VM: Materialize stub pc-markers (smi 0) eagerly on deoptimization.

runtime/vm/deopt_instructions.cc

Index: runtime/vm/deopt_instructions.cc
diff --git a/runtime/vm/deopt_instructions.cc b/runtime/vm/deopt_instructions.cc
index d6e2568a9856fe51b78a38b57cc1319986d4f4ac..2632261a0fb63083396aeadc3cf63592c8aff99e 100644
--- a/runtime/vm/deopt_instructions.cc
+++ b/runtime/vm/deopt_instructions.cc
@@ -651,7 +651,13 @@ class DeoptPcMarkerInstr : public DeoptInstr {
   }
 
   void Execute(DeoptContext* deopt_context, intptr_t* dest_addr) {
-    *dest_addr = Smi::RawValue(0);
+    Function& function = Function::Handle(deopt_context->zone());
+    function ^= deopt_context->ObjectAt(object_table_index_);
+    if (function.IsNull()) {
+      // Callee's PC marker is not used (pc of Deoptimize stub). Set to 0.
+      *dest_addr = Smi::RawValue(0);
+      return;
+    }
     deopt_context->DeferPcMarkerMaterialization(
         object_table_index_, dest_addr);
   }