[turbofan] Introduce TruncateTaggedToWord32 simplified operator.

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

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/base/adapters.h"
 #include "src/base/bits.h"
 #include "src/compiler/instruction-selector-impl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties.h"
 
@@ skipping 701 matching lines @@
   // instruction.
   if (CanCover(node, value) &&
       value->opcode() == IrOpcode::kChangeInt32ToFloat64) {
     Emit(kMipsCvtSW, g.DefineAsRegister(node),
          g.UseRegister(value->InputAt(0)));
     return;
   }
   VisitRR(this, kMipsCvtSD, node);
 }
 
-
-void InstructionSelector::VisitTruncateFloat64ToInt32(Node* node) {
-  switch (TruncationModeOf(node->op())) {
-    case TruncationMode::kJavaScript:
-      return VisitRR(this, kArchTruncateDoubleToI, node);
-    case TruncationMode::kRoundToZero:
-      return VisitRR(this, kMipsTruncWD, node);
-  }
-  UNREACHABLE();
+void InstructionSelector::VisitTruncateFloat64ToWord32(Node* node) {
+  VisitRR(this, kArchTruncateDoubleToI, node);
 }
 
+void InstructionSelector::VisitRoundFloat64ToInt32(Node* node) {
+  VisitRR(this, kMipsTruncWD, node);
+}
 
 void InstructionSelector::VisitBitcastFloat32ToInt32(Node* node) {
   VisitRR(this, kMipsFloat64ExtractLowWord32, node);
 }
 
 
 void InstructionSelector::VisitBitcastInt32ToFloat32(Node* node) {
   MipsOperandGenerator g(this);
   Emit(kMipsFloat64InsertLowWord32, g.DefineAsRegister(node),
        ImmediateOperand(ImmediateOperand::INLINE, 0),
@@ skipping 764 matching lines @@
          MachineOperatorBuilder::kFloat32Max |
          MachineOperatorBuilder::kFloat32RoundDown |
          MachineOperatorBuilder::kFloat32RoundUp |
          MachineOperatorBuilder::kFloat32RoundTruncate |
          MachineOperatorBuilder::kFloat32RoundTiesEven;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8