[turbofan] Implemented the optional Float32RoundDown operator.

src/x64/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.
 
 #include "src/x64/assembler-x64.h"
 
 #include <cstring>
 
 #if V8_TARGET_ARCH_X64
 
@@ skipping 3463 matching lines @@
   EnsureSpace ensure_space(this);
   emit(0xF2);
   emit_optional_rex_32(dst, src);
   emit(0x0F);
   emit(0xC2);
   emit_sse_operand(dst, src);
   emit(0x01);  // LT == 1
 }
 
 
+void Assembler::roundss(XMMRegister dst, XMMRegister src, RoundingMode mode) {
+  DCHECK(!IsEnabled(AVX));
+  DCHECK(IsEnabled(SSE4_1));
+  EnsureSpace ensure_space(this);
+  emit(0x66);
+  emit_optional_rex_32(dst, src);
+  emit(0x0f);
+  emit(0x3a);
+  emit(0x0a);
+  emit_sse_operand(dst, src);
+  // Mask precision exception.
+  emit(static_cast<byte>(mode) | 0x8);
+}
+
+
 void Assembler::roundsd(XMMRegister dst, XMMRegister src, RoundingMode mode) {
   DCHECK(!IsEnabled(AVX));
   DCHECK(IsEnabled(SSE4_1));
   EnsureSpace ensure_space(this);
   emit(0x66);
   emit_optional_rex_32(dst, src);
   emit(0x0f);
   emit(0x3a);
   emit(0x0b);
   emit_sse_operand(dst, src);
@@ skipping 605 matching lines @@
 
 bool RelocInfo::IsInConstantPool() {
   return false;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64