cppgc: Don't verify stack if PC is enabled.

V8 compaction, which currently runs before verification, can update
stack slots, which could lead to more false positives when we scan
compressed pointers on stack. The CL disables the stack verification if
pointer compression. The intent is to investigate if verification can be
moved before compaction.

Bug: chromium:1325007
Change-Id: Idc01df9c58bfbf338b5e95caf5f03a88593c6478
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3789381
Auto-Submit: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81997}

src/heap/cppgc/marking-verifier.cc

@@ -54,7 +54,13 @@ void MarkingVerifierBase::Run(
 // marking. This means that the conservative iteration below may find more
 // objects then the regular marker. The difference is benign as the delta of
 // objects is not reachable from user code but it prevents verification.
-#if !defined(THREAD_SANITIZER)
+// We also avoid verifying the stack when pointer compression is enabled.
+// Currently, verification happens after compaction, V8 compaction can change
+// slots on stack, which could lead to false positives in verifier. Those are
+// more likely with checking compressed pointers on stack.
+// TODO(chromium:1325007): Investigate if Oilpan verification can be moved
+// before V8 compaction or compaction never runs with stack.
+#if !defined(THREAD_SANITIZER) && !defined(CPPGC_POINTER_COMPRESSION)
   if (stack_state == Heap::Config::StackState::kMayContainHeapPointers) {
     in_construction_objects_ = &in_construction_objects_stack_;
     heap_.stack()->IteratePointersUnsafe(this, stack_end);