1 /*
2 * Copyright (c) 2018, 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 "gc/g1/c2/g1BarrierSetC2.hpp"
27 #include "gc/g1/g1BarrierSet.hpp"
28 #include "gc/g1/g1CardTable.hpp"
29 #include "gc/g1/g1ThreadLocalData.hpp"
30 #include "gc/g1/heapRegion.hpp"
31 #include "opto/arraycopynode.hpp"
32 #include "opto/graphKit.hpp"
33 #include "opto/idealKit.hpp"
34 #include "opto/macro.hpp"
35 #include "opto/type.hpp"
36 #include "runtime/sharedRuntime.hpp"
37 #include "utilities/macros.hpp"
38
39 const TypeFunc *G1BarrierSetC2::g1_wb_pre_Type() {
40 const Type **fields = TypeTuple::fields(2);
41 fields[TypeFunc::Parms+0] = TypeInstPtr::NOTNULL; // original field value
42 fields[TypeFunc::Parms+1] = TypeRawPtr::NOTNULL; // thread
43 const TypeTuple *domain = TypeTuple::make(TypeFunc::Parms+2, fields);
44
45 // create result type (range)
46 fields = TypeTuple::fields(0);
47 const TypeTuple *range = TypeTuple::make(TypeFunc::Parms+0, fields);
48
49 return TypeFunc::make(domain, range);
50 }
51
52 const TypeFunc *G1BarrierSetC2::g1_wb_post_Type() {
53 const Type **fields = TypeTuple::fields(2);
54 fields[TypeFunc::Parms+0] = TypeRawPtr::NOTNULL; // Card addr
55 fields[TypeFunc::Parms+1] = TypeRawPtr::NOTNULL; // thread
56 const TypeTuple *domain = TypeTuple::make(TypeFunc::Parms+2, fields);
57
58 // create result type (range)
59 fields = TypeTuple::fields(0);
60 const TypeTuple *range = TypeTuple::make(TypeFunc::Parms, fields);
61
62 return TypeFunc::make(domain, range);
63 }
64
65 #define __ ideal.
66 /*
67 * Determine if the G1 pre-barrier can be removed. The pre-barrier is
68 * required by SATB to make sure all objects live at the start of the
69 * marking are kept alive, all reference updates need to any previous
70 * reference stored before writing.
71 *
72 * If the previous value is NULL there is no need to save the old value.
73 * References that are NULL are filtered during runtime by the barrier
74 * code to avoid unnecessary queuing.
75 *
76 * However in the case of newly allocated objects it might be possible to
77 * prove that the reference about to be overwritten is NULL during compile
78 * time and avoid adding the barrier code completely.
79 *
80 * The compiler needs to determine that the object in which a field is about
81 * to be written is newly allocated, and that no prior store to the same field
82 * has happened since the allocation.
83 *
84 * Returns true if the pre-barrier can be removed
85 */
86 bool G1BarrierSetC2::g1_can_remove_pre_barrier(GraphKit* kit,
87 PhaseTransform* phase,
88 Node* adr,
89 BasicType bt,
90 uint adr_idx) const {
91 intptr_t offset = 0;
92 Node* base = AddPNode::Ideal_base_and_offset(adr, phase, offset);
93 AllocateNode* alloc = AllocateNode::Ideal_allocation(base, phase);
94
95 if (offset == Type::OffsetBot) {
96 return false; // cannot unalias unless there are precise offsets
97 }
98
99 if (alloc == NULL) {
100 return false; // No allocation found
101 }
102
103 intptr_t size_in_bytes = type2aelembytes(bt);
104
105 Node* mem = kit->memory(adr_idx); // start searching here...
106
107 for (int cnt = 0; cnt < 50; cnt++) {
108
109 if (mem->is_Store()) {
110
111 Node* st_adr = mem->in(MemNode::Address);
112 intptr_t st_offset = 0;
113 Node* st_base = AddPNode::Ideal_base_and_offset(st_adr, phase, st_offset);
114
115 if (st_base == NULL) {
116 break; // inscrutable pointer
117 }
118
119 // Break we have found a store with same base and offset as ours so break
120 if (st_base == base && st_offset == offset) {
121 break;
122 }
123
124 if (st_offset != offset && st_offset != Type::OffsetBot) {
125 const int MAX_STORE = BytesPerLong;
126 if (st_offset >= offset + size_in_bytes ||
127 st_offset <= offset - MAX_STORE ||
128 st_offset <= offset - mem->as_Store()->memory_size()) {
129 // Success: The offsets are provably independent.
130 // (You may ask, why not just test st_offset != offset and be done?
131 // The answer is that stores of different sizes can co-exist
132 // in the same sequence of RawMem effects. We sometimes initialize
133 // a whole 'tile' of array elements with a single jint or jlong.)
134 mem = mem->in(MemNode::Memory);
135 continue; // advance through independent store memory
136 }
137 }
138
139 if (st_base != base
140 && MemNode::detect_ptr_independence(base, alloc, st_base,
141 AllocateNode::Ideal_allocation(st_base, phase),
142 phase)) {
143 // Success: The bases are provably independent.
144 mem = mem->in(MemNode::Memory);
145 continue; // advance through independent store memory
146 }
147 } else if (mem->is_Proj() && mem->in(0)->is_Initialize()) {
148
149 InitializeNode* st_init = mem->in(0)->as_Initialize();
150 AllocateNode* st_alloc = st_init->allocation();
151
152 // Make sure that we are looking at the same allocation site.
153 // The alloc variable is guaranteed to not be null here from earlier check.
154 if (alloc == st_alloc) {
155 // Check that the initialization is storing NULL so that no previous store
156 // has been moved up and directly write a reference
157 Node* captured_store = st_init->find_captured_store(offset,
158 type2aelembytes(T_OBJECT),
159 phase);
160 if (captured_store == NULL || captured_store == st_init->zero_memory()) {
161 return true;
162 }
163 }
164 }
165
166 // Unless there is an explicit 'continue', we must bail out here,
167 // because 'mem' is an inscrutable memory state (e.g., a call).
168 break;
169 }
170
171 return false;
172 }
173
174 // G1 pre/post barriers
175 void G1BarrierSetC2::pre_barrier(GraphKit* kit,
176 bool do_load,
177 Node* ctl,
178 Node* obj,
179 Node* adr,
180 uint alias_idx,
181 Node* val,
182 const TypeOopPtr* val_type,
183 Node* pre_val,
184 BasicType bt) const {
185 // Some sanity checks
186 // Note: val is unused in this routine.
187
188 if (do_load) {
189 // We need to generate the load of the previous value
190 assert(obj != NULL, "must have a base");
191 assert(adr != NULL, "where are loading from?");
192 assert(pre_val == NULL, "loaded already?");
193 assert(val_type != NULL, "need a type");
194
195 if (use_ReduceInitialCardMarks()
196 && g1_can_remove_pre_barrier(kit, &kit->gvn(), adr, bt, alias_idx)) {
197 return;
198 }
199
200 } else {
201 // In this case both val_type and alias_idx are unused.
202 assert(pre_val != NULL, "must be loaded already");
203 // Nothing to be done if pre_val is null.
204 if (pre_val->bottom_type() == TypePtr::NULL_PTR) return;
205 assert(pre_val->bottom_type()->basic_type() == T_OBJECT, "or we shouldn't be here");
206 }
207 assert(bt == T_OBJECT, "or we shouldn't be here");
208
209 IdealKit ideal(kit, true);
210
211 Node* tls = __ thread(); // ThreadLocalStorage
212
213 Node* no_base = __ top();
214 Node* zero = __ ConI(0);
215 Node* zeroX = __ ConX(0);
216
217 float likely = PROB_LIKELY(0.999);
218 float unlikely = PROB_UNLIKELY(0.999);
219
220 BasicType active_type = in_bytes(SATBMarkQueue::byte_width_of_active()) == 4 ? T_INT : T_BYTE;
221 assert(in_bytes(SATBMarkQueue::byte_width_of_active()) == 4 || in_bytes(SATBMarkQueue::byte_width_of_active()) == 1, "flag width");
222
223 // Offsets into the thread
224 const int marking_offset = in_bytes(G1ThreadLocalData::satb_mark_queue_active_offset());
225 const int index_offset = in_bytes(G1ThreadLocalData::satb_mark_queue_index_offset());
226 const int buffer_offset = in_bytes(G1ThreadLocalData::satb_mark_queue_buffer_offset());
227
228 // Now the actual pointers into the thread
229 Node* marking_adr = __ AddP(no_base, tls, __ ConX(marking_offset));
230 Node* buffer_adr = __ AddP(no_base, tls, __ ConX(buffer_offset));
231 Node* index_adr = __ AddP(no_base, tls, __ ConX(index_offset));
232
233 // Now some of the values
234 Node* marking = __ load(__ ctrl(), marking_adr, TypeInt::INT, active_type, Compile::AliasIdxRaw);
235
236 // if (!marking)
237 __ if_then(marking, BoolTest::ne, zero, unlikely); {
238 BasicType index_bt = TypeX_X->basic_type();
239 assert(sizeof(size_t) == type2aelembytes(index_bt), "Loading G1 SATBMarkQueue::_index with wrong size.");
240 Node* index = __ load(__ ctrl(), index_adr, TypeX_X, index_bt, Compile::AliasIdxRaw);
241
242 if (do_load) {
243 // load original value
244 // alias_idx correct??
245 pre_val = __ load(__ ctrl(), adr, val_type, bt, alias_idx);
246 }
247
248 // if (pre_val != NULL)
249 __ if_then(pre_val, BoolTest::ne, kit->null()); {
250 Node* buffer = __ load(__ ctrl(), buffer_adr, TypeRawPtr::NOTNULL, T_ADDRESS, Compile::AliasIdxRaw);
251
252 // is the queue for this thread full?
253 __ if_then(index, BoolTest::ne, zeroX, likely); {
254
255 // decrement the index
256 Node* next_index = kit->gvn().transform(new SubXNode(index, __ ConX(sizeof(intptr_t))));
257
258 // Now get the buffer location we will log the previous value into and store it
259 Node *log_addr = __ AddP(no_base, buffer, next_index);
260 __ store(__ ctrl(), log_addr, pre_val, T_OBJECT, Compile::AliasIdxRaw, MemNode::unordered);
261 // update the index
262 __ store(__ ctrl(), index_adr, next_index, index_bt, Compile::AliasIdxRaw, MemNode::unordered);
263
264 } __ else_(); {
265
266 // logging buffer is full, call the runtime
267 const TypeFunc *tf = g1_wb_pre_Type();
268 __ make_leaf_call(tf, CAST_FROM_FN_PTR(address, SharedRuntime::g1_wb_pre), "g1_wb_pre", pre_val, tls);
269 } __ end_if(); // (!index)
270 } __ end_if(); // (pre_val != NULL)
271 } __ end_if(); // (!marking)
272
273 // Final sync IdealKit and GraphKit.
274 kit->final_sync(ideal);
275 }
276
277 /*
278 * G1 similar to any GC with a Young Generation requires a way to keep track of
279 * references from Old Generation to Young Generation to make sure all live
280 * objects are found. G1 also requires to keep track of object references
281 * between different regions to enable evacuation of old regions, which is done
282 * as part of mixed collections. References are tracked in remembered sets and
283 * is continuously updated as reference are written to with the help of the
284 * post-barrier.
285 *
286 * To reduce the number of updates to the remembered set the post-barrier
287 * filters updates to fields in objects located in the Young Generation,
288 * the same region as the reference, when the NULL is being written or
289 * if the card is already marked as dirty by an earlier write.
290 *
291 * Under certain circumstances it is possible to avoid generating the
292 * post-barrier completely if it is possible during compile time to prove
293 * the object is newly allocated and that no safepoint exists between the
294 * allocation and the store.
295 *
296 * In the case of slow allocation the allocation code must handle the barrier
297 * as part of the allocation in the case the allocated object is not located
298 * in the nursery, this would happen for humongous objects. This is similar to
299 * how CMS is required to handle this case, see the comments for the method
300 * CollectedHeap::new_deferred_store_barrier and OptoRuntime::new_deferred_store_barrier.
301 * A deferred card mark is required for these objects and handled in the above
302 * mentioned methods.
303 *
304 * Returns true if the post barrier can be removed
305 */
306 bool G1BarrierSetC2::g1_can_remove_post_barrier(GraphKit* kit,
307 PhaseTransform* phase, Node* store,
308 Node* adr) const {
309 intptr_t offset = 0;
310 Node* base = AddPNode::Ideal_base_and_offset(adr, phase, offset);
311 AllocateNode* alloc = AllocateNode::Ideal_allocation(base, phase);
312
313 if (offset == Type::OffsetBot) {
314 return false; // cannot unalias unless there are precise offsets
315 }
316
317 if (alloc == NULL) {
318 return false; // No allocation found
319 }
320
321 // Start search from Store node
322 Node* mem = store->in(MemNode::Control);
323 if (mem->is_Proj() && mem->in(0)->is_Initialize()) {
324
325 InitializeNode* st_init = mem->in(0)->as_Initialize();
326 AllocateNode* st_alloc = st_init->allocation();
327
328 // Make sure we are looking at the same allocation
329 if (alloc == st_alloc) {
330 return true;
331 }
332 }
333
334 return false;
335 }
336
337 //
338 // Update the card table and add card address to the queue
339 //
340 void G1BarrierSetC2::g1_mark_card(GraphKit* kit,
341 IdealKit& ideal,
342 Node* card_adr,
343 Node* oop_store,
344 uint oop_alias_idx,
345 Node* index,
346 Node* index_adr,
347 Node* buffer,
348 const TypeFunc* tf) const {
349 Node* zero = __ ConI(0);
350 Node* zeroX = __ ConX(0);
351 Node* no_base = __ top();
352 BasicType card_bt = T_BYTE;
353 // Smash zero into card. MUST BE ORDERED WRT TO STORE
354 __ storeCM(__ ctrl(), card_adr, zero, oop_store, oop_alias_idx, card_bt, Compile::AliasIdxRaw);
355
356 // Now do the queue work
357 __ if_then(index, BoolTest::ne, zeroX); {
358
359 Node* next_index = kit->gvn().transform(new SubXNode(index, __ ConX(sizeof(intptr_t))));
360 Node* log_addr = __ AddP(no_base, buffer, next_index);
361
362 // Order, see storeCM.
363 __ store(__ ctrl(), log_addr, card_adr, T_ADDRESS, Compile::AliasIdxRaw, MemNode::unordered);
364 __ store(__ ctrl(), index_adr, next_index, TypeX_X->basic_type(), Compile::AliasIdxRaw, MemNode::unordered);
365
366 } __ else_(); {
367 __ make_leaf_call(tf, CAST_FROM_FN_PTR(address, SharedRuntime::g1_wb_post), "g1_wb_post", card_adr, __ thread());
368 } __ end_if();
369
370 }
371
372 void G1BarrierSetC2::post_barrier(GraphKit* kit,
373 Node* ctl,
374 Node* oop_store,
375 Node* obj,
376 Node* adr,
377 uint alias_idx,
378 Node* val,
379 BasicType bt,
380 bool use_precise) const {
381 // If we are writing a NULL then we need no post barrier
382
383 if (val != NULL && val->is_Con() && val->bottom_type() == TypePtr::NULL_PTR) {
384 // Must be NULL
385 const Type* t = val->bottom_type();
386 assert(t == Type::TOP || t == TypePtr::NULL_PTR, "must be NULL");
387 // No post barrier if writing NULLx
388 return;
389 }
390
391 if (use_ReduceInitialCardMarks() && obj == kit->just_allocated_object(kit->control())) {
392 // We can skip marks on a freshly-allocated object in Eden.
393 // Keep this code in sync with new_deferred_store_barrier() in runtime.cpp.
394 // That routine informs GC to take appropriate compensating steps,
395 // upon a slow-path allocation, so as to make this card-mark
396 // elision safe.
397 return;
398 }
399
400 if (use_ReduceInitialCardMarks()
401 && g1_can_remove_post_barrier(kit, &kit->gvn(), oop_store, adr)) {
402 return;
403 }
404
405 if (!use_precise) {
406 // All card marks for a (non-array) instance are in one place:
407 adr = obj;
408 }
409 // (Else it's an array (or unknown), and we want more precise card marks.)
410 assert(adr != NULL, "");
411
412 IdealKit ideal(kit, true);
413
414 Node* tls = __ thread(); // ThreadLocalStorage
415
416 Node* no_base = __ top();
417 float unlikely = PROB_UNLIKELY(0.999);
418 Node* young_card = __ ConI((jint)G1CardTable::g1_young_card_val());
419 Node* dirty_card = __ ConI((jint)G1CardTable::dirty_card_val());
420 Node* zeroX = __ ConX(0);
421
422 const TypeFunc *tf = g1_wb_post_Type();
423
424 // Offsets into the thread
425 const int index_offset = in_bytes(G1ThreadLocalData::dirty_card_queue_index_offset());
426 const int buffer_offset = in_bytes(G1ThreadLocalData::dirty_card_queue_buffer_offset());
427
428 // Pointers into the thread
429
430 Node* buffer_adr = __ AddP(no_base, tls, __ ConX(buffer_offset));
431 Node* index_adr = __ AddP(no_base, tls, __ ConX(index_offset));
432
433 // Now some values
434 // Use ctrl to avoid hoisting these values past a safepoint, which could
435 // potentially reset these fields in the JavaThread.
436 Node* index = __ load(__ ctrl(), index_adr, TypeX_X, TypeX_X->basic_type(), Compile::AliasIdxRaw);
437 Node* buffer = __ load(__ ctrl(), buffer_adr, TypeRawPtr::NOTNULL, T_ADDRESS, Compile::AliasIdxRaw);
438
439 // Convert the store obj pointer to an int prior to doing math on it
440 // Must use ctrl to prevent "integerized oop" existing across safepoint
441 Node* cast = __ CastPX(__ ctrl(), adr);
442
443 // Divide pointer by card size
444 Node* card_offset = __ URShiftX( cast, __ ConI(CardTable::card_shift) );
445
446 // Combine card table base and card offset
447 Node* card_adr = __ AddP(no_base, byte_map_base_node(kit), card_offset );
448
449 // If we know the value being stored does it cross regions?
450
451 if (val != NULL) {
452 // Does the store cause us to cross regions?
453
454 // Should be able to do an unsigned compare of region_size instead of
455 // and extra shift. Do we have an unsigned compare??
456 // Node* region_size = __ ConI(1 << HeapRegion::LogOfHRGrainBytes);
457 Node* xor_res = __ URShiftX ( __ XorX( cast, __ CastPX(__ ctrl(), val)), __ ConI(HeapRegion::LogOfHRGrainBytes));
458
459 // if (xor_res == 0) same region so skip
460 __ if_then(xor_res, BoolTest::ne, zeroX); {
461
462 // No barrier if we are storing a NULL
463 __ if_then(val, BoolTest::ne, kit->null(), unlikely); {
464
465 // Ok must mark the card if not already dirty
466
467 // load the original value of the card
468 Node* card_val = __ load(__ ctrl(), card_adr, TypeInt::INT, T_BYTE, Compile::AliasIdxRaw);
469
470 __ if_then(card_val, BoolTest::ne, young_card); {
471 kit->sync_kit(ideal);
472 kit->insert_mem_bar(Op_MemBarVolatile, oop_store);
473 __ sync_kit(kit);
474
475 Node* card_val_reload = __ load(__ ctrl(), card_adr, TypeInt::INT, T_BYTE, Compile::AliasIdxRaw);
476 __ if_then(card_val_reload, BoolTest::ne, dirty_card); {
477 g1_mark_card(kit, ideal, card_adr, oop_store, alias_idx, index, index_adr, buffer, tf);
478 } __ end_if();
479 } __ end_if();
480 } __ end_if();
481 } __ end_if();
482 } else {
483 // The Object.clone() intrinsic uses this path if !ReduceInitialCardMarks.
484 // We don't need a barrier here if the destination is a newly allocated object
485 // in Eden. Otherwise, GC verification breaks because we assume that cards in Eden
486 // are set to 'g1_young_gen' (see G1CardTable::verify_g1_young_region()).
487 assert(!use_ReduceInitialCardMarks(), "can only happen with card marking");
488 Node* card_val = __ load(__ ctrl(), card_adr, TypeInt::INT, T_BYTE, Compile::AliasIdxRaw);
489 __ if_then(card_val, BoolTest::ne, young_card); {
490 g1_mark_card(kit, ideal, card_adr, oop_store, alias_idx, index, index_adr, buffer, tf);
491 } __ end_if();
492 }
493
494 // Final sync IdealKit and GraphKit.
495 kit->final_sync(ideal);
496 }
497
498 // Helper that guards and inserts a pre-barrier.
499 void G1BarrierSetC2::insert_pre_barrier(GraphKit* kit, Node* base_oop, Node* offset,
500 Node* pre_val, bool need_mem_bar) const {
501 // We could be accessing the referent field of a reference object. If so, when G1
502 // is enabled, we need to log the value in the referent field in an SATB buffer.
503 // This routine performs some compile time filters and generates suitable
504 // runtime filters that guard the pre-barrier code.
505 // Also add memory barrier for non volatile load from the referent field
506 // to prevent commoning of loads across safepoint.
507
508 // Some compile time checks.
509
510 // If offset is a constant, is it java_lang_ref_Reference::_reference_offset?
511 const TypeX* otype = offset->find_intptr_t_type();
512 if (otype != NULL && otype->is_con() &&
513 otype->get_con() != java_lang_ref_Reference::referent_offset) {
514 // Constant offset but not the reference_offset so just return
515 return;
516 }
517
518 // We only need to generate the runtime guards for instances.
519 const TypeOopPtr* btype = base_oop->bottom_type()->isa_oopptr();
520 if (btype != NULL) {
521 if (btype->isa_aryptr()) {
522 // Array type so nothing to do
523 return;
524 }
525
526 const TypeInstPtr* itype = btype->isa_instptr();
527 if (itype != NULL) {
528 // Can the klass of base_oop be statically determined to be
529 // _not_ a sub-class of Reference and _not_ Object?
530 ciKlass* klass = itype->klass();
531 if ( klass->is_loaded() &&
532 !klass->is_subtype_of(kit->env()->Reference_klass()) &&
533 !kit->env()->Object_klass()->is_subtype_of(klass)) {
534 return;
535 }
536 }
537 }
538
539 // The compile time filters did not reject base_oop/offset so
540 // we need to generate the following runtime filters
541 //
542 // if (offset == java_lang_ref_Reference::_reference_offset) {
543 // if (instance_of(base, java.lang.ref.Reference)) {
544 // pre_barrier(_, pre_val, ...);
545 // }
546 // }
547
548 float likely = PROB_LIKELY( 0.999);
549 float unlikely = PROB_UNLIKELY(0.999);
550
551 IdealKit ideal(kit);
552
553 Node* referent_off = __ ConX(java_lang_ref_Reference::referent_offset);
554
555 __ if_then(offset, BoolTest::eq, referent_off, unlikely); {
556 // Update graphKit memory and control from IdealKit.
557 kit->sync_kit(ideal);
558
559 Node* ref_klass_con = kit->makecon(TypeKlassPtr::make(kit->env()->Reference_klass()));
560 Node* is_instof = kit->gen_instanceof(base_oop, ref_klass_con);
561
562 // Update IdealKit memory and control from graphKit.
563 __ sync_kit(kit);
564
565 Node* one = __ ConI(1);
566 // is_instof == 0 if base_oop == NULL
567 __ if_then(is_instof, BoolTest::eq, one, unlikely); {
568
569 // Update graphKit from IdeakKit.
570 kit->sync_kit(ideal);
571
572 // Use the pre-barrier to record the value in the referent field
573 pre_barrier(kit, false /* do_load */,
574 __ ctrl(),
575 NULL /* obj */, NULL /* adr */, max_juint /* alias_idx */, NULL /* val */, NULL /* val_type */,
576 pre_val /* pre_val */,
577 T_OBJECT);
578 if (need_mem_bar) {
579 // Add memory barrier to prevent commoning reads from this field
580 // across safepoint since GC can change its value.
581 kit->insert_mem_bar(Op_MemBarCPUOrder);
582 }
583 // Update IdealKit from graphKit.
584 __ sync_kit(kit);
585
586 } __ end_if(); // _ref_type != ref_none
587 } __ end_if(); // offset == referent_offset
588
589 // Final sync IdealKit and GraphKit.
590 kit->final_sync(ideal);
591 }
592
593 #undef __
594
595 Node* G1BarrierSetC2::load_at_resolved(C2Access& access, const Type* val_type) const {
596 DecoratorSet decorators = access.decorators();
597 GraphKit* kit = access.kit();
598
599 Node* adr = access.addr().node();
600 Node* obj = access.base();
601
602 bool mismatched = (decorators & C2_MISMATCHED) != 0;
603 bool unknown = (decorators & ON_UNKNOWN_OOP_REF) != 0;
604 bool on_heap = (decorators & IN_HEAP) != 0;
605 bool on_weak = (decorators & ON_WEAK_OOP_REF) != 0;
606 bool is_unordered = (decorators & MO_UNORDERED) != 0;
607 bool need_cpu_mem_bar = !is_unordered || mismatched || !on_heap;
608
609 Node* offset = adr->is_AddP() ? adr->in(AddPNode::Offset) : kit->top();
610 Node* load = CardTableBarrierSetC2::load_at_resolved(access, val_type);
611
612 // If we are reading the value of the referent field of a Reference
613 // object (either by using Unsafe directly or through reflection)
614 // then, if G1 is enabled, we need to record the referent in an
615 // SATB log buffer using the pre-barrier mechanism.
616 // Also we need to add memory barrier to prevent commoning reads
617 // from this field across safepoint since GC can change its value.
618 bool need_read_barrier = on_heap && (on_weak ||
619 (unknown && offset != kit->top() && obj != kit->top()));
620
621 if (!access.is_oop() || !need_read_barrier) {
622 return load;
623 }
624
625 if (on_weak) {
626 // Use the pre-barrier to record the value in the referent field
627 pre_barrier(kit, false /* do_load */,
628 kit->control(),
629 NULL /* obj */, NULL /* adr */, max_juint /* alias_idx */, NULL /* val */, NULL /* val_type */,
630 load /* pre_val */, T_OBJECT);
631 // Add memory barrier to prevent commoning reads from this field
632 // across safepoint since GC can change its value.
633 kit->insert_mem_bar(Op_MemBarCPUOrder);
634 } else if (unknown) {
635 // We do not require a mem bar inside pre_barrier if need_mem_bar
636 // is set: the barriers would be emitted by us.
637 insert_pre_barrier(kit, obj, offset, load, !need_cpu_mem_bar);
638 }
639
640 return load;
641 }
642
643 bool G1BarrierSetC2::is_gc_barrier_node(Node* node) const {
644 if (CardTableBarrierSetC2::is_gc_barrier_node(node)) {
645 return true;
646 }
647 if (node->Opcode() != Op_CallLeaf) {
648 return false;
649 }
650 CallLeafNode *call = node->as_CallLeaf();
651 if (call->_name == NULL) {
652 return false;
653 }
654
655 return strcmp(call->_name, "g1_wb_pre") == 0 || strcmp(call->_name, "g1_wb_post") == 0;
656 }
657
658 void G1BarrierSetC2::eliminate_gc_barrier(PhaseMacroExpand* macro, Node* node) const {
659 assert(node->Opcode() == Op_CastP2X, "ConvP2XNode required");
660 assert(node->outcnt() <= 2, "expects 1 or 2 users: Xor and URShift nodes");
661 // It could be only one user, URShift node, in Object.clone() intrinsic
662 // but the new allocation is passed to arraycopy stub and it could not
663 // be scalar replaced. So we don't check the case.
664
665 // An other case of only one user (Xor) is when the value check for NULL
666 // in G1 post barrier is folded after CCP so the code which used URShift
667 // is removed.
668
669 // Take Region node before eliminating post barrier since it also
670 // eliminates CastP2X node when it has only one user.
671 Node* this_region = node->in(0);
672 assert(this_region != NULL, "");
673
674 // Remove G1 post barrier.
675
676 // Search for CastP2X->Xor->URShift->Cmp path which
677 // checks if the store done to a different from the value's region.
678 // And replace Cmp with #0 (false) to collapse G1 post barrier.
679 Node* xorx = node->find_out_with(Op_XorX);
680 if (xorx != NULL) {
681 Node* shift = xorx->unique_out();
682 Node* cmpx = shift->unique_out();
683 assert(cmpx->is_Cmp() && cmpx->unique_out()->is_Bool() &&
684 cmpx->unique_out()->as_Bool()->_test._test == BoolTest::ne,
685 "missing region check in G1 post barrier");
686 macro->replace_node(cmpx, macro->makecon(TypeInt::CC_EQ));
687
688 // Remove G1 pre barrier.
689
690 // Search "if (marking != 0)" check and set it to "false".
691 // There is no G1 pre barrier if previous stored value is NULL
692 // (for example, after initialization).
693 if (this_region->is_Region() && this_region->req() == 3) {
694 int ind = 1;
695 if (!this_region->in(ind)->is_IfFalse()) {
696 ind = 2;
697 }
698 if (this_region->in(ind)->is_IfFalse()) {
699 Node* bol = this_region->in(ind)->in(0)->in(1);
700 assert(bol->is_Bool(), "");
701 cmpx = bol->in(1);
702 if (bol->as_Bool()->_test._test == BoolTest::ne &&
703 cmpx->is_Cmp() && cmpx->in(2) == macro->intcon(0) &&
704 cmpx->in(1)->is_Load()) {
705 Node* adr = cmpx->in(1)->as_Load()->in(MemNode::Address);
706 const int marking_offset = in_bytes(G1ThreadLocalData::satb_mark_queue_active_offset());
707 if (adr->is_AddP() && adr->in(AddPNode::Base) == macro->top() &&
708 adr->in(AddPNode::Address)->Opcode() == Op_ThreadLocal &&
709 adr->in(AddPNode::Offset) == macro->MakeConX(marking_offset)) {
710 macro->replace_node(cmpx, macro->makecon(TypeInt::CC_EQ));
711 }
712 }
713 }
714 }
715 } else {
716 assert(!use_ReduceInitialCardMarks(), "can only happen with card marking");
717 // This is a G1 post barrier emitted by the Object.clone() intrinsic.
718 // Search for the CastP2X->URShiftX->AddP->LoadB->Cmp path which checks if the card
719 // is marked as young_gen and replace the Cmp with 0 (false) to collapse the barrier.
720 Node* shift = node->find_out_with(Op_URShiftX);
721 assert(shift != NULL, "missing G1 post barrier");
722 Node* addp = shift->unique_out();
723 Node* load = addp->find_out_with(Op_LoadB);
724 assert(load != NULL, "missing G1 post barrier");
725 Node* cmpx = load->unique_out();
726 assert(cmpx->is_Cmp() && cmpx->unique_out()->is_Bool() &&
727 cmpx->unique_out()->as_Bool()->_test._test == BoolTest::ne,
728 "missing card value check in G1 post barrier");
729 macro->replace_node(cmpx, macro->makecon(TypeInt::CC_EQ));
730 // There is no G1 pre barrier in this case
731 }
732 // Now CastP2X can be removed since it is used only on dead path
733 // which currently still alive until igvn optimize it.
734 assert(node->outcnt() == 0 || node->unique_out()->Opcode() == Op_URShiftX, "");
735 macro->replace_node(node, macro->top());
736 }
737
738 Node* G1BarrierSetC2::step_over_gc_barrier(Node* c) const {
739 if (!use_ReduceInitialCardMarks() &&
740 c != NULL && c->is_Region() && c->req() == 3) {
741 for (uint i = 1; i < c->req(); i++) {
742 if (c->in(i) != NULL && c->in(i)->is_Region() &&
743 c->in(i)->req() == 3) {
744 Node* r = c->in(i);
745 for (uint j = 1; j < r->req(); j++) {
746 if (r->in(j) != NULL && r->in(j)->is_Proj() &&
747 r->in(j)->in(0) != NULL &&
748 r->in(j)->in(0)->Opcode() == Op_CallLeaf &&
749 r->in(j)->in(0)->as_Call()->entry_point() == CAST_FROM_FN_PTR(address, SharedRuntime::g1_wb_post)) {
750 Node* call = r->in(j)->in(0);
751 c = c->in(i == 1 ? 2 : 1);
752 if (c != NULL) {
753 c = c->in(0);
754 if (c != NULL) {
755 c = c->in(0);
756 assert(call->in(0) == NULL ||
757 call->in(0)->in(0) == NULL ||
758 call->in(0)->in(0)->in(0) == NULL ||
759 call->in(0)->in(0)->in(0)->in(0) == NULL ||
760 call->in(0)->in(0)->in(0)->in(0)->in(0) == NULL ||
761 c == call->in(0)->in(0)->in(0)->in(0)->in(0), "bad barrier shape");
762 return c;
763 }
764 }
765 }
766 }
767 }
768 }
769 }
770 return c;
771 }