Add fast Smi op version of switchable instance calls.

runtime/vm/code_generator.cc

Index: runtime/vm/code_generator.cc
diff --git a/runtime/vm/code_generator.cc b/runtime/vm/code_generator.cc
index 9b3eb295c83059e52210650f7fca07def7f3d33b..54613cdff366a07a4ba6eaf6ce838260fed31f05 100644
--- a/runtime/vm/code_generator.cc
+++ b/runtime/vm/code_generator.cc
@@ -1049,7 +1049,17 @@ DEFINE_RUNTIME_ENTRY(MegamorphicCacheMissHandler, 3) {
 
   if (ic_data_or_cache.IsICData()) {
     const ICData& ic_data = ICData::Cast(ic_data_or_cache);
-    ic_data.AddReceiverCheck(receiver.GetClassId(), target_function);
+
+    if (ic_data.NumArgsTested() == 1) {
+      ic_data.AddReceiverCheck(receiver.GetClassId(), target_function);
+    } else {
+      ASSERT(ic_data.NumArgsTested() == 2);
+      GrowableArray<intptr_t> class_ids(2);
+      class_ids.Add(receiver.GetClassId());
+      class_ids.Add(kDynamicCid);  // No one will read this.
+      ic_data.AddCheck(class_ids, target_function);
+    }
+
     if (ic_data.NumberOfChecks() > FLAG_max_polymorphic_checks) {
       // Switch to megamorphic call.
       const MegamorphicCache& cache = MegamorphicCache::Handle(zone,