Don't fast RemoveArrayHoles in case of arguments arrays.

src/runtime.cc

 // Copyright 2012 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 10490 matching lines @@
   }
   return string;
 }
 
 
 // Moves all own elements of an object, that are below a limit, to positions
 // starting at zero. All undefined values are placed after non-undefined values,
 // and are followed by non-existing element. Does not change the length
 // property.
 // Returns the number of non-undefined elements collected.
+// Returns -1 if hole removal is not supported by this method.
 RUNTIME_FUNCTION(MaybeObject*, Runtime_RemoveArrayHoles) {
   HandleScope scope(isolate);
   ASSERT(args.length() == 2);
   CONVERT_ARG_HANDLE_CHECKED(JSObject, object, 0);
   CONVERT_NUMBER_CHECKED(uint32_t, limit, Uint32, args[1]);
+  if (object->HasFastArgumentsElements() ||

[Michael Starzinger, 2014/03/12 13:31:57]

nit: Instead of putting this logic here, can we move it into
JSObject::PrepareElementsForSort instead?

+      object->HasDictionaryArgumentsElements() ||

[Michael Starzinger, 2014/03/12 13:31:57]

nit: Better use object->HasNonStrictArgumentsElements() instead of asking for
"fast" and "dictionary" separately.

+      object->map()->is_observed()) {
+    return Smi::FromInt(-1);
+  }
   return *JSObject::PrepareElementsForSort(object, limit);
 }
 
 
 // Move contents of argument 0 (an array) to argument 1 (an array)
 RUNTIME_FUNCTION(MaybeObject*, Runtime_MoveArrayContents) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 2);
   CONVERT_ARG_CHECKED(JSArray, from, 0);
   CONVERT_ARG_CHECKED(JSArray, to, 1);
@@ skipping 4444 matching lines @@
     // Handle last resort GC and make sure to allow future allocations
     // to grow the heap without causing GCs (if possible).
     isolate->counters()->gc_last_resort_from_js()->Increment();
     isolate->heap()->CollectAllGarbage(Heap::kNoGCFlags,
                                        "Runtime::PerformGC");
   }
 }
 
 
 } }  // namespace v8::internal