[handles] Simplify global handle state machine

Remove PENDING state as handles were always immediately transitioned
into FREE or NEAR_DEATH state.

Bug: v8:12672
Change-Id: I9a9d40b573e862282d41d7a4a3f9c8c8ed21b9e4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3599473Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80119}

include/v8-internal.h

@@ -406,7 +406,6 @@ class Internals {
   static const int kNodeFlagsOffset = 1 * kApiSystemPointerSize + 3;
   static const int kNodeStateMask = 0x7;
   static const int kNodeStateIsWeakValue = 2;
-  static const int kNodeStateIsPendingValue = 3;
 
   static const int kFirstNonstringType = 0x80;
   static const int kOddballType = 0x83;

src/handles/global-handles.h

@@ -143,14 +143,18 @@ class V8_EXPORT_PRIVATE GlobalHandles final {
   // Iterates over strong and dependent handles. See the note above.
   void IterateYoungStrongAndDependentRoots(RootVisitor* v);
 
-  // Iterates over weak independent or unmodified handles.
-  // See the note above.
-  void IterateYoungWeakObjectsForPhantomHandles(
-      RootVisitor* v, WeakSlotCallbackWithHeap should_reset_handle);
-
-  // Identify unmodified objects that are in weak state and marks them
-  // unmodified
-  void IdentifyWeakUnmodifiedObjects(WeakSlotCallback is_unmodified);
+  // Processes all young weak objects. Weak objects for which
+  // `should_reset_handle()` returns true are reset and others are passed to the
+  // visitor `v`.
+  void ProcessWeakYoungObjects(RootVisitor* v,
+                               WeakSlotCallbackWithHeap should_reset_handle);
+
+  // Computes whether young weak objects should be considered roots for young
+  // generation garbage collections  or just be treated weakly. Per default
+  // objects are considered as roots. Objects are treated not as root when both
+  // - `is_unmodified()` returns true;
+  // - the `EmbedderRootsHandler` also does not consider them as roots;
+  void ComputeWeaknessForYoungObjects(WeakSlotCallback is_unmodified);
 
   Isolate* isolate() const { return isolate_; }
 
@@ -205,6 +209,13 @@ class V8_EXPORT_PRIVATE GlobalHandles final {
   void ApplyPersistentHandleVisitor(v8::PersistentHandleVisitor* visitor,
                                     Node* node);
 
+  // Clears a weak `node` for which `should_reset_node()` returns true.
+  //
+  // Returns false if a node is weak and alive which requires further
+  // processing, and true in all other cases (e.g. also strong nodes).
+  bool ResetWeakNodeIfDead(Node* node,
+                           WeakSlotCallbackWithHeap should_reset_node);
+
   Isolate* const isolate_;
   bool is_marking_ = false;
 

src/heap/mark-compact.cc

@@ -5805,7 +5805,7 @@ void MinorMarkCompactCollector::MarkRootSetInParallel(
     // Seed the root set (roots + old->new set).
     {
       TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK_SEED);
-      isolate()->global_handles()->IdentifyWeakUnmodifiedObjects(
+      isolate()->global_handles()->ComputeWeaknessForYoungObjects(
           &JSObject::IsUnmodifiedApiObject);
       // MinorMC treats all weak roots except for global handles as strong.
       // That is why we don't set skip_weak = true here and instead visit
@@ -5859,7 +5859,7 @@ void MinorMarkCompactCollector::MarkLiveObjects() {
 
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK_GLOBAL_HANDLES);
-    isolate()->global_handles()->IterateYoungWeakObjectsForPhantomHandles(
+    isolate()->global_handles()->ProcessWeakYoungObjects(
         &root_visitor, &IsUnmarkedObjectForYoungGeneration);
     DrainMarkingWorklist();
   }

src/heap/scavenger.cc

@@ -322,7 +322,7 @@ void ScavengerCollector::CollectGarbage() {
       TRACE_GC(
           heap_->tracer(),
           GCTracer::Scope::SCAVENGER_SCAVENGE_WEAK_GLOBAL_HANDLES_IDENTIFY);
-      isolate_->global_handles()->IdentifyWeakUnmodifiedObjects(
+      isolate_->global_handles()->ComputeWeaknessForYoungObjects(
           &JSObject::IsUnmodifiedApiObject);
     }
     {
@@ -366,7 +366,7 @@ void ScavengerCollector::CollectGarbage() {
       // Scavenge weak global handles.
       TRACE_GC(heap_->tracer(),
                GCTracer::Scope::SCAVENGER_SCAVENGE_WEAK_GLOBAL_HANDLES_PROCESS);
-      isolate_->global_handles()->IterateYoungWeakObjectsForPhantomHandles(
+      isolate_->global_handles()->ProcessWeakYoungObjects(
           &root_scavenge_visitor, &IsUnscavengedHeapObjectSlot);
       DCHECK(copied_list.IsEmpty());
       DCHECK(promotion_list.IsEmpty());