heap: Fix bug in minor MC heap verification

Minor MC heap verification requires heap iterability. This however was
not directly ensured. Coincidentally, there was an unrelated call to
`Heap::Verify` that ensured `Heap::MakeHeapIterable` had been called,
so the precondition was met. This call was moved to an earlier point
by https://crrev.com/c/3497318 and, because of that, some combination
of flags now results in a crash.

This CL fixes the issue by directly ensuring heap iterability. It also
moves back the call to `Heap::Verify`, so that it takes place inside
the GC safepoint.

Bug: v8:12768
Change-Id: I2c66de0d0a735b84dd9435ff503e78bb3611ce55
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3569224Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Nikolaos Papaspyrou <nikolaos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79844}

src/heap/heap.cc

@@ -2241,17 +2241,17 @@ size_t Heap::PerformGarbageCollection(
     const char* collector_reason, const v8::GCCallbackFlags gc_callback_flags) {
   DisallowJavascriptExecution no_js(isolate());
 
-#ifdef VERIFY_HEAP
-  if (FLAG_verify_heap) {
-    // We don't really perform a GC here but need this scope for the nested
-    // SafepointScope inside Verify().
-    AllowGarbageCollection allow_gc;
-    Verify();
-  }
-#endif  // VERIFY_HEAP
-
   if (IsYoungGenerationCollector(collector)) {
     CompleteSweepingYoung(collector);
+#ifdef VERIFY_HEAP
+    if (FLAG_verify_heap) {
+      // If heap verification is enabled, we want to ensure that sweeping is
+      // completed here, as it will be triggered from Heap::Verify anyway.
+      // In this way, sweeping finalization is accounted to the corresponding
+      // full GC cycle.
+      CompleteSweepingFull();
+    }
+#endif  // VERIFY_HEAP
     tracer()->StartCycle(collector, gc_reason, collector_reason,
                          GCTracer::MarkingType::kAtomic);
   } else {
@@ -2284,6 +2284,15 @@ size_t Heap::PerformGarbageCollection(
 
   collection_barrier_->StopTimeToCollectionTimer();
 
+#ifdef VERIFY_HEAP
+  if (FLAG_verify_heap) {
+    // We don't really perform a GC here but need this scope for the nested
+    // SafepointScope inside Verify().
+    AllowGarbageCollection allow_gc;
+    Verify();
+  }
+#endif  // VERIFY_HEAP
+
   tracer()->StartInSafepoint();
 
   GarbageCollectionPrologueInSafepoint();

src/heap/mark-compact.cc

@@ -395,6 +395,7 @@ class FullEvacuationVerifier : public EvacuationVerifier {
   explicit FullEvacuationVerifier(Heap* heap) : EvacuationVerifier(heap) {}
 
   void Run() override {
+    DCHECK(!heap_->mark_compact_collector()->sweeping_in_progress());
     VerifyRoots();
     VerifyEvacuation(heap_->new_space());
     VerifyEvacuation(heap_->old_space());
@@ -4929,6 +4930,7 @@ class YoungGenerationEvacuationVerifier : public EvacuationVerifier {
       : EvacuationVerifier(heap) {}
 
   void Run() override {
+    DCHECK(!heap_->mark_compact_collector()->sweeping_in_progress());
     VerifyRoots();
     VerifyEvacuation(heap_->new_space());
     VerifyEvacuation(heap_->old_space());