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

src/x64/macro-assembler-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 1092 matching lines @@
   ASSERT(!dst.is(src2));
   if (!dst.is(src1)) {
     movq(dst, src1);
   }
   and_(dst, src2);
 }
 
 
 void MacroAssembler::SmiAndConstant(Register dst, Register src, Smi* constant) {
   if (constant->value() == 0) {
-    xor_(dst, dst);
+    Set(dst, 0);
   } else if (dst.is(src)) {
     ASSERT(!dst.is(kScratchRegister));
     Register constant_reg = GetSmiConstant(constant);
     and_(dst, constant_reg);
   } else {
     LoadSmiConstant(dst, constant);
     and_(dst, src);
   }
 }
 
@@ skipping 474 matching lines @@
     } else {
       subl(operand, Immediate(value));
     }
   }
 }
 
 
 #ifdef ENABLE_DEBUGGER_SUPPORT
 void MacroAssembler::DebugBreak() {
   ASSERT(allow_stub_calls());
-  xor_(rax, rax);  // no arguments
+  Set(rax, 0);  // No arguments.
   movq(rbx, ExternalReference(Runtime::kDebugBreak));
   CEntryStub ces(1);
   Call(ces.GetCode(), RelocInfo::DEBUG_BREAK);
 }
 #endif  // ENABLE_DEBUGGER_SUPPORT
 
 
 void MacroAssembler::InvokeCode(Register code,
                                 const ParameterCount& expected,
                                 const ParameterCount& actual,
@@ skipping 727 matching lines @@
   CPU::FlushICache(address_, size_);
 
   // Check that the code was patched as expected.
   ASSERT(masm_.pc_ == address_ + size_);
   ASSERT(masm_.reloc_info_writer.pos() == address_ + size_ + Assembler::kGap);
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64