The check for internalized strings relied on the fact that we had less

src/ia32/macro-assembler-ia32.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 2789 matching lines @@
   // Interleave bits from both instance types and compare them in one check.
   ASSERT_EQ(0, kFlatAsciiStringMask & (kFlatAsciiStringMask << 3));
   and_(scratch1, kFlatAsciiStringMask);
   and_(scratch2, kFlatAsciiStringMask);
   lea(scratch1, Operand(scratch1, scratch2, times_8, 0));
   cmp(scratch1, kFlatAsciiStringTag | (kFlatAsciiStringTag << 3));
   j(not_equal, failure);
 }
 
 
+void MacroAssembler::JumpIfNotUniqueName(Operand operand,
+                                         Label* not_unique_name,
+                                         Label::Distance distance) {
+  STATIC_ASSERT(((SYMBOL_TYPE - 1) & kIsInternalizedMask) == kInternalizedTag);
+  cmp(operand, Immediate(kInternalizedTag));
+  j(less, not_unique_name, distance);
+  cmp(operand, Immediate(SYMBOL_TYPE));
+  j(greater, not_unique_name, distance);
+}
+
+
 void MacroAssembler::PrepareCallCFunction(int num_arguments, Register scratch) {
   int frame_alignment = OS::ActivationFrameAlignment();
   if (frame_alignment != 0) {
     // Make stack end at alignment and make room for num_arguments words
     // and the original value of esp.
     mov(scratch, esp);
     sub(esp, Immediate((num_arguments + 1) * kPointerSize));
     ASSERT(IsPowerOf2(frame_alignment));
     and_(esp, -frame_alignment);
     mov(Operand(esp, num_arguments * kPointerSize), scratch);
@@ skipping 348 matching lines @@
   j(greater, &no_info_available);
   cmp(MemOperand(scratch_reg, -AllocationSiteInfo::kSize),
       Immediate(Handle<Map>(isolate()->heap()->allocation_site_info_map())));
   bind(&no_info_available);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32