[heap] ExternalStringTable: Separate Iterate and CleanUp methods

This way we can just process new space strings when needed.

BUG=chromium:651354

Review-Url: https://codereview.chromium.org/2515643002
Cr-Commit-Position: refs/heads/master@{#41107}

src/heap/heap-inl.h

@@ -702,12 +702,15 @@ void Heap::ExternalStringTable::AddString(String* string) {
   }
 }
 
-
-void Heap::ExternalStringTable::Iterate(ObjectVisitor* v) {
+void Heap::ExternalStringTable::IterateNewSpaceStrings(ObjectVisitor* v) {
   if (!new_space_strings_.is_empty()) {
     Object** start = &new_space_strings_[0];
     v->VisitPointers(start, start + new_space_strings_.length());
   }
+}
+
+void Heap::ExternalStringTable::IterateAll(ObjectVisitor* v) {
+  IterateNewSpaceStrings(v);
   if (!old_space_strings_.is_empty()) {
     Object** start = &old_space_strings_[0];
     v->VisitPointers(start, start + old_space_strings_.length());

src/heap/heap.cc

@@ -1859,7 +1859,7 @@ void Heap::VisitExternalResources(v8::ExternalResourceVisitor* visitor) {
     v8::ExternalResourceVisitor* visitor_;
   } external_string_table_visitor(visitor);
 
-  external_string_table_.Iterate(&external_string_table_visitor);
+  external_string_table_.IterateAll(&external_string_table_visitor);
 }
 
 Address Heap::DoScavenge(ObjectVisitor* scavenge_visitor,
@@ -4817,7 +4817,7 @@ void Heap::IterateWeakRoots(ObjectVisitor* v, VisitMode mode) {
   v->Synchronize(VisitorSynchronization::kStringTable);
   if (mode != VISIT_ALL_IN_SCAVENGE && mode != VISIT_ALL_IN_SWEEP_NEWSPACE) {
     // Scavenge collections have special processing for this.
-    external_string_table_.Iterate(v);
+    external_string_table_.IterateAll(v);
   }
   v->Synchronize(VisitorSynchronization::kExternalStringsTable);
 }
@@ -6308,7 +6308,7 @@ void Heap::UpdateTotalGCTime(double duration) {
   }
 }
 
-void Heap::ExternalStringTable::CleanUp() {
+void Heap::ExternalStringTable::CleanUpNewSpaceStrings() {
   int last = 0;
   Isolate* isolate = heap_->isolate();
   for (int i = 0; i < new_space_strings_.length(); ++i) {
@@ -6324,8 +6324,12 @@ void Heap::ExternalStringTable::CleanUp() {
   }
   new_space_strings_.Rewind(last);
   new_space_strings_.Trim();
+}
 
-  last = 0;
+void Heap::ExternalStringTable::CleanUpAll() {
+  CleanUpNewSpaceStrings();
+  int last = 0;
+  Isolate* isolate = heap_->isolate();
   for (int i = 0; i < old_space_strings_.length(); ++i) {
     if (old_space_strings_[i]->IsTheHole(isolate)) {
       continue;

src/heap/heap.h

@@ -1511,11 +1511,13 @@ class Heap {
     // Registers an external string.
     inline void AddString(String* string);
 
-    inline void Iterate(ObjectVisitor* v);
+    inline void IterateAll(ObjectVisitor* v);
+    inline void IterateNewSpaceStrings(ObjectVisitor* v);
 
-    // Restores internal invariant and gets rid of collected strings.
-    // Must be called after each Iterate() that modified the strings.
-    void CleanUp();
+    // Restores internal invariant and gets rid of collected strings. Must be
+    // called after each Iterate*() that modified the strings.
+    void CleanUpAll();
+    void CleanUpNewSpaceStrings();
 
     // Destroys all allocated memory.
     void TearDown();

src/heap/mark-compact.cc

@@ -2514,8 +2514,8 @@ void MarkCompactCollector::ClearNonLiveReferences() {
     string_table->ElementsRemoved(internalized_visitor.PointersRemoved());
 
     ExternalStringTableCleaner external_visitor(heap(), nullptr);
-    heap()->external_string_table_.Iterate(&external_visitor);
-    heap()->external_string_table_.CleanUp();
+    heap()->external_string_table_.IterateAll(&external_visitor);
+    heap()->external_string_table_.CleanUpAll();
   }
 
   {