Compute the def-use list on-demand by walking the dominator tree.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index ed72ea0cac11468664297c04ba2c2529bfe72bd8..20a816c8564372e880e453a8a2d3284650ff9f00 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -165,6 +165,7 @@ static bool CompileParsedFunctionHelper(const ParsedFunction& parsed_function,
       // Transform to SSA.
       if (optimized) {
         flow_graph->ComputeSSA();
+        flow_graph->ComputeUseLists();
       }
 
       if (FLAG_print_flow_graph) {
@@ -181,22 +182,27 @@ static bool CompileParsedFunctionHelper(const ParsedFunction& parsed_function,
       if (optimized) {
         FlowGraphOptimizer optimizer(*flow_graph);
         optimizer.ApplyICData();
+        ASSERT(flow_graph->ComputeUseLists());

[Vyacheslav Egorov (Google), 2012/08/23 13:51:10]

ASSERT is compiled out in Release mode so this will not be executed and in the
same time ComputeUseList always returns true? This is confusing. 

 
         // Propagate types and eliminate more type tests.
         FlowGraphTypePropagator propagator(*flow_graph);
         propagator.PropagateTypes();
+        ASSERT(flow_graph->ComputeUseLists());
 
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
+        ASSERT(flow_graph->ComputeUseLists());
 
         if (FLAG_local_cse) {
           LocalCSE local_cse(*flow_graph);
           local_cse.Optimize();
+          ASSERT(flow_graph->ComputeUseLists());
         }
 
         // Perform register allocation on the SSA graph.
         FlowGraphAllocator allocator(*flow_graph);
         allocator.AllocateRegisters();
+        ASSERT(flow_graph->ComputeUseLists());
 
         if (FLAG_print_flow_graph) {
           OS::Print("After Optimizations:\n");