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

src/code-stub-assembler.cc

 // Copyright 2016 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/code-stub-assembler.h"
 #include "src/code-factory.h"
 #include "src/frames-inl.h"
 #include "src/frames.h"
 #include "src/ic/handler-configuration.h"
 #include "src/ic/stub-cache.h"
 
@@ skipping 109 matching lines @@
       return IntPtrConstant(left_constant - right_constant);
     }
   } else if (is_right_constant) {
     if (right_constant == 0) {
       return left;
     }
   }
   return IntPtrSub(left, right);
 }
 
+Node* CodeStubAssembler::IntPtrRoundUpToPowerOfTwo32(Node* value) {
+  CSA_ASSERT(UintPtrLessThanOrEqual(value, IntPtrConstant(0x80000000u)));
+  value = IntPtrSubWithOverflow(value, IntPtrConstant(1));

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

You should use normal IntPtrSub() here since you don't care if the overflow
happened or not.

[Camillo Bruni, 2016/10/24 09:53:07]

done.

+  for (int i = 1; i <= 16; i *= 2) {

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

This implementation is actually for word32. I don't know how to express this
fact in the name :( It's already quite long. Maybe s/value/word32/ and a comment
will help...

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

The CSA_ASSERT is there for this. Will add a proper comment though.

[Camillo Bruni, 2016/10/24 09:53:07]

done.

+    value = WordOr(value, WordShr(value, IntPtrConstant(i)));
+  }
+  return IntPtrAdd(value, IntPtrConstant(1));
+}
+
+Node* CodeStubAssembler::WordIsPowerOfTwo(Node* value) {
+  // value && !(value & (value - 1))
+  return WordEqual(
+      Select(WordEqual(value, IntPtrConstant(0)), IntPtrConstant(1),
+             WordAnd(value, IntPtrSubWithOverflow(value, IntPtrConstant(1)))),

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

Same here.

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

If I do IntPtrSub the whole second part of the select instruction disappears.

[Camillo Bruni, 2016/10/24 09:53:07]

done.

+      IntPtrConstant(0));
+}
+
 Node* CodeStubAssembler::Float64Round(Node* x) {
   Node* one = Float64Constant(1.0);
   Node* one_half = Float64Constant(0.5);
 
   Variable var_x(this, MachineRepresentation::kFloat64);
   Label return_x(this);
 
   // Round up {x} towards Infinity.
   var_x.Bind(Float64Ceil(x));
 
@@ skipping 959 matching lines @@
   Assert(Word32Equal(Word32And(bit_field, mask), Int32Constant(0)));
   return IsSpecialReceiverInstanceType(LoadMapInstanceType(map));
 }
 
 Node* CodeStubAssembler::IsSpecialReceiverInstanceType(Node* instance_type) {
   STATIC_ASSERT(JS_GLOBAL_OBJECT_TYPE <= LAST_SPECIAL_RECEIVER_TYPE);
   return Int32LessThanOrEqual(instance_type,
                               Int32Constant(LAST_SPECIAL_RECEIVER_TYPE));
 }
 
+Node* CodeStubAssembler::IsDictionaryMap(Node* map) {
+  Node* bit_field3 = LoadMapBitField3(map);
+  return Word32NotEqual(BitFieldDecode<Map::DictionaryMap>(bit_field3),

[Igor Sheludko, 2016/10/21 15:01:09]

  return IsSetWord32<Map::DictionaryMap>(bit_field3);

[Camillo Bruni, 2016/10/24 09:53:07]

done.

+                        Int32Constant(0));
+}
+
 Node* CodeStubAssembler::LoadNameHashField(Node* name) {
   return LoadObjectField(name, Name::kHashFieldOffset, MachineType::Uint32());
 }
 
 Node* CodeStubAssembler::LoadNameHash(Node* name, Label* if_hash_not_computed) {
   Node* hash_field = LoadNameHashField(name);
   if (if_hash_not_computed != nullptr) {
     GotoIf(Word32Equal(
                Word32And(hash_field, Int32Constant(Name::kHashNotComputedMask)),
                Int32Constant(0)),
@@ skipping 534 matching lines @@
       AllocateFixedArray(elements_kind, length_intptr, parameter_mode);
   StoreObjectField(result, JSArray::kElementsOffset, elements);
 
   // Fill in the elements with undefined.
   FillFixedArrayWithValue(elements_kind, elements, zero, length_intptr,
                           Heap::kUndefinedValueRootIndex, parameter_mode);
 
   return result;
 }
 
+Node* CodeStubAssembler::AllocateNameDictionary(int at_least_space_for) {
+  return AllocateNameDictionary(IntPtrConstant(at_least_space_for));
+}
+
+Node* CodeStubAssembler::AllocateNameDictionary(Node* at_least_space_for) {
+  CSA_ASSERT(UintPtrLessThanOrEqual(
+      at_least_space_for, IntPtrConstant(NameDictionary::kMaxCapacity)));
+
+  Node* capacity = HashTableComputeCapacity(at_least_space_for);
+  CSA_ASSERT(WordIsPowerOfTwo(capacity));
+
+  Node* length = EntryToIndex<NameDictionary>(capacity);
+  Node* store_size =
+      IntPtrAddFoldConstants(WordShl(length, IntPtrConstant(kPointerSizeLog2)),
+                             IntPtrConstant(NameDictionary::kHeaderSize));
+
+  Node* result = Allocate(store_size);
+  // Initialize FixedArray fields.
+  StoreObjectFieldRoot(result, Internals::kHeapObjectMapOffset,

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

Why not FixedArray::kMapOffset to be consistent?

[Camillo Bruni, 2016/10/24 09:53:07]

yup, done.

+                       Heap::kHashTableMapRootIndex);
+  StoreObjectFieldNoWriteBarrier(result, FixedArray::kLengthOffset,
+                                 SmiFromWord(length));
+  // Initialized HashTable fields.
+  Node* zero = SmiConstant(0);
+  StoreFixedArrayElement(result, NameDictionary::kNumberOfElementsIndex, zero,
+                         SKIP_WRITE_BARRIER);
+  StoreFixedArrayElement(result, NameDictionary::kNumberOfDeletedElementsIndex,
+                         zero, SKIP_WRITE_BARRIER);
+  StoreFixedArrayElement(result, NameDictionary::kCapacityIndex,
+                         SmiTag(capacity), SKIP_WRITE_BARRIER);
+  // Initialize Dictionary fields.
+  Node* filler = LoadRoot(Heap::kUndefinedValueRootIndex);
+  StoreFixedArrayElement(result, NameDictionary::kMaxNumberKeyIndex, filler,
+                         SKIP_WRITE_BARRIER);
+  StoreFixedArrayElement(result, NameDictionary::kNextEnumerationIndexIndex,
+                         SmiConstant(PropertyDetails::kInitialIndex),
+                         SKIP_WRITE_BARRIER);
+
+  // Initialize NameDictionary elements.
+  Node* start_address = IntPtrAdd(
+      result,
+      IntPtrConstant(NameDictionary::kElementsStartOffset - kHeapObjectTag));

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

(NameDictionay::OffsetOfElementAt(NameDictionary::kElementsStartIndex) -
kHeapObjectTag)
 or something...

[Camillo Bruni, 2016/10/21 16:27:31]

oh, somehow missed that :)

+  Node* end_address = IntPtrAdd(
+      result,
+      IntPtrSubFoldConstants(store_size, IntPtrConstant(kHeapObjectTag)));
+  StoreFieldsNoWriteBarrier(start_address, end_address, filler);
+  return result;
+}
+
 Node* CodeStubAssembler::AllocateJSObjectFromMap(Node* map, Node* properties,
                                                  Node* elements) {
   Node* size =
       IntPtrMul(LoadMapInstanceSize(map), IntPtrConstant(kPointerSize));
   CSA_ASSERT(IsRegularHeapObjectSize(size));
   Node* object = Allocate(size);
   StoreMapNoWriteBarrier(object, map);
   InitializeJSObjectFromMap(object, map, size, properties, elements);
   return object;
 }
 
 void CodeStubAssembler::InitializeJSObjectFromMap(Node* object, Node* map,
                                                   Node* size, Node* properties,
                                                   Node* elements) {
   // This helper assumes that the object is in new-space, as guarded by the
   // check in AllocatedJSObjectFromMap.
   if (properties == nullptr) {
+    CSA_ASSERT(Word32BinaryNot(IsDictionaryMap((map))));
     StoreObjectFieldRoot(object, JSObject::kPropertiesOffset,
                          Heap::kEmptyFixedArrayRootIndex);
   } else {
     StoreObjectFieldNoWriteBarrier(object, JSObject::kPropertiesOffset,
                                    properties);
   }
   if (elements == nullptr) {
     StoreObjectFieldRoot(object, JSObject::kElementsOffset,
                          Heap::kEmptyFixedArrayRootIndex);
   } else {
@@ skipping 2128 matching lines @@
   Goto(if_keyisindex);
 }
 
 template <typename Dictionary>
 Node* CodeStubAssembler::EntryToIndex(Node* entry, int field_index) {
   Node* entry_index = IntPtrMul(entry, IntPtrConstant(Dictionary::kEntrySize));
   return IntPtrAdd(entry_index, IntPtrConstant(Dictionary::kElementsStartIndex +
                                                field_index));
 }
 
+template Node* CodeStubAssembler::EntryToIndex<NameDictionary>(Node*, int);
+template Node* CodeStubAssembler::EntryToIndex<GlobalDictionary>(Node*, int);
+
+Node* CodeStubAssembler::HashTableComputeCapacity(Node* at_least_space_for) {
+  Node* capacity = IntPtrRoundUpToPowerOfTwo32(
+      WordShl(at_least_space_for, IntPtrConstant(1)));
+  return IntPtrMax(capacity, IntPtrConstant(HashTableBase::kMinCapacity));
+}
+
+Node* CodeStubAssembler::IntPtrMax(Node* left, Node* right) {
+  return Select(IntPtrGreaterThanOrEqual(left, right), left, right);
+}
+
 template <typename Dictionary>
 void CodeStubAssembler::NameDictionaryLookup(Node* dictionary,
                                              Node* unique_name, Label* if_found,
                                              Variable* var_name_index,
                                              Label* if_not_found,
                                              int inlined_probes) {
   DCHECK_EQ(MachineType::PointerRepresentation(), var_name_index->rep());
   Comment("NameDictionaryLookup");
 
   Node* capacity = SmiUntag(LoadFixedArrayElement(
@@ skipping 4491 matching lines @@
   Node* buffer_bit_field = LoadObjectField(
       buffer, JSArrayBuffer::kBitFieldOffset, MachineType::Uint32());
   Node* was_neutered_mask = Int32Constant(JSArrayBuffer::WasNeutered::kMask);
 
   return Word32NotEqual(Word32And(buffer_bit_field, was_neutered_mask),
                         Int32Constant(0));
 }
 
 }  // namespace internal
 }  // namespace v8