Prefill allocated objects with one word fillers if we do not use allocation folding.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 41f9d0d5ccdecae37ed1cf08206f09136a6f8476..721c5cdda9f477efcd76e89d6a093f88e269620e 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5120,8 +5120,15 @@ class HAllocate: public HTemplateInstruction<2> {
             ? ALLOCATE_IN_OLD_POINTER_SPACE : ALLOCATE_IN_OLD_DATA_SPACE)
         : ALLOCATE_IN_NEW_SPACE;
     if (instance_type == FIXED_DOUBLE_ARRAY_TYPE) {
-      flags_ = static_cast<HAllocate::Flags>(flags_ |
-          ALLOCATE_DOUBLE_ALIGNED);
+      flags_ = static_cast<HAllocate::Flags>(flags_ | ALLOCATE_DOUBLE_ALIGNED);
+    }
+    // We have to fill the allocated object with one word fillers if we do
+    // not use allocation folding since some allocations may depend on each
+    // other, i.e., have a pointer to each other. A GC in between these
+    // allocations may leave such objects behind in a not completely initialized
+    // state.
+    if (!FLAG_use_gvn || !FLAG_use_allocation_folding) {
+      flags_ = static_cast<HAllocate::Flags>(flags_ | PREFILL_WITH_FILLER);
     }
   }