deps: cherry-pick a803fad from upstream V8

Original commit message:

    Make sure the identity hash is uniform (at least in the lower bits).

    In the current implementation of hash code for objects (identity hash),
    we do not bother to shift the hash when we retrieve it from the
    hash-length bitfield in a property array. (Even worse, we store shifted
    value even if we do not have property array or inside dictionaries.)
    That means that the hash-code for objects is always divisible by 1024.
    Since our hash table uses a simple masking with (2^logsize - 1) to
    obtain the bucket, we get terrible hash collisions - essentially, our
    hash table degenerates to a linked list for fewer than 1024 elements.

    This CL always shifts the hash code so that the value in the lowest
    21 bits is uniformly distributed.

    This results in big improvements on medium to large hash tables.
    A program storing 1M elements into a WeakMap gets roughly
    17x faster.  A program retrieving 1M elements from a Map
    improves even more dramatically (>100x).

    const a = [];
    for (let i = 0; i < 1e6; i++) a[i] = {};

    const m = new Map();
    console.time("Map.set");
    for (let i = 0; i < 1e6; i++) {
      m.set(a[i], i);
    }
    console.timeEnd("Map.set");

    console.time("Map.get");
    let s = 0;
    for (let i = 0; i < 1e6; i++) {
      s += m.get(a[i]);
    }
    console.timeEnd("Map.get");

    const w = new WeakMap();
    console.time("WeakMap.set");
    for (let i = 0; i < 1e6; i++) {
      w.set(a[i], i);
    }
    console.timeEnd("WeakMap.set");

    Before the fix:

    Map.set: 157.575000
    Map.get: 28333.182000
    WeakMap.set: 6923.826000

    After the fix:

    Map.set: 178.382000
    Map.get: 185.930000
    WeakMap.set: 409.529000

    Note that Map does not suffer from the hash collision on insertion because
    it uses chaining (insertion into linked list is fast regardless of size!), and
    we cleverly avoid lookup in the hash table on update if the key does not have
    identity hash yet. This is in contrast to the WeakMap, which uses
    open-addressing, and deals with collisions on insertion.

    Bug: v8:6916
    Change-Id: Ic5497bd4501e3b767b3f4acb7efb4784cbb3a2e4
    Reviewed-on: https://chromium-review.googlesource.com/713616
    Reviewed-by: Benedikt Meurer <[email protected]>
    Commit-Queue: Benedikt Meurer <[email protected]>
    Cr-Commit-Position: refs/heads/master@{#48480}

PR-URL: #19824
Refs: v8/v8@a803fad
Fixes: #19769
Reviewed-By: Yang Guo <[email protected]>
Reviewed-By: Gibson Fahnestock <[email protected]>

Author: targos

deps/v8/include/v8-version.h

@@ -11,7 +11,7 @@
 #define V8_MAJOR_VERSION 6
 #define V8_MINOR_VERSION 2
 #define V8_BUILD_NUMBER 414
-#define V8_PATCH_LEVEL 52
+#define V8_PATCH_LEVEL 53
 
 // Use 1 for candidates and 0 otherwise.
 // (Boolean macro values are not supported by all preprocessors.)

deps/v8/src/code-stub-assembler.cc

@@ -1187,8 +1187,8 @@ TNode<Int32T> CodeStubAssembler::LoadHashForJSObject(
   {
     Node* length_and_hash_int32 = LoadAndUntagToWord32ObjectField(
         properties_or_hash, PropertyArray::kLengthAndHashOffset);
-    var_hash.Bind(Word32And(length_and_hash_int32,
-                            Int32Constant(PropertyArray::kHashMask)));
+    var_hash.Bind(
+        DecodeWord32<PropertyArray::HashField>(length_and_hash_int32));
     Goto(&done);
   }
 
@@ -2508,7 +2508,8 @@ void CodeStubAssembler::InitializePropertyArrayLength(Node* property_array,
   CSA_ASSERT(
       this,
       IntPtrOrSmiLessThanOrEqual(
-          length, IntPtrOrSmiConstant(PropertyArray::kMaxLength, mode), mode));
+          length, IntPtrOrSmiConstant(PropertyArray::LengthField::kMax, mode),
+          mode));
   StoreObjectFieldNoWriteBarrier(
       property_array, PropertyArray::kLengthAndHashOffset,
       ParameterToTagged(length, mode), MachineRepresentation::kTaggedSigned);

deps/v8/src/compiler/js-native-context-specialization.cc

@@ -2255,14 +2255,18 @@ Node* JSNativeContextSpecialization::BuildExtendPropertiesBackingStore(
         jsgraph()->SmiConstant(PropertyArray::kNoHashSentinel));
     hash = graph()->NewNode(common()->TypeGuard(Type::SignedSmall()), hash,
                             control);
+    hash =
+        graph()->NewNode(simplified()->NumberShiftLeft(), hash,
+                         jsgraph()->Constant(PropertyArray::HashField::kShift));
   } else {
     hash = effect = graph()->NewNode(
         simplified()->LoadField(AccessBuilder::ForPropertyArrayLengthAndHash()),
         properties, effect, control);
     effect = graph()->NewNode(
         common()->BeginRegion(RegionObservability::kNotObservable), effect);
-    hash = graph()->NewNode(simplified()->NumberBitwiseAnd(), hash,
-                            jsgraph()->Constant(JSReceiver::kHashMask));
+    hash =
+        graph()->NewNode(simplified()->NumberBitwiseAnd(), hash,
+                         jsgraph()->Constant(PropertyArray::HashField::kMask));
   }
 
   Node* new_length_and_hash = graph()->NewNode(

deps/v8/src/ic/accessor-assembler.cc

@@ -1091,7 +1091,7 @@ void AccessorAssembler::ExtendPropertiesBackingStore(Node* object,
   // TODO(gsathya): Clean up the type conversions by creating smarter
   // helpers that do the correct op based on the mode.
   VARIABLE(var_properties, MachineRepresentation::kTaggedPointer);
-  VARIABLE(var_hash, MachineRepresentation::kWord32);
+  VARIABLE(var_encoded_hash, MachineRepresentation::kWord32);
   VARIABLE(var_length, ParameterRepresentation(mode));
 
   Node* properties = LoadObjectField(object, JSObject::kPropertiesOrHashOffset);
@@ -1102,7 +1102,10 @@ void AccessorAssembler::ExtendPropertiesBackingStore(Node* object,
 
   BIND(&if_smi_hash);
   {
-    var_hash.Bind(SmiToWord32(properties));
+    Node* hash = SmiToWord32(properties);
+    Node* encoded_hash =
+        Word32Shl(hash, Int32Constant(PropertyArray::HashField::kShift));
+    var_encoded_hash.Bind(encoded_hash);
     var_length.Bind(IntPtrOrSmiConstant(0, mode));
     var_properties.Bind(EmptyFixedArrayConstant());
     Goto(&extend_store);
@@ -1112,10 +1115,11 @@ void AccessorAssembler::ExtendPropertiesBackingStore(Node* object,
   {
     Node* length_and_hash_int32 = LoadAndUntagToWord32ObjectField(
         var_properties.value(), PropertyArray::kLengthAndHashOffset);
-    var_hash.Bind(Word32And(length_and_hash_int32,
-                            Int32Constant(PropertyArray::kHashMask)));
-    Node* length_intptr = ChangeInt32ToIntPtr(Word32And(
-        length_and_hash_int32, Int32Constant(PropertyArray::kLengthMask)));
+    var_encoded_hash.Bind(Word32And(
+        length_and_hash_int32, Int32Constant(PropertyArray::HashField::kMask)));
+    Node* length_intptr = ChangeInt32ToIntPtr(
+        Word32And(length_and_hash_int32,
+                  Int32Constant(PropertyArray::LengthField::kMask)));
     Node* length = WordToParameter(length_intptr, mode);
     var_length.Bind(length);
     Goto(&extend_store);
@@ -1161,7 +1165,7 @@ void AccessorAssembler::ExtendPropertiesBackingStore(Node* object,
     Node* new_capacity_int32 =
         TruncateWordToWord32(ParameterToWord(new_capacity, mode));
     Node* new_length_and_hash_int32 =
-        Word32Or(var_hash.value(), new_capacity_int32);
+        Word32Or(var_encoded_hash.value(), new_capacity_int32);
     StoreObjectField(new_properties, PropertyArray::kLengthAndHashOffset,
                      SmiFromWord32(new_length_and_hash_int32));
     StoreObjectField(object, JSObject::kPropertiesOrHashOffset, new_properties);

deps/v8/src/objects-inl.h

@@ -2679,33 +2679,31 @@ SYNCHRONIZED_SMI_ACCESSORS(FixedArrayBase, length, kLengthOffset)
 int PropertyArray::length() const {
   Object* value_obj = READ_FIELD(this, kLengthAndHashOffset);
   int value = Smi::ToInt(value_obj);
-  return value & kLengthMask;
+  return LengthField::decode(value);
 }
 
 void PropertyArray::initialize_length(int len) {
   SLOW_DCHECK(len >= 0);
-  SLOW_DCHECK(len < kMaxLength);
+  SLOW_DCHECK(len < LengthField::kMax);
   WRITE_FIELD(this, kLengthAndHashOffset, Smi::FromInt(len));
 }
 
 int PropertyArray::synchronized_length() const {
   Object* value_obj = ACQUIRE_READ_FIELD(this, kLengthAndHashOffset);
   int value = Smi::ToInt(value_obj);
-  return value & kLengthMask;
+  return LengthField::decode(value);
 }
 
 int PropertyArray::Hash() const {
   Object* value_obj = READ_FIELD(this, kLengthAndHashOffset);
   int value = Smi::ToInt(value_obj);
-  int hash = value & kHashMask;
-  return hash;
+  return HashField::decode(value);
 }
 
-void PropertyArray::SetHash(int masked_hash) {
-  DCHECK_EQ(masked_hash & JSReceiver::kHashMask, masked_hash);
+void PropertyArray::SetHash(int hash) {
   Object* value_obj = READ_FIELD(this, kLengthAndHashOffset);
   int value = Smi::ToInt(value_obj);
-  value = (value & kLengthMask) | masked_hash;
+  value = HashField::update(value, hash);
   WRITE_FIELD(this, kLengthAndHashOffset, Smi::FromInt(value));
 }
 

deps/v8/src/objects.cc

@@ -6269,22 +6269,22 @@ Handle<SeededNumberDictionary> JSObject::NormalizeElements(
 
 namespace {
 
-Object* SetHashAndUpdateProperties(HeapObject* properties, int masked_hash) {
-  DCHECK_NE(PropertyArray::kNoHashSentinel, masked_hash);
-  DCHECK_EQ(masked_hash & JSReceiver::kHashMask, masked_hash);
+Object* SetHashAndUpdateProperties(HeapObject* properties, int hash) {
+  DCHECK_NE(PropertyArray::kNoHashSentinel, hash);
+  DCHECK(PropertyArray::HashField::is_valid(hash));
 
   if (properties == properties->GetHeap()->empty_fixed_array() ||
       properties == properties->GetHeap()->empty_property_dictionary()) {
-    return Smi::FromInt(masked_hash);
+    return Smi::FromInt(hash);
   }
 
   if (properties->IsPropertyArray()) {
-    PropertyArray::cast(properties)->SetHash(masked_hash);
+    PropertyArray::cast(properties)->SetHash(hash);
     return properties;
   }
 
   DCHECK(properties->IsDictionary());
-  NameDictionary::cast(properties)->SetHash(masked_hash);
+  NameDictionary::cast(properties)->SetHash(hash);
   return properties;
 }
 
@@ -6315,14 +6315,14 @@ int GetIdentityHashHelper(Isolate* isolate, JSReceiver* object) {
 }
 }  // namespace
 
-void JSReceiver::SetIdentityHash(int masked_hash) {
+void JSReceiver::SetIdentityHash(int hash) {
   DisallowHeapAllocation no_gc;
-  DCHECK_NE(PropertyArray::kNoHashSentinel, masked_hash);
-  DCHECK_EQ(masked_hash & JSReceiver::kHashMask, masked_hash);
+  DCHECK_NE(PropertyArray::kNoHashSentinel, hash);
+  DCHECK(PropertyArray::HashField::is_valid(hash));
 
   HeapObject* existing_properties = HeapObject::cast(raw_properties_or_hash());
   Object* new_properties =
-      SetHashAndUpdateProperties(existing_properties, masked_hash);
+      SetHashAndUpdateProperties(existing_properties, hash);
   set_raw_properties_or_hash(new_properties);
 }
 
@@ -6377,11 +6377,11 @@ Smi* JSObject::GetOrCreateIdentityHash(Isolate* isolate) {
     return Smi::cast(hash_obj);
   }
 
-  int masked_hash = isolate->GenerateIdentityHash(JSReceiver::kHashMask);
-  DCHECK_NE(PropertyArray::kNoHashSentinel, masked_hash);
+  int hash = isolate->GenerateIdentityHash(PropertyArray::HashField::kMax);
+  DCHECK_NE(PropertyArray::kNoHashSentinel, hash);
 
-  SetIdentityHash(masked_hash);
-  return Smi::FromInt(masked_hash);
+  SetIdentityHash(hash);
+  return Smi::FromInt(hash);
 }
 
 Object* JSProxy::GetIdentityHash() { return hash(); }

deps/v8/src/objects.h

@@ -1953,17 +1953,10 @@ class PropertyArray : public HeapObject {
   // No weak fields.
   typedef BodyDescriptor BodyDescriptorWeak;
 
-  static const int kLengthMask = 0x3ff;
-#if V8_TARGET_ARCH_64_BIT
-  static const int kHashMask = 0x7ffffc00;
-  STATIC_ASSERT(kLengthMask + kHashMask == 0x7fffffff);
-#else
-  static const int kHashMask = 0x3ffffc00;
-  STATIC_ASSERT(kLengthMask + kHashMask == 0x3fffffff);
-#endif
-
-  static const int kMaxLength = kLengthMask;
-  STATIC_ASSERT(kMaxLength > kMaxNumberOfDescriptors);
+  static const int kLengthFieldSize = 10;
+  class LengthField : public BitField<int, 0, kLengthFieldSize> {};
+  class HashField : public BitField<int, kLengthFieldSize,
+                                    kSmiValueSize - kLengthFieldSize - 1> {};
 
   static const int kNoHashSentinel = 0;
 
@@ -2190,7 +2183,7 @@ class JSReceiver: public HeapObject {
   MUST_USE_RESULT static MaybeHandle<FixedArray> GetOwnEntries(
       Handle<JSReceiver> object, PropertyFilter filter);
 
-  static const int kHashMask = PropertyArray::kHashMask;
+  static const int kHashMask = PropertyArray::HashField::kMask;
 
   // Layout description.
   static const int kPropertiesOrHashOffset = HeapObject::kHeaderSize;

deps/v8/src/objects/dictionary.h

@@ -138,14 +138,16 @@ class BaseNameDictionary : public Dictionary<Derived, Shape> {
     return Smi::ToInt(this->get(kNextEnumerationIndexIndex));
   }
 
-  void SetHash(int masked_hash) {
-    DCHECK_EQ(masked_hash & JSReceiver::kHashMask, masked_hash);
-    this->set(kObjectHashIndex, Smi::FromInt(masked_hash));
+  void SetHash(int hash) {
+    DCHECK(PropertyArray::HashField::is_valid(hash));
+    this->set(kObjectHashIndex, Smi::FromInt(hash));
   }
 
   int Hash() const {
     Object* hash_obj = this->get(kObjectHashIndex);
-    return Smi::ToInt(hash_obj);
+    int hash = Smi::ToInt(hash_obj);
+    DCHECK(PropertyArray::HashField::is_valid(hash));
+    return hash;
   }
 
   // Creates a new dictionary.

deps/v8/test/cctest/test-weakmaps.cc

@@ -191,7 +191,7 @@ TEST(Regress2060a) {
       Handle<JSObject> object = factory->NewJSObject(function, TENURED);
       CHECK(!heap->InNewSpace(*object));
       CHECK(!first_page->Contains(object->address()));
-      int32_t hash = object->GetOrCreateHash(isolate)->value();
+      int32_t hash = key->GetOrCreateHash(isolate)->value();
       JSWeakCollection::Set(weakmap, key, object, hash);
     }
   }