Consistently make the bounds check for AccessArgumentsAt explicit.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index fea0afa7842c2a784a97cb7b2f94ee5ff43a059d..c08ca7b78cf4caf4018ce23dbd2b97e1f30f55fb 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -2601,16 +2601,13 @@ 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));
 }