Sped up hashCode by removing megamorphic call to _identityHashCode.

runtime/lib/object.cc

Index: runtime/lib/object.cc
diff --git a/runtime/lib/object.cc b/runtime/lib/object.cc
index b450038b0f5a832117a6b8c458eee5da46f28e3d..ac1e1725e4ea6cff86e964fd0d9e485058bdf70b 100644
--- a/runtime/lib/object.cc
+++ b/runtime/lib/object.cc
@@ -39,9 +39,11 @@ DEFINE_NATIVE_ENTRY(Object_equals, 1) {
 
 
 DEFINE_NATIVE_ENTRY(Object_getHash, 1) {
-  const Instance& instance = Instance::CheckedHandle(arguments->NativeArgAt(0));
+  // Please note that no handle is created for the argument.
+  // This is safe since the argument is only used in a tail call.
+  // The performance benefit is more than 5% when using hashCode.

[siva, 2016/07/08 22:12:10]

Maybe add:

ASSERT(arguments->NativeArgAt(0)->IsDartInstance());

[bakster, 2016/07/08 22:15:11]

Done.

   Heap* heap = isolate->heap();
-  return Smi::New(heap->GetHash(instance.raw()));
+  return Smi::New(heap->GetHash(arguments->NativeArgAt(0)));
 }