VM: Correctly intrinsify implicit getters/setters when using field guards

runtime/vm/flow_graph_compiler.cc

Index: runtime/vm/flow_graph_compiler.cc
diff --git a/runtime/vm/flow_graph_compiler.cc b/runtime/vm/flow_graph_compiler.cc
index 34a6eec06d2cb94f5c953db25157e55609ee4048..ef109ac8a8f4243658a862594c9ef8d017f26950 100644
--- a/runtime/vm/flow_graph_compiler.cc
+++ b/runtime/vm/flow_graph_compiler.cc
@@ -1096,7 +1096,7 @@ bool FlowGraphCompiler::TryIntrinsify() {
       // Reading from a mutable double box requires allocating a fresh double.
       if (load_node.field().guarded_cid() == kDynamicCid) {
         GenerateInlinedGetter(load_node.field().Offset());
-        return true;
+        return !FLAG_use_field_guards;

[srdjan, 2016/02/12 17:03:50]

It would have been helpful to add comment why it depends on field guards

       }
       return false;
     }
@@ -1111,7 +1111,7 @@ bool FlowGraphCompiler::TryIntrinsify() {
           *sequence_node.NodeAt(0)->AsStoreInstanceFieldNode();
       if (store_node.field().guarded_cid() == kDynamicCid) {
         GenerateInlinedSetter(store_node.field().Offset());
-        return true;
+        return !FLAG_use_field_guards;
       }
     }
   }