[super ic] Fix more receiver vs lookup start object vs holder confusion

The actual fix is in LoadIC::ComputeHandler (checking
lookup_start_object == holder instead of receiver == holder) + the
LookupIterator changes for preserving lookup_start_object.

The rest is renaming / refactoring.

Bug: v8:9237, chromium:1127653
Change-Id: Ieef46fb46ababa79623951c48639429c5b552d2d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2414039
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70045}

src/ic/accessor-assembler.cc

@@ -200,7 +200,8 @@ void AccessorAssembler::HandleLoadAccessor(
   // Context is stored either in data2 or data3 field depending on whether
   // the access check is enabled for this handler or not.
   TNode<MaybeObject> maybe_context = Select<MaybeObject>(
-      IsSetWord<LoadHandler::DoAccessCheckOnReceiverBits>(handler_word),
+      IsSetWord<LoadHandler::DoAccessCheckOnLookupStartObjectBits>(
+          handler_word),
       [=] { return LoadHandlerDataField(handler, 3); },
       [=] { return LoadHandlerDataField(handler, 2); });
 
@@ -790,12 +791,14 @@ void AccessorAssembler::HandleLoadICSmiHandlerHasNamedCase(
 //    generate a code that handles Code handlers.
 //    If |on_code_handler| is not provided, then only smi sub handler are
 //    expected.
-// 3. Does access check on receiver if ICHandler::DoAccessCheckOnReceiverBits
-//    bit is set in the smi handler.
-// 4. Does dictionary lookup on receiver if ICHandler::LookupOnReceiverBits bit
-//    is set in the smi handler. If |on_found_on_receiver| is provided then
-//    it calls it to generate a code that handles the "found on receiver case"
-//    or just misses if the |on_found_on_receiver| is not provided.
+// 3. Does access check on lookup start object if
+//    ICHandler::DoAccessCheckOnLookupStartObjectBits bit is set in the smi
+//    handler.
+// 4. Does dictionary lookup on receiver if
+//    ICHandler::LookupOnLookupStartObjectBits bit is set in the smi handler. If
+//    |on_found_on_lookup_start_object| is provided then it calls it to
+//    generate a code that handles the "found on receiver case" or just misses
+//    if the |on_found_on_lookup_start_object| is not provided.
 // 5. Falls through in a case of a smi handler which is returned from this
 //    function (tagged!).
 // TODO(ishell): Remove templatezation once we move common bits from
@@ -804,8 +807,8 @@ template <typename ICHandler, typename ICParameters>
 TNode<Object> AccessorAssembler::HandleProtoHandler(
     const ICParameters* p, TNode<DataHandler> handler,
     const OnCodeHandler& on_code_handler,
-    const OnFoundOnReceiver& on_found_on_receiver, Label* miss,
-    ICMode ic_mode) {
+    const OnFoundOnLookupStartObject& on_found_on_lookup_start_object,
+    Label* miss, ICMode ic_mode) {
   //
   // Check prototype validity cell.
   //
@@ -835,21 +838,24 @@ TNode<Object> AccessorAssembler::HandleProtoHandler(
     // because in the former case the validity cell check guards modifications
     // of the global object and the latter is not applicable to the global
     // object.
-    int mask = ICHandler::LookupOnReceiverBits::kMask |
-               ICHandler::DoAccessCheckOnReceiverBits::kMask;
+    int mask = ICHandler::LookupOnLookupStartObjectBits::kMask |
+               ICHandler::DoAccessCheckOnLookupStartObjectBits::kMask;
     if (ic_mode == ICMode::kGlobalIC) {
       CSA_ASSERT(this, IsClearWord(handler_flags, mask));
     } else {
       DCHECK_EQ(ICMode::kNonGlobalIC, ic_mode);
 
-      Label done(this), if_do_access_check(this), if_lookup_on_receiver(this);
+      Label done(this), if_do_access_check(this),
+          if_lookup_on_lookup_start_object(this);
       GotoIf(IsClearWord(handler_flags, mask), &done);
       // Only one of the bits can be set at a time.
       CSA_ASSERT(this,
                  WordNotEqual(WordAnd(handler_flags, IntPtrConstant(mask)),
                               IntPtrConstant(mask)));
-      Branch(IsSetWord<LoadHandler::DoAccessCheckOnReceiverBits>(handler_flags),
-             &if_do_access_check, &if_lookup_on_receiver);
+      Branch(
+          IsSetWord<typename ICHandler::DoAccessCheckOnLookupStartObjectBits>(
+              handler_flags),
+          &if_do_access_check, &if_lookup_on_lookup_start_object);
 
       BIND(&if_do_access_check);
       {
@@ -857,29 +863,39 @@ TNode<Object> AccessorAssembler::HandleProtoHandler(
         CSA_ASSERT(this, IsWeakOrCleared(data2));
         TNode<Context> expected_native_context =
             CAST(GetHeapObjectAssumeWeak(data2, miss));
-        EmitAccessCheck(expected_native_context, p->context(), p->receiver(),
-                        &done, miss);
+        EmitAccessCheck(expected_native_context, p->context(),
+                        p->lookup_start_object(), &done, miss);
       }
 
-      // Dictionary lookup on receiver is not necessary for Load/StoreGlobalIC
-      // because prototype validity cell check already guards modifications of
-      // the global object.
-      BIND(&if_lookup_on_receiver);
+      BIND(&if_lookup_on_lookup_start_object);
       {
-        DCHECK_EQ(ICMode::kNonGlobalIC, ic_mode);
-        CSA_ASSERT(this, Word32BinaryNot(HasInstanceType(
-                             CAST(p->receiver()), JS_GLOBAL_OBJECT_TYPE)));
+        // Assert that the LookupOnLookupStartObjectBits is never set for
+        // Load/StoreSuperIC case (which is when receiver !=
+        // lookup_start_object). For the super IC case the lookup start object
+        // is guaranteed to be a prototype of a home object and thus the
+        // prototype validity cell check already guards modifications of the
+        // lookup start object.
+        CSA_ASSERT(this, TaggedEqual(p->receiver(), p->lookup_start_object()));
+
+        // Dictionary lookup on lookup start object is not necessary for
+        // Load/StoreGlobalIC (which is the only case when the
+        // lookup_start_object can be a JSGlobalObject) because prototype
+        // validity cell check already guards modifications of the global
+        // object.
+        CSA_ASSERT(this,
+                   Word32BinaryNot(HasInstanceType(
+                       CAST(p->lookup_start_object()), JS_GLOBAL_OBJECT_TYPE)));
 
         TNode<NameDictionary> properties =
-            CAST(LoadSlowProperties(CAST(p->receiver())));
+            CAST(LoadSlowProperties(CAST(p->lookup_start_object())));
         TVARIABLE(IntPtrT, var_name_index);
         Label found(this, &var_name_index);
         NameDictionaryLookup<NameDictionary>(properties, CAST(p->name()),
                                              &found, &var_name_index, &done);
         BIND(&found);
         {
-          if (on_found_on_receiver) {
-            on_found_on_receiver(properties, var_name_index.value());
+          if (on_found_on_lookup_start_object) {
+            on_found_on_lookup_start_object(properties, var_name_index.value());
           } else {
             Goto(miss);
           }
@@ -901,7 +917,7 @@ void AccessorAssembler::HandleLoadICProtoHandler(
       p, handler,
       // Code sub-handlers are not expected in LoadICs, so no |on_code_handler|.
       nullptr,
-      // on_found_on_receiver
+      // on_found_on_lookup_start_object
       [=](TNode<NameDictionary> properties, TNode<IntPtrT> name_index) {
         if (access_mode == LoadAccessMode::kHas) {
           exit_point->Return(TrueConstant());
@@ -1542,7 +1558,7 @@ void AccessorAssembler::HandleStoreICProtoHandler(
 
   TNode<Object> smi_handler = HandleProtoHandler<StoreHandler>(
       p, handler, on_code_handler,
-      // on_found_on_receiver
+      // on_found_on_lookup_start_object
       [=](TNode<NameDictionary> properties, TNode<IntPtrT> name_index) {
         TNode<Uint32T> details = LoadDetailsByKeyIndex(properties, name_index);
         // Check that the property is a writable data property (no accessor).
@@ -1618,7 +1634,8 @@ void AccessorAssembler::HandleStoreICProtoHandler(
     {
       // This is a case of "transitioning store" to a dictionary mode object
       // when the property does not exist. The "existing property" case is
-      // covered above by LookupOnReceiver bit handling of the smi handler.
+      // covered above by LookupOnLookupStartObject bit handling of the smi
+      // handler.
       Label slow(this);
       TNode<Map> receiver_map = LoadMap(CAST(p->receiver()));
       InvalidateValidityCellIfPrototype(receiver_map);
@@ -1648,7 +1665,8 @@ void AccessorAssembler::HandleStoreICProtoHandler(
       // Context is stored either in data2 or data3 field depending on whether
       // the access check is enabled for this handler or not.
       TNode<MaybeObject> maybe_context = Select<MaybeObject>(
-          IsSetWord32<LoadHandler::DoAccessCheckOnReceiverBits>(handler_word),
+          IsSetWord32<StoreHandler::DoAccessCheckOnLookupStartObjectBits>(
+              handler_word),
           [=] { return LoadHandlerDataField(handler, 3); },
           [=] { return LoadHandlerDataField(handler, 2); });
 

src/ic/accessor-assembler.h

@@ -199,6 +199,8 @@ class V8_EXPORT_PRIVATE AccessorAssembler : public CodeStubAssembler {
     TNode<TaggedIndex> slot() const { return slot_; }
     TNode<HeapObject> vector() const { return vector_; }
 
+    TNode<Object> lookup_start_object() const { return receiver(); }
+
     bool receiver_is_null() const { return !receiver_.has_value(); }
 
    private:
@@ -415,15 +417,15 @@ class V8_EXPORT_PRIVATE AccessorAssembler : public CodeStubAssembler {
   // Low-level helpers.
 
   using OnCodeHandler = std::function<void(TNode<Code> code_handler)>;
-  using OnFoundOnReceiver = std::function<void(TNode<NameDictionary> properties,
-                                               TNode<IntPtrT> name_index)>;
+  using OnFoundOnLookupStartObject = std::function<void(
+      TNode<NameDictionary> properties, TNode<IntPtrT> name_index)>;
 
   template <typename ICHandler, typename ICParameters>
   TNode<Object> HandleProtoHandler(
       const ICParameters* p, TNode<DataHandler> handler,
       const OnCodeHandler& on_code_handler,
-      const OnFoundOnReceiver& on_found_on_receiver, Label* miss,
-      ICMode ic_mode);
+      const OnFoundOnLookupStartObject& on_found_on_lookup_start_object,
+      Label* miss, ICMode ic_mode);
 
   void CheckHeapObjectTypeMatchesDescriptor(TNode<Word32T> handler_word,
                                             TNode<JSObject> holder,

src/ic/handler-configuration.cc

@@ -27,16 +27,20 @@ Handle<Smi> SetBitFieldValue(Isolate* isolate, Handle<Smi> smi_handler,
 // Load/StoreHandler to the base class.
 template <typename ICHandler, bool fill_handler = true>
 int InitPrototypeChecksImpl(Isolate* isolate, Handle<ICHandler> handler,
-                            Handle<Smi>* smi_handler, Handle<Map> receiver_map,
+                            Handle<Smi>* smi_handler,
+                            Handle<Map> lookup_start_object_map,
                             Handle<JSReceiver> holder, MaybeObjectHandle data1,
                             MaybeObjectHandle maybe_data2) {
   int data_size = 1;
   // Holder-is-receiver case itself does not add entries unless there is an
   // optional data2 value provided.
 
-  if (receiver_map->IsPrimitiveMap() ||
-      receiver_map->is_access_check_needed()) {
-    DCHECK(!receiver_map->IsJSGlobalObjectMap());
+  DCHECK_IMPLIES(lookup_start_object_map->IsJSGlobalObjectMap(),
+                 lookup_start_object_map->is_prototype_map());
+
+  if (lookup_start_object_map->IsPrimitiveMap() ||
+      lookup_start_object_map->is_access_check_needed()) {
+    DCHECK(!lookup_start_object_map->IsJSGlobalObjectMap());
     // The validity cell check for primitive and global proxy receivers does
     // not guarantee that certain native context ever had access to other
     // native context. However, a handler created for one native context could
@@ -47,17 +51,23 @@ int InitPrototypeChecksImpl(Isolate* isolate, Handle<ICHandler> handler,
       Handle<Context> native_context = isolate->native_context();
       handler->set_data2(HeapObjectReference::Weak(*native_context));
     } else {
-      // Enable access checks on receiver.
-      using Bit = typename ICHandler::DoAccessCheckOnReceiverBits;
-      *smi_handler = SetBitFieldValue<Bit>(isolate, *smi_handler, true);
+      // Enable access checks on the lookup start object.
+      *smi_handler = SetBitFieldValue<
+          typename ICHandler::DoAccessCheckOnLookupStartObjectBits>(
+          isolate, *smi_handler, true);
     }
     data_size++;
-  } else if (receiver_map->is_dictionary_map() &&
-             !receiver_map->IsJSGlobalObjectMap()) {
+  } else if (lookup_start_object_map->is_dictionary_map() &&
+             !lookup_start_object_map->is_prototype_map()) {
     if (!fill_handler) {
-      // Enable lookup on receiver.
-      using Bit = typename ICHandler::LookupOnReceiverBits;
-      *smi_handler = SetBitFieldValue<Bit>(isolate, *smi_handler, true);
+      // The lookup on lookup start object is only required for dictionary mode
+      // objects which are not prototypes. When we start lookup from a prototype
+      // object, the prototype validity cell guards modifications of the lookup
+      // start object. This includes both Load/StoreGlobalIC and
+      // Load/StoreSuperIC cases.
+      *smi_handler =
+          SetBitFieldValue<typename ICHandler::LookupOnLookupStartObjectBits>(
+              isolate, *smi_handler, true);
     }
   }
   if (fill_handler) {
@@ -80,40 +90,39 @@ int InitPrototypeChecksImpl(Isolate* isolate, Handle<ICHandler> handler,
 }
 
 // Returns 0 if the validity cell check is enough to ensure that the
-// prototype chain from |receiver_map| till |holder| did not change.
+// prototype chain from |lookup_start_object_map| till |holder| did not change.
 // If the |holder| is an empty handle then the full prototype chain is
 // checked.
 // Returns -1 if the handler has to be compiled or the number of prototype
 // checks otherwise.
 template <typename ICHandler>
 int GetHandlerDataSize(Isolate* isolate, Handle<Smi>* smi_handler,
-                       Handle<Map> receiver_map, Handle<JSReceiver> holder,
-                       MaybeObjectHandle data1,
+                       Handle<Map> lookup_start_object_map,
+                       Handle<JSReceiver> holder, MaybeObjectHandle data1,
                        MaybeObjectHandle maybe_data2 = MaybeObjectHandle()) {
   DCHECK_NOT_NULL(smi_handler);
-  return InitPrototypeChecksImpl<ICHandler, false>(isolate, Handle<ICHandler>(),
-                                                   smi_handler, receiver_map,
+  return InitPrototypeChecksImpl<ICHandler, false>(
+      isolate, Handle<ICHandler>(), smi_handler, lookup_start_object_map,
       holder, data1, maybe_data2);
 }
 
 template <typename ICHandler>
 void InitPrototypeChecks(Isolate* isolate, Handle<ICHandler> handler,
-                         Handle<Map> receiver_map, Handle<JSReceiver> holder,
-                         MaybeObjectHandle data1,
+                         Handle<Map> lookup_start_object_map,
+                         Handle<JSReceiver> holder, MaybeObjectHandle data1,
                          MaybeObjectHandle maybe_data2 = MaybeObjectHandle()) {
-  InitPrototypeChecksImpl<ICHandler, true>(
-      isolate, handler, nullptr, receiver_map, holder, data1, maybe_data2);
+  InitPrototypeChecksImpl<ICHandler, true>(isolate, handler, nullptr,
+                                           lookup_start_object_map, holder,
+                                           data1, maybe_data2);
 }
 
 }  // namespace
 
 // static
-Handle<Object> LoadHandler::LoadFromPrototype(Isolate* isolate,
-                                              Handle<Map> receiver_map,
-                                              Handle<JSReceiver> holder,
-                                              Handle<Smi> smi_handler,
-                                              MaybeObjectHandle maybe_data1,
-                                              MaybeObjectHandle maybe_data2) {
+Handle<Object> LoadHandler::LoadFromPrototype(
+    Isolate* isolate, Handle<Map> lookup_start_object_map,
+    Handle<JSReceiver> holder, Handle<Smi> smi_handler,
+    MaybeObjectHandle maybe_data1, MaybeObjectHandle maybe_data2) {
   MaybeObjectHandle data1;
   if (maybe_data1.is_null()) {
     data1 = MaybeObjectHandle::Weak(holder);
@@ -121,44 +130,48 @@ Handle<Object> LoadHandler::LoadFromPrototype(Isolate* isolate,
     data1 = maybe_data1;
   }
 
-  int data_size = GetHandlerDataSize<LoadHandler>(
-      isolate, &smi_handler, receiver_map, holder, data1, maybe_data2);
+  int data_size = GetHandlerDataSize<LoadHandler>(isolate, &smi_handler,
+                                                  lookup_start_object_map,
+                                                  holder, data1, maybe_data2);
 
-  Handle<Object> validity_cell =
-      Map::GetOrCreatePrototypeChainValidityCell(receiver_map, isolate);
+  Handle<Object> validity_cell = Map::GetOrCreatePrototypeChainValidityCell(
+      lookup_start_object_map, isolate);
 
   Handle<LoadHandler> handler = isolate->factory()->NewLoadHandler(data_size);
 
   handler->set_smi_handler(*smi_handler);
   handler->set_validity_cell(*validity_cell);
-  InitPrototypeChecks(isolate, handler, receiver_map, holder, data1,
+  InitPrototypeChecks(isolate, handler, lookup_start_object_map, holder, data1,
                       maybe_data2);
   return handler;
 }
 
 // static
 Handle<Object> LoadHandler::LoadFullChain(Isolate* isolate,
-                                          Handle<Map> receiver_map,
+                                          Handle<Map> lookup_start_object_map,
                                           const MaybeObjectHandle& holder,
                                           Handle<Smi> smi_handler) {
   Handle<JSReceiver> end;  // null handle, means full prototype chain lookup.
   MaybeObjectHandle data1 = holder;
-  int data_size = GetHandlerDataSize<LoadHandler>(isolate, &smi_handler,
-                                                  receiver_map, end, data1);
+  int data_size = GetHandlerDataSize<LoadHandler>(
+      isolate, &smi_handler, lookup_start_object_map, end, data1);
 
-  Handle<Object> validity_cell =
-      Map::GetOrCreatePrototypeChainValidityCell(receiver_map, isolate);
+  Handle<Object> validity_cell = Map::GetOrCreatePrototypeChainValidityCell(
+      lookup_start_object_map, isolate);
   if (validity_cell->IsSmi()) {
     DCHECK_EQ(1, data_size);
-    // Lookup on receiver isn't supported in case of a simple smi handler.
-    if (!LookupOnReceiverBits::decode(smi_handler->value())) return smi_handler;
+    // Lookup on lookup start object isn't supported in case of a simple smi
+    // handler.
+    if (!LookupOnLookupStartObjectBits::decode(smi_handler->value())) {
+      return smi_handler;
+    }
   }
 
   Handle<LoadHandler> handler = isolate->factory()->NewLoadHandler(data_size);
 
   handler->set_smi_handler(*smi_handler);
   handler->set_validity_cell(*validity_cell);
-  InitPrototypeChecks(isolate, handler, receiver_map, end, data1);
+  InitPrototypeChecks(isolate, handler, lookup_start_object_map, end, data1);
   return handler;
 }
 
@@ -247,7 +260,8 @@ MaybeObjectHandle StoreHandler::StoreTransition(Isolate* isolate,
     DCHECK(!transition_map->IsJSGlobalObjectMap());
     Handle<StoreHandler> handler = isolate->factory()->NewStoreHandler(0);
     // Store normal with enabled lookup on receiver.
-    int config = KindBits::encode(kNormal) | LookupOnReceiverBits::encode(true);
+    int config =
+        KindBits::encode(kNormal) | LookupOnLookupStartObjectBits::encode(true);
     handler->set_smi_handler(Smi::FromInt(config));
     handler->set_validity_cell(*validity_cell);
     return MaybeObjectHandle(handler);

src/ic/handler-configuration.h

@@ -50,15 +50,17 @@ class LoadHandler final : public DataHandler {
   };
   using KindBits = base::BitField<Kind, 0, 4>;
 
-  // Defines whether access rights check should be done on receiver object.
+  // Defines whether access rights check should be done on lookup start object.
   // Applicable to named property kinds only when loading value from prototype
-  // chain. Ignored when loading from holder.
-  using DoAccessCheckOnReceiverBits = KindBits::Next<bool, 1>;
+  // chain. Ignored when loading from lookup start object.
+  using DoAccessCheckOnLookupStartObjectBits = KindBits::Next<bool, 1>;
 
-  // Defines whether a lookup should be done on receiver object before
+  // Defines whether a lookup should be done on lookup start object before
   // proceeding to the prototype chain. Applicable to named property kinds only
-  // when loading value from prototype chain. Ignored when loading from holder.
-  using LookupOnReceiverBits = DoAccessCheckOnReceiverBits::Next<bool, 1>;
+  // when loading value from prototype chain. Ignored when loading from lookup
+  // start object.
+  using LookupOnLookupStartObjectBits =
+      DoAccessCheckOnLookupStartObjectBits::Next<bool, 1>;
 
   //
   // Encoding when KindBits contains kForConstants.
@@ -66,14 +68,14 @@ class LoadHandler final : public DataHandler {
 
   // Index of a value entry in the descriptor array.
   using DescriptorBits =
-      LookupOnReceiverBits::Next<unsigned, kDescriptorIndexBitCount>;
+      LookupOnLookupStartObjectBits::Next<unsigned, kDescriptorIndexBitCount>;
   // Make sure we don't overflow the smi.
   STATIC_ASSERT(DescriptorBits::kLastUsedBit < kSmiValueSize);
 
   //
   // Encoding when KindBits contains kField.
   //
-  using IsInobjectBits = LookupOnReceiverBits::Next<bool, 1>;
+  using IsInobjectBits = LookupOnLookupStartObjectBits::Next<bool, 1>;
   using IsDoubleBits = IsInobjectBits::Next<bool, 1>;
   // +1 here is to cover all possible JSObject header sizes.
   using FieldIndexBits =
@@ -85,7 +87,7 @@ class LoadHandler final : public DataHandler {
   //
   // Encoding when KindBits contains kElement or kIndexedString.
   //
-  using AllowOutOfBoundsBits = LookupOnReceiverBits::Next<bool, 1>;
+  using AllowOutOfBoundsBits = LookupOnLookupStartObjectBits::Next<bool, 1>;
 
   //
   // Encoding when KindBits contains kElement.
@@ -99,8 +101,9 @@ class LoadHandler final : public DataHandler {
   //
   // Encoding when KindBits contains kModuleExport.
   //
-  using ExportsIndexBits = LookupOnReceiverBits::Next<
-      unsigned, kSmiValueSize - LookupOnReceiverBits::kLastUsedBit - 1>;
+  using ExportsIndexBits = LookupOnLookupStartObjectBits::Next<
+      unsigned,
+      kSmiValueSize - LookupOnLookupStartObjectBits::kLastUsedBit - 1>;
 
   // Decodes kind from Smi-handler.
   static inline Kind GetHandlerKind(Smi smi_handler);
@@ -213,20 +216,21 @@ class StoreHandler final : public DataHandler {
 
   // Applicable to kGlobalProxy, kProxy kinds.
 
-  // Defines whether access rights check should be done on receiver object.
-  using DoAccessCheckOnReceiverBits = KindBits::Next<bool, 1>;
+  // Defines whether access rights check should be done on lookup start object.
+  using DoAccessCheckOnLookupStartObjectBits = KindBits::Next<bool, 1>;
 
-  // Defines whether a lookup should be done on receiver object before
+  // Defines whether a lookup should be done on lookup start object before
   // proceeding to the prototype chain. Applicable to named property kinds only
   // when storing through prototype chain. Ignored when storing to holder.
-  using LookupOnReceiverBits = DoAccessCheckOnReceiverBits::Next<bool, 1>;
+  using LookupOnLookupStartObjectBits =
+      DoAccessCheckOnLookupStartObjectBits::Next<bool, 1>;
 
   // Applicable to kField, kTransitionToField and kTransitionToConstant
   // kinds.
 
   // Index of a value entry in the descriptor array.
   using DescriptorBits =
-      LookupOnReceiverBits::Next<unsigned, kDescriptorIndexBitCount>;
+      LookupOnLookupStartObjectBits::Next<unsigned, kDescriptorIndexBitCount>;
 
   //
   // Encodes the bits when StoreSlow contains KeyedAccessStoreMode.

src/ic/ic-inl.h

@@ -16,11 +16,12 @@
 namespace v8 {
 namespace internal {
 
-void IC::update_receiver_map(Handle<Object> receiver) {
-  if (receiver->IsSmi()) {
-    receiver_map_ = isolate_->factory()->heap_number_map();
+void IC::update_lookup_start_object_map(Handle<Object> object) {
+  if (object->IsSmi()) {
+    lookup_start_object_map_ = isolate_->factory()->heap_number_map();
   } else {
-    receiver_map_ = handle(HeapObject::cast(*receiver).map(), isolate_);
+    lookup_start_object_map_ =
+        handle(HeapObject::cast(*object).map(), isolate_);
   }
 }
 

src/ic/ic.cc

@@ -97,7 +97,7 @@ void IC::TraceIC(const char* type, Handle<Object> name, State old_state,
                  State new_state) {
   if (V8_LIKELY(!TracingFlags::is_ic_stats_enabled())) return;
 
-  Handle<Map> map = receiver_map();  // Might be empty.
+  Handle<Map> map = lookup_start_object_map();  // Might be empty.
 
   const char* modifier = "";
   if (state() == NO_FEEDBACK) {
@@ -217,7 +217,8 @@ bool IC::ShouldRecomputeHandler(Handle<String> name) {
   // monomorphic.
   if (IsGlobalIC()) return true;
 
-  MaybeObjectHandle maybe_handler = nexus()->FindHandlerForMap(receiver_map());
+  MaybeObjectHandle maybe_handler =
+      nexus()->FindHandlerForMap(lookup_start_object_map());
 
   // The current map wasn't handled yet. There's no reason to stay monomorphic,
   // *unless* we're moving from a deprecated map to its replacement, or
@@ -225,13 +226,13 @@ bool IC::ShouldRecomputeHandler(Handle<String> name) {
   // TODO(verwaest): Check if the current map is actually what the old map
   // would transition to.
   if (maybe_handler.is_null()) {
-    if (!receiver_map()->IsJSObjectMap()) return false;
+    if (!lookup_start_object_map()->IsJSObjectMap()) return false;
     Map first_map = FirstTargetMap();
     if (first_map.is_null()) return false;
     Handle<Map> old_map(first_map, isolate());
     if (old_map->is_deprecated()) return true;
-    return IsMoreGeneralElementsKindTransition(old_map->elements_kind(),
-                                               receiver_map()->elements_kind());
+    return IsMoreGeneralElementsKindTransition(
+        old_map->elements_kind(), lookup_start_object_map()->elements_kind());
   }
 
   return true;
@@ -248,12 +249,12 @@ bool IC::RecomputeHandlerForName(Handle<Object> name) {
   return true;
 }
 
-void IC::UpdateState(Handle<Object> receiver, Handle<Object> name) {
+void IC::UpdateState(Handle<Object> lookup_start_object, Handle<Object> name) {
   if (state() == NO_FEEDBACK) return;
-  update_receiver_map(receiver);
+  update_lookup_start_object_map(lookup_start_object);
   if (!name->IsString()) return;
   if (state() != MONOMORPHIC && state() != POLYMORPHIC) return;
-  if (receiver->IsNullOrUndefined(isolate())) return;
+  if (lookup_start_object->IsNullOrUndefined(isolate())) return;
 
   // Remove the target from the code cache if it became invalid
   // because of changes in the prototype chain to avoid hitting it
@@ -399,7 +400,7 @@ MaybeHandle<Object> LoadIC::Load(Handle<Object> object, Handle<Name> name,
     if (use_ic) {
       // Ensure the IC state progresses.
       TRACE_HANDLER_STATS(isolate(), LoadIC_NonReceiver);
-      update_receiver_map(object);
+      update_lookup_start_object_map(object);
       SetCache(name, LoadHandler::LoadSlow(isolate()));
       TraceIC("LoadIC", name);
     }
@@ -421,11 +422,10 @@ MaybeHandle<Object> LoadIC::Load(Handle<Object> object, Handle<Name> name,
   if (MigrateDeprecated(isolate(), object)) use_ic = false;
 
   JSObject::MakePrototypesFast(object, kStartAtReceiver, isolate());
-  update_receiver_map(object);
+  update_lookup_start_object_map(object);
 
   LookupIterator::Key key(isolate(), name);
-  LookupIterator it =
-      LookupIterator::LookupWithReceiver(isolate(), receiver, key, object);
+  LookupIterator it = LookupIterator(isolate(), receiver, key, object);
 
   // Named lookup in the object.
   LookupForRead(&it, IsAnyHas());
@@ -570,7 +570,7 @@ bool IC::UpdatePolymorphicIC(Handle<Name> name,
   if (is_keyed() && state() != RECOMPUTE_HANDLER) {
     if (nexus()->GetName() != *name) return false;
   }
-  Handle<Map> map = receiver_map();
+  Handle<Map> map = lookup_start_object_map();
 
   std::vector<MapAndHandler> maps_and_handlers;
   maps_and_handlers.reserve(FLAG_max_valid_polymorphic_map_count);
@@ -642,7 +642,7 @@ bool IC::UpdatePolymorphicIC(Handle<Name> name,
 
   number_of_valid_maps++;
   if (number_of_valid_maps == 1) {
-    ConfigureVectorState(name, receiver_map(), handler);
+    ConfigureVectorState(name, lookup_start_object_map(), handler);
   } else {
     if (is_keyed() && nexus()->GetName() != *name) return false;
     if (handler_to_overwrite >= 0) {
@@ -664,7 +664,7 @@ bool IC::UpdatePolymorphicIC(Handle<Name> name,
 void IC::UpdateMonomorphicIC(const MaybeObjectHandle& handler,
                              Handle<Name> name) {
   DCHECK(IsHandler(*handler));
-  ConfigureVectorState(name, receiver_map(), handler);
+  ConfigureVectorState(name, lookup_start_object_map(), handler);
 }
 
 void IC::CopyICToMegamorphicCache(Handle<Name> name) {
@@ -721,7 +721,7 @@ void IC::SetCache(Handle<Name> name, const MaybeObjectHandle& handler) {
       ConfigureVectorState(MEGAMORPHIC, name);
       V8_FALLTHROUGH;
     case MEGAMORPHIC:
-      UpdateMegamorphicCache(receiver_map(), name, handler);
+      UpdateMegamorphicCache(lookup_start_object_map(), name, handler);
       // Indicate that we've handled this case.
       vector_set_ = true;
       break;
@@ -738,7 +738,7 @@ void LoadIC::UpdateCaches(LookupIterator* lookup) {
     TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNonexistentDH);
     Handle<Smi> smi_handler = LoadHandler::LoadNonExistent(isolate());
     code = LoadHandler::LoadFullChain(
-        isolate(), receiver_map(),
+        isolate(), lookup_start_object_map(),
         MaybeObjectHandle(isolate()->factory()->null_value()), smi_handler);
   } else if (IsLoadGlobalIC() && lookup->state() == LookupIterator::JSPROXY) {
     // If there is proxy just install the slow stub since we need to call the
@@ -746,8 +746,8 @@ void LoadIC::UpdateCaches(LookupIterator* lookup) {
     // handle this case.
     Handle<Smi> slow_handler = LoadHandler::LoadSlow(isolate());
     Handle<JSProxy> holder = lookup->GetHolder<JSProxy>();
-    code = LoadHandler::LoadFromPrototype(isolate(), receiver_map(), holder,
-                                          slow_handler);
+    code = LoadHandler::LoadFromPrototype(isolate(), lookup_start_object_map(),
+                                          holder, slow_handler);
   } else {
     if (IsLoadGlobalIC()) {
       if (lookup->TryLookupCachedProperty()) {
@@ -816,12 +816,13 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
     }
   }
 
-  Handle<Map> map = receiver_map();
+  Handle<Map> map = lookup_start_object_map();
   Handle<JSObject> holder;
-  bool receiver_is_holder;
+  bool holder_is_lookup_start_object;
   if (lookup->state() != LookupIterator::JSPROXY) {
     holder = lookup->GetHolder<JSObject>();
-    receiver_is_holder = receiver.is_identical_to(holder);
+    holder_is_lookup_start_object =
+        lookup->lookup_start_object().is_identical_to(holder);
   }
 
   switch (lookup->state()) {
@@ -830,7 +831,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
 
       if (holder->GetNamedInterceptor().non_masking()) {
         MaybeObjectHandle holder_ref(isolate()->factory()->null_value());
-        if (!receiver_is_holder || IsLoadGlobalIC()) {
+        if (!holder_is_lookup_start_object || IsLoadGlobalIC()) {
           holder_ref = MaybeObjectHandle::Weak(holder);
         }
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNonMaskingInterceptorDH);
@@ -838,7 +839,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
                                           smi_handler);
       }
 
-      if (receiver_is_holder) {
+      if (holder_is_lookup_start_object) {
         DCHECK(map->has_named_interceptor());
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadInterceptorDH);
         return smi_handler;
@@ -852,7 +853,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
     case LookupIterator::ACCESSOR: {
       // Use simple field loads for some well-known callback properties.
       // The method will only return true for absolute truths based on the
-      // receiver maps.
+      // lookup start object maps.
       FieldIndex index;
       if (Accessors::IsJSObjectFieldAccessor(isolate(), map, lookup->name(),
                                              &index)) {
@@ -926,7 +927,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
               LoadHandler::LoadAccessor(isolate(), lookup->GetAccessorIndex());
 
           TRACE_HANDLER_STATS(isolate(), LoadIC_LoadAccessorDH);
-          if (receiver_is_holder) return smi_handler;
+          if (holder_is_lookup_start_object) return smi_handler;
           TRACE_HANDLER_STATS(isolate(), LoadIC_LoadAccessorFromPrototypeDH);
         } else if (holder->IsJSGlobalObject()) {
           TRACE_HANDLER_STATS(isolate(), LoadIC_LoadGlobalFromPrototypeDH);
@@ -938,7 +939,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
           smi_handler = LoadHandler::LoadNormal(isolate());
 
           TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNormalDH);
-          if (receiver_is_holder) return smi_handler;
+          if (holder_is_lookup_start_object) return smi_handler;
           TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNormalFromPrototypeDH);
         }
 
@@ -959,7 +960,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
       Handle<Smi> smi_handler = LoadHandler::LoadNativeDataProperty(
           isolate(), lookup->GetAccessorIndex());
       TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNativeDataPropertyDH);
-      if (receiver_is_holder) return smi_handler;
+      if (holder_is_lookup_start_object) return smi_handler;
       TRACE_HANDLER_STATS(isolate(),
                           LoadIC_LoadNativeDataPropertyFromPrototypeDH);
       return LoadHandler::LoadFromPrototype(isolate(), map, holder,
@@ -982,7 +983,7 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
 
         smi_handler = LoadHandler::LoadNormal(isolate());
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNormalDH);
-        if (receiver_is_holder) return smi_handler;
+        if (holder_is_lookup_start_object) return smi_handler;
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadNormalFromPrototypeDH);
       } else if (lookup->IsElement(*holder)) {
         TRACE_HANDLER_STATS(isolate(), LoadIC_SlowStub);
@@ -993,11 +994,11 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
         smi_handler =
             LoadHandler::LoadField(isolate(), field, map->elements_kind());
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadFieldDH);
-        if (receiver_is_holder) return smi_handler;
+        if (holder_is_lookup_start_object) return smi_handler;
         TRACE_HANDLER_STATS(isolate(), LoadIC_LoadFieldFromPrototypeDH);
       }
       if (lookup->constness() == PropertyConstness::kConst &&
-          !receiver_is_holder) {
+          !holder_is_lookup_start_object) {
         DCHECK(!lookup->is_dictionary_holder());
 
         Handle<Object> value = lookup->GetDataValue();
@@ -1032,9 +1033,10 @@ Handle<Object> LoadIC::ComputeHandler(LookupIterator* lookup) {
       return LoadHandler::LoadNonExistent(isolate());
     case LookupIterator::JSPROXY: {
       Handle<JSProxy> holder_proxy = lookup->GetHolder<JSProxy>();
-      bool receiver_is_holder_proxy = receiver.is_identical_to(holder_proxy);
+      bool holder_proxy_is_lookup_start_object =
+          lookup->lookup_start_object().is_identical_to(holder_proxy);
       Handle<Smi> smi_handler = LoadHandler::LoadProxy(isolate());
-      if (receiver_is_holder_proxy) {
+      if (holder_proxy_is_lookup_start_object) {
         return smi_handler;
       }
       return LoadHandler::LoadFromPrototype(isolate(), map, holder_proxy,
@@ -1442,7 +1444,7 @@ bool StoreIC::LookupForWrite(LookupIterator* it, Handle<Object> value,
             it->PrepareForDataProperty(value);
             // The previous receiver map might just have been deprecated,
             // so reload it.
-            update_receiver_map(receiver);
+            update_lookup_start_object_map(receiver);
             return true;
           }
 
@@ -1565,7 +1567,7 @@ MaybeHandle<Object> StoreIC::Store(Handle<Object> object, Handle<Name> name,
     if (use_ic) {
       // Ensure the IC state progresses.
       TRACE_HANDLER_STATS(isolate(), StoreIC_NonReceiver);
-      update_receiver_map(object);
+      update_lookup_start_object_map(object);
       SetCache(name, StoreHandler::StoreSlow(isolate()));
       TraceIC("StoreIC", name);
     }
@@ -1635,7 +1637,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
       if (store_target->IsJSGlobalObject()) {
         TRACE_HANDLER_STATS(isolate(), StoreIC_StoreGlobalTransitionDH);
 
-        if (receiver_map()->IsJSGlobalObject()) {
+        if (lookup_start_object_map()->IsJSGlobalObject()) {
           DCHECK(IsStoreGlobalIC());
 #ifdef DEBUG
           Handle<JSObject> holder = lookup->GetHolder<JSObject>();
@@ -1647,13 +1649,13 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
 
         Handle<Smi> smi_handler = StoreHandler::StoreGlobalProxy(isolate());
         Handle<Object> handler = StoreHandler::StoreThroughPrototype(
-            isolate(), receiver_map(), store_target, smi_handler,
+            isolate(), lookup_start_object_map(), store_target, smi_handler,
             MaybeObjectHandle::Weak(lookup->transition_cell()));
         return MaybeObjectHandle(handler);
       }
       // Dictionary-to-fast transitions are not expected and not supported.
       DCHECK_IMPLIES(!lookup->transition_map()->is_dictionary_map(),
-                     !receiver_map()->is_dictionary_map());
+                     !lookup_start_object_map()->is_dictionary_map());
 
       DCHECK(lookup->IsCacheableTransition());
 
@@ -1680,7 +1682,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
       DCHECK(!info.getter().IsUndefined(isolate()) ||
              !info.query().IsUndefined(isolate()));
       Handle<Object> handler = StoreHandler::StoreThroughPrototype(
-          isolate(), receiver_map(), holder,
+          isolate(), lookup_start_object_map(), holder,
           StoreHandler::StoreSlow(isolate()));
       return MaybeObjectHandle(handler);
     }
@@ -1712,7 +1714,8 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
           TRACE_HANDLER_STATS(isolate(), StoreIC_SlowStub);
           return MaybeObjectHandle(StoreHandler::StoreSlow(isolate()));
         }
-        if (!AccessorInfo::IsCompatibleReceiverMap(info, receiver_map())) {
+        if (!AccessorInfo::IsCompatibleReceiverMap(info,
+                                                   lookup_start_object_map())) {
           set_slow_stub_reason("incompatible receiver type");
           TRACE_HANDLER_STATS(isolate(), StoreIC_SlowStub);
           return MaybeObjectHandle(StoreHandler::StoreSlow(isolate()));
@@ -1727,7 +1730,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
         TRACE_HANDLER_STATS(isolate(),
                             StoreIC_StoreNativeDataPropertyOnPrototypeDH);
         return MaybeObjectHandle(StoreHandler::StoreThroughPrototype(
-            isolate(), receiver_map(), holder, smi_handler));
+            isolate(), lookup_start_object_map(), holder, smi_handler));
 
       } else if (accessors->IsAccessorPair()) {
         Handle<Object> setter(Handle<AccessorPair>::cast(accessors)->setter(),
@@ -1751,8 +1754,8 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
         if (call_optimization.is_simple_api_call()) {
           if (call_optimization.IsCompatibleReceiver(receiver, holder)) {
             CallOptimization::HolderLookup holder_lookup;
-            call_optimization.LookupHolderOfExpectedType(receiver_map(),
-                                                         &holder_lookup);
+            call_optimization.LookupHolderOfExpectedType(
+                lookup_start_object_map(), &holder_lookup);
 
             Handle<Smi> smi_handler = StoreHandler::StoreApiSetter(
                 isolate(),
@@ -1762,7 +1765,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
                 call_optimization.GetAccessorContext(holder->map()), isolate());
             TRACE_HANDLER_STATS(isolate(), StoreIC_StoreApiSetterOnPrototypeDH);
             return MaybeObjectHandle(StoreHandler::StoreThroughPrototype(
-                isolate(), receiver_map(), holder, smi_handler,
+                isolate(), lookup_start_object_map(), holder, smi_handler,
                 MaybeObjectHandle::Weak(call_optimization.api_call_info()),
                 MaybeObjectHandle::Weak(context)));
           }
@@ -1785,7 +1788,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
         TRACE_HANDLER_STATS(isolate(), StoreIC_StoreAccessorOnPrototypeDH);
 
         return MaybeObjectHandle(StoreHandler::StoreThroughPrototype(
-            isolate(), receiver_map(), holder, smi_handler));
+            isolate(), lookup_start_object_map(), holder, smi_handler));
       }
       TRACE_HANDLER_STATS(isolate(), StoreIC_SlowStub);
       return MaybeObjectHandle(StoreHandler::StoreSlow(isolate()));
@@ -1844,7 +1847,7 @@ MaybeObjectHandle StoreIC::ComputeHandler(LookupIterator* lookup) {
           Handle<JSReceiver>::cast(lookup->GetReceiver());
       Handle<JSProxy> holder = lookup->GetHolder<JSProxy>();
       return MaybeObjectHandle(StoreHandler::StoreProxy(
-          isolate(), receiver_map(), holder, receiver));
+          isolate(), lookup_start_object_map(), holder, receiver));
     }
 
     case LookupIterator::INTEGER_INDEXED_EXOTIC:

src/ic/ic.h

@@ -37,8 +37,9 @@ class IC {
 
   State state() const { return state_; }
 
-  // Compute the current IC state based on the target stub, receiver and name.
-  void UpdateState(Handle<Object> receiver, Handle<Object> name);
+  // Compute the current IC state based on the target stub, lookup_start_object
+  // and name.
+  void UpdateState(Handle<Object> lookup_start_object, Handle<Object> name);
 
   bool RecomputeHandlerForName(Handle<Object> name);
   void MarkRecomputeHandler(Handle<Object> name) {
@@ -121,8 +122,8 @@ class IC {
   }
   bool ShouldRecomputeHandler(Handle<String> name);
 
-  Handle<Map> receiver_map() { return receiver_map_; }
-  inline void update_receiver_map(Handle<Object> receiver);
+  Handle<Map> lookup_start_object_map() { return lookup_start_object_map_; }
+  inline void update_lookup_start_object_map(Handle<Object> object);
 
   void TargetMaps(MapHandles* list) {
     FindTargetMaps();
@@ -152,7 +153,7 @@ class IC {
   State old_state_;  // For saving if we marked as prototype failure.
   State state_;
   FeedbackSlotKind kind_;
-  Handle<Map> receiver_map_;
+  Handle<Map> lookup_start_object_map_;
 
   MapHandles target_maps_;
   bool target_maps_set_;

src/objects/lookup-inl.h

@@ -20,67 +20,60 @@ namespace internal {
 
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
                                Handle<Name> name, Configuration configuration)
-    : LookupIterator(isolate, receiver, name, kInvalidIndex,
-                     GetRoot(isolate, receiver, kInvalidIndex), configuration) {
-}
+    : LookupIterator(isolate, receiver, name, kInvalidIndex, receiver,
+                     configuration) {}
 
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
-                               Handle<Name> name, Handle<JSReceiver> holder,
+                               Handle<Name> name,
+                               Handle<Object> lookup_start_object,
                                Configuration configuration)
-    : LookupIterator(isolate, receiver, name, kInvalidIndex, holder,
-                     configuration) {}
+    : LookupIterator(isolate, receiver, name, kInvalidIndex,
+                     lookup_start_object, configuration) {}
 
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
                                size_t index, Configuration configuration)
-    : LookupIterator(isolate, receiver, Handle<Name>(), index,
-                     GetRoot(isolate, receiver, index), configuration) {
+    : LookupIterator(isolate, receiver, Handle<Name>(), index, receiver,
+                     configuration) {
   DCHECK_NE(index, kInvalidIndex);
 }
 
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
-                               size_t index, Handle<JSReceiver> holder,
+                               size_t index, Handle<Object> lookup_start_object,
                                Configuration configuration)
-    : LookupIterator(isolate, receiver, Handle<Name>(), index, holder,
-                     configuration) {
+    : LookupIterator(isolate, receiver, Handle<Name>(), index,
+                     lookup_start_object, configuration) {
   DCHECK_NE(index, kInvalidIndex);
 }
 
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
                                const Key& key, Configuration configuration)
-    : LookupIterator(isolate, receiver, key.name(), key.index(),
-                     GetRoot(isolate, receiver, key.index()), configuration) {}
-
-LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
-                               const Key& key, Handle<JSReceiver> holder,
-                               Configuration configuration)
-    : LookupIterator(isolate, receiver, key.name(), key.index(), holder,
+    : LookupIterator(isolate, receiver, key.name(), key.index(), receiver,
                      configuration) {}
 
-LookupIterator LookupIterator::LookupWithReceiver(Isolate* isolate,
-                                                  Handle<Object> receiver,
+LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
                                const Key& key,
-                                                  Handle<Object> holder,
-                                                  Configuration configuration) {
-  return LookupIterator(isolate, receiver, key,
-                        GetRoot(isolate, holder, key.index()), configuration);
-}
+                               Handle<Object> lookup_start_object,
+                               Configuration configuration)
+    : LookupIterator(isolate, receiver, key.name(), key.index(),
+                     lookup_start_object, configuration) {}
 
 // This private constructor is the central bottleneck that all the other
 // constructors use.
 LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
                                Handle<Name> name, size_t index,
-                               Handle<JSReceiver> holder,
+                               Handle<Object> lookup_start_object,
                                Configuration configuration)
     : configuration_(ComputeConfiguration(isolate, configuration, name)),
       isolate_(isolate),
       name_(name),
       receiver_(receiver),
-      initial_holder_(holder),
+      lookup_start_object_(lookup_start_object),
       index_(index) {
   if (IsElement()) {
     // If we're not looking at a TypedArray, we will need the key represented
     // as an internalized string.
-    if (index_ > JSArray::kMaxArrayIndex && !holder->IsJSTypedArray()) {
+    if (index_ > JSArray::kMaxArrayIndex &&
+        !lookup_start_object->IsJSTypedArray()) {
       if (name_.is_null()) {
         name_ = isolate->factory()->SizeToString(index_);
       }
@@ -94,10 +87,10 @@ LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
     name_ = isolate->factory()->InternalizeName(name_);
 #ifdef DEBUG
     // Assert that the name is not an index.
-    // If we're not looking at the prototype chain and the initial holder is
-    // not a typed array, then this means "array index", otherwise we need to
+    // If we're not looking at the prototype chain and the lookup start object
+    // is not a typed array, then this means "array index", otherwise we need to
     // ensure the full generality so that typed arrays are handled correctly.
-    if (!check_prototype_chain() && !holder->IsJSTypedArray()) {
+    if (!check_prototype_chain() && !lookup_start_object->IsJSTypedArray()) {
       uint32_t index;
       DCHECK(!name_->AsArrayIndex(&index));
     } else {
@@ -251,12 +244,12 @@ LookupIterator::Configuration LookupIterator::ComputeConfiguration(
 
 // static
 Handle<JSReceiver> LookupIterator::GetRoot(Isolate* isolate,
-                                           Handle<Object> receiver,
+                                           Handle<Object> lookup_start_object,
                                            size_t index) {
-  if (receiver->IsJSReceiver(isolate)) {
-    return Handle<JSReceiver>::cast(receiver);
+  if (lookup_start_object->IsJSReceiver(isolate)) {
+    return Handle<JSReceiver>::cast(lookup_start_object);
   }
-  return GetRootForNonJSReceiver(isolate, receiver, index);
+  return GetRootForNonJSReceiver(isolate, lookup_start_object, index);
 }
 
 template <class T>

src/objects/lookup.cc

@@ -49,18 +49,21 @@ LookupIterator::LookupIterator(Isolate* isolate, Handle<Object> receiver,
       name_(name),
       transition_(transition_map),
       receiver_(receiver),
-      initial_holder_(GetRoot(isolate, receiver)),
+      lookup_start_object_(receiver),
       index_(kInvalidIndex) {
-  holder_ = initial_holder_;
+  holder_ = GetRoot(isolate, lookup_start_object_);
 }
 
 template <bool is_element>
 void LookupIterator::Start() {
+  // GetRoot might allocate if lookup_start_object_ is a string.
+  holder_ = GetRoot(isolate_, lookup_start_object_, index_);
+
+  {
     DisallowHeapAllocation no_gc;
 
     has_property_ = false;
     state_ = NOT_FOUND;
-  holder_ = initial_holder_;
 
     JSReceiver holder = *holder_;
     Map map = holder.map(isolate_);
@@ -69,6 +72,7 @@ void LookupIterator::Start() {
     if (IsFound()) return;
 
     NextInternal<is_element>(map, holder);
+  }
 }
 
 template void LookupIterator::Start<true>();
@@ -127,22 +131,25 @@ template void LookupIterator::RestartInternal<false>(InterceptorState);
 
 // static
 Handle<JSReceiver> LookupIterator::GetRootForNonJSReceiver(
-    Isolate* isolate, Handle<Object> receiver, size_t index) {
+    Isolate* isolate, Handle<Object> lookup_start_object, size_t index) {
   // Strings are the only objects with properties (only elements) directly on
   // the wrapper. Hence we can skip generating the wrapper for all other cases.
-  if (receiver->IsString(isolate) &&
-      index < static_cast<size_t>(String::cast(*receiver).length())) {
+  if (lookup_start_object->IsString(isolate) &&
+      index <
+          static_cast<size_t>(String::cast(*lookup_start_object).length())) {
     // TODO(verwaest): Speed this up. Perhaps use a cached wrapper on the native
     // context, ensuring that we don't leak it into JS?
     Handle<JSFunction> constructor = isolate->string_function();
     Handle<JSObject> result = isolate->factory()->NewJSObject(constructor);
-    Handle<JSPrimitiveWrapper>::cast(result)->set_value(*receiver);
+    Handle<JSPrimitiveWrapper>::cast(result)->set_value(*lookup_start_object);
     return result;
   }
   Handle<HeapObject> root(
-      receiver->GetPrototypeChainRootMap(isolate).prototype(isolate), isolate);
+      lookup_start_object->GetPrototypeChainRootMap(isolate).prototype(isolate),
+      isolate);
   if (root->IsNull(isolate)) {
-    isolate->PushStackTraceAndDie(reinterpret_cast<void*>(receiver->ptr()));
+    isolate->PushStackTraceAndDie(
+        reinterpret_cast<void*>(lookup_start_object->ptr()));
   }
   return Handle<JSReceiver>::cast(root);
 }

src/objects/lookup.h

@@ -70,27 +70,21 @@ class V8_EXPORT_PRIVATE LookupIterator final {
                         Handle<Name> name,
                         Configuration configuration = DEFAULT);
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver,
-                        Handle<Name> name, Handle<JSReceiver> holder,
+                        Handle<Name> name, Handle<Object> lookup_start_object,
                         Configuration configuration = DEFAULT);
 
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver, size_t index,
                         Configuration configuration = DEFAULT);
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver, size_t index,
-                        Handle<JSReceiver> holder,
+                        Handle<Object> lookup_start_object,
                         Configuration configuration = DEFAULT);
 
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver,
                         const Key& key, Configuration configuration = DEFAULT);
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver,
-                        const Key& key, Handle<JSReceiver> holder,
+                        const Key& key, Handle<Object> lookup_start_object,
                         Configuration configuration = DEFAULT);
 
-  // Usable for cases where "holder" is not necessarily a JSReceiver (a separate
-  // overloaded constructor is not possible).
-  static inline LookupIterator LookupWithReceiver(
-      Isolate* isolate, Handle<Object> receiver, const Key& key,
-      Handle<Object> holder, Configuration configuration = DEFAULT);
-
   void Restart() {
     InterceptorState state = InterceptorState::kUninitialized;
     IsElement() ? RestartInternal<true>(state) : RestartInternal<false>(state);
@@ -134,6 +128,8 @@ class V8_EXPORT_PRIVATE LookupIterator final {
   template <class T>
   inline Handle<T> GetHolder() const;
 
+  Handle<Object> lookup_start_object() const { return lookup_start_object_; }
+
   bool HolderIsReceiver() const;
   bool HolderIsReceiverOrHiddenPrototype() const;
 
@@ -202,7 +198,8 @@ class V8_EXPORT_PRIVATE LookupIterator final {
 
   inline LookupIterator(Isolate* isolate, Handle<Object> receiver,
                         Handle<Name> name, size_t index,
-                        Handle<JSReceiver> holder, Configuration configuration);
+                        Handle<Object> lookup_start_object,
+                        Configuration configuration);
 
   // For |ForTransitionHandler|.
   LookupIterator(Isolate* isolate, Handle<Object> receiver, Handle<Name> name,
@@ -267,9 +264,10 @@ class V8_EXPORT_PRIVATE LookupIterator final {
                                                    Handle<Name> name);
 
   static Handle<JSReceiver> GetRootForNonJSReceiver(
-      Isolate* isolate, Handle<Object> receiver, size_t index = kInvalidIndex);
+      Isolate* isolate, Handle<Object> lookup_start_object,
+      size_t index = kInvalidIndex);
   static inline Handle<JSReceiver> GetRoot(Isolate* isolate,
-                                           Handle<Object> receiver,
+                                           Handle<Object> lookup_start_object,
                                            size_t index = kInvalidIndex);
 
   State NotFound(JSReceiver const holder) const;
@@ -286,7 +284,7 @@ class V8_EXPORT_PRIVATE LookupIterator final {
   Handle<Object> transition_;
   const Handle<Object> receiver_;
   Handle<JSReceiver> holder_;
-  const Handle<JSReceiver> initial_holder_;
+  const Handle<Object> lookup_start_object_;
   const size_t index_;
   InternalIndex number_ = InternalIndex::NotFound();
 };

src/runtime/runtime-object.cc

@@ -39,8 +39,7 @@ MaybeHandle<Object> Runtime::GetObjectProperty(Isolate* isolate,
   bool success = false;
   LookupIterator::Key lookup_key(isolate, key, &success);
   if (!success) return MaybeHandle<Object>();
-  LookupIterator it =
-      LookupIterator::LookupWithReceiver(isolate, receiver, lookup_key, holder);
+  LookupIterator it = LookupIterator(isolate, receiver, lookup_key, holder);
 
   MaybeHandle<Object> result = Object::GetProperty(&it);
   if (is_found) *is_found = it.IsFound();

test/mjsunit/es6/super-ic.js

@@ -4,6 +4,12 @@
 
 // Flags: --allow-natives-syntax --super-ic
 
+function forceDictionaryMode(obj) {
+  for (let i = 0; i < 2000; ++i) {
+    obj["prop" + i] = "prop_value";
+  }
+}
+
 (function TestHomeObjectPrototypeNull() {
   class A {}
 
@@ -303,10 +309,7 @@
 
   // Create a "home object proto" object which is a bound function.
   let home_object_proto = (function() {}).bind({});
-  // Force home_object_proto to dictionary mode.
-  for (let i = 0; i < 2000; ++i) {
-    home_object_proto["prop" + i] = "prop_value";
-  }
+  forceDictionaryMode(home_object_proto);
   B.prototype.__proto__ = home_object_proto;
 
   assertEquals(0, home_object_proto.length);
@@ -342,3 +345,98 @@
   assertEquals(A.prototype.foo, (new B).m());
   assertEquals(A.prototype.foo, (new B).n()());
 })();
+
+// Regression test for a receiver vs lookup start object confusion.
+(function TestProxyAsLookupStartObject1() {
+  class A {}
+  class B extends A {
+    bar() {
+      return super.foo;
+    }
+  }
+
+  const o = new B();
+  B.prototype.__proto__ = new Proxy({}, {});
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(undefined, o.bar());
+  }
+})();
+
+(function TestProxyAsLookupStartObject2() {
+  class A {}
+  class B extends A {
+    bar() {
+      return super.foo;
+    }
+  }
+
+  const o = new B();
+  forceDictionaryMode(o);
+  o.foo = "wrong value";
+  B.prototype.__proto__ = new Proxy({}, {});
+
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(undefined, o.bar());
+  }
+})();
+
+(function TestProxyAsLookupStartObject3() {
+  class A {}
+  class B extends A {
+    bar() {
+      return super.foo;
+    }
+  }
+
+  const o = new B();
+  B.prototype.__proto__ = new Proxy({}, {});
+  B.prototype.__proto__.foo = "correct value";
+
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(B.prototype.__proto__.foo, o.bar());
+  }
+})();
+
+(function TestDictionaryModeHomeObjectProto1() {
+  class A {}
+  forceDictionaryMode(A.prototype);
+  A.prototype.foo = "correct value";
+  class B extends A {
+    bar() {
+      return super.foo;
+    }
+  }
+  const o = new B();
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(A.prototype.foo, o.bar());
+  }
+})();
+
+(function TestDictionaryModeHomeObjectProto2() {
+  class A {}
+  A.prototype.foo = "correct value";
+  class B extends A {};
+  forceDictionaryMode(B.prototype);
+  class C extends B {
+    bar() {
+      return super.foo;
+    }
+  }
+  const o = new C();
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(A.prototype.foo, o.bar());
+  }
+})();
+
+(function TestHomeObjectProtoIsGlobalThis() {
+  class A {};
+  class B extends A {
+    bar() { return super.foo; }
+  }
+  B.prototype.__proto__ = globalThis;
+
+  const o = new B();
+  for (let i = 0; i < 1000; ++i) {
+    assertEquals(undefined, o.bar());
+  }
+})();