Remove JSReceiver::GetPrototype and replace it with PrototypeIterator calls

src/builtins.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
 #include "src/bootstrapper.h"
@@ skipping 236 matching lines @@
 
 
 static bool ArrayPrototypeHasNoElements(Heap* heap,
                                         Context* native_context,
                                         JSObject* array_proto) {
   DisallowHeapAllocation no_gc;
   // This method depends on non writability of Object and Array prototype
   // fields.
   if (array_proto->elements() != heap->empty_fixed_array()) return false;
   // Object.prototype
-  Object* proto = array_proto->GetPrototype();
-  if (proto == heap->null_value()) return false;
-  array_proto = JSObject::cast(proto);
+  PrototypeIterator iter(heap->isolate(), array_proto);
+  if (iter.IsAtEnd()) {
+    return false;
+  }
+  array_proto = JSObject::cast(iter.GetCurrent());
   if (array_proto != native_context->initial_object_prototype()) return false;
   if (array_proto->elements() != heap->empty_fixed_array()) return false;
-  return array_proto->GetPrototype()->IsNull();
+  return true;

[Toon Verwaest, 2014/07/16 15:41:01]

We still need to check whether we are actually at the end after array_proto.
Otherwise you could sneak something above Object.prototype with element
accessors.

[jochen (gone - plz use gerrit), 2014/07/17 06:58:02]

that's handled by the check in line 258. The prototype iterator always goes to
the first prototype (unless you pass START_AT_RECEIVER to the ctor).

[Toon Verwaest, 2014/07/17 08:00:37]

No it's not, due to line 259. We are checking Object.prototype, and ensuring
that's the last object in the chain.

On 2014/07/17 06:58:02, jochen wrote:

 }
 
 
 // Returns empty handle if not applicable.
 MUST_USE_RESULT
 static inline MaybeHandle<FixedArrayBase> EnsureJSArrayWithWritableFastElements(
     Isolate* isolate,
     Handle<Object> receiver,
     Arguments* args,
     int first_added_arg) {
@@ skipping 52 matching lines @@
 }
 
 
 static inline bool IsJSArrayFastElementMovingAllowed(Heap* heap,
                                                      JSArray* receiver) {
   if (!FLAG_clever_optimizations) return false;
   DisallowHeapAllocation no_gc;
   Context* native_context = heap->isolate()->context()->native_context();
   JSObject* array_proto =
       JSObject::cast(native_context->array_function()->prototype());
-  return receiver->GetPrototype() == array_proto &&
+  PrototypeIterator iter(heap->isolate(), receiver);
+  return iter.GetCurrent() == array_proto &&
          ArrayPrototypeHasNoElements(heap, native_context, array_proto);
 }
 
 
 MUST_USE_RESULT static Object* CallJsBuiltin(
     Isolate* isolate,
     const char* name,
     BuiltinArguments<NO_EXTRA_ARGUMENTS> args) {
   HandleScope handleScope(isolate);
 
@@ skipping 647 matching lines @@
     if (!ArrayPrototypeHasNoElements(heap, native_context, array_proto)) {
       AllowHeapAllocation allow_allocation;
       return CallJsBuiltin(isolate, "ArrayConcatJS", args);
     }
 
     // Iterate through all the arguments performing checks
     // and calculating total length.
     bool is_holey = false;
     for (int i = 0; i < n_arguments; i++) {
       Object* arg = args[i];
-      if (!arg->IsJSArray() ||
-          !JSArray::cast(arg)->HasFastElements() ||
-          JSArray::cast(arg)->GetPrototype() != array_proto) {
+      PrototypeIterator iter(isolate, arg);
+      if (!arg->IsJSArray() || !JSArray::cast(arg)->HasFastElements() ||
+          iter.GetCurrent() != array_proto) {
         AllowHeapAllocation allow_allocation;
         return CallJsBuiltin(isolate, "ArrayConcatJS", args);
       }
       int len = Smi::cast(JSArray::cast(arg)->length())->value();
 
       // We shouldn't overflow when adding another len.
       const int kHalfOfMaxInt = 1 << (kBitsPerInt - 2);
       STATIC_ASSERT(FixedArray::kMaxLength < kHalfOfMaxInt);
       USE(kHalfOfMaxInt);
       result_len += len;
@@ skipping 697 matching lines @@
 }
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 } }  // namespace v8::internal