[runtime] Read and write layout descriptor words with atomics

This fixes benign data races reported by TSAN when a shared layout
descriptor is updated at the end.

Change-Id: I76662cb5fc2b8ab1728e3d1bf42a55a107442eed
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1709422Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62863}

src/objects/fixed-array-inl.h

@@ -560,6 +560,16 @@ void ByteArray::set_uint32(int index, uint32_t value) {
   WriteField<uint32_t>(kHeaderSize + index * kUInt32Size, value);
 }
 
+uint32_t ByteArray::get_uint32_relaxed(int index) const {
+  DCHECK(index >= 0 && index < this->length() / kUInt32Size);
+  return RELAXED_READ_UINT32_FIELD(*this, kHeaderSize + index * kUInt32Size);
+}
+
+void ByteArray::set_uint32_relaxed(int index, uint32_t value) {
+  DCHECK(index >= 0 && index < this->length() / kUInt32Size);
+  RELAXED_WRITE_UINT32_FIELD(*this, kHeaderSize + index * kUInt32Size, value);
+}
+
 void ByteArray::clear_padding() {
   int data_size = length() + kHeaderSize;
   memset(reinterpret_cast<void*>(address() + data_size), 0, Size() - data_size);

src/objects/fixed-array.h

@@ -488,6 +488,9 @@ class ByteArray : public FixedArrayBase {
   inline uint32_t get_uint32(int index) const;
   inline void set_uint32(int index, uint32_t value);
 
+  inline uint32_t get_uint32_relaxed(int index) const;
+  inline void set_uint32_relaxed(int index, uint32_t value);
+
   // Clear uninitialized padding space. This ensures that the snapshot content
   // is deterministic.
   inline void clear_padding();

src/objects/layout-descriptor-inl.h

@@ -209,11 +209,11 @@ int LayoutDescriptor::number_of_layout_words() {
 }
 
 uint32_t LayoutDescriptor::get_layout_word(int index) const {
-  return get_uint32(index);
+  return get_uint32_relaxed(index);
 }
 
 void LayoutDescriptor::set_layout_word(int index, uint32_t value) {
-  set_uint32(index, value);
+  set_uint32_relaxed(index, value);
 }
 
 // LayoutDescriptorHelper is a helper class for querying whether inobject