[turbofan] Do not generate unnecessary moves when casting a tagged value to a word.

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 b7a08bf8ac780f5e7de5223ca29c3eef7f68197f..7d8f937eeeb1977decada6406d920992b453d381 100644
--- a/src/compiler/instruction-selector.cc
+++ b/src/compiler/instruction-selector.cc
@@ -1636,8 +1636,7 @@ void InstructionSelector::VisitStackSlot(Node* node) {
 }
 
 void InstructionSelector::VisitBitcastTaggedToWord(Node* node) {
-  OperandGenerator g(this);
-  Emit(kArchNop, g.DefineSameAsFirst(node), g.Use(node->InputAt(0)));
+  EmitIdentity(node);
 }
 
 void InstructionSelector::VisitBitcastWordToTagged(Node* node) {