Eliminate unnecessary deoptimization environments.

vm/flow_graph_allocator.cc

Index: vm/flow_graph_allocator.cc
===================================================================
--- vm/flow_graph_allocator.cc	(revision 10050)
+++ vm/flow_graph_allocator.cc	(working copy)
@@ -82,6 +82,17 @@
 }
 
 
+void FlowGraphAllocator::EliminateEnvironmentUses() {
+  for (intptr_t i = 0; i < block_order_.length(); ++i) {
+    BlockEntryInstr* block = block_order_[i];
+    for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
+      Instruction* current = it.Current();
+      if (!current->CanDeoptimize()) current->set_env(NULL);
+    }
+  }
+}
+
+
 void FlowGraphAllocator::ComputeInitialSets() {
   const intptr_t block_count = postorder_.length();
   for (intptr_t i = 0; i < block_count; i++) {
@@ -1654,6 +1665,8 @@
 
 
 void FlowGraphAllocator::AllocateRegisters() {
+  EliminateEnvironmentUses();
+
   AnalyzeLiveness();
 
   BuildLiveRanges();