Fix problem with arguments object ICs not checking for dictionary mode elements.

src/x64/ic-x64.cc

 // Copyright 2011 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 1248 matching lines @@
                                                Register parameter_map,
                                                Register scratch,
                                                Label* slow_case) {
   // Element is in arguments backing store, which is referenced by the
   // second element of the parameter_map. The parameter_map register
   // must be loaded with the parameter map of the arguments object and is
   // overwritten.
   const int kBackingStoreOffset = FixedArray::kHeaderSize + kPointerSize;
   Register backing_store = parameter_map;
   __ movq(backing_store, FieldOperand(parameter_map, kBackingStoreOffset));
+  Handle<Map> fixed_array_map(masm->isolate()->heap()->fixed_array_map());
+  __ CheckMap(backing_store, fixed_array_map, slow_case, DONT_DO_SMI_CHECK);
   __ movq(scratch, FieldOperand(backing_store, FixedArray::kLengthOffset));
   __ cmpq(key, scratch);
   __ j(greater_equal, slow_case);
   __ SmiToInteger64(scratch, key);
   return FieldOperand(backing_store,
                       scratch,
                       times_pointer_size,
                       FixedArray::kHeaderSize);
 }
 
@@ skipping 485 matching lines @@
   Condition cc = *jmp_address == Assembler::kJncShortOpcode
       ? not_zero
       : zero;
   *jmp_address = static_cast<byte>(Assembler::kJccShortPrefix | cc);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64