Avoid creating weak cells for literal arrays that are empty of literals.

src/type-feedback-vector.cc

 // Copyright 2014 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/type-feedback-vector.h"
 
 #include "src/code-stubs.h"
 #include "src/ic/ic.h"
 #include "src/ic/ic-state.h"
 #include "src/objects.h"
@@ skipping 261 matching lines @@
 // static
 void TypeFeedbackVector::ClearAllKeyedStoreICs(Isolate* isolate) {
   SharedFunctionInfo::Iterator iterator(isolate);
   SharedFunctionInfo* shared;
   while ((shared = iterator.Next())) {
     if (!shared->OptimizedCodeMapIsCleared()) {
       FixedArray* optimized_code_map = shared->optimized_code_map();
       int length = optimized_code_map->length();
       for (int i = SharedFunctionInfo::kEntriesStart; i < length;
            i += SharedFunctionInfo::kEntryLength) {
-        WeakCell* cell = WeakCell::cast(
-            optimized_code_map->get(i + SharedFunctionInfo::kLiteralsOffset));
-        if (cell->value()->IsLiteralsArray()) {
-          TypeFeedbackVector* vector =
-              LiteralsArray::cast(cell->value())->feedback_vector();
+        Object* lits =
+            optimized_code_map->get(i + SharedFunctionInfo::kLiteralsOffset);
+        TypeFeedbackVector* vector = NULL;

[Michael Starzinger, 2016/06/07 09:41:37]

nit: s/NULL/nullptr/

[mvstanton, 2016/06/07 11:35:33]

Done.

+        if (lits->IsWeakCell()) {
+          WeakCell* cell = WeakCell::cast(lits);
+          if (cell->value()->IsLiteralsArray()) {
+            vector = LiteralsArray::cast(cell->value())->feedback_vector();
+          }
+        } else {
+          DCHECK(lits->IsLiteralsArray());
+          vector = LiteralsArray::cast(lits)->feedback_vector();
+        }
+        if (vector != NULL) {

[Michael Starzinger, 2016/06/07 09:41:37]

nit: s/NULL/nullptr/

[mvstanton, 2016/06/07 11:35:33]

Done.

           vector->ClearKeyedStoreICs(shared);
         }
       }
     }
   }
 }
 
 
 void TypeFeedbackVector::ClearKeyedStoreICs(SharedFunctionInfo* shared) {
   Isolate* isolate = GetIsolate();
@@ skipping 590 matching lines @@
 
 IcCheckType KeyedStoreICNexus::GetKeyType() const {
   Object* feedback = GetFeedback();
   if (feedback == *TypeFeedbackVector::MegamorphicSentinel(GetIsolate())) {
     return static_cast<IcCheckType>(Smi::cast(GetFeedbackExtra())->value());
   }
   return IsPropertyNameFeedback(feedback) ? PROPERTY : ELEMENT;
 }
 }  // namespace internal
 }  // namespace v8