[turbofan] Introduce DeadValue and DeadEffect operators.

src/compiler/pipeline.cc

Index: src/compiler/pipeline.cc
diff --git a/src/compiler/pipeline.cc b/src/compiler/pipeline.cc
index 84995be5970643168447e8af529c49bbe6aeadf8..1aa84a8d1ae7b566ffa8e22db9cd8abe8cbe86ce 100644
--- a/src/compiler/pipeline.cc
+++ b/src/compiler/pipeline.cc
@@ -407,7 +407,7 @@ class SourcePositionWrapper final : public Reducer {
 class JSGraphReducer final : public GraphReducer {
  public:
   JSGraphReducer(JSGraph* jsgraph, Zone* zone)
-      : GraphReducer(zone, jsgraph->graph(), jsgraph->TheHoleConstant(),
+      : GraphReducer(zone, jsgraph->graph(), jsgraph->DeadValue(),
                      jsgraph->DeadControl()) {}
   ~JSGraphReducer() final {}
 };