[turbofan] Implemented the optional Float32RoundTruncate operator.

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

Index: src/compiler/x64/instruction-selector-x64.cc
diff --git a/src/compiler/x64/instruction-selector-x64.cc b/src/compiler/x64/instruction-selector-x64.cc
index 69e797f6eb91b3f286d2cc63d89e9f006e27d4e8..44024094bc47ba12769a43e5e319060cf3adf428 100644
--- a/src/compiler/x64/instruction-selector-x64.cc
+++ b/src/compiler/x64/instruction-selector-x64.cc
@@ -1158,6 +1158,11 @@ void InstructionSelector::VisitFloat64RoundUp(Node* node) {
 }
 
 
+void InstructionSelector::VisitFloat32RoundTruncate(Node* node) {
+  VisitRR(this, node, kSSEFloat32Round | MiscField::encode(kRoundToZero));
+}
+
+
 void InstructionSelector::VisitFloat64RoundTruncate(Node* node) {
   VisitRR(this, node, kSSEFloat64Round | MiscField::encode(kRoundToZero));
 }
@@ -1705,6 +1710,7 @@ InstructionSelector::SupportedMachineOperatorFlags() {
              MachineOperatorBuilder::kFloat64RoundDown |
              MachineOperatorBuilder::kFloat32RoundUp |
              MachineOperatorBuilder::kFloat64RoundUp |
+             MachineOperatorBuilder::kFloat32RoundTruncate |
              MachineOperatorBuilder::kFloat64RoundTruncate |
              MachineOperatorBuilder::kFloat64RoundTiesEven;
   }