Elements field of newly allocated JSArray could be left uninitialized in some cases (fast literal c…

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 9888 matching lines @@
 
   Handle<FixedArrayBase> elements(boilerplate_object->elements());
   int elements_size = (elements->length() > 0 &&
       elements->map() != isolate()->heap()->fixed_cow_array_map()) ?
           elements->Size() : 0;
 
   HInstruction* object_elements = NULL;
   if (elements_size > 0) {
     HValue* object_elements_size = Add<HConstant>(elements_size);
     if (boilerplate_object->HasFastDoubleElements()) {
+      // Allocation folding will not be able to fold |object| and
+      // |object_elements| together in some cases, so initialize
+      // elements with the undefined to make GC happy.
+      HConstant* empty_fixed_array = Add<HConstant>(
+          isolate()->factory()->empty_fixed_array());
+      Add<HStoreNamedField>(object, HObjectAccess::ForElementsPointer(),
+                            empty_fixed_array, INITIALIZING_STORE);
       object_elements = Add<HAllocate>(object_elements_size, HType::JSObject(),
           pretenure_flag, FIXED_DOUBLE_ARRAY_TYPE, site_context->current());
     } else {
       object_elements = Add<HAllocate>(object_elements_size, HType::JSObject(),
           pretenure_flag, FIXED_ARRAY_TYPE, site_context->current());
     }
   }
   BuildInitElementsInObjectHeader(boilerplate_object, object, object_elements);
 
   // Copy object elements if non-COW.
@@ skipping 1446 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal