[turbofan] Use unreliable receiver maps for __proto__ lowering.

src/compiler/js-call-reducer.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/js-call-reducer.h"
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/js-graph.h"
@@ skipping 319 matching lines @@
 // ES6 section B.2.2.1.1 get Object.prototype.__proto__
 Reduction JSCallReducer::ReduceObjectPrototypeGetProto(Node* node) {
   DCHECK_EQ(IrOpcode::kJSCall, node->opcode());
   Node* receiver = NodeProperties::GetValueInput(node, 1);
   Node* effect = NodeProperties::GetEffectInput(node);
 
   // Try to determine the {receiver} map.
   ZoneHandleSet<Map> receiver_maps;
   NodeProperties::InferReceiverMapsResult result =
       NodeProperties::InferReceiverMaps(receiver, effect, &receiver_maps);
-  if (result == NodeProperties::kReliableReceiverMaps) {
+  if (result != NodeProperties::kNoReceiverMaps) {
     Handle<Map> candidate_map(
         receiver_maps[0]->GetPrototypeChainRootMap(isolate()));
     Handle<Object> candidate_prototype(candidate_map->prototype(), isolate());
 
     // Check if we can constant-fold the {candidate_prototype}.
     for (size_t i = 0; i < receiver_maps.size(); ++i) {
       Handle<Map> const receiver_map(
           receiver_maps[i]->GetPrototypeChainRootMap(isolate()));
       if (receiver_map->IsJSProxyMap() ||
           receiver_map->has_hidden_prototype() ||
           receiver_map->is_access_check_needed() ||
           receiver_map->prototype() != *candidate_prototype) {
         return NoChange();
       }
+      if (result == NodeProperties::kUnreliableReceiverMaps &&
+          !receiver_map->is_stable()) {
+        return NoChange();
+      }
+    }
+    if (result == NodeProperties::kUnreliableReceiverMaps) {
+      for (size_t i = 0; i < receiver_maps.size(); ++i) {
+        dependencies()->AssumeMapStable(receiver_maps[i]);
+      }
     }
     Node* value = jsgraph()->Constant(candidate_prototype);
     ReplaceWithValue(node, value);
     return Replace(value);
   }
 
   return NoChange();
 }
 
 Reduction JSCallReducer::ReduceCallApiFunction(
@@ skipping 469 matching lines @@
   return jsgraph()->javascript();
 }
 
 SimplifiedOperatorBuilder* JSCallReducer::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8