[turbofan] Eliminate unused effectful nodes during representation selection.

src/compiler/representation-change.h

 // 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.
 
 #ifndef V8_COMPILER_REPRESENTATION_CHANGE_H_
 #define V8_COMPILER_REPRESENTATION_CHANGE_H_
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/simplified-operator.h"
 
@@ skipping 10 matching lines @@
   static Truncation Word64() { return Truncation(TruncationKind::kWord64); }
   static Truncation Float32() { return Truncation(TruncationKind::kFloat32); }
   static Truncation Float64() { return Truncation(TruncationKind::kFloat64); }
   static Truncation Any() { return Truncation(TruncationKind::kAny); }
 
   static Truncation Generalize(Truncation t1, Truncation t2) {
     return Truncation(Generalize(t1.kind(), t2.kind()));
   }
 
   // Queries.
+  bool IsUnused() const { return kind_ == TruncationKind::kNone; }
   bool TruncatesToWord32() const {
     return LessGeneral(kind_, TruncationKind::kWord32);
   }
   bool TruncatesToFloat64() const {
     return LessGeneral(kind_, TruncationKind::kFloat64);
   }
   bool TruncatesNaNToZero() {
     return LessGeneral(kind_, TruncationKind::kWord32) ||
            LessGeneral(kind_, TruncationKind::kBool);
   }
@@ skipping 201 matching lines @@
   Factory* factory() const { return isolate()->factory(); }
   SimplifiedOperatorBuilder* simplified() { return jsgraph()->simplified(); }
   MachineOperatorBuilder* machine() { return jsgraph()->machine(); }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_REPRESENTATION_CHANGE_H_