Reland parts of 'Use weak cells in map checks in polymorphic ICs'

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 89451524076a19e5a7356515e00db8c9e2304bb7..d3e58e8a000da26a8c20b52cd1b54a3582db701c 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -1577,6 +1577,14 @@ void HeapObject::HeapObjectShortPrint(std::ostream& os) {  // NOLINT
       os << accumulator.ToCString().get();
       break;
     }
+    case WEAK_CELL_TYPE: {
+      os << "WeakCell for ";
+      HeapStringAllocator allocator;
+      StringStream accumulator(&allocator);
+      WeakCell::cast(this)->value()->ShortPrint(&accumulator);
+      os << accumulator.ToCString().get();
+      break;
+    }
     default:
       os << "<Other heap object (" << map()->instance_type() << ")>";
       break;
@@ -3425,6 +3433,21 @@ bool Map::IsMapInArrayPrototypeChain() {
 }
 
 
+Handle<WeakCell> Map::WeakCellForMap(Handle<Map> map) {
+  Isolate* isolate = map->GetIsolate();
+  if (map->code_cache()->IsFixedArray()) {
+    return isolate->factory()->NewWeakCell(map);
+  }
+  Handle<CodeCache> code_cache(CodeCache::cast(map->code_cache()), isolate);
+  if (code_cache->weak_cell_cache()->IsWeakCell()) {
+    return Handle<WeakCell>(WeakCell::cast(code_cache->weak_cell_cache()));
+  }
+  Handle<WeakCell> weak_cell = isolate->factory()->NewWeakCell(map);
+  code_cache->set_weak_cell_cache(*weak_cell);
+  return weak_cell;
+}
+
+
 static Handle<Map> AddMissingElementsTransitions(Handle<Map> map,
                                                  ElementsKind to_kind) {
   DCHECK(IsTransitionElementsKind(map->elements_kind()));
@@ -10567,6 +10590,7 @@ Object* Code::FindNthObject(int n, Map* match_map) {
   for (RelocIterator it(this, mask); !it.done(); it.next()) {
     RelocInfo* info = it.rinfo();
     Object* object = info->target_object();
+    if (object->IsWeakCell()) object = WeakCell::cast(object)->value();
     if (object->IsHeapObject()) {
       if (HeapObject::cast(object)->map() == match_map) {
         if (--n == 0) return object;
@@ -10599,6 +10623,7 @@ void Code::FindAndReplace(const FindAndReplacePattern& pattern) {
     RelocInfo* info = it.rinfo();
     Object* object = info->target_object();
     if (object->IsHeapObject()) {
+      DCHECK(!object->IsWeakCell());
       Map* map = HeapObject::cast(object)->map();
       if (map == *pattern.find_[current_pattern]) {
         info->set_target_object(*pattern.replace_[current_pattern]);
@@ -10617,6 +10642,7 @@ void Code::FindAllMaps(MapHandleList* maps) {
   for (RelocIterator it(this, mask); !it.done(); it.next()) {
     RelocInfo* info = it.rinfo();
     Object* object = info->target_object();
+    if (object->IsWeakCell()) object = WeakCell::cast(object)->value();
     if (object->IsMap()) maps->Add(handle(Map::cast(object)));
   }
 }
@@ -10625,11 +10651,21 @@ void Code::FindAllMaps(MapHandleList* maps) {
 Code* Code::FindFirstHandler() {
   DCHECK(is_inline_cache_stub());
   DisallowHeapAllocation no_allocation;
-  int mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET);
+  int mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET) |
+             RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT);
+  bool skip_next_handler = false;
   for (RelocIterator it(this, mask); !it.done(); it.next()) {
     RelocInfo* info = it.rinfo();
-    Code* code = Code::GetCodeFromTargetAddress(info->target_address());
-    if (code->kind() == Code::HANDLER) return code;
+    if (info->rmode() == RelocInfo::EMBEDDED_OBJECT) {
+      Object* obj = info->target_object();
+      skip_next_handler |= obj->IsWeakCell() && WeakCell::cast(obj)->cleared();
+    } else {
+      Code* code = Code::GetCodeFromTargetAddress(info->target_address());
+      if (code->kind() == Code::HANDLER) {
+        if (!skip_next_handler) return code;
+        skip_next_handler = false;
+      }
+    }
   }
   return NULL;
 }
@@ -10638,17 +10674,27 @@ Code* Code::FindFirstHandler() {
 bool Code::FindHandlers(CodeHandleList* code_list, int length) {
   DCHECK(is_inline_cache_stub());
   DisallowHeapAllocation no_allocation;
-  int mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET);
+  int mask = RelocInfo::ModeMask(RelocInfo::CODE_TARGET) |
+             RelocInfo::ModeMask(RelocInfo::EMBEDDED_OBJECT);
+  bool skip_next_handler = false;
   int i = 0;
   for (RelocIterator it(this, mask); !it.done(); it.next()) {
     if (i == length) return true;
     RelocInfo* info = it.rinfo();
-    Code* code = Code::GetCodeFromTargetAddress(info->target_address());
-    // IC stubs with handlers never contain non-handler code objects before
-    // handler targets.
-    if (code->kind() != Code::HANDLER) break;
-    code_list->Add(Handle<Code>(code));
-    i++;
+    if (info->rmode() == RelocInfo::EMBEDDED_OBJECT) {
+      Object* obj = info->target_object();
+      skip_next_handler |= obj->IsWeakCell() && WeakCell::cast(obj)->cleared();
+    } else {
+      Code* code = Code::GetCodeFromTargetAddress(info->target_address());
+      // IC stubs with handlers never contain non-handler code objects before
+      // handler targets.
+      if (code->kind() != Code::HANDLER) break;
+      if (!skip_next_handler) {
+        code_list->Add(Handle<Code>(code));
+        i++;
+      }
+      skip_next_handler = false;
+    }
   }
   return i == length;
 }
@@ -10663,6 +10709,7 @@ MaybeHandle<Code> Code::FindHandlerForMap(Map* map) {
     RelocInfo* info = it.rinfo();
     if (info->rmode() == RelocInfo::EMBEDDED_OBJECT) {
       Object* object = info->target_object();
+      if (object->IsWeakCell()) object = WeakCell::cast(object)->value();
       if (object == map) return_next = true;
     } else if (return_next) {
       Code* code = Code::GetCodeFromTargetAddress(info->target_address());