Old space cannot be assumed to be iterable between GCs, even if swept precisely.

src/heap/mark-compact.cc

Index: src/heap/mark-compact.cc
diff --git a/src/heap/mark-compact.cc b/src/heap/mark-compact.cc
index 4a11d3b082273cb5c2bfae0ed112e85315797825..abb4e1beb8e7e51936657e70d14dec33649a7faf 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2009,16 +2009,11 @@ int MarkCompactCollector::DiscoverAndEvacuateBlackObjectsOnPage(
 
 static void DiscoverGreyObjectsInSpace(Heap* heap, MarkingDeque* marking_deque,
                                        PagedSpace* space) {
-  if (space->swept_precisely()) {
-    HeapObjectIterator it(space);
-    DiscoverGreyObjectsWithIterator(heap, marking_deque, &it);
-  } else {
-    PageIterator it(space);
-    while (it.has_next()) {
-      Page* p = it.next();
-      DiscoverGreyObjectsOnPage(marking_deque, p);
-      if (marking_deque->IsFull()) return;
-    }
+  PageIterator it(space);
+  while (it.has_next()) {
+    Page* p = it.next();
+    DiscoverGreyObjectsOnPage(marking_deque, p);
+    if (marking_deque->IsFull()) return;
   }
 }