[turbofan] Implemented the optional Float32RoundDown operator.

src/compiler/ia32/instruction-selector-ia32.cc

Index: src/compiler/ia32/instruction-selector-ia32.cc
diff --git a/src/compiler/ia32/instruction-selector-ia32.cc b/src/compiler/ia32/instruction-selector-ia32.cc
index fd976bc3b3ac3bd851acc79a2b3d8912ae6878bc..b59a798decf69f5dae2658d7258b99524c6ad1b7 100644
--- a/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/src/compiler/ia32/instruction-selector-ia32.cc
@@ -851,6 +851,11 @@ void InstructionSelector::VisitFloat64Sqrt(Node* node) {
 }
 
 
+void InstructionSelector::VisitFloat32RoundDown(Node* node) {
+  VisitRR(this, node, kSSEFloat32Round | MiscField::encode(kRoundDown));
+}
+
+
 void InstructionSelector::VisitFloat64RoundDown(Node* node) {
   VisitRR(this, node, kSSEFloat64Round | MiscField::encode(kRoundDown));
 }
@@ -1287,7 +1292,8 @@ InstructionSelector::SupportedMachineOperatorFlags() {
     flags |= MachineOperatorBuilder::kFloat64RoundDown |
              MachineOperatorBuilder::kFloat64RoundUp |
              MachineOperatorBuilder::kFloat64RoundTruncate |
-             MachineOperatorBuilder::kFloat64RoundTiesEven;
+             MachineOperatorBuilder::kFloat64RoundTiesEven |
+             MachineOperatorBuilder::kFloat32RoundDown;
   }
   return flags;
 }