ReceiverCheckMode needs to be utilized further.

src/ia32/code-stubs-ia32.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_IA32
 
 #include "src/base/bits.h"
 #include "src/bootstrapper.h"
@@ skipping 684 matching lines @@
   // Return address is on the stack.
   Label miss;
 
   Register receiver = LoadDescriptor::ReceiverRegister();
   Register index = LoadDescriptor::NameRegister();
   Register scratch = ebx;
   DCHECK(!scratch.is(receiver) && !scratch.is(index));
   Register result = eax;
   DCHECK(!result.is(scratch));
 
-  // TODO(mvstanton): the generator doesn't need to verify that
-  // receiver is a string map, that is done outside the handler.
   StringCharAtGenerator char_at_generator(receiver, index, scratch, result,
                                           &miss,  // When not a string.
                                           &miss,  // When not a number.
                                           &miss,  // When index out of range.
                                           STRING_INDEX_IS_ARRAY_INDEX,
                                           RECEIVER_IS_STRING);
   char_at_generator.GenerateFast(masm);
   __ ret(0);
 
   StubRuntimeCallHelper call_helper;
@@ skipping 2435 matching lines @@
 
   // Just jump to runtime to create the sub string.
   __ bind(&runtime);
   __ TailCallRuntime(Runtime::kSubString, 3, 1);
 
   __ bind(&single_char);
   // eax: string
   // ebx: instance type
   // ecx: sub string length (smi)
   // edx: from index (smi)
-  StringCharAtGenerator generator(
-      eax, edx, ecx, eax, &runtime, &runtime, &runtime, STRING_INDEX_IS_NUMBER);
+  StringCharAtGenerator generator(eax, edx, ecx, eax, &runtime, &runtime,
+                                  &runtime, STRING_INDEX_IS_NUMBER,
+                                  RECEIVER_IS_STRING);
   generator.GenerateFast(masm);
   __ ret(3 * kPointerSize);
   generator.SkipSlow(masm, &runtime);
 }
 
 
 void StringHelper::GenerateFlatOneByteStringEquals(MacroAssembler* masm,
                                                    Register left,
                                                    Register right,
                                                    Register scratch1,
@@ skipping 1561 matching lines @@
                               Operand(ebp, 7 * kPointerSize),
                               NULL);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32