ReceiverCheckMode needs to be utilized further.

src/arm/code-stubs-arm.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"
 
 #if V8_TARGET_ARCH_ARM
 
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
@@ skipping 3149 matching lines @@
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kSubString, 3, 1);
 
   __ bind(&single_char);
   // r0: original string
   // r1: instance type
   // r2: length
   // r3: from index (untagged)
   __ SmiTag(r3, r3);
-  StringCharAtGenerator generator(
-      r0, r3, r2, r0, &runtime, &runtime, &runtime, STRING_INDEX_IS_NUMBER);
+  StringCharAtGenerator generator(r0, r3, r2, r0, &runtime, &runtime, &runtime,
+                                  STRING_INDEX_IS_NUMBER, RECEIVER_IS_STRING);
   generator.GenerateFast(masm);
   __ Drop(3);
   __ Ret();
   generator.SkipSlow(masm, &runtime);
 }
 
 
 void StringHelper::GenerateFlatOneByteStringEquals(
     MacroAssembler* masm, Register left, Register right, Register scratch1,
     Register scratch2, Register scratch3) {
@@ skipping 1526 matching lines @@
                               MemOperand(fp, 6 * kPointerSize),
                               NULL);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM