[turbofan] Introduce TruncateTaggedToWord32 simplified operator.

src/compiler/mips64/instruction-selector-mips64.cc

Index: src/compiler/mips64/instruction-selector-mips64.cc
diff --git a/src/compiler/mips64/instruction-selector-mips64.cc b/src/compiler/mips64/instruction-selector-mips64.cc
index 3e7603cd8c276cf4d1889e591e31cc3475a7d975..924b10b5f903c0492f9ad31f2a9390c3483aaad3 100644
--- a/src/compiler/mips64/instruction-selector-mips64.cc
+++ b/src/compiler/mips64/instruction-selector-mips64.cc
@@ -1094,17 +1094,13 @@ void InstructionSelector::VisitTruncateFloat64ToFloat32(Node* node) {
   VisitRR(this, kMips64CvtSD, node);
 }
 
-
-void InstructionSelector::VisitTruncateFloat64ToInt32(Node* node) {
-  switch (TruncationModeOf(node->op())) {
-    case TruncationMode::kJavaScript:
-      return VisitRR(this, kArchTruncateDoubleToI, node);
-    case TruncationMode::kRoundToZero:
-      return VisitRR(this, kMips64TruncWD, node);
-  }
-  UNREACHABLE();
+void InstructionSelector::VisitTruncateFloat64ToWord32(Node* node) {
+  VisitRR(this, kArchTruncateDoubleToI, node);
 }
 
+void InstructionSelector::VisitRoundFloat64ToInt32(Node* node) {
+  VisitRR(this, kMips64TruncWD, node);
+}
 
 void InstructionSelector::VisitRoundInt64ToFloat32(Node* node) {
   VisitRR(this, kMips64CvtSL, node);