[turbofan] Properly optimize immutable property loads.

src/compiler/js-native-context-specialization.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-native-context-specialization.h"
 
 #include "src/accessors.h"
 #include "src/code-factory.h"
 #include "src/compilation-dependencies.h"
 #include "src/compiler/access-builder.h"
@@ skipping 867 matching lines @@
         control = graph()->NewNode(common()->IfSuccess(), effect);
         break;
       }
     }
   } else {
     DCHECK(access_info.IsDataField());
     FieldIndex const field_index = access_info.field_index();
     Type* const field_type = access_info.field_type();
     MachineRepresentation const field_representation =
         access_info.field_representation();
-    if (access_mode == AccessMode::kLoad &&
-        access_info.holder().ToHandle(&holder)) {
-      receiver = jsgraph()->Constant(holder);
+    if (access_mode == AccessMode::kLoad) {
+      if (access_info.holder().ToHandle(&holder)) {
+        receiver = jsgraph()->Constant(holder);
+      }
+      // Optimize immutable property loads.
+      HeapObjectMatcher m(receiver);
+      if (m.HasValue() && m.Value()->IsJSObject()) {
+        // TODO(turbofan): Given that we already have the field_index here, we
+        // might be smarter in the future and not rely on the LookupIterator,
+        // but for now let's just do what Crankshaft does.
+        LookupIterator it(m.Value(), name,
+                          LookupIterator::OWN_SKIP_INTERCEPTOR);
+        if (it.IsFound() && it.IsReadOnly() && !it.IsConfigurable()) {
+          Node* value = jsgraph()->Constant(JSReceiver::GetDataProperty(&it));
+          return ValueEffectControl(value, effect, control);
+        }
+      }
     }
     Node* storage = receiver;
     if (!field_index.is_inobject()) {
       storage = effect = graph()->NewNode(
           simplified()->LoadField(AccessBuilder::ForJSObjectProperties()),
           storage, effect, control);
     }
     FieldAccess field_access = {
         kTaggedBase,
         field_index.offset(),
@@ skipping 614 matching lines @@
 }
 
 
 SimplifiedOperatorBuilder* JSNativeContextSpecialization::simplified() const {
   return jsgraph()->simplified();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8