Use shorter write-barrier filtering sequence when value is known to be non-smi.

runtime/vm/intermediate_language.h

Index: runtime/vm/intermediate_language.h
diff --git a/runtime/vm/intermediate_language.h b/runtime/vm/intermediate_language.h
index 6105fc3538f7ee06f73c73edc74f7ab6154a9978..d11cc8461ada366a4559fd6181ab33d7c0248756 100644
--- a/runtime/vm/intermediate_language.h
+++ b/runtime/vm/intermediate_language.h
@@ -2837,6 +2837,13 @@ class StoreInstanceFieldInstr : public TemplateDefinition<2> {
   virtual bool HasSideEffect() const { return true; }
 
  private:
+  bool CanValueBeSmi() const {
+    const intptr_t cid = value()->Type()->ToNullableCid();
+    // Write barrier is skipped for nullable and non-nullable smis.
+    ASSERT(cid != kSmiCid);
+    return (cid == kDynamicCid);
+  }
+
   const Field& field_;
   const StoreBarrierType emit_store_barrier_;