Type and constant propagator should guard against mutable class ids.

runtime/vm/flow_graph_type_propagator.cc

Index: runtime/vm/flow_graph_type_propagator.cc
diff --git a/runtime/vm/flow_graph_type_propagator.cc b/runtime/vm/flow_graph_type_propagator.cc
index 2b7001f656104549b25930aefbf2c9124cc4f30f..9d0829d0dd7416f9d6127b9c42db5007940d3549 100644
--- a/runtime/vm/flow_graph_type_propagator.cc
+++ b/runtime/vm/flow_graph_type_propagator.cc
@@ -318,7 +318,9 @@ void FlowGraphTypePropagator::VisitCheckClassId(CheckClassIdInstr* check) {
 void FlowGraphTypePropagator::VisitGuardFieldClass(
     GuardFieldClassInstr* guard) {
   const intptr_t cid = guard->field().guarded_cid();
-  if ((cid == kIllegalCid) || (cid == kDynamicCid)) {
+  if ((cid == kIllegalCid) ||
+      (cid == kDynamicCid) ||
+      !CheckClassInstr::IsImmutableClassId(cid)) {
     return;
   }
 
@@ -794,13 +796,17 @@ CompileType ConstantInstr::ComputeType() const {
     return CompileType::Null();
   }
 
+  intptr_t cid = value().GetClassId();
+  if (!CheckClassInstr::IsImmutableClassId(cid)) {
+    cid = kDynamicCid;
+  }
+
   if (value().IsInstance()) {
-    return CompileType::Create(
-        value().GetClassId(),
+    return CompileType::Create(cid,
         AbstractType::ZoneHandle(Instance::Cast(value()).GetType()));
   } else {
     // Type info for non-instance objects.
-    return CompileType::FromCid(value().GetClassId());
+    return CompileType::FromCid(cid);
   }
 }