[runtime] Object.create(null) creates a slow object

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index a125f5b91d11a2c8febc7e0b5b3deb194059d5f2..82518dacd3d613a7ce1769a45190e4cde1da42fb 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -3482,13 +3482,22 @@ class HashTableBase : public FixedArray {
   }
 
   static const int kNumberOfElementsIndex = 0;
+  static const int kNumberOfElementsOffset = kHeaderSize;
   static const int kNumberOfDeletedElementsIndex = 1;
+  static const int kNumberOfDeletedElementsOffset =
+      kNumberOfElementsOffset + kPointerSize;
   static const int kCapacityIndex = 2;
+  static const int kCapacityOffset =
+      kNumberOfDeletedElementsOffset + kPointerSize;
   static const int kPrefixStartIndex = 3;
+  static const int kPrefixStartOffset = kCapacityOffset + kPointerSize;

[Igor Sheludko, 2016/10/21 15:01:10]

I think you can remove these *Offset constants.

[Camillo Bruni, 2016/10/21 16:27:32]

thought I did ;)

 
   // Constant used for denoting a absent entry.
   static const int kNotFound = -1;
 
+  // Minimum capacity for newly created hash tables.
+  static const int kMinCapacity = 4;
+
  protected:
   // Update the number of elements in the hash table.
   inline void SetNumberOfElements(int nof);
@@ -3566,8 +3575,11 @@ class HashTable : public HashTableBase {
   static const int kEntryKeyIndex = 0;
   static const int kElementsStartOffset =
       kHeaderSize + kElementsStartIndex * kPointerSize;
-  static const int kCapacityOffset =
-      kHeaderSize + kCapacityIndex * kPointerSize;
+  // Maximal capacity of HashTable. Based on maximal length of underlying
+  // FixedArray. Staying below kMaxCapacity also ensures that EntryToIndex
+  // cannot overflow.
+  static const int kMaxCapacity =
+      (FixedArray::kMaxLength - kElementsStartIndex) / kEntrySize;

[Camillo Bruni, 2016/10/21 13:37:15]

Note: I change kElementsStartOffset to kElementsStartIndex from the original
code.

 
   // Returns the index for an entry (of the key)
   static inline int EntryToIndex(int entry) {
@@ -3604,12 +3616,6 @@ class HashTable : public HashTableBase {
     set(kCapacityIndex, Smi::FromInt(capacity));
   }
 
-  // Maximal capacity of HashTable. Based on maximal length of underlying
-  // FixedArray. Staying below kMaxCapacity also ensures that EntryToIndex
-  // cannot overflow.
-  static const int kMaxCapacity =
-      (FixedArray::kMaxLength - kElementsStartOffset) / kEntrySize;
-
  private:
   // Returns _expected_ if one of entries given by the first _probe_ probes is
   // equal to  _expected_. Otherwise, returns the entry given by the probe
@@ -3838,6 +3844,13 @@ class Dictionary: public HashTable<Derived, Shape, Key> {
   static Handle<FixedArray> BuildIterationIndicesArray(
       Handle<Derived> dictionary);
 
+  // Generate new enumeration indices to avoid enumeration index overflow.
+  // Returns iteration indices array for the |dictionary|.
+  static Handle<FixedArray> GenerateNewEnumerationIndices(
+      Handle<Derived> dictionary);
+  static const int kMaxNumberKeyIndex = DerivedHashTable::kPrefixStartIndex;
+  static const int kNextEnumerationIndexIndex = kMaxNumberKeyIndex + 1;
+
  protected:
   // Generic at put operation.
   MUST_USE_RESULT static Handle<Derived> AtPut(
@@ -3848,13 +3861,6 @@ class Dictionary: public HashTable<Derived, Shape, Key> {
   // Add entry to dictionary. Returns entry value.
   static int AddEntry(Handle<Derived> dictionary, Key key, Handle<Object> value,
                       PropertyDetails details, uint32_t hash);
-
-  // Generate new enumeration indices to avoid enumeration index overflow.
-  // Returns iteration indices array for the |dictionary|.
-  static Handle<FixedArray> GenerateNewEnumerationIndices(
-      Handle<Derived> dictionary);
-  static const int kMaxNumberKeyIndex = DerivedHashTable::kPrefixStartIndex;
-  static const int kNextEnumerationIndexIndex = kMaxNumberKeyIndex + 1;
 };
 
 
@@ -3926,6 +3932,7 @@ class NameDictionary
 
   static const int kEntryValueIndex = 1;
   static const int kEntryDetailsIndex = 2;
+  static const int kInitialCapacity = 2;
 };