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

runtime/vm/compiler.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/compiler.h"
 
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 145 matching lines @@
           isolate->set_ic_data_array(
               ExtractTypeFeedbackArray(unoptimized_code));
         }
       }
 
       // Build the flow graph.
       FlowGraphBuilder builder(parsed_function);
       flow_graph = builder.BuildGraph();
 
       // Transform to SSA.
-      if (optimized) {
-        flow_graph->ComputeSSA();
-      }
+      if (optimized) flow_graph->ComputeSSA();
 
       if (FLAG_print_flow_graph) {
         OS::Print("Before Optimizations\n");
         FlowGraphPrinter printer(*flow_graph);
         printer.PrintBlocks();
       }
       if (Dart::flow_graph_writer() != NULL) {
         // Write flow graph to file.
         FlowGraphVisualizer printer(*flow_graph);
         printer.PrintFunction();
       }
 
       if (optimized) {
         FlowGraphOptimizer optimizer(*flow_graph);
         optimizer.ApplyICData();
 
+        // Compute the use lists.
+        flow_graph->ComputeUseLists();
+
         // Propagate types and eliminate more type tests.
         FlowGraphTypePropagator propagator(*flow_graph);
         propagator.PropagateTypes();
 
+        // TODO(zerny): Here we assume that the use lists remain valid after
+        // type propagation. We should construct a use-list validator to make
+        // this explicit in DEBUG mode.
+
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
 
         if (FLAG_local_cse) {
           LocalCSE local_cse(*flow_graph);
           local_cse.Optimize();
         }
 
         // Perform register allocation on the SSA graph.
         FlowGraphAllocator allocator(*flow_graph);
@@ skipping 352 matching lines @@
     result = isolate->object_store()->sticky_error();
     isolate->object_store()->clear_sticky_error();
     isolate->set_long_jump_base(base);
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart