Revert parts of r45502 and always generate guard field instructions.

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
===================================================================
--- runtime/vm/flow_graph_builder.cc	(revision 45502)
+++ runtime/vm/flow_graph_builder.cc	(working copy)
@@ -3504,30 +3504,19 @@
   }
 
   if (FLAG_use_field_guards) {
-    if (node->field().guarded_cid() != kDynamicCid) {
-      store_value = Bind(BuildStoreExprTemp(store_value));
-      GuardFieldClassInstr* guard_field_class =
-          new(Z) GuardFieldClassInstr(store_value,
-                                   node->field(),
-                                   isolate()->GetNextDeoptId());
-      AddInstruction(guard_field_class);
-      store_value = Bind(BuildLoadExprTemp());
-      if (node->field().guarded_list_length() != Field::kNoFixedLength) {
-        GuardFieldLengthInstr* guard_field_length =
-            new(Z) GuardFieldLengthInstr(store_value,
-                                         node->field(),
-                                         isolate()->GetNextDeoptId());
-        AddInstruction(guard_field_length);
-        store_value = Bind(BuildLoadExprTemp());
-      } else {
-        // Advance deopt-id counter to remain in sync.
-        isolate()->GetNextDeoptId();
-      }
-    } else {
-      // Advance deopt-id counter to remain in sync.
-      isolate()->GetNextDeoptId();
-      isolate()->GetNextDeoptId();
-    }
+    store_value = Bind(BuildStoreExprTemp(store_value));
+    GuardFieldClassInstr* guard_field_class =
+        new(Z) GuardFieldClassInstr(store_value,
+                                 node->field(),
+                                 isolate()->GetNextDeoptId());
+    AddInstruction(guard_field_class);
+    store_value = Bind(BuildLoadExprTemp());
+    GuardFieldLengthInstr* guard_field_length =
+        new(Z) GuardFieldLengthInstr(store_value,
+                                     node->field(),
+                                     isolate()->GetNextDeoptId());
+    AddInstruction(guard_field_length);
+    store_value = Bind(BuildLoadExprTemp());
   }
   StoreInstanceFieldInstr* store =
       new(Z) StoreInstanceFieldInstr(node->field(),