Recognize and optimize a.runtimeType == b.runtimeType pattern.

runtime/lib/object_patch.dart

Index: runtime/lib/object_patch.dart
diff --git a/runtime/lib/object_patch.dart b/runtime/lib/object_patch.dart
index 0af593d779c0157e881701fd796d5ff13caf6635..4fb4db5a8996abf2484f25611f9600a14b5e3daa 100644
--- a/runtime/lib/object_patch.dart
+++ b/runtime/lib/object_patch.dart
@@ -53,6 +53,8 @@
 
   @patch Type get runtimeType native "Object_runtimeType";

[siva, 2016/09/29 02:28:20]

One could recover some of the lost effectiveness of the over rides by changing
this to have some dart code for those cases? Something like

Type get _runtimeType native "Object_runtimeType";
@patch Type get runtimeType {
  int cid = ClassId.getId(this);
  if (cid == ClassID.double) return double;
  else if (cid == ClassID.smi || cid .....) return int;
  else if (cid == ClassId.oneByteString....) return String;
  else return _runtimeType;
}

[Vyacheslav Egorov (Google), 2016/09/29 15:01:43]

This is precisely what intrinsic is doing. 

However even with intrinsic effectiveness was in monomorphic JIT case - which I
origianlly considered unimportant (it's unlikely that x.runtimeType call site is
monomorphic).

To match previous behavior and performance I added support for polymorphic
inlining of Object.get:runtimeType.

Now performance of monomorphic/polymorphic cases are on par or better in both
AOT and JIT case. 

[Florian Schneider, 2016/09/29 18:03:28]

I think Siva's suggestion would simplify the hand-written assembly with being
acceptable fast at the same time.

[Vyacheslav Egorov (Google), 2016/09/30 09:56:27]

I did measurements: it's 30-50% slower than the intrinsic on x64. If we consider
such hit acceptable - then we can certainly move to this instead of the
intrinsic. 

But I think 50% faster code is better.

[Florian Schneider, 2016/09/30 17:42:56]

Sounds good!

 
+  static bool _haveSameRuntimeType(a, b) native "Object_haveSameRuntimeType";
+
   // Call this function instead of inlining instanceof, thus collecting
   // type feedback and reducing code size of unoptimized code.
   bool _instanceOf(instantiator_type_arguments, type, bool negate)