[turbofan] Introduce TruncateTaggedToWord32 simplified 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 cb208f08106672e3b433556caf6e7fb35f1f8936..8a4899011dcedcd9b7a2e2ab1c244b686442355a 100644
--- a/src/compiler/ia32/instruction-selector-ia32.cc
+++ b/src/compiler/ia32/instruction-selector-ia32.cc
@@ -872,15 +872,12 @@ void InstructionSelector::VisitTruncateFloat64ToFloat32(Node* node) {
   VisitRO(this, node, kSSEFloat64ToFloat32);
 }
 
+void InstructionSelector::VisitTruncateFloat64ToWord32(Node* node) {
+  VisitRR(this, node, kArchTruncateDoubleToI);
+}
 
-void InstructionSelector::VisitTruncateFloat64ToInt32(Node* node) {
-  switch (TruncationModeOf(node->op())) {
-    case TruncationMode::kJavaScript:
-      return VisitRR(this, node, kArchTruncateDoubleToI);
-    case TruncationMode::kRoundToZero:
-      return VisitRO(this, node, kSSEFloat64ToInt32);
-  }
-  UNREACHABLE();
+void InstructionSelector::VisitRoundFloat64ToInt32(Node* node) {
+  VisitRO(this, node, kSSEFloat64ToInt32);
 }