Optimistically hoist SmiCheck through phi when the only value of unknown type coming into the phi i…

runtime/vm/flow_graph_optimizer.h

Index: runtime/vm/flow_graph_optimizer.h
diff --git a/runtime/vm/flow_graph_optimizer.h b/runtime/vm/flow_graph_optimizer.h
index ddb40f22cd45cbae45593cc08566e621b49bed8f..b6df5e2163b9fd7f348369fe4f73a0c1b080a06a 100644
--- a/runtime/vm/flow_graph_optimizer.h
+++ b/runtime/vm/flow_graph_optimizer.h
@@ -124,6 +124,16 @@ class FlowGraphTypePropagator : public FlowGraphVisitor {
 class LICM : public AllStatic {
  public:
   static void Optimize(FlowGraph* flow_graph);
+
+ private:
+  static void Hoist(ForwardInstructionIterator* it,
+                    BlockEntryInstr* pre_header,
+                    Definition* current);
+
+  static void TryHoistCheckSmiThroughPhi(ForwardInstructionIterator* it,
+                                         BlockEntryInstr* header,
+                                         BlockEntryInstr* pre_header,
+                                         Definition* current);
 };