[ptr-compr] Remove default implementation of ObjectVisitor::VisitEmbeddedPointer()

which used to treat off-heap slots as on-heap ones and implement embedded objects
visitation in derived visitor classes.

Bug: v8:8518
Change-Id: Ia40d8135078379cca990e9167d3f1bebb3b5be0a
Reviewed-on: https://chromium-review.googlesource.com/c/1367747Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58123}

src/heap/concurrent-marking.cc

@@ -447,6 +447,12 @@ class ConcurrentMarkingVisitor final
       UNREACHABLE();
     }
 
+    void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
+      // This should never happen, because snapshotting is performed only on
+      // JSObjects (and derived classes).
+      UNREACHABLE();
+    }
+
     void VisitCustomWeakPointers(HeapObject* host, ObjectSlot start,
                                  ObjectSlot end) override {
       DCHECK(host->IsJSWeakCell());

src/heap/heap.cc

@@ -1477,6 +1477,10 @@ class StringTableVerifier : public ObjectVisitor {
 
   void VisitCodeTarget(Code host, RelocInfo* rinfo) override { UNREACHABLE(); }
 
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    UNREACHABLE();
+  }
+
  private:
   Isolate* isolate_;
 };
@@ -2998,6 +3002,10 @@ class SlotCollectingVisitor final : public ObjectVisitor {
 
   void VisitCodeTarget(Code host, RelocInfo* rinfo) final { UNREACHABLE(); }
 
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    UNREACHABLE();
+  }
+
   int number_of_slots() { return static_cast<int>(slots_.size()); }
 
   MaybeObjectSlot slot(int i) { return slots_[i]; }
@@ -5039,6 +5047,9 @@ class UnreachableObjectsFilter : public HeapObjectsFilter {
       Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
       MarkHeapObject(target);
     }
+    void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
+      MarkHeapObject(rinfo->target_object());
+    }
 
     void VisitRootPointers(Root root, const char* description,
                            FullObjectSlot start, FullObjectSlot end) override {
@@ -5442,6 +5453,10 @@ void VerifyPointersVisitor::VisitCodeTarget(Code host, RelocInfo* rinfo) {
   VerifyHeapObjectImpl(target);
 }
 
+void VerifyPointersVisitor::VisitEmbeddedPointer(Code host, RelocInfo* rinfo) {
+  VerifyHeapObjectImpl(rinfo->target_object());
+}
+
 void VerifySmisVisitor::VisitRootPointers(Root root, const char* description,
                                           FullObjectSlot start,
                                           FullObjectSlot end) {

src/heap/heap.h

@@ -2162,6 +2162,7 @@ class VerifyPointersVisitor : public ObjectVisitor, public RootVisitor {
   void VisitPointers(HeapObject* host, MaybeObjectSlot start,
                      MaybeObjectSlot end) override;
   void VisitCodeTarget(Code host, RelocInfo* rinfo) override;
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override;
 
   void VisitRootPointers(Root root, const char* description,
                          FullObjectSlot start, FullObjectSlot end) override;

src/heap/mark-compact.cc

@@ -346,6 +346,9 @@ class FullEvacuationVerifier : public EvacuationVerifier {
     Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     VerifyHeapObjectImpl(target);
   }
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    VerifyHeapObjectImpl(rinfo->target_object());
+  }
   void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) override {
     VerifyPointersImpl(start, end);
   }
@@ -942,6 +945,9 @@ class MarkCompactCollector::CustomRootBodyMarkingVisitor final
     Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     MarkObject(host, target);
   }
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    MarkObject(host, rinfo->target_object());
+  }
 
  private:
   V8_INLINE void MarkObject(HeapObject* host, Object* object) {
@@ -987,6 +993,10 @@ class InternalizedStringTableCleaner : public ObjectVisitor {
 
   void VisitCodeTarget(Code host, RelocInfo* rinfo) final { UNREACHABLE(); }
 
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
+    UNREACHABLE();
+  }
+
   int PointersRemoved() {
     return pointers_removed_;
   }
@@ -3668,7 +3678,9 @@ class YoungGenerationMarkingVerifier : public MarkingVerifier {
     Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     VerifyHeapObjectImpl(target);
   }
-
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    VerifyHeapObjectImpl(rinfo->target_object());
+  }
   void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) override {
     VerifyPointersImpl(start, end);
   }
@@ -3732,6 +3744,9 @@ class YoungGenerationEvacuationVerifier : public EvacuationVerifier {
     Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     VerifyHeapObjectImpl(target);
   }
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    VerifyHeapObjectImpl(rinfo->target_object());
+  }
   void VerifyRootPointers(FullObjectSlot start, FullObjectSlot end) override {
     VerifyPointersImpl(start, end);
   }
@@ -3793,6 +3808,11 @@ class YoungGenerationMarkingVisitor final
     UNREACHABLE();
   }
 
+  V8_INLINE void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
+    // Code objects are not expected in new space.
+    UNREACHABLE();
+  }
+
  private:
   template <typename TSlot>
   V8_INLINE void VisitPointersImpl(HeapObject* host, TSlot start, TSlot end) {

src/heap/object-stats.cc

@@ -82,6 +82,10 @@ class FieldStatsCollector : public ObjectVisitor {
     // as a full tagged value, so there's nothing to count.
   }
 
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    *tagged_fields_count_ += 1;
+  }
+
  private:
   struct JSObjectFieldStats {
     JSObjectFieldStats()

src/heap/scavenger-inl.h

@@ -425,8 +425,32 @@ void ScavengeVisitor::VisitPointers(HeapObject* host, MaybeObjectSlot start,
 
 void ScavengeVisitor::VisitCodeTarget(Code host, RelocInfo* rinfo) {
   Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
+#ifdef DEBUG
+  Code old_target = target;
+#endif
   FullObjectSlot slot(&target);
-  VisitPointersImpl(host, slot, slot + 1);
+  VisitHeapObjectImpl(slot, target);
+  // Code objects are never in new-space, so the slot contents must not change.
+  DCHECK_EQ(old_target, target);
+}
+
+void ScavengeVisitor::VisitEmbeddedPointer(Code host, RelocInfo* rinfo) {
+  HeapObject* heap_object = rinfo->target_object();
+#ifdef DEBUG
+  HeapObject* old_heap_object = heap_object;
+#endif
+  FullObjectSlot slot(&heap_object);
+  VisitHeapObjectImpl(slot, heap_object);
+  // We don't embed new-space objects into code, so the slot contents must not
+  // change.
+  DCHECK_EQ(old_heap_object, heap_object);
+}
+
+template <typename TSlot>
+void ScavengeVisitor::VisitHeapObjectImpl(TSlot slot, HeapObject* heap_object) {
+  if (Heap::InNewSpace(heap_object)) {
+    scavenger_->ScavengeObject(HeapObjectSlot(slot), heap_object);
+  }
 }
 
 template <typename TSlot>
@@ -436,8 +460,8 @@ void ScavengeVisitor::VisitPointersImpl(HeapObject* host, TSlot start,
     typename TSlot::TObject object = slot.load();
     HeapObject* heap_object;
     // Treat weak references as strong.
-    if (object.GetHeapObject(&heap_object) && Heap::InNewSpace(heap_object)) {
-      scavenger_->ScavengeObject(HeapObjectSlot(slot), heap_object);
+    if (object.GetHeapObject(&heap_object)) {
+      VisitHeapObjectImpl(slot, heap_object);
     }
   }
 }

src/heap/scavenger.cc

@@ -76,12 +76,12 @@ class IterateAndScavengePromotedObjectsVisitor final : public ObjectVisitor {
                                            bool record_slots)
       : heap_(heap), scavenger_(scavenger), record_slots_(record_slots) {}
 
-  inline void VisitPointers(HeapObject* host, ObjectSlot start,
+  V8_INLINE void VisitPointers(HeapObject* host, ObjectSlot start,
                                ObjectSlot end) final {
     VisitPointersImpl(host, start, end);
   }
 
-  inline void VisitPointers(HeapObject* host, MaybeObjectSlot start,
+  V8_INLINE void VisitPointers(HeapObject* host, MaybeObjectSlot start,
                                MaybeObjectSlot end) final {
     VisitPointersImpl(host, start, end);
   }
@@ -90,6 +90,10 @@ class IterateAndScavengePromotedObjectsVisitor final : public ObjectVisitor {
     Code target = Code::GetCodeFromTargetAddress(rinfo->target_address());
     HandleSlot(host, FullHeapObjectSlot(&target), target);
   }
+  V8_INLINE void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final {
+    HeapObject* heap_object = rinfo->target_object();
+    HandleSlot(host, FullHeapObjectSlot(&heap_object), heap_object);
+  }
 
  private:
   template <typename TSlot>
@@ -105,7 +109,7 @@ class IterateAndScavengePromotedObjectsVisitor final : public ObjectVisitor {
     }
   }
 
-  inline void HandleSlot(HeapObject* host, HeapObjectSlot slot,
+  V8_INLINE void HandleSlot(HeapObject* host, HeapObjectSlot slot,
                             HeapObject* target) {
     scavenger_->PageMemoryFence(MaybeObject::FromObject(target));
 

src/heap/scavenger.h

@@ -236,8 +236,12 @@ class ScavengeVisitor final : public NewSpaceVisitor<ScavengeVisitor> {
                                MaybeObjectSlot end) final;
 
   V8_INLINE void VisitCodeTarget(Code host, RelocInfo* rinfo) final;
+  V8_INLINE void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) final;
 
  private:
+  template <typename TSlot>
+  V8_INLINE void VisitHeapObjectImpl(TSlot slot, HeapObject* heap_object);
+
   template <typename TSlot>
   V8_INLINE void VisitPointersImpl(HeapObject* host, TSlot start, TSlot end);
 

src/objects.cc

@@ -14488,16 +14488,6 @@ void Map::StartInobjectSlackTracking() {
   set_construction_counter(Map::kSlackTrackingCounterStart);
 }
 
-void ObjectVisitor::VisitEmbeddedPointer(Code host, RelocInfo* rinfo) {
-  DCHECK(rinfo->rmode() == RelocInfo::EMBEDDED_OBJECT);
-  Object* old_pointer = rinfo->target_object();
-  Object* new_pointer = old_pointer;
-  // TODO(ishell): we are actually visiting off-heap slot here.
-  STATIC_ASSERT(kTaggedSize == kSystemPointerSize);
-  VisitPointer(host, FullObjectSlot(&new_pointer));
-  DCHECK_EQ(old_pointer, new_pointer);
-}
-
 void ObjectVisitor::VisitRelocInfo(RelocIterator* it) {
   for (; !it->done(); it->next()) {
     it->rinfo()->Visit(this);

src/objects/slots.h

@@ -104,6 +104,8 @@ class FullObjectSlot
   inline explicit FullObjectSlot(ObjectPtr* object);
   explicit FullObjectSlot(Object const* const* ptr)
       : SlotBase(reinterpret_cast<Address>(ptr)) {}
+  explicit FullObjectSlot(HeapObject** ptr)
+      : SlotBase(reinterpret_cast<Address>(ptr)) {}
   template <typename T>
   explicit FullObjectSlot(SlotBase<T, TData, kSlotDataSize> slot)
       : SlotBase(slot.address()) {}
@@ -181,6 +183,8 @@ class FullHeapObjectSlot
   explicit FullHeapObjectSlot(Address ptr) : SlotBase(ptr) {}
   explicit FullHeapObjectSlot(ObjectPtr* ptr)
       : SlotBase(reinterpret_cast<Address>(ptr)) {}
+  explicit FullHeapObjectSlot(HeapObject** ptr)
+      : SlotBase(reinterpret_cast<Address>(ptr)) {}
   template <typename T>
   explicit FullHeapObjectSlot(SlotBase<T, TData, kSlotDataSize> slot)
       : SlotBase(slot.address()) {}

src/profiler/heap-snapshot-generator.cc

@@ -678,17 +678,16 @@ class IndexedReferencesExtractor : public ObjectVisitor {
   }
   void VisitPointers(HeapObject* host, MaybeObjectSlot start,
                      MaybeObjectSlot end) override {
+    // [start,end) must be a sub-region of [parent_start_, parent_end), i.e.
+    // all the slots must point inside the object.
+    CHECK_LE(parent_start_, start);
+    CHECK_LE(end, parent_end_);
     for (MaybeObjectSlot p = start; p < end; ++p) {
-      int field_index = -1;
-      // |p| could be outside of the object, e.g., while visiting RelocInfo of
-      // code objects.
-      if (parent_start_ <= p && p < parent_end_) {
-        field_index = static_cast<int>(p - parent_start_);
+      int field_index = static_cast<int>(p - parent_start_);
       if (generator_->visited_fields_[field_index]) {
         generator_->visited_fields_[field_index] = false;
         continue;
       }
-      }
       HeapObject* heap_object;
       if ((*p)->GetHeapObject(&heap_object)) {
         VisitHeapObjectImpl(heap_object, field_index);
@@ -701,6 +700,10 @@ class IndexedReferencesExtractor : public ObjectVisitor {
     VisitHeapObjectImpl(target, -1);
   }
 
+  void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) override {
+    VisitHeapObjectImpl(rinfo->target_object(), -1);
+  }
+
  private:
   V8_INLINE void VisitHeapObjectImpl(HeapObject* heap_object, int field_index) {
     DCHECK_LE(-1, field_index);

src/visitors.h

@@ -123,12 +123,12 @@ class ObjectVisitor {
   // Visits a code target in the instruction stream.
   virtual void VisitCodeTarget(Code host, RelocInfo* rinfo) = 0;
 
+  // Visit pointer embedded into a code object.
+  virtual void VisitEmbeddedPointer(Code host, RelocInfo* rinfo) = 0;
+
   // Visits a runtime entry in the instruction stream.
   virtual void VisitRuntimeEntry(Code host, RelocInfo* rinfo) {}
 
-  // Visit pointer embedded into a code object.
-  virtual void VisitEmbeddedPointer(Code host, RelocInfo* rinfo);
-
   // Visits an external reference embedded into a code object.
   virtual void VisitExternalReference(Code host, RelocInfo* rinfo) {}