[turbofan] Implemented the optional Float32RoundDown operator.

src/x64/macro-assembler-x64.cc

 // 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.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/base/bits.h"
 #include "src/base/division-by-constant.h"
 #include "src/bootstrapper.h"
 #include "src/codegen.h"
@@ skipping 2746 matching lines @@
 void MacroAssembler::Movmskpd(Register dst, XMMRegister src) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
     vmovmskpd(dst, src);
   } else {
     movmskpd(dst, src);
   }
 }
 
 
+void MacroAssembler::Roundss(XMMRegister dst, XMMRegister src,
+                             RoundingMode mode) {
+  if (CpuFeatures::IsSupported(AVX)) {
+    CpuFeatureScope scope(this, AVX);
+    vroundss(dst, dst, src, mode);
+  } else {
+    roundss(dst, src, mode);
+  }
+}
+
+
 void MacroAssembler::Roundsd(XMMRegister dst, XMMRegister src,
                              RoundingMode mode) {
   if (CpuFeatures::IsSupported(AVX)) {
     CpuFeatureScope scope(this, AVX);
     vroundsd(dst, dst, src, mode);
   } else {
     roundsd(dst, src, mode);
   }
 }
 
@@ skipping 2735 matching lines @@
   movl(rax, dividend);
   shrl(rax, Immediate(31));
   addl(rdx, rax);
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64