[turbofan] Implemented the optional Float32RoundDown operator.

src/compiler/instruction-selector.cc

Index: src/compiler/instruction-selector.cc
diff --git a/src/compiler/instruction-selector.cc b/src/compiler/instruction-selector.cc
index a8a5d5dfd67154826fa43cbecb6101adbef7b76b..20c283a993b12b989f05f1a0b3d63269f18c0e14 100644
--- a/src/compiler/instruction-selector.cc
+++ b/src/compiler/instruction-selector.cc
@@ -923,6 +923,8 @@ void InstructionSelector::VisitNode(Node* node) {
       return VisitFloat64LessThan(node);
     case IrOpcode::kFloat64LessThanOrEqual:
       return VisitFloat64LessThanOrEqual(node);
+    case IrOpcode::kFloat32RoundDown:
+      return MarkAsFloat32(node), VisitFloat32RoundDown(node);
     case IrOpcode::kFloat64RoundDown:
       return MarkAsFloat64(node), VisitFloat64RoundDown(node);
     case IrOpcode::kFloat64RoundUp: