Use xorps to break the cvtsi2sd unnecessary dependence due to its partially written

src/ia32/macro-assembler-ia32.h

Index: src/ia32/macro-assembler-ia32.h
diff --git a/src/ia32/macro-assembler-ia32.h b/src/ia32/macro-assembler-ia32.h
index e4e4533bf5f8e2f4b2b66360ba166666353ad130..fa1128ccf84aa683d44f2d4fa0b63744a3d9ed38 100644
--- a/src/ia32/macro-assembler-ia32.h
+++ b/src/ia32/macro-assembler-ia32.h
@@ -366,6 +366,10 @@ class MacroAssembler: public Assembler {
   void Set(Register dst, const Immediate& x);
   void Set(const Operand& dst, const Immediate& x);
 
+  // Use xorps to clear out the destination register before cvtsi2sd

[Yang, 2013/09/12 11:56:49]

Could you add a comment on why we do this? I mean, it's not entirely obvious why
we need to clear out the destination register, so it would be great if somebody
working on this code in the future can figure out what the background of this
change is.

+  void Cvtsi2sd(XMMRegister dst, Register src) { Cvtsi2sd(dst, Operand(src)); }
+  void Cvtsi2sd(XMMRegister dst, const Operand& src);
+
   // Support for constant splitting.
   bool IsUnsafeImmediate(const Immediate& x);
   void SafeSet(Register dst, const Immediate& x);