Ported ia32 optimization of revision 3487 to x64.

src/x64/assembler-x64.h

Index: src/x64/assembler-x64.h
diff --git a/src/x64/assembler-x64.h b/src/x64/assembler-x64.h
index 64fbd8887fcee3902c9a70803e761de689610177..c455a268077c44283411a7aae7be07882c1a45eb 100644
--- a/src/x64/assembler-x64.h
+++ b/src/x64/assembler-x64.h
@@ -1122,6 +1122,10 @@ class Assembler : public Malloced {
   void mulsd(XMMRegister dst, XMMRegister src);
   void divsd(XMMRegister dst, XMMRegister src);
 
+  void xorpd(XMMRegister dst, XMMRegister src);
+
+  void comisd(XMMRegister dst, XMMRegister src);
+  void ucomisd(XMMRegister dst, XMMRegister src);
 
   void emit_sse_operand(XMMRegister dst, XMMRegister src);
   void emit_sse_operand(XMMRegister reg, const Operand& adr);
@@ -1168,14 +1172,6 @@ class Assembler : public Malloced {
   static const int kMaximalBufferSize = 512*MB;
   static const int kMinimalBufferSize = 4*KB;
 
- protected:
-  // void movsd(XMMRegister dst, const Operand& src);
-  // void movsd(const Operand& dst, XMMRegister src);
-
-  // void emit_sse_operand(XMMRegister reg, const Operand& adr);
-  // void emit_sse_operand(XMMRegister dst, XMMRegister src);
-
-
  private:
   byte* addr_at(int pos)  { return buffer_ + pos; }
   byte byte_at(int pos)  { return buffer_[pos]; }