[turbofan] Implemented the optional Float32RoundDown operator.

src/x64/macro-assembler-x64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_X64_MACRO_ASSEMBLER_X64_H_
 #define V8_X64_MACRO_ASSEMBLER_X64_H_
 
 #include "src/assembler.h"
 #include "src/bailout-reason.h"
 #include "src/base/flags.h"
@@ skipping 952 matching lines @@
   void Movd(XMMRegister dst, Register src);
   void Movd(XMMRegister dst, const Operand& src);
   void Movd(Register dst, XMMRegister src);
   void Movq(XMMRegister dst, Register src);
   void Movq(Register dst, XMMRegister src);
 
   void Movaps(XMMRegister dst, XMMRegister src);
   void Movapd(XMMRegister dst, XMMRegister src);
   void Movmskpd(Register dst, XMMRegister src);
 
+  void Roundss(XMMRegister dst, XMMRegister src, RoundingMode mode);
   void Roundsd(XMMRegister dst, XMMRegister src, RoundingMode mode);
   void Sqrtsd(XMMRegister dst, XMMRegister src);
   void Sqrtsd(XMMRegister dst, const Operand& src);
 
   void Ucomiss(XMMRegister src1, XMMRegister src2);
   void Ucomiss(XMMRegister src1, const Operand& src2);
   void Ucomisd(XMMRegister src1, XMMRegister src2);
   void Ucomisd(XMMRegister src1, const Operand& src2);
 
   // Control Flow
@@ skipping 751 matching lines @@
   }                                                                          \
   masm->
 #else
 #define ACCESS_MASM(masm) masm->
 #endif
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_