Validate well-formedness of the use lists in debug mode.

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 175 matching lines @@
         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.
+        // Verify that the use lists are still valid.
+        DEBUG_ASSERT(flow_graph->ValidateUseLists());
 
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
 
         if (FLAG_cse) {
           DominatorBasedCSE::Optimize(flow_graph->graph_entry());
         }
 
         // 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