[runtime] Change backing store of LayoutDescriptor to ByteArray.

BUG=v8:6277

Change-Id: I80314e6c5146e1f5021d07081b9eda3da5da6834
Reviewed-on: https://chromium-review.googlesource.com/518047
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45632}

src/globals.h

@@ -153,6 +153,7 @@ const int kShortSize = sizeof(short);  // NOLINT
 const int kIntSize = sizeof(int);
 const int kInt32Size = sizeof(int32_t);
 const int kInt64Size = sizeof(int64_t);
+const int kUInt32Size = sizeof(uint32_t);
 const int kSizetSize = sizeof(size_t);
 const int kFloatSize = sizeof(float);
 const int kDoubleSize = sizeof(double);

src/layout-descriptor-inl.h

@@ -20,9 +20,11 @@ Handle<LayoutDescriptor> LayoutDescriptor::New(Isolate* isolate, int length) {
     // The whole bit vector fits into a smi.
     return handle(LayoutDescriptor::FromSmi(Smi::kZero), isolate);
   }
-  length = GetSlowModeBackingStoreLength(length);
-  return Handle<LayoutDescriptor>::cast(isolate->factory()->NewFixedTypedArray(
-      length, kExternalUint32Array, true));
+  int backing_store_length = GetSlowModeBackingStoreLength(length);
+  Handle<LayoutDescriptor> result = Handle<LayoutDescriptor>::cast(
+      isolate->factory()->NewByteArray(backing_store_length));
+  memset(result->GetDataStartAddress(), 0, result->DataSize());
+  return result;
 }
 
 
@@ -47,11 +49,11 @@ bool LayoutDescriptor::GetIndexes(int field_index, int* layout_word_index,
     return false;
   }
 
-  *layout_word_index = field_index / kNumberOfBits;
+  *layout_word_index = field_index / kBitsPerLayoutWord;
   CHECK((!IsSmi() && (*layout_word_index < length())) ||
         (IsSmi() && (*layout_word_index < 1)));
 
-  *layout_bit_index = field_index % kNumberOfBits;
+  *layout_bit_index = field_index % kBitsPerLayoutWord;
   return true;
 }
 
@@ -72,13 +74,13 @@ LayoutDescriptor* LayoutDescriptor::SetTagged(int field_index, bool tagged) {
   uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index;
 
   if (IsSlowLayout()) {
-    uint32_t value = get_scalar(layout_word_index);
+    uint32_t value = get_layout_word(layout_word_index);
     if (tagged) {
       value &= ~layout_mask;
     } else {
       value |= layout_mask;
     }
-    set(layout_word_index, value);
+    set_layout_word(layout_word_index, value);
     return this;
   } else {
     uint32_t value = static_cast<uint32_t>(Smi::cast(this)->value());
@@ -105,7 +107,7 @@ bool LayoutDescriptor::IsTagged(int field_index) {
   uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index;
 
   if (IsSlowLayout()) {
-    uint32_t value = get_scalar(layout_word_index);
+    uint32_t value = get_layout_word(layout_word_index);
     return (value & layout_mask) == 0;
   } else {
     uint32_t value = static_cast<uint32_t>(Smi::cast(this)->value());
@@ -128,7 +130,7 @@ bool LayoutDescriptor::IsSlowLayout() { return !IsSmi(); }
 
 
 int LayoutDescriptor::capacity() {
-  return IsSlowLayout() ? (length() * kNumberOfBits) : kSmiValueSize;
+  return IsSlowLayout() ? (length() * kBitsPerByte) : kSmiValueSize;
 }
 
 
@@ -147,20 +149,12 @@ LayoutDescriptor* LayoutDescriptor::cast_gc_safe(Object* object) {
   return LayoutDescriptor::cast(object);
 }
 
-
 int LayoutDescriptor::GetSlowModeBackingStoreLength(int length) {
-  length = (length + kNumberOfBits - 1) / kNumberOfBits;
   DCHECK_LT(0, length);
-
-  if (SmiValuesAre32Bits() && (length & 1)) {
-    // On 64-bit systems if the length is odd then the half-word space would be
-    // lost anyway (due to alignment and the fact that we are allocating
-    // uint32-typed array), so we increase the length of allocated array
-    // to utilize that "lost" space which could also help to avoid layout
-    // descriptor reallocations.
-    ++length;
-  }
-  return length;
+  // We allocate kPointerSize rounded blocks of memory anyway so we increase
+  // the length  of allocated array to utilize that "lost" space which could
+  // also help to avoid layout descriptor reallocations.
+  return RoundUp(length, kBitsPerByte * kPointerSize) / kBitsPerByte;
 }
 
 

src/layout-descriptor.cc

@@ -107,14 +107,15 @@ Handle<LayoutDescriptor> LayoutDescriptor::EnsureCapacity(
   DCHECK(new_layout_descriptor->IsSlowLayout());
 
   if (layout_descriptor->IsSlowLayout()) {
-    memcpy(new_layout_descriptor->DataPtr(), layout_descriptor->DataPtr(),
+    memcpy(new_layout_descriptor->GetDataStartAddress(),
+           layout_descriptor->GetDataStartAddress(),
            layout_descriptor->DataSize());
     return new_layout_descriptor;
   } else {
     // Fast layout.
     uint32_t value =
         static_cast<uint32_t>(Smi::cast(*layout_descriptor)->value());
-    new_layout_descriptor->set(0, value);
+    new_layout_descriptor->set_layout_word(0, value);
     return new_layout_descriptor;
   }
 }
@@ -139,7 +140,7 @@ bool LayoutDescriptor::IsTagged(int field_index, int max_sequence_length,
   uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index;
 
   uint32_t value = IsSlowLayout()
-                       ? get_scalar(layout_word_index)
+                       ? get_layout_word(layout_word_index)
                        : static_cast<uint32_t>(Smi::cast(this)->value());
 
   bool is_tagged = (value & layout_mask) == 0;
@@ -147,21 +148,21 @@ bool LayoutDescriptor::IsTagged(int field_index, int max_sequence_length,
   value = value & ~(layout_mask - 1);  // Clear bits we are not interested in.
   int sequence_length = CountTrailingZeros32(value) - layout_bit_index;
 
-  if (layout_bit_index + sequence_length == kNumberOfBits) {
+  if (layout_bit_index + sequence_length == kBitsPerLayoutWord) {
     // This is a contiguous sequence till the end of current word, proceed
     // counting in the subsequent words.
     if (IsSlowLayout()) {
-      int len = length();
       ++layout_word_index;
-      for (; layout_word_index < len; layout_word_index++) {
-        value = get_scalar(layout_word_index);
+      int num_words = number_of_layout_words();
+      for (; layout_word_index < num_words; layout_word_index++) {
+        value = get_layout_word(layout_word_index);
         bool cur_is_tagged = (value & 1) == 0;
         if (cur_is_tagged != is_tagged) break;
         if (!is_tagged) value = ~value;  // Count set bits instead.
         int cur_sequence_length = CountTrailingZeros32(value);
         sequence_length += cur_sequence_length;
         if (sequence_length >= max_sequence_length) break;
-        if (cur_sequence_length != kNumberOfBits) break;
+        if (cur_sequence_length != kBitsPerLayoutWord) break;
       }
     }
     if (is_tagged && (field_index + sequence_length == capacity())) {
@@ -241,14 +242,15 @@ LayoutDescriptor* LayoutDescriptor::Trim(Heap* heap, Map* map,
   DCHECK_LT(kSmiValueSize, layout_descriptor_length);
 
   // Trim, clean and reinitialize this slow-mode layout descriptor.
-  int array_length = GetSlowModeBackingStoreLength(layout_descriptor_length);
-  int current_length = length();
-  if (current_length != array_length) {
-    DCHECK_LT(array_length, current_length);
-    int delta = current_length - array_length;
+  int new_backing_store_length =
+      GetSlowModeBackingStoreLength(layout_descriptor_length);
+  int backing_store_length = length();
+  if (new_backing_store_length != backing_store_length) {
+    DCHECK_LT(new_backing_store_length, backing_store_length);
+    int delta = backing_store_length - new_backing_store_length;
     heap->RightTrimFixedArray(this, delta);
   }
-  memset(DataPtr(), 0, DataSize());
+  memset(GetDataStartAddress(), 0, DataSize());
   LayoutDescriptor* layout_descriptor =
       Initialize(this, map, descriptors, num_descriptors);
   DCHECK_EQ(this, layout_descriptor);

src/layout-descriptor.h

@@ -21,8 +21,10 @@ namespace internal {
 // Otherwise the field is considered tagged. If the queried bit lays "outside"
 // of the descriptor then the field is also considered tagged.
 // Once a layout descriptor is created it is allowed only to append properties
-// to it.
-class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
+// to it. GC uses layout descriptors to iterate objects. Avoid heap pointers
+// in a layout descriptor because they can lead to data races in GC when
+// GC moves objects in parallel.
+class LayoutDescriptor : public ByteArray {
  public:
   V8_INLINE bool IsTagged(int field_index);
 
@@ -94,7 +96,10 @@ class LayoutDescriptor : public FixedTypedArray<Uint32ArrayTraits> {
   LayoutDescriptor* SetTaggedForTesting(int field_index, bool tagged);
 
  private:
-  static const int kNumberOfBits = 32;
+  static const int kBitsPerLayoutWord = 32;
+  int number_of_layout_words() { return length() / kUInt32Size; }
+  uint32_t get_layout_word(int index) const { return get_uint32(index); }
+  void set_layout_word(int index, uint32_t value) { set_uint32(index, value); }
 
   V8_INLINE static Handle<LayoutDescriptor> New(Isolate* isolate, int length);
   V8_INLINE static LayoutDescriptor* FromSmi(Smi* smi);

src/objects-inl.h

@@ -310,9 +310,7 @@ bool HeapObject::IsArrayList() const { return IsFixedArray(); }
 
 bool HeapObject::IsRegExpMatchInfo() const { return IsFixedArray(); }
 
-bool Object::IsLayoutDescriptor() const {
-  return IsSmi() || IsFixedTypedArrayBase();
-}
+bool Object::IsLayoutDescriptor() const { return IsSmi() || IsByteArray(); }
 
 bool HeapObject::IsFeedbackVector() const {
   return map() == GetHeap()->feedback_vector_map();
@@ -3694,7 +3692,7 @@ void StringCharacterStream::VisitTwoByteString(
 
 int ByteArray::Size() { return RoundUp(length() + kHeaderSize, kPointerSize); }
 
-byte ByteArray::get(int index) {
+byte ByteArray::get(int index) const {
   DCHECK(index >= 0 && index < this->length());
   return READ_BYTE_FIELD(this, kHeaderSize + index * kCharSize);
 }
@@ -3718,7 +3716,7 @@ void ByteArray::copy_out(int index, byte* buffer, int length) {
   memcpy(buffer, src_addr, length);
 }
 
-int ByteArray::get_int(int index) {
+int ByteArray::get_int(int index) const {
   DCHECK(index >= 0 && index < this->length() / kIntSize);
   return READ_INT_FIELD(this, kHeaderSize + index * kIntSize);
 }
@@ -3728,11 +3726,22 @@ void ByteArray::set_int(int index, int value) {
   WRITE_INT_FIELD(this, kHeaderSize + index * kIntSize, value);
 }
 
+uint32_t ByteArray::get_uint32(int index) const {
+  DCHECK(index >= 0 && index < this->length() / kUInt32Size);
+  return READ_UINT32_FIELD(this, kHeaderSize + index * kUInt32Size);
+}
+
+void ByteArray::set_uint32(int index, uint32_t value) {
+  DCHECK(index >= 0 && index < this->length() / kUInt32Size);
+  WRITE_UINT32_FIELD(this, kHeaderSize + index * kUInt32Size, value);
+}
+
 ByteArray* ByteArray::FromDataStartAddress(Address address) {
   DCHECK_TAG_ALIGNED(address);
   return reinterpret_cast<ByteArray*>(address - kHeaderSize + kHeapObjectTag);
 }
 
+int ByteArray::DataSize() const { return RoundUp(length(), kPointerSize); }
 
 int ByteArray::ByteArraySize() { return SizeFor(this->length()); }
 

src/objects-printer.cc

@@ -1526,10 +1526,10 @@ void LayoutDescriptor::Print(std::ostream& os) {  // NOLINT
     os << "<uninitialized>";
   } else {
     os << "slow";
-    int len = length();
-    for (int i = 0; i < len; i++) {
+    int num_words = number_of_layout_words();
+    for (int i = 0; i < num_words; i++) {
       if (i > 0) os << " |";
-      PrintBitMask(os, get_scalar(i));
+      PrintBitMask(os, get_layout_word(i));
     }
   }
   os << "\n";

src/objects.h

@@ -3187,7 +3187,7 @@ class ByteArray: public FixedArrayBase {
   inline int Size();
 
   // Setter and getter.
-  inline byte get(int index);
+  inline byte get(int index) const;
   inline void set(int index, byte value);
 
   // Copy in / copy out whole byte slices.
@@ -3195,9 +3195,12 @@ class ByteArray: public FixedArrayBase {
   inline void copy_in(int index, const byte* buffer, int length);
 
   // Treat contents as an int array.
-  inline int get_int(int index);
+  inline int get_int(int index) const;
   inline void set_int(int index, int value);
 
+  inline uint32_t get_uint32(int index) const;
+  inline void set_uint32(int index, uint32_t value);
+
   static int SizeFor(int length) {
     return OBJECT_POINTER_ALIGN(kHeaderSize + length);
   }
@@ -3214,6 +3217,8 @@ class ByteArray: public FixedArrayBase {
   // Returns data start address.
   inline Address GetDataStartAddress();
 
+  inline int DataSize() const;
+
   // Returns a pointer to the ByteArray object for a given data start address.
   static inline ByteArray* FromDataStartAddress(Address address);
 

test/cctest/test-unboxed-doubles.cc

@@ -602,7 +602,7 @@ TEST(LayoutDescriptorCreateNewSlow) {
     LayoutDescriptor* layout_desc = *layout_descriptor;
     CHECK_EQ(layout_desc, LayoutDescriptor::cast(layout_desc));
     CHECK_EQ(layout_desc, LayoutDescriptor::cast_gc_safe(layout_desc));
-    CHECK(layout_descriptor->IsFixedTypedArrayBase());
+    CHECK(layout_desc->IsSlowLayout());
     // Now make it look like a forwarding pointer to layout_descriptor_copy.
     MapWord map_word = layout_desc->map_word();
     CHECK(!map_word.IsForwardingAddress());
@@ -982,7 +982,7 @@ TEST(DescriptorArrayTrimming) {
   CHECK(map->layout_descriptor()->IsConsistentWithMap(*map, true));
   CHECK(map->layout_descriptor()->IsSlowLayout());
   CHECK(map->owns_descriptors());
-  CHECK_EQ(2, map->layout_descriptor()->length());
+  CHECK_EQ(8, map->layout_descriptor()->length());
 
   {
     // Add transitions to double fields.
@@ -1002,7 +1002,7 @@ TEST(DescriptorArrayTrimming) {
     CHECK_EQ(map->layout_descriptor(), tmp_map->layout_descriptor());
   }
   CHECK(map->layout_descriptor()->IsSlowLayout());
-  CHECK_EQ(4, map->layout_descriptor()->length());
+  CHECK_EQ(16, map->layout_descriptor()->length());
 
   // The unused tail of the layout descriptor is now "durty" because of sharing.
   CHECK(map->layout_descriptor()->IsConsistentWithMap(*map));
@@ -1022,7 +1022,7 @@ TEST(DescriptorArrayTrimming) {
   CHECK_EQ(map->NumberOfOwnDescriptors(),
            map->instance_descriptors()->number_of_descriptors());
   CHECK(map->layout_descriptor()->IsSlowLayout());
-  CHECK_EQ(2, map->layout_descriptor()->length());
+  CHECK_EQ(8, map->layout_descriptor()->length());
 
   {
     // Add transitions to tagged fields.