Clear use lists for globals and definitions in start environment in release mode.

runtime/vm/flow_graph.cc

Index: runtime/vm/flow_graph.cc
diff --git a/runtime/vm/flow_graph.cc b/runtime/vm/flow_graph.cc
index 2b11396f846026e65ce5e90d9bc086345d526ebc..5a53345fa05461697860cdf8fb3d516ef95bd192 100644
--- a/runtime/vm/flow_graph.cc
+++ b/runtime/vm/flow_graph.cc
@@ -282,6 +282,12 @@ static void ComputeUseListsRecursive(BlockEntryInstr* block) {
 
 void FlowGraph::ComputeUseLists() {
   DEBUG_ASSERT(ResetUseLists());
+  // Clear global constants.
+  ClearUseLists(graph_entry_->constant_null());
+  // Clear definitions in the start environment.
+  for (intptr_t i = 0; i < graph_entry_->start_env()->values().length(); ++i) {

[srdjan, 2012/08/30 18:32:02]

You could cache  graph_entry_->start_env()->values() in a local variable.

+    ClearUseLists(graph_entry_->start_env()->values()[i]->definition());
+  }
   ComputeUseListsRecursive(graph_entry_);
   DEBUG_ASSERT(ValidateUseLists());
 }