Fix dead phis elimination.

runtime/vm/flow_graph_optimizer.cc

 // Copyright (c) 2013, 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/flow_graph_optimizer.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/cpu.h"
 #include "vm/dart_entry.h"
@@ skipping 7285 matching lines @@
 };
 
 
 void DeadStoreElimination::Optimize(FlowGraph* graph) {
   if (FLAG_dead_store_elimination) {
     StoreOptimizer::OptimizeGraph(graph);
   }
 }
 
 
+// Returns true iff this definition is used in a non-phi instruction.
+static bool HasRealUse(Definition* def) {
+  // Environment uses are real (non-phi) uses.
+  if (def->env_use_list() != NULL) return true;
+  for (Value::Iterator it(def->input_use_list());
+       !it.Done();
+       it.Advance()) {
+    if (!it.Current()->instruction()->IsPhi()) return true;
+  }
+  return false;
+}
+
+
 void DeadCodeElimination::EliminateDeadPhis(FlowGraph* flow_graph) {
   GrowableArray<PhiInstr*> live_phis;
   for (BlockIterator b = flow_graph->postorder_iterator();
        !b.Done();
        b.Advance()) {
     JoinEntryInstr* join = b.Current()->AsJoinEntry();
     if (join != NULL) {
       for (PhiIterator it(join); !it.Done(); it.Advance()) {
         PhiInstr* phi = it.Current();
         // Phis that have uses and phis inside try blocks are
         // marked as live.
-        if (phi->HasUses() || join->InsideTryBlock()) {
+        if (HasRealUse(phi) || join->InsideTryBlock()) {
           live_phis.Add(phi);
           phi->mark_alive();
         } else {
           phi->mark_dead();
         }
       }
     }
   }
 
   while (!live_phis.is_empty()) {
@@ skipping 2736 matching lines @@
 
   // Insert materializations at environment uses.
   for (intptr_t i = 0; i < exits_collector_.exits().length(); i++) {
     CreateMaterializationAt(
         exits_collector_.exits()[i], alloc, *slots);
   }
 }
 
 
 }  // namespace dart