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

src/arm/ic-arm.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 303 matching lines @@
   __ CompareObjectType(key, map, hash, LAST_UNIQUE_NAME_TYPE);
   __ b(hi, not_unique);
   STATIC_ASSERT(LAST_UNIQUE_NAME_TYPE == FIRST_NONSTRING_TYPE);
   __ b(eq, &unique);
 
   // Is the string an array index, with cached numeric value?
   __ ldr(hash, FieldMemOperand(key, Name::kHashFieldOffset));
   __ tst(hash, Operand(Name::kContainsCachedArrayIndexMask));
   __ b(eq, index_string);
 
-  // Is the string internalized?
+  // Is the string internalized? We know it's a string, so a single
+  // bit test is enough.
   // map: key map
   __ ldrb(hash, FieldMemOperand(map, Map::kInstanceTypeOffset));
   STATIC_ASSERT(kInternalizedTag != 0);
   __ tst(hash, Operand(kIsInternalizedMask));
   __ b(eq, not_unique);
 
   __ bind(&unique);
 }
 
 
@@ skipping 1361 matching lines @@
   } else {
     ASSERT(Assembler::GetCondition(branch_instr) == ne);
     patcher.EmitCondition(eq);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM