Add fast Smi op version of switchable instance calls.

runtime/vm/flow_graph_compiler_x64.cc

Index: runtime/vm/flow_graph_compiler_x64.cc
diff --git a/runtime/vm/flow_graph_compiler_x64.cc b/runtime/vm/flow_graph_compiler_x64.cc
index 42b3677bc82c3adf48a372fd084373708321f716..05ac0dedb49799bcdeaec328a280a02f7e9a9b5a 100644
--- a/runtime/vm/flow_graph_compiler_x64.cc
+++ b/runtime/vm/flow_graph_compiler_x64.cc
@@ -1325,17 +1325,29 @@ void FlowGraphCompiler::EmitSwitchableInstanceCall(
     __ CallPatchable(*StubCode::ICLookup_entry());
   } else {
     const String& name = String::Handle(zone(), ic_data.target_name());
-    const Array& arguments_descriptor =
-        Array::ZoneHandle(zone(), ic_data.arguments_descriptor());
-    ASSERT(!arguments_descriptor.IsNull() &&
-           (arguments_descriptor.Length() > 0));
-    const MegamorphicCache& cache = MegamorphicCache::ZoneHandle(zone(),
-        MegamorphicCacheTable::Lookup(isolate(), name, arguments_descriptor));
-
-    __ LoadUniqueObject(RBX, cache);
-    __ CallPatchable(*StubCode::MegamorphicLookup_entry());
+
+    if (name.raw() == Symbols::Plus().raw()) {
+      __ LoadUniqueObject(RBX, ic_data);
+      __ CallPatchable(*StubCode::ICSmiAddLookup_entry());
+    } else if (name.raw() == Symbols::Minus().raw()) {
+      __ LoadUniqueObject(RBX, ic_data);
+      __ CallPatchable(*StubCode::ICSmiSubLookup_entry());
+    } else if (name.raw() == Symbols::Equals().raw()) {
+      __ LoadUniqueObject(RBX, ic_data);
+      __ CallPatchable(*StubCode::ICSmiEqualLookup_entry());
+    } else {
+      const Array& arguments_descriptor =
+          Array::ZoneHandle(zone(), ic_data.arguments_descriptor());
+      ASSERT(!arguments_descriptor.IsNull() &&
+             (arguments_descriptor.Length() > 0));
+      const MegamorphicCache& cache = MegamorphicCache::ZoneHandle(zone(),
+          MegamorphicCacheTable::Lookup(isolate(), name, arguments_descriptor));
+
+      __ LoadUniqueObject(RBX, cache);
+      __ CallPatchable(*StubCode::MegamorphicLookup_entry());
+    }
   }
-  __ call(RCX);
+  __ call(RCX);  // A fast Smi operation may return past this call.
 
   AddCurrentDescriptor(RawPcDescriptors::kOther,
                        Thread::kNoDeoptId, token_pos);