }
910 clear_last_explicit_null_check();
911 }
912
913
914 void NullCheckEliminator::handle_ArrayLength(ArrayLength* x) {
915 Value array = x->array();
916 if (set_contains(array)) {
917 // Value is non-null => update AccessArray
918 if (last_explicit_null_check_obj() == array) {
919 x->set_explicit_null_check(consume_last_explicit_null_check());
920 x->set_needs_null_check(true);
921 if (PrintNullCheckElimination) {
922 tty->print_cr("Folded NullCheck %d into ArrayLength %d's null check for value %d",
923 x->explicit_null_check()->id(), x->id(), array->id());
924 }
925 } else {
926 x->set_explicit_null_check(NULL);
927 x->set_needs_null_check(false);
928 if (PrintNullCheckElimination) {
929 tty->print_cr("Eliminated ArrayLength %d's null check for value %d", x->id(), array->id());
930 }
931 }
932 } else {
933 set_put(array);
934 if (PrintNullCheckElimination) {
935 tty->print_cr("ArrayLength %d of value %d proves value to be non-null", x->id(), array->id());
936 }
937 // Ensure previous passes do not cause wrong state
938 x->set_needs_null_check(true);
939 x->set_explicit_null_check(NULL);
940 }
941 clear_last_explicit_null_check();
942 }
943
944
945 void NullCheckEliminator::handle_LoadIndexed(LoadIndexed* x) {
946 Value array = x->array();
947 if (set_contains(array)) {
948 // Value is non-null => update AccessArray
949 if (last_explicit_null_check_obj() == array) {
950 x->set_explicit_null_check(consume_last_explicit_null_check());
951 x->set_needs_null_check(true);
952 if (PrintNullCheckElimination) {
953 tty->print_cr("Folded NullCheck %d into LoadIndexed %d's null check for value %d",
954 x->explicit_null_check()->id(), x->id(), array->id());
955 }
956 } else {
957 x->set_explicit_null_check(NULL);
958 x->set_needs_null_check(false);
959 if (PrintNullCheckElimination) {
960 tty->print_cr("Eliminated LoadIndexed %d's null check for value %d", x->id(), array->id());
961 }
962 }
963 } else {
964 set_put(array);
965 if (PrintNullCheckElimination) {
966 tty->print_cr("LoadIndexed %d of value %d proves value to be non-null", x->id(), array->id());
967 }
968 // Ensure previous passes do not cause wrong state
969 x->set_needs_null_check(true);
970 x->set_explicit_null_check(NULL);
971 }
972 clear_last_explicit_null_check();
973 }
974
975
976 void NullCheckEliminator::handle_StoreIndexed(StoreIndexed* x) {
977 Value array = x->array();
978 if (set_contains(array)) {
979 // Value is non-null => update AccessArray
980 if (PrintNullCheckElimination) {
981 tty->print_cr("Eliminated StoreIndexed %d's null check for value %d", x->id(), array->id());
982 }
983 x->set_needs_null_check(false);
984 } else {
985 set_put(array);
986 if (PrintNullCheckElimination) {
987 tty->print_cr("StoreIndexed %d of value %d proves value to be non-null", x->id(), array->id());
988 }
989 // Ensure previous passes do not cause wrong state
990 x->set_needs_null_check(true);
991 }
992 clear_last_explicit_null_check();
993 }
994
995
996 void NullCheckEliminator::handle_NullCheck(NullCheck* x) {
997 Value obj = x->obj();
998 if (set_contains(obj)) {
999 // Already proven to be non-null => this NullCheck is useless
1000 if (PrintNullCheckElimination) {
1001 tty->print_cr("Eliminated NullCheck %d for value %d", x->id(), obj->id());
1002 }
1003 // Don't unpin since that may shrink obj's live range and make it unavailable for debug info.
1004 // The code generator won't emit LIR for a NullCheck that cannot trap.
1005 x->set_can_trap(false);
1006 } else {
1007 // May be null => add to map and set last explicit NullCheck
1008 x->set_can_trap(true);
1009 // make sure it's pinned if it can trap
1010 x->pin(Instruction::PinExplicitNullCheck);
1011 set_put(obj);
1012 set_last_explicit_null_check(x);
1013 if (PrintNullCheckElimination) {
1014 tty->print_cr("NullCheck %d of value %d proves value to be non-null", x->id(), obj->id());
1015 }
1016 }
1017 }
1018
1019
1020 void NullCheckEliminator::handle_Invoke(Invoke* x) {
1021 if (!x->has_receiver()) {
1022 // Be conservative
1023 clear_last_explicit_null_check();
1024 return;
1025 }
1026
1027 Value recv = x->receiver();
1028 if (!set_contains(recv)) {
1029 set_put(recv);
1030 if (PrintNullCheckElimination) {
1031 tty->print_cr("Invoke %d of value %d proves value to be non-null", x->id(), recv->id());
1032 }
1033 }
1034 clear_last_explicit_null_check();
1035 }
1036
1037
1038 void NullCheckEliminator::handle_NewInstance(NewInstance* x) {
1039 set_put(x);
1040 if (PrintNullCheckElimination) {
1041 tty->print_cr("NewInstance %d is non-null", x->id());
1042 }
1043 }
1044
1045
1046 void NullCheckEliminator::handle_NewArray(NewArray* x) {
1047 set_put(x);
1048 if (PrintNullCheckElimination) {
1049 tty->print_cr("NewArray %d is non-null", x->id());
1050 }
1051 }
1052
1053
1054 void NullCheckEliminator::handle_ExceptionObject(ExceptionObject* x) {
1055 set_put(x);
1056 if (PrintNullCheckElimination) {
1057 tty->print_cr("ExceptionObject %d is non-null", x->id());
1058 }
1059 }
1060
1061
1062 void NullCheckEliminator::handle_AccessMonitor(AccessMonitor* x) {
1063 Value obj = x->obj();
1064 if (set_contains(obj)) {
1065 // Value is non-null => update AccessMonitor
1066 if (PrintNullCheckElimination) {
1067 tty->print_cr("Eliminated AccessMonitor %d's null check for value %d", x->id(), obj->id());
1068 }
1069 x->set_needs_null_check(false);
1070 } else {
1071 set_put(obj);
1072 if (PrintNullCheckElimination) {
1073 tty->print_cr("AccessMonitor %d of value %d proves value to be non-null", x->id(), obj->id());
1074 }
1075 // Ensure previous passes do not cause wrong state
1076 x->set_needs_null_check(true);
1077 }
1078 clear_last_explicit_null_check();
1079 }
1080
1081
1082 void NullCheckEliminator::handle_Intrinsic(Intrinsic* x) {
1083 if (!x->has_receiver()) {
1084 if (x->id() == vmIntrinsics::_arraycopy) {
1085 for (int i = 0; i < x->number_of_arguments(); i++) {
1086 x->set_arg_needs_null_check(i, !set_contains(x->argument_at(i)));
1087 }
1088 }
1089
1090 // Be conservative
1091 clear_last_explicit_null_check();
1092 return;
1093 }
1094
1095 Value recv = x->receiver();
1096 if (set_contains(recv)) {
1097 // Value is non-null => update Intrinsic
1098 if (PrintNullCheckElimination) {
1099 tty->print_cr("Eliminated Intrinsic %d's null check for value %d", x->id(), recv->id());
1100 }
1101 x->set_needs_null_check(false);
1102 } else {
1103 set_put(recv);
1104 if (PrintNullCheckElimination) {
1105 tty->print_cr("Intrinsic %d of value %d proves value to be non-null", x->id(), recv->id());
1106 }
1107 // Ensure previous passes do not cause wrong state
1108 x->set_needs_null_check(true);
1109 }
1110 clear_last_explicit_null_check();
1111 }
1112
1113
1114 void NullCheckEliminator::handle_Phi(Phi* x) {
1115 int i;
1116 bool all_non_null = true;
1117 if (x->is_illegal()) {
1118 all_non_null = false;
1119 } else {
1120 for (i = 0; i < x->operand_count(); i++) {
1121 Value input = x->operand_at(i);
1122 if (!set_contains(input)) {
1123 all_non_null = false;
1124 }
1125 }
1126 }
1127
1128 if (all_non_null) {
1129 // Value is non-null => update Phi
1130 if (PrintNullCheckElimination) {
1131 tty->print_cr("Eliminated Phi %d's null check for phifun because all inputs are non-null", x->id());
1132 }
1133 x->set_needs_null_check(false);
1134 } else if (set_contains(x)) {
1135 set_remove(x);
1136 }
1137 }
1138
1139 void NullCheckEliminator::handle_ProfileCall(ProfileCall* x) {
1140 for (int i = 0; i < x->nb_profiled_args(); i++) {
1141 x->set_arg_needs_null_check(i, !set_contains(x->profiled_arg_at(i)));
1142 }
1143 }
1144
1145 void Optimizer::eliminate_null_checks() {
1146 ResourceMark rm;
1147
1148 NullCheckEliminator nce(this);
1149
1150 if (PrintNullCheckElimination) {
1151 tty->print_cr("Starting null check elimination for method %s::%s%s",
1152 ir()->method()->holder()->name()->as_utf8(),
1153 ir()->method()->name()->as_utf8(),
1154 ir()->method()->signature()->as_symbol()->as_utf8());
1155 }
1156
1157 // Apply to graph
1158 nce.iterate(ir()->start());
1159
1160 // walk over the graph looking for exception
1161 // handlers and iterate over them as well
1162 int nblocks = BlockBegin::number_of_blocks();
1163 BlockList blocks(nblocks);
1164 boolArray visited_block(nblocks, false);
1165
1166 blocks.push(ir()->start());
1167 visited_block[ir()->start()->block_id()] = true;
1168 for (int i = 0; i < blocks.length(); i++) {
1169 BlockBegin* b = blocks[i];
1170 // exception handlers need to be treated as additional roots
1171 for (int e = b->number_of_exception_handlers(); e-- > 0; ) {
1172 BlockBegin* excp = b->exception_handler_at(e);
1173 int id = excp->block_id();
1174 if (!visited_block[id]) {
1175 blocks.push(excp);
1176 visited_block[id] = true;
1177 nce.iterate(excp);
1178 }
1179 }
1180 // traverse successors
1181 BlockEnd *end = b->end();
1182 for (int s = end->number_of_sux(); s-- > 0; ) {
1183 BlockBegin* next = end->sux_at(s);
1184 int id = next->block_id();
1185 if (!visited_block[id]) {
1186 blocks.push(next);
1187 visited_block[id] = true;
1188 }
1189 }
1190 }
1191
1192
1193 if (PrintNullCheckElimination) {
1194 tty->print_cr("Done with null check elimination for method %s::%s%s",
1195 ir()->method()->holder()->name()->as_utf8(),
1196 ir()->method()->name()->as_utf8(),
1197 ir()->method()->signature()->as_symbol()->as_utf8());
1198 }
1199 }