[heap] Avoid the use of cells to point from code to new-space objects.

src/heap/mark-compact.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/heap/mark-compact.h"
 
 #include "src/base/atomicops.h"
 #include "src/base/bits.h"
 #include "src/base/sys-info.h"
 #include "src/code-stubs.h"
@@ skipping 1545 matching lines @@
       RememberedSet<OLD_TO_OLD>::InsertTyped(Page::FromAddress(code_entry_slot),
                                              nullptr, CODE_ENTRY_SLOT,
                                              code_entry_slot);
     }
   }
 
   inline void VisitCodeTarget(RelocInfo* rinfo) final {
     DCHECK(RelocInfo::IsCodeTarget(rinfo->rmode()));
     Code* target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     Code* host = rinfo->host();
+    collector_->heap()->RecordWriteIntoCode(host, rinfo, target);

[ulan, 2016/06/09 14:45:22]

Replace it with a comment that we don't need to record old->new slot because
target is always in old space.

[ahaas, 2016/06/10 11:00:34]

done.

     collector_->RecordRelocSlot(host, rinfo, target);
   }
 
   inline void VisitDebugTarget(RelocInfo* rinfo) final {
     DCHECK(RelocInfo::IsDebugBreakSlot(rinfo->rmode()) &&
            rinfo->IsPatchedDebugBreakSlotSequence());
     Code* target = Code::GetCodeFromTargetAddress(rinfo->debug_call_address());
     Code* host = rinfo->host();
+    collector_->heap()->RecordWriteIntoCode(host, rinfo, target);

[ulan, 2016/06/09 14:45:22]

ditto

[ahaas, 2016/06/10 11:00:34]

done.

     collector_->RecordRelocSlot(host, rinfo, target);
   }
 
   inline void VisitEmbeddedPointer(RelocInfo* rinfo) final {
     DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
     HeapObject* object = HeapObject::cast(rinfo->target_object());
     Code* host = rinfo->host();
+    collector_->heap()->RecordWriteIntoCode(host, rinfo, object);
     collector_->RecordRelocSlot(host, rinfo, object);
   }
 
   inline void VisitCell(RelocInfo* rinfo) final {
     DCHECK(rinfo->rmode() == RelocInfo::CELL);
     Cell* cell = rinfo->target_cell();
     Code* host = rinfo->host();
+    collector_->heap()->RecordWriteIntoCode(host, rinfo, cell);

[ulan, 2016/06/09 14:45:22]

ditto

[ahaas, 2016/06/10 11:00:34]

done.

     collector_->RecordRelocSlot(host, rinfo, cell);
   }
 
   // Entries that will never move.
   inline void VisitCodeAgeSequence(RelocInfo* rinfo) final {
     DCHECK(RelocInfo::IsCodeAgeSequence(rinfo->rmode()));
     Code* stub = rinfo->code_age_stub();
     USE(stub);
     DCHECK(!Page::FromAddress(stub->address())->IsEvacuationCandidate());
   }
@@ skipping 843 matching lines @@
     DependentCode* list_head) {
   TRACE_GC(heap()->tracer(), GCTracer::Scope::MC_CLEAR_DEPENDENT_CODE);
   Isolate* isolate = this->isolate();
   DependentCode* current = list_head;
   while (current->length() > 0) {
     have_code_to_deoptimize_ |= current->MarkCodeForDeoptimization(
         isolate, DependentCode::kWeakCodeGroup);
     current = current->next_link();
   }
 
+  {
+    ArrayList* list = heap_->weak_new_space_object_to_code_list();
+    int counter = 0;
+    for (int i = 0; i < list->Length(); i += 2) {
+      WeakCell* obj = WeakCell::cast(list->Get(i));
+      WeakCell* dep = WeakCell::cast(list->Get(i + 1));
+      if (obj->cleared() || dep->cleared()) {
+        if (!dep->cleared()) {
+          Code* code = Code::cast(dep->value());
+          if (!code->marked_for_deoptimization()) {
+            DependentCode::SetMarkedForDeoptimization(
+                code, DependentCode::DependencyGroup::kWeakCodeGroup);
+            code->InvalidateEmbeddedObjects();
+            have_code_to_deoptimize_ = true;
+          }
+        }
+      } else {
+        list->Set(counter, obj, SKIP_WRITE_BARRIER);

[titzer, 2016/06/09 11:10:21]

I don't understand why this is a SKIP_WRITE_BARRIER and then a RecordSlot
directly afterwards. Would a full barrier just do the right thing?

[ahaas, 2016/06/09 11:20:40]

We skip the write barrier because this code is executed from the GC, not the
mutator and GC does not execute write barriers. Ulan, is that correct?

[ulan, 2016/06/09 14:45:22]

Yes, the barrier will bailout because marking is finished at this point, so we
need to manually record slot here.

[titzer, 2016/06/10 13:27:06]

Let's add a comment to document this.

+        RecordSlot(list, list->Slot(counter), obj);
+        counter++;
+        list->Set(counter, dep, SKIP_WRITE_BARRIER);
+        RecordSlot(list, list->Slot(counter), dep);
+        counter++;
+      }
+    }
+  }
+
   WeakHashTable* table = heap_->weak_object_to_code_table();
   uint32_t capacity = table->Capacity();
   for (uint32_t i = 0; i < capacity; i++) {
     uint32_t key_index = table->EntryToIndex(i);
     Object* key = table->get(key_index);
     if (!table->IsKey(isolate, key)) continue;
     uint32_t value_index = table->EntryToValueIndex(i);
     Object* value = table->get(value_index);
     DCHECK(key->IsWeakCell());
     if (WeakCell::cast(key)->cleared()) {
@@ skipping 324 matching lines @@
   HeapObject* undefined = heap()->undefined_value();
   Object* obj = heap()->encountered_transition_arrays();
   while (obj != Smi::FromInt(0)) {
     TransitionArray* array = TransitionArray::cast(obj);
     obj = array->next_link();
     array->set_next_link(undefined, SKIP_WRITE_BARRIER);
   }
   heap()->set_encountered_transition_arrays(Smi::FromInt(0));
 }
 
-static inline SlotType SlotTypeForRMode(RelocInfo::Mode rmode) {
-  if (RelocInfo::IsCodeTarget(rmode)) {
-    return CODE_TARGET_SLOT;
-  } else if (RelocInfo::IsCell(rmode)) {
-    return CELL_TARGET_SLOT;
-  } else if (RelocInfo::IsEmbeddedObject(rmode)) {
-    return EMBEDDED_OBJECT_SLOT;
-  } else if (RelocInfo::IsDebugBreakSlot(rmode)) {
-    return DEBUG_TARGET_SLOT;
-  }
-  UNREACHABLE();
-  return NUMBER_OF_SLOT_TYPES;
-}
-
 void MarkCompactCollector::RecordRelocSlot(Code* host, RelocInfo* rinfo,
                                            Object* target) {
   Page* target_page = Page::FromAddress(reinterpret_cast<Address>(target));
   Page* source_page = Page::FromAddress(reinterpret_cast<Address>(host));
-  RelocInfo::Mode rmode = rinfo->rmode();
   if (target_page->IsEvacuationCandidate() &&
       (rinfo->host() == NULL ||
        !ShouldSkipEvacuationSlotRecording(rinfo->host()))) {
+    RelocInfo::Mode rmode = rinfo->rmode();
     Address addr = rinfo->pc();
-    SlotType slot_type = SlotTypeForRMode(rmode);
+    SlotType slot_type = SlotTypeForRelocInfoMode(rmode);
     if (rinfo->IsInConstantPool()) {
       addr = rinfo->constant_pool_entry_address();
       if (RelocInfo::IsCodeTarget(rmode)) {
         slot_type = CODE_ENTRY_SLOT;
       } else {
         DCHECK(RelocInfo::IsEmbeddedObject(rmode));
         slot_type = OBJECT_SLOT;
       }
     }
     RememberedSet<OLD_TO_OLD>::InsertTyped(
@@ skipping 596 matching lines @@
       memset(free_start, 0xcc, size);
     }
     freed_bytes = space->UnaccountedFree(free_start, size);
     max_freed_bytes = Max(freed_bytes, max_freed_bytes);
   }
   p->concurrent_sweeping_state().SetValue(Page::kSweepingDone);
   return FreeList::GuaranteedAllocatable(static_cast<int>(max_freed_bytes));
 }
 
 void MarkCompactCollector::InvalidateCode(Code* code) {
+  Page* page = Page::FromAddress(code->address());
+  Address start = code->instruction_start();
+  Address end = code->address() + code->Size();
+
+  RememberedSet<OLD_TO_NEW>::RemoveRangeTyped(page, start, end);
+
   if (heap_->incremental_marking()->IsCompacting() &&
       !ShouldSkipEvacuationSlotRecording(code)) {
     DCHECK(compacting_);
 
     // If the object is white than no slots were recorded on it yet.
     MarkBit mark_bit = Marking::MarkBitFrom(code);
     if (Marking::IsWhite(mark_bit)) return;
 
     // Ignore all slots that might have been recorded in the body of the
     // deoptimized code object. Assumption: no slots will be recorded for
     // this object after invalidating it.
-    Page* page = Page::FromAddress(code->address());
-    Address start = code->instruction_start();
-    Address end = code->address() + code->Size();
     RememberedSet<OLD_TO_OLD>::RemoveRangeTyped(page, start, end);
-    RememberedSet<OLD_TO_NEW>::RemoveRangeTyped(page, start, end);
   }
 }
 
 
 // Return true if the given code is deoptimized or will be deoptimized.
 bool MarkCompactCollector::WillBeDeoptimized(Code* code) {
   return code->is_optimized_code() && code->marked_for_deoptimization();
 }
 
 
@@ skipping 525 matching lines @@
 
 void MarkCompactCollector::RecordCodeTargetPatch(Address pc, Code* target) {
   DCHECK(heap()->gc_state() == Heap::MARK_COMPACT);
   if (is_compacting()) {
     Code* host =
         isolate()->inner_pointer_to_code_cache()->GcSafeFindCodeForInnerPointer(
             pc);
     MarkBit mark_bit = Marking::MarkBitFrom(host);
     if (Marking::IsBlack(mark_bit)) {
       RelocInfo rinfo(isolate(), pc, RelocInfo::CODE_TARGET, 0, host);
+      heap()->RecordWriteIntoCode(host, &rinfo, target);

[ulan, 2016/06/09 14:45:22]

ditto

[ahaas, 2016/06/10 11:00:34]

done.

       RecordRelocSlot(host, &rinfo, target);
     }
   }
 }
 
 }  // namespace internal
 }  // namespace v8