Fix false x64 argument index assertion

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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 2900 matching lines @@
 
 
 void LCodeGen::DoAccessArgumentsAt(LAccessArgumentsAt* instr) {
   Register arguments = ToRegister(instr->arguments());
   Register result = ToRegister(instr->result());
 
   if (instr->length()->IsConstantOperand() &&
       instr->index()->IsConstantOperand()) {
     int32_t const_index = ToInteger32(LConstantOperand::cast(instr->index()));
     int32_t const_length = ToInteger32(LConstantOperand::cast(instr->length()));
-    StackArgumentsAccessor args(arguments, const_length,
-                                ARGUMENTS_DONT_CONTAIN_RECEIVER);
-    __ movp(result, args.GetArgumentOperand(const_index));
+    if (const_index < const_length) {
+      StackArgumentsAccessor args(arguments, const_length,
+                                  ARGUMENTS_DONT_CONTAIN_RECEIVER);
+      __ movp(result, args.GetArgumentOperand(const_index));
+    } else {
+      // This code should never be executed; just stop here.
+      __ int3();
+    }
   } else {
     Register length = ToRegister(instr->length());
     // 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()));
     }
     StackArgumentsAccessor args(arguments, length,
@@ skipping 2725 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64