Hydrogen object literals: always initialize in-object properties

src/hydrogen.cc

 // Copyright 2013 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/hydrogen.h"
 
 #include <sstream>
 
 #include "src/v8.h"
 
@@ skipping 9649 matching lines @@
           Add<HConstant>(initial_map));
       HValue* empty_fixed_array = Add<HConstant>(factory->empty_fixed_array());
       Add<HStoreNamedField>(receiver,
           HObjectAccess::ForMapAndOffset(initial_map,
                                          JSObject::kPropertiesOffset),
           empty_fixed_array);
       Add<HStoreNamedField>(receiver,
           HObjectAccess::ForMapAndOffset(initial_map,
                                          JSObject::kElementsOffset),
           empty_fixed_array);
-      if (initial_map->inobject_properties() != 0) {
-        HConstant* undefined = graph()->GetConstantUndefined();
-        for (int i = 0; i < initial_map->inobject_properties(); i++) {
-          int property_offset = initial_map->GetInObjectPropertyOffset(i);
-          Add<HStoreNamedField>(receiver,
-              HObjectAccess::ForMapAndOffset(initial_map, property_offset),
-              undefined);
-        }
-      }
+      BuildInitializeInobjectProperties(receiver, initial_map);
     }
 
     // Replace the constructor function with a newly allocated receiver using
     // the index of the receiver from the top of the expression stack.
     const int receiver_index = argument_count - 1;
     DCHECK(environment()->ExpressionStackAt(receiver_index) == function);
     environment()->SetExpressionStackAt(receiver_index, receiver);
 
     if (TryInlineConstruct(expr, receiver)) {
       // Inlining worked, add a dependency on the initial map to make sure that
@@ skipping 22 matching lines @@
     // argument to the construct call.
     if (TryHandleArrayCallNew(expr, function)) return;
 
     HInstruction* call =
         PreProcessCall(New<HCallNew>(function, argument_count));
     return ast_context()->ReturnInstruction(call, expr->id());
   }
 }
 
 
+void HOptimizedGraphBuilder::BuildInitializeInobjectProperties(
+    HValue* receiver, Handle<Map> initial_map) {
+  if (initial_map->inobject_properties() != 0) {
+    HConstant* undefined = graph()->GetConstantUndefined();
+    for (int i = 0; i < initial_map->inobject_properties(); i++) {
+      int property_offset = initial_map->GetInObjectPropertyOffset(i);
+      Add<HStoreNamedField>(receiver, HObjectAccess::ForMapAndOffset(
+                                          initial_map, property_offset),
+                            undefined);
+    }
+  }
+}
+
+
 HValue* HGraphBuilder::BuildAllocateEmptyArrayBuffer(HValue* byte_length) {
   HAllocate* result =
       BuildAllocate(Add<HConstant>(JSArrayBuffer::kSizeWithInternalFields),
                     HType::JSObject(), JS_ARRAY_BUFFER_TYPE, HAllocationMode());
 
   HValue* global_object = Add<HLoadNamedField>(
       context(), nullptr,
       HObjectAccess::ForContextSlot(Context::GLOBAL_OBJECT_INDEX));
   HValue* native_context = Add<HLoadNamedField>(
       global_object, nullptr, HObjectAccess::ForGlobalObjectNativeContext());
@@ skipping 1564 matching lines @@
   } else {
       return New<HThisFunction>();
   }
 }
 
 
 HInstruction* HOptimizedGraphBuilder::BuildFastLiteral(
     Handle<JSObject> boilerplate_object,
     AllocationSiteUsageContext* site_context) {
   NoObservableSideEffectsScope no_effects(this);
-  InstanceType instance_type = boilerplate_object->map()->instance_type();
+  Handle<Map> initial_map(boilerplate_object->map());
+  InstanceType instance_type = initial_map->instance_type();
   DCHECK(instance_type == JS_ARRAY_TYPE || instance_type == JS_OBJECT_TYPE);
 
   HType type = instance_type == JS_ARRAY_TYPE
       ? HType::JSArray() : HType::JSObject();
-  HValue* object_size_constant = Add<HConstant>(
-      boilerplate_object->map()->instance_size());
+  HValue* object_size_constant = Add<HConstant>(initial_map->instance_size());
 
   PretenureFlag pretenure_flag = NOT_TENURED;
   Handle<AllocationSite> current_site(*site_context->current(), isolate());
   if (FLAG_allocation_site_pretenuring) {
     pretenure_flag = current_site->GetPretenureMode();
     top_info()->dependencies()->AssumeTenuringDecision(current_site);
   }
 
   top_info()->dependencies()->AssumeTransitionStable(current_site);
 
   HInstruction* object = Add<HAllocate>(
       object_size_constant, type, pretenure_flag, instance_type, current_site);
 
   // If allocation folding reaches Page::kMaxRegularHeapObjectSize the
   // elements array may not get folded into the object. Hence, we set the
   // elements pointer to empty fixed array and let store elimination remove
   // this store in the folding case.
   HConstant* empty_fixed_array = Add<HConstant>(
       isolate()->factory()->empty_fixed_array());
   Add<HStoreNamedField>(object, HObjectAccess::ForElementsPointer(),
       empty_fixed_array);
 
   BuildEmitObjectHeader(boilerplate_object, object);
 
+  // Similarly to the elements pointer, there is no guarantee that all
+  // property allocations can get folded, so pre-initialize all in-object
+  // properties to a safe value.
+  BuildInitializeInobjectProperties(object, initial_map);
+
   Handle<FixedArrayBase> elements(boilerplate_object->elements());
   int elements_size = (elements->length() > 0 &&
       elements->map() != isolate()->heap()->fixed_cow_array_map()) ?
           elements->Size() : 0;
 
   if (pretenure_flag == TENURED &&
       elements->map() == isolate()->heap()->fixed_cow_array_map() &&
       isolate()->heap()->InNewSpace(*elements)) {
     // If we would like to pretenure a fixed cow array, we must ensure that the
     // array is already in old space, otherwise we'll create too many old-to-
@@ skipping 18 matching lines @@
                           object_elements);
   } else {
     Handle<Object> elements_field =
         Handle<Object>(boilerplate_object->elements(), isolate());
     HInstruction* object_elements_cow = Add<HConstant>(elements_field);
     Add<HStoreNamedField>(object, HObjectAccess::ForElementsPointer(),
                           object_elements_cow);
   }
 
   // Copy in-object properties.
-  if (boilerplate_object->map()->NumberOfFields() != 0 ||
-      boilerplate_object->map()->unused_property_fields() > 0) {
+  if (initial_map->NumberOfFields() != 0 ||
+      initial_map->unused_property_fields() > 0) {
     BuildEmitInObjectProperties(boilerplate_object, object, site_context,
                                 pretenure_flag);
   }
   return object;
 }
 
 
 void HOptimizedGraphBuilder::BuildEmitObjectHeader(
     Handle<JSObject> boilerplate_object,
     HInstruction* object) {
@@ skipping 1803 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8