Reland [Object.observe] Don't force normalization of elements for observed objects

Original Issue: https://codereview.chromium.org/29353003/

TBR=danno
BUG=v8:2946

Review URL: https://codereview.chromium.org/66933003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17607 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/ic-arm.cc

@@ -1432,10 +1432,10 @@ void KeyedStoreIC::GenerateGeneric(MacroAssembler* masm,
   __ JumpIfSmi(receiver, &slow);
   // Get the map of the object.
   __ ldr(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
-  // Check that the receiver does not require access checks.  We need
-  // to do this because this generic stub does not perform map checks.
+  // Check that the receiver does not require access checks and is not observed.
+  // The generic stub does not perform map checks or handle observed objects.
   __ ldrb(ip, FieldMemOperand(receiver_map, Map::kBitFieldOffset));
-  __ tst(ip, Operand(1 << Map::kIsAccessCheckNeeded));
+  __ tst(ip, Operand(1 << Map::kIsAccessCheckNeeded | 1 << Map::kIsObserved));
   __ b(ne, &slow);
   // Check if the object is a JS array or not.
   __ ldrb(r4, FieldMemOperand(receiver_map, Map::kInstanceTypeOffset));

src/builtins.cc

@@ -311,6 +311,7 @@ static inline MaybeObject* EnsureJSArrayWithWritableFastElements(
     Heap* heap, Object* receiver, Arguments* args, int first_added_arg) {
   if (!receiver->IsJSArray()) return NULL;
   JSArray* array = JSArray::cast(receiver);
+  if (array->map()->is_observed()) return NULL;
   HeapObject* elms = array->elements();
   Map* map = elms->map();
   if (map == heap->fixed_array_map()) {

src/ia32/ic-ia32.cc

@@ -874,10 +874,10 @@ void KeyedStoreIC::GenerateGeneric(MacroAssembler* masm,
   __ JumpIfSmi(edx, &slow);
   // Get the map from the receiver.
   __ mov(edi, FieldOperand(edx, HeapObject::kMapOffset));
-  // Check that the receiver does not require access checks.  We need
-  // to do this because this generic stub does not perform map checks.
+  // Check that the receiver does not require access checks and is not observed.
+  // The generic stub does not perform map checks or handle observed objects.
   __ test_b(FieldOperand(edi, Map::kBitFieldOffset),
-            1 << Map::kIsAccessCheckNeeded);
+            1 << Map::kIsAccessCheckNeeded | 1 << Map::kIsObserved);
   __ j(not_zero, &slow);
   // Check that the key is a smi.
   __ JumpIfNotSmi(ecx, &slow);

src/mips/ic-mips.cc

@@ -1354,10 +1354,11 @@ void KeyedStoreIC::GenerateGeneric(MacroAssembler* masm,
   __ JumpIfSmi(receiver, &slow);
   // Get the map of the object.
   __ lw(receiver_map, FieldMemOperand(receiver, HeapObject::kMapOffset));
-  // Check that the receiver does not require access checks.  We need
-  // to do this because this generic stub does not perform map checks.
+  // Check that the receiver does not require access checks and is not observed.
+  // The generic stub does not perform map checks or handle observed objects.
   __ lbu(t0, FieldMemOperand(receiver_map, Map::kBitFieldOffset));
-  __ And(t0, t0, Operand(1 << Map::kIsAccessCheckNeeded));
+  __ And(t0, t0, Operand(1 << Map::kIsAccessCheckNeeded |
+                         1 << Map::kIsObserved));
   __ Branch(&slow, ne, t0, Operand(zero_reg));
   // Check if the object is a JS array or not.
   __ lbu(t0, FieldMemOperand(receiver_map, Map::kInstanceTypeOffset));

src/objects-debug.cc

@@ -366,9 +366,6 @@ void Map::MapVerify() {
     SLOW_ASSERT(transitions()->IsSortedNoDuplicates());
     SLOW_ASSERT(transitions()->IsConsistentWithBackPointers(this));
   }
-  ASSERT(!is_observed() || instance_type() < FIRST_JS_OBJECT_TYPE ||
-         instance_type() > LAST_JS_OBJECT_TYPE ||
-         has_slow_elements_kind() || has_external_array_elements());
 }
 
 

src/objects-inl.h

@@ -3649,16 +3649,13 @@ bool Map::owns_descriptors() {
 }
 
 
-void Map::set_is_observed(bool is_observed) {
-  ASSERT(instance_type() < FIRST_JS_OBJECT_TYPE ||
-         instance_type() > LAST_JS_OBJECT_TYPE ||
-         has_slow_elements_kind() || has_external_array_elements());
-  set_bit_field3(IsObserved::update(bit_field3(), is_observed));
+void Map::set_has_instance_call_handler() {
+  set_bit_field3(HasInstanceCallHandler::update(bit_field3(), true));
 }
 
 
-bool Map::is_observed() {
-  return IsObserved::decode(bit_field3());
+bool Map::has_instance_call_handler() {
+  return HasInstanceCallHandler::decode(bit_field3());
 }
 
 

src/objects.cc

@@ -5614,12 +5614,6 @@ void JSObject::SetObserved(Handle<JSObject> object) {
   if (object->map()->is_observed())
     return;
 
-  if (!object->HasExternalArrayElements()) {
-    // Go to dictionary mode, so that we don't skip map checks.
-    NormalizeElements(object);
-    ASSERT(!object->HasFastElements());
-  }
-
   LookupResult result(isolate);
   object->map()->LookupTransition(*object,
                                   isolate->heap()->observed_symbol(),
@@ -5633,7 +5627,7 @@ void JSObject::SetObserved(Handle<JSObject> object) {
     new_map = Map::CopyForObserved(handle(object->map()));
   } else {
     new_map = Map::Copy(handle(object->map()));
-    new_map->set_is_observed(true);
+    new_map->set_is_observed();
   }
   object->set_map(*new_map);
 }
@@ -6971,7 +6965,7 @@ Handle<Map> Map::CopyForObserved(Handle<Map> map) {
 
   map->set_transitions(*transitions);
 
-  new_map->set_is_observed(true);
+  new_map->set_is_observed();
 
   if (map->owns_descriptors()) {
     new_map->InitializeDescriptors(map->instance_descriptors());
@@ -11226,7 +11220,6 @@ MaybeObject* JSObject::SetFastElementsCapacityAndLength(
   Heap* heap = GetHeap();
   // We should never end in here with a pixel or external array.
   ASSERT(!HasExternalArrayElements());
-  ASSERT(!map()->is_observed());
 
   // Allocate a new fast elements backing store.
   FixedArray* new_elements;
@@ -11311,7 +11304,6 @@ MaybeObject* JSObject::SetFastDoubleElementsCapacityAndLength(
   Heap* heap = GetHeap();
   // We should never end in here with a pixel or external array.
   ASSERT(!HasExternalArrayElements());
-  ASSERT(!map()->is_observed());
 
   FixedArrayBase* elems;
   { MaybeObject* maybe_obj =
@@ -11460,10 +11452,6 @@ MaybeObject* JSArray::SetElementsLength(Object* len) {
   if (!new_length_handle->ToArrayIndex(&new_length))
     return Failure::InternalError();
 
-  // Observed arrays should always be in dictionary mode;
-  // if they were in fast mode, the below is slower than necessary
-  // as it iterates over the array backing store multiple times.
-  ASSERT(self->HasDictionaryElements());
   static const PropertyAttributes kNoAttrFilter = NONE;
   int num_elements = self->NumberOfLocalElements(kNoAttrFilter);
   if (num_elements > 0) {
@@ -11474,6 +11462,8 @@ MaybeObject* JSArray::SetElementsLength(Object* len) {
       }
     } else {
       // For sparse arrays, only iterate over existing elements.
+      // TODO(rafaelw): For fast, sparse arrays, we can avoid iterating over
+      // the to-be-removed indices twice.
       Handle<FixedArray> keys = isolate->factory()->NewFixedArray(num_elements);
       self->GetLocalElementKeys(*keys, kNoAttrFilter);
       while (num_elements-- > 0) {
@@ -12872,7 +12862,6 @@ MaybeObject* JSObject::UpdateAllocationSite(ElementsKind to_kind) {
 
 
 MaybeObject* JSObject::TransitionElementsKind(ElementsKind to_kind) {
-  ASSERT(!map()->is_observed());
   ElementsKind from_kind = map()->elements_kind();
 
   if (IsFastHoleyElementsKind(from_kind)) {

src/objects.h

@@ -5664,7 +5664,7 @@ class Map: public HeapObject {
   class FunctionWithPrototype:      public BitField<bool, 23,  1> {};
   class DictionaryMap:              public BitField<bool, 24,  1> {};
   class OwnsDescriptors:            public BitField<bool, 25,  1> {};
-  class IsObserved:                 public BitField<bool, 26,  1> {};
+  class HasInstanceCallHandler:     public BitField<bool, 26,  1> {};
   class Deprecated:                 public BitField<bool, 27,  1> {};
   class IsFrozen:                   public BitField<bool, 28,  1> {};
   class IsUnstable:                 public BitField<bool, 29,  1> {};
@@ -5727,12 +5727,12 @@ class Map: public HeapObject {
   }
 
   // Tells whether the instance has a call-as-function handler.
-  inline void set_has_instance_call_handler() {
-    set_bit_field(bit_field() | (1 << kHasInstanceCallHandler));
+  inline void set_is_observed() {
+    set_bit_field(bit_field() | (1 << kIsObserved));
   }
 
-  inline bool has_instance_call_handler() {
-    return ((1 << kHasInstanceCallHandler) & bit_field()) != 0;
+  inline bool is_observed() {
+    return ((1 << kIsObserved) & bit_field()) != 0;
   }
 
   inline void set_is_extensible(bool value);
@@ -5741,10 +5741,6 @@ class Map: public HeapObject {
   inline void set_elements_kind(ElementsKind elements_kind) {
     ASSERT(elements_kind < kElementsKindCount);
     ASSERT(kElementsKindCount <= (1 << kElementsKindBitCount));
-    ASSERT(!is_observed() ||
-           elements_kind == DICTIONARY_ELEMENTS ||
-           elements_kind == NON_STRICT_ARGUMENTS_ELEMENTS ||
-           IsExternalArrayElementsKind(elements_kind));
     set_bit_field2((bit_field2() & ~kElementsKindMask) |
         (elements_kind << kElementsKindShift));
     ASSERT(this->elements_kind() == elements_kind);
@@ -5997,8 +5993,8 @@ class Map: public HeapObject {
 
   inline bool owns_descriptors();
   inline void set_owns_descriptors(bool is_shared);
-  inline bool is_observed();
-  inline void set_is_observed(bool is_observed);
+  inline bool has_instance_call_handler();
+  inline void set_has_instance_call_handler();
   inline void freeze();
   inline bool is_frozen();
   inline void mark_unstable();
@@ -6257,7 +6253,7 @@ class Map: public HeapObject {
   static const int kHasNamedInterceptor = 3;
   static const int kHasIndexedInterceptor = 4;
   static const int kIsUndetectable = 5;
-  static const int kHasInstanceCallHandler = 6;
+  static const int kIsObserved = 6;
   static const int kIsAccessCheckNeeded = 7;
 
   // Bit positions for bit field 2

src/x64/ic-x64.cc

@@ -749,10 +749,10 @@ void KeyedStoreIC::GenerateGeneric(MacroAssembler* masm,
   __ JumpIfSmi(rdx, &slow_with_tagged_index);
   // Get the map from the receiver.
   __ movq(r9, FieldOperand(rdx, HeapObject::kMapOffset));
-  // Check that the receiver does not require access checks.  We need
-  // to do this because this generic stub does not perform map checks.
+  // Check that the receiver does not require access checks and is not observed.
+  // The generic stub does not perform map checks or handle observed objects.
   __ testb(FieldOperand(r9, Map::kBitFieldOffset),
-           Immediate(1 << Map::kIsAccessCheckNeeded));
+           Immediate(1 << Map::kIsAccessCheckNeeded | 1 << Map::kIsObserved));
   __ j(not_zero, &slow_with_tagged_index);
   // Check that the key is a smi.
   __ JumpIfNotSmi(rcx, &slow_with_tagged_index);