Fixed issue 303 by not shortcutting cons-symbols and added

symbol table verification after mark-compact GCs.
Review URL: http://codereview.chromium.org/73029

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@1698 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.cc

@@ -813,12 +813,20 @@ void Heap::ScavengeObject(HeapObject** p, HeapObject* object) {
 
 
 static inline bool IsShortcutCandidate(HeapObject* object, Map* map) {
-  // A ConsString object with Heap::empty_string() as the right side
-  // is a candidate for being shortcut by the scavenger.
+  // A ConsString with an empty string as the right side is a
+  // candidate for being shortcut by the scavenger unless it is a
+  // symbol. It's not common to have non-flat symbols, so we do not
+  // shortcut them thereby avoiding turning symbols into strings.
+  ASSERT(kNotStringTag != 0 && kSymbolTag != 0);
+  static const uint32_t kShortcutTypeMask =
+      kIsNotStringMask |
+      kIsSymbolMask |
+      kStringRepresentationMask;
   ASSERT(object->map() == map);
-  if (map->instance_type() >= FIRST_NONSTRING_TYPE) return false;
-  return (StringShape(map).representation_tag() == kConsStringTag) &&
-         (ConsString::cast(object)->unchecked_second() == Heap::empty_string());
+  InstanceType type = map->instance_type();
+  if ((type & kShortcutTypeMask) != kConsStringTag) return false;
+  ASSERT(object->IsString() && !object->IsSymbol());
+  return ConsString::cast(object)->unchecked_second() == Heap::empty_string();
 }
 
 

src/mark-compact.cc

@@ -183,6 +183,10 @@ void MarkCompactCollector::Prepare(GCTracer* tracer) {
 
 void MarkCompactCollector::Finish() {
 #ifdef DEBUG
+  SymbolTable* symbol_table = SymbolTable::cast(Heap::symbol_table());
+  SymbolTableVerifier v;
+  symbol_table->IterateElements(&v);
+
   ASSERT(state_ == SWEEP_SPACES || state_ == REBUILD_RSETS);
   state_ = IDLE;
 #endif