Collect type feedback for fields.

runtime/vm/flow_graph.h

Index: runtime/vm/flow_graph.h
diff --git a/runtime/vm/flow_graph.h b/runtime/vm/flow_graph.h
index 14c298a9ec22526962a85d3d5ab82c932d283998..d09efa0db65caf9cc0ee2f726a4c433ffb348c39 100644
--- a/runtime/vm/flow_graph.h
+++ b/runtime/vm/flow_graph.h
@@ -141,6 +141,11 @@ class FlowGraph : public ZoneAllocated {
   bool VerifyUseLists();
 #endif  // DEBUG
 
+  // Return all instance fields that are loaded in the graph and
+  // have non-generic type feedback attached to them that can
+  // potentially affect optimizations.
+  const ZoneGrowableArray<Field*>& FieldDependencies() const;

[Ivan Posva, 2013/03/19 04:42:05]

Please do not return references as this makes the other side hard to read as
well, such as this:
guarded_fields = &flow_graph->FieldDependencies();

By returning a "const ZoneGrowableArray<Field*>*" you avoid that, no?

[Vyacheslav Egorov (Google), 2013/03/19 06:58:59]

I actually agree that it makes caller harder to read. I was returning a pointer
but Srdjan suggested to return reference here to indicate that it is not NULL. 

I am fine returning either as there is a single call-site.

Should I switch back to the pointer?

[srdjan, 2013/03/19 14:35:19]

I see advantages of both ways. You pick.

+
  private:
   friend class BranchSimplifier;
   friend class ConstantPropagator;