[turbofan] Introduce CheckIf node (deopt without explicit frame state).

src/compiler/node-properties.cc

 // Copyright 2015 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.
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/node-properties.h"
 #include "src/compiler/operator-properties.h"
@@ skipping 197 matching lines @@
   // Requires distinguishing between value, effect and control edges.
   for (Edge edge : node->use_edges()) {
     if (IsControlEdge(edge)) {
       if (edge.from()->opcode() == IrOpcode::kIfSuccess) {
         DCHECK_NOT_NULL(success);
         edge.UpdateTo(success);
       } else if (edge.from()->opcode() == IrOpcode::kIfException) {
         DCHECK_NOT_NULL(exception);
         edge.UpdateTo(exception);
       } else {
-        UNREACHABLE();
+        DCHECK_NOT_NULL(success);
+        edge.UpdateTo(success);
       }
     } else if (IsEffectEdge(edge)) {
       DCHECK_NOT_NULL(effect);
       edge.UpdateTo(effect);
     } else {
       DCHECK_NOT_NULL(value);
       edge.UpdateTo(value);
     }
   }
 }
@@ skipping 196 matching lines @@
 // static
 bool NodeProperties::IsInputRange(Edge edge, int first, int num) {
   if (num == 0) return false;
   int const index = edge.index();
   return first <= index && index < first + num;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8