[offthread] Use acq/rel for string table read/write

When creating and inserting strings into the string table, we have to
make sure that the writes to the string's fields (including its
characters) are not reordered to after the write of the string into the
table itself.

Thanks TSAN!

Bug: chromium:1011762
Change-Id: Ib8a22e3980f6b5c57561ca23549c1462c4c017c8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2404767
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69838}

src/objects/compressed-slots-inl.h

@@ -164,11 +164,21 @@ Object OffHeapCompressedObjectSlot::Relaxed_Load(const Isolate* isolate) const {
   return Object(DecompressTaggedAny(isolate, value));
 }
 
+Object OffHeapCompressedObjectSlot::Acquire_Load(const Isolate* isolate) const {
+  AtomicTagged_t value = AsAtomicTagged::Acquire_Load(location());
+  return Object(DecompressTaggedAny(isolate, value));
+}
+
 void OffHeapCompressedObjectSlot::Relaxed_Store(Object value) const {
   Tagged_t ptr = CompressTagged(value.ptr());
   AsAtomicTagged::Relaxed_Store(location(), ptr);
 }
 
+void OffHeapCompressedObjectSlot::Release_Store(Object value) const {
+  Tagged_t ptr = CompressTagged(value.ptr());
+  AsAtomicTagged::Release_Store(location(), ptr);
+}
+
 void OffHeapCompressedObjectSlot::Release_CompareAndSwap(Object old,
                                                          Object target) const {
   Tagged_t old_ptr = CompressTagged(old.ptr());

src/objects/compressed-slots.h

@@ -135,7 +135,9 @@ class OffHeapCompressedObjectSlot
   inline void store(Object value) const;
 
   inline Object Relaxed_Load(const Isolate* isolate) const;
+  inline Object Acquire_Load(const Isolate* isolate) const;
   inline void Relaxed_Store(Object value) const;
+  inline void Release_Store(Object value) const;
   inline void Release_CompareAndSwap(Object old, Object target) const;
 };
 

src/objects/slots-inl.h

@@ -39,6 +39,10 @@ Object FullObjectSlot::Acquire_Load() const {
   return Object(base::AsAtomicPointer::Acquire_Load(location()));
 }
 
+Object FullObjectSlot::Acquire_Load(const Isolate* isolate) const {
+  return Acquire_Load();
+}
+
 Object FullObjectSlot::Relaxed_Load() const {
   return Object(base::AsAtomicPointer::Relaxed_Load(location()));
 }

src/objects/slots.h

@@ -114,6 +114,7 @@ class FullObjectSlot : public SlotBase<FullObjectSlot, Address> {
   inline void store(Object value) const;
 
   inline Object Acquire_Load() const;
+  inline Object Acquire_Load(const Isolate* isolate) const;
   inline Object Relaxed_Load() const;
   inline Object Relaxed_Load(const Isolate* isolate) const;
   inline void Relaxed_Store(Object value) const;

src/objects/string-table.cc

@@ -4,6 +4,7 @@
 
 #include "src/objects/string-table.h"
 
+#include "src/base/atomicops.h"
 #include "src/base/macros.h"
 #include "src/common/assert-scope.h"
 #include "src/common/globals.h"
@@ -95,11 +96,11 @@ class StringTable::Data {
   }
 
   Object Get(const Isolate* isolate, InternalIndex index) const {
-    return slot(index).Relaxed_Load(isolate);
+    return slot(index).Acquire_Load(isolate);
   }
 
   void Set(InternalIndex index, String entry) {
-    slot(index).Relaxed_Store(entry);
+    slot(index).Release_Store(entry);
   }
 
   void ElementAdded() {