Implement range analysis for smi values.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index 0095b13eda8e9dcce4c08be3b105496d6c42fb2e..8e6b77a0470e15836a282e534f16322218fe9375 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -205,6 +205,12 @@ static bool CompileParsedFunctionHelper(const ParsedFunction& parsed_function,
         if (FLAG_cse) DominatorBasedCSE::Optimize(flow_graph);
         if (FLAG_licm) LICM::Optimize(flow_graph);
 
+        // We have to perform range analysis after LICM because it
+        // optimistically moves CheckSmi through phis into loop preheaders
+        // making some phis smi.

[ngeoffray, 2012/09/24 21:44:15]

The first part of the sentence makes you think it's a requirement, but the
second part makes you think it's actually just an optimization.

+        flow_graph->ComputeUseLists();
+        optimizer.InferSmiRanges();
+
         // Perform register allocation on the SSA graph.
         FlowGraphAllocator allocator(*flow_graph);
         allocator.AllocateRegisters();