Precise sweeping makes zapping of garbage memory in UpdatePointer obsolete.

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 87def09f684d0552e164f2ff4296e75c7292d0cb..bc1ab2d93f194fde4686cb6783ed137b000166a3 100644
--- a/src/heap/mark-compact.cc
+++ b/src/heap/mark-compact.cc
@@ -2945,16 +2945,6 @@ static void UpdatePointer(HeapObject** address, HeapObject* object) {
         reinterpret_cast<base::AtomicWord*>(address),
         reinterpret_cast<base::AtomicWord>(object),
         reinterpret_cast<base::AtomicWord>(HeapObject::FromAddress(new_addr)));
-  } else {
-    // We have to zap this pointer, because the store buffer may overflow later,
-    // and then we have to scan the entire heap and we don't want to find
-    // spurious newspace pointers in the old space.
-    // TODO(mstarzinger): This was changed to a sentinel value to track down
-    // rare crashes, change it back to Smi::FromInt(0) later.
-    base::NoBarrier_CompareAndSwap(
-        reinterpret_cast<base::AtomicWord*>(address),
-        reinterpret_cast<base::AtomicWord>(object),
-        reinterpret_cast<base::AtomicWord>(Smi::FromInt(0x0f100d00 >> 1)));
   }
 }