x64: Make sure that the upper half of a 64bit register contains 0 for int32 values.

test/cctest/test-disasm-x64.cc

 // Copyright 2011 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 86 matching lines @@
   __ andq(rdx, Operand(rsp, 4));
   __ cmpq(rdx, Immediate(3));
   __ cmpq(rdx, Operand(rsp, 4));
   __ cmpq(Operand(rbp, rcx, times_4, 0), Immediate(1000));
   __ cmpb(rbx, Operand(rbp, rcx, times_2, 0));
   __ cmpb(Operand(rbp, rcx, times_2, 0), rbx);
   __ orq(rdx, Immediate(3));
   __ xorq(rdx, Immediate(3));
   __ nop();
   __ cpuid();
+  __ movsxbl(rdx, Operand(rcx, 0));
   __ movsxbq(rdx, Operand(rcx, 0));
+  __ movsxwl(rdx, Operand(rcx, 0));
   __ movsxwq(rdx, Operand(rcx, 0));
   __ movzxbl(rdx, Operand(rcx, 0));
   __ movzxwl(rdx, Operand(rcx, 0));
   __ movzxbq(rdx, Operand(rcx, 0));
   __ movzxwq(rdx, Operand(rcx, 0));
 
   __ nop();
   __ imulq(rdx, rcx);
   __ shld(rdx, rcx);
   __ shrd(rdx, rcx);
@@ skipping 318 matching lines @@
   CHECK(code->IsCode());
 #ifdef OBJECT_PRINT
   Code::cast(code)->Print();
   byte* begin = Code::cast(code)->instruction_start();
   byte* end = begin + Code::cast(code)->instruction_size();
   disasm::Disassembler::Disassemble(stdout, begin, end);
 #endif
 }
 
 #undef __