Revert "[heap] Allow shared references in WeakMap"

This reverts commit a1838956.

Reason for revert: https://bugs.chromium.org/p/v8/issues/detail?id=12642

Original change's description:
> [heap] Allow shared references in WeakMap
>
> Shared references can also be stored in WeakMaps and during marking we
> need to be able to deal with such references. In a client GC shared
> objects are treated as live, so we don't need to update or check mark
> bits for such objects.
>
> Bug: v8:11708
> Change-Id: I0dbf797472c4779f462750dab63cc9b012aad091
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3447365
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#79153}

Bug: v8:11708
Change-Id: I113672aceba0ef5aa71f6fbedda7e0df854a437d
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3474673
Auto-Submit: Nico Hartmann <nicohartmann@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Owners-Override: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79168}

src/heap/mark-compact.cc

@@ -2912,16 +2912,12 @@ void MarkCompactCollector::ClearWeakCollections() {
       if (FLAG_verify_heap) {
         Object value = table.ValueAt(i);
         if (value.IsHeapObject()) {
-          HeapObject heap_object = HeapObject::cast(value);
-          CHECK_IMPLIES(
-              (!is_shared_heap_ && key.InSharedHeap()) ||
-                  non_atomic_marking_state()->IsBlackOrGrey(key),
-              (!is_shared_heap_ && heap_object.InSharedHeap()) ||
-                  non_atomic_marking_state()->IsBlackOrGrey(heap_object));
+          CHECK_IMPLIES(non_atomic_marking_state()->IsBlackOrGrey(key),
+                        non_atomic_marking_state()->IsBlackOrGrey(
+                            HeapObject::cast(value)));
         }
       }
 #endif
-      if (!is_shared_heap_ && key.InSharedHeap()) continue;
       if (!non_atomic_marking_state()->IsBlackOrGrey(key)) {
         table.RemoveEntry(i);
       }

src/heap/marking-visitor-inl.h

@@ -355,8 +355,7 @@ int MarkingVisitorBase<ConcreteVisitor, MarkingState>::VisitEphemeronHashTable(
     ObjectSlot value_slot =
         table.RawFieldOfElementAt(EphemeronHashTable::EntryToValueIndex(i));
 
-    if ((!is_shared_heap_ && key.InSharedHeap()) ||
-        concrete_visitor()->marking_state()->IsBlackOrGrey(key)) {
+    if (concrete_visitor()->marking_state()->IsBlackOrGrey(key)) {
       VisitPointer(table, value_slot);
     } else {
       Object value_obj = table.ValueAt(i);
@@ -367,8 +366,6 @@ int MarkingVisitorBase<ConcreteVisitor, MarkingState>::VisitEphemeronHashTable(
         concrete_visitor()->RecordSlot(table, value_slot, value);
         AddWeakReferenceForReferenceSummarizer(table, value);
 
-        if (!is_shared_heap_ && value.InSharedHeap()) continue;
-
         // Revisit ephemerons with both key and value unreachable at end
         // of concurrent marking cycle.
         if (concrete_visitor()->marking_state()->IsWhite(value)) {

test/mjsunit/shared-memory/shared-string-in-weak-map.js

-// Copyright 2022 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.
-//
-// Flags: --shared-string-table --allow-natives-syntax --stress-compaction --expose-gc
-
-const val1 = "some value";
-assertTrue(%IsSharedString(val1));
-
-const wm = new WeakMap();
-const key1 = {};
-
-wm.set(key1, val1);
-assertTrue(wm.get(key1) == val1);
-assertTrue(%IsSharedString(wm.get(key1)));
-
-gc();
-assertTrue(wm.get(key1) == val1);
-assertTrue(%IsSharedString(wm.get(key1)));
-
-%SharedGC();
-assertTrue(wm.get(key1) == val1);
-assertTrue(%IsSharedString(wm.get(key1)));