Use the macro assembler Set instead of explicit xor for clearing registers.

src/x64/full-codegen-x64.cc

 // Copyright 2010 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 181 matching lines @@
 
   { Comment cmnt(masm_, "[ return <undefined>;");
     // Emit a 'return undefined' in case control fell off the end of the body.
     __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
     EmitReturnSequence();
   }
 }
 
 
 void FullCodeGenerator::ClearAccumulator() {
-  __ xor_(rax, rax);
+  __ Set(rax, 0);
 }
 
 
 void FullCodeGenerator::EmitStackCheck(IterationStatement* stmt) {
   Comment cmnt(masm_, "[ Stack check");
   NearLabel ok;
   __ CompareRoot(rsp, Heap::kStackLimitRootIndex);
   __ j(above_equal, &ok);
   StackCheckStub stub;
   __ CallStub(&stub);
@@ skipping 3308 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64