Consistently make the bounds check for AccessArgumentsAt explicit.

src/x64/lithium-codegen-x64.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 2583 matching lines @@
   Register input = ToRegister(instr->object());
   __ movq(result, FieldOperand(input,
                                ExternalPixelArray::kExternalPointerOffset));
 }
 
 
 void LCodeGen::DoAccessArgumentsAt(LAccessArgumentsAt* instr) {
   Register arguments = ToRegister(instr->arguments());
   Register length = ToRegister(instr->length());
   Register result = ToRegister(instr->result());
-
+  // There are two words between the frame pointer and the last argument.
+  // Subtracting from length accounts for one of them add one more.
   if (instr->index()->IsRegister()) {
     __ subl(length, ToRegister(instr->index()));
   } else {
     __ subl(length, ToOperand(instr->index()));
   }
-  DeoptimizeIf(below_equal, instr->environment());
-
-  // There are two words between the frame pointer and the last argument.
-  // Subtracting from length accounts for one of them add one more.
   __ movq(result, Operand(arguments, length, times_pointer_size, kPointerSize));
 }
 
 
 void LCodeGen::DoLoadKeyedFastElement(LLoadKeyedFastElement* instr) {
   Register result = ToRegister(instr->result());
   LOperand* key = instr->key();
   if (!key->IsConstantOperand()) {
     Register key_reg = ToRegister(key);
     // Even though the HLoad/StoreKeyedFastElement instructions force the input
@@ skipping 2692 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64