Internalize strings in-place

src/heap/heap.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/heap.h"
 
 #include "src/accessors.h"
 #include "src/api.h"
 #include "src/ast/context-slot-cache.h"
 #include "src/base/bits.h"
@@ skipping 1720 matching lines @@
   SetGCState(NOT_IN_GC);
 }
 
 
 String* Heap::UpdateNewSpaceReferenceInExternalStringTableEntry(Heap* heap,
                                                                 Object** p) {
   MapWord first_word = HeapObject::cast(*p)->map_word();
 
   if (!first_word.IsForwardingAddress()) {
     // Unreachable external string can be finalized.
-    heap->FinalizeExternalString(String::cast(*p));
+    String* string = String::cast(*p);
+    if (!string->IsExternalString()) {
+      // Original external string has been internalized.
+      DCHECK(string->IsThinString());
+      return NULL;
+    }
+    heap->FinalizeExternalString(string);
     return NULL;
   }
 
   // String is still reachable.
-  return String::cast(first_word.ToForwardingAddress());
+  String* string = String::cast(first_word.ToForwardingAddress());
+  if (string->IsThinString()) string = ThinString::cast(string)->actual();
+  // Internalization can replace external strings with non-external strings.
+  return string->IsExternalString() ? string : nullptr;
 }
 
 
 void Heap::UpdateNewSpaceReferencesInExternalStringTable(
     ExternalStringTableUpdaterCallback updater_func) {
   if (external_string_table_.new_space_strings_.is_empty()) return;
 
   Object** start = &external_string_table_.new_space_strings_[0];
   Object** end = start + external_string_table_.new_space_strings_.length();
   Object** last = start;
@@ skipping 4673 matching lines @@
 void Heap::UpdateTotalGCTime(double duration) {
   if (FLAG_trace_gc_verbose) {
     total_gc_time_ms_ += duration;
   }
 }
 
 void Heap::ExternalStringTable::CleanUpNewSpaceStrings() {
   int last = 0;
   Isolate* isolate = heap_->isolate();
   for (int i = 0; i < new_space_strings_.length(); ++i) {
-    if (new_space_strings_[i]->IsTheHole(isolate)) {
+    Object* o = new_space_strings_[i];
+    if (o->IsTheHole(isolate)) {
       continue;
     }
-    DCHECK(new_space_strings_[i]->IsExternalString());
-    if (heap_->InNewSpace(new_space_strings_[i])) {
-      new_space_strings_[last++] = new_space_strings_[i];
+    if (o->IsThinString()) {
+      o = ThinString::cast(o)->actual();
+      if (!o->IsExternalString()) continue;
+    }
+    DCHECK(o->IsExternalString());
+    if (heap_->InNewSpace(o)) {
+      new_space_strings_[last++] = o;
     } else {
-      old_space_strings_.Add(new_space_strings_[i]);
+      old_space_strings_.Add(o);
     }
   }
   new_space_strings_.Rewind(last);
   new_space_strings_.Trim();
 }
 
 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)) {
+    Object* o = old_space_strings_[i];
+    if (o->IsTheHole(isolate)) {
       continue;
     }
-    DCHECK(old_space_strings_[i]->IsExternalString());
-    DCHECK(!heap_->InNewSpace(old_space_strings_[i]));
-    old_space_strings_[last++] = old_space_strings_[i];
+    if (o->IsThinString()) {
+      o = ThinString::cast(o)->actual();
+      if (!o->IsExternalString()) continue;
+    }
+    DCHECK(o->IsExternalString());
+    DCHECK(!heap_->InNewSpace(o));
+    old_space_strings_[last++] = o;
   }
   old_space_strings_.Rewind(last);
   old_space_strings_.Trim();
 #ifdef VERIFY_HEAP
   if (FLAG_verify_heap) {
     Verify();
   }
 #endif
 }
 
 void Heap::ExternalStringTable::TearDown() {
   for (int i = 0; i < new_space_strings_.length(); ++i) {
-    heap_->FinalizeExternalString(ExternalString::cast(new_space_strings_[i]));
+    Object* o = new_space_strings_[i];
+    if (o->IsThinString()) {
+      o = ThinString::cast(o)->actual();
+      if (!o->IsExternalString()) continue;
+    }
+    heap_->FinalizeExternalString(ExternalString::cast(o));
   }
   new_space_strings_.Free();
   for (int i = 0; i < old_space_strings_.length(); ++i) {
-    heap_->FinalizeExternalString(ExternalString::cast(old_space_strings_[i]));
+    Object* o = old_space_strings_[i];
+    if (o->IsThinString()) {
+      o = ThinString::cast(o)->actual();
+      if (!o->IsExternalString()) continue;
+    }
+    heap_->FinalizeExternalString(ExternalString::cast(o));
   }
   old_space_strings_.Free();
 }
 
 
 void Heap::RememberUnmappedPage(Address page, bool compacted) {
   uintptr_t p = reinterpret_cast<uintptr_t>(page);
   // Tag the page pointer to make it findable in the dump file.
   if (compacted) {
     p ^= 0xc1ead & (Page::kPageSize - 1);  // Cleared.
@@ skipping 94 matching lines @@
 }
 
 
 // static
 int Heap::GetStaticVisitorIdForMap(Map* map) {
   return StaticVisitorBase::GetVisitorId(map);
 }
 
 }  // namespace internal
 }  // namespace v8