[turbofan] Implement rounding of floats on x64 and ia32 without sse4.1.

src/compiler/x64/instruction-selector-x64.cc

 // Copyright 2014 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 <algorithm>
 
 #include "src/base/adapters.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
@@ skipping 1769 matching lines @@
 
 // static
 MachineOperatorBuilder::Flags
 InstructionSelector::SupportedMachineOperatorFlags() {
   MachineOperatorBuilder::Flags flags =
       MachineOperatorBuilder::kFloat32Max |
       MachineOperatorBuilder::kFloat32Min |
       MachineOperatorBuilder::kFloat64Max |
       MachineOperatorBuilder::kFloat64Min |
       MachineOperatorBuilder::kWord32ShiftIsSafe |
-      MachineOperatorBuilder::kWord32Ctz | MachineOperatorBuilder::kWord64Ctz;
+      MachineOperatorBuilder::kWord32Ctz | MachineOperatorBuilder::kWord64Ctz |
+      MachineOperatorBuilder::kFloat32RoundDown |
+      MachineOperatorBuilder::kFloat32RoundUp |
+      MachineOperatorBuilder::kFloat32RoundTruncate |
+      MachineOperatorBuilder::kFloat32RoundTiesEven |
+      MachineOperatorBuilder::kFloat64RoundDown |
+      MachineOperatorBuilder::kFloat64RoundUp |
+      MachineOperatorBuilder::kFloat64RoundTruncate |
+      MachineOperatorBuilder::kFloat64RoundTiesEven;
   if (CpuFeatures::IsSupported(POPCNT)) {
     flags |= MachineOperatorBuilder::kWord32Popcnt |
              MachineOperatorBuilder::kWord64Popcnt;
   }
-  if (CpuFeatures::IsSupported(SSE4_1)) {
-    flags |= MachineOperatorBuilder::kFloat32RoundDown |
-             MachineOperatorBuilder::kFloat64RoundDown |
-             MachineOperatorBuilder::kFloat32RoundUp |
-             MachineOperatorBuilder::kFloat64RoundUp |
-             MachineOperatorBuilder::kFloat32RoundTruncate |
-             MachineOperatorBuilder::kFloat64RoundTruncate |
-             MachineOperatorBuilder::kFloat32RoundTiesEven |
-             MachineOperatorBuilder::kFloat64RoundTiesEven;
-  }
   return flags;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8