[turbofan] Introduce DeadValue and DeadEffect operators.

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index f80c1f6dd6bc33c708307e0240883d43bfaee9c0..69b356063b15b3204c04bd91c853a0acbb7af4b0 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -489,7 +489,7 @@ class AstGraphBuilder::Environment : public ZoneObject {
     liveness_block_ = nullptr;
   }
   bool IsMarkedAsUnreachable() {
-    return GetControlDependency()->opcode() == IrOpcode::kDead;
+    return GetControlDependency()->opcode() == IrOpcode::kDeadControl;
   }
 
   // Merge another environment into this one.