[turbofan] Introduce DeadValue and DeadEffect operators.

src/compiler/js-graph.h

Index: src/compiler/js-graph.h
diff --git a/src/compiler/js-graph.h b/src/compiler/js-graph.h
index dda1277419437389e9dcd46a29e7eedad4f5e2f9..b6b1322f331c9a0c1fd508a7e5245eed61f96ebf 100644
--- a/src/compiler/js-graph.h
+++ b/src/compiler/js-graph.h
@@ -117,7 +117,10 @@ class JSGraph : public ZoneObject {
   // cannot deopt.
   Node* EmptyFrameState();
 
-  // Create a control node that serves as control dependency for dead nodes.
+  // Creates a value node that servers as value input for dead nodes.
+  Node* DeadValue();
+
+  // Creates a control node that serves as control dependency for dead nodes.
   Node* DeadControl();
 
   JSOperatorBuilder* javascript() const { return javascript_; }
@@ -142,6 +145,7 @@ class JSGraph : public ZoneObject {
     kOneConstant,
     kNaNConstant,
     kEmptyFrameState,
+    kDeadValue,
     kDeadControl,
     kNumCachedNodes  // Must remain last.
   };