Fix our initial dead phi elimination in the presence of try-catch.

runtime/vm/flow_graph.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/flow_graph.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/intermediate_language.h"
 #include "vm/longjump.h"
@@ skipping 982 matching lines @@
           Value* use = new(isolate()) Value((*env)[i]);
           phi->SetInputAt(pred_index, use);
         }
       }
     }
   }
 }
 
 
 void FlowGraph::RemoveDeadPhis(GrowableArray<PhiInstr*>* live_phis) {
+  // Augment live_phis with those that have implicit real used at
+  // potentially throwing instructions if there is a try-catch in this graph.
+  if (graph_entry()->SuccessorCount() > 1) {
+    for (BlockIterator it(postorder_iterator()); !it.Done(); it.Advance()) {
+      JoinEntryInstr* join = it.Current()->AsJoinEntry();
+      if (join == NULL) continue;
+      for (PhiIterator phi_it(join); !phi_it.Done(); phi_it.Advance()) {
+        PhiInstr* phi = phi_it.Current();
+        if (phi == NULL ||
+            phi->is_alive() ||
+            (phi->input_use_list() != NULL) ||
+            (phi->env_use_list() == NULL)) {
+          continue;
+        }
+        for (Value::Iterator it(phi->env_use_list());
+             !it.Done();
+             it.Advance()) {
+          Value* use = it.Current();
+          if (use->instruction()->MayThrow() &&
+              use->instruction()->GetBlock()->InsideTryBlock()) {
+            live_phis->Add(phi);
+            phi->mark_alive();
+            break;
+          }
+        }
+      }
+    }
+  }
+
   while (!live_phis->is_empty()) {
     PhiInstr* phi = live_phis->RemoveLast();
     for (intptr_t i = 0; i < phi->InputCount(); i++) {
       Value* val = phi->InputAt(i);
       PhiInstr* used_phi = val->definition()->AsPhi();
       if ((used_phi != NULL) && !used_phi->is_alive()) {
         used_phi->mark_alive();
         live_phis->Add(used_phi);
       }
     }
   }
 
   for (BlockIterator it(postorder_iterator()); !it.Done(); it.Advance()) {
     JoinEntryInstr* join = it.Current()->AsJoinEntry();
-    if (join != NULL) join->RemoveDeadPhis(constant_null());
+    if (join != NULL) join->RemoveDeadPhis(constant_dead());
   }
 }
 
 
 void FlowGraph::RemoveRedefinitions() {
   // Remove redefinition instructions inserted to inhibit hoisting.
   for (BlockIterator block_it = reverse_postorder_iterator();
        !block_it.Done();
        block_it.Advance()) {
     for (ForwardInstructionIterator instr_it(block_it.Current());
@@ skipping 222 matching lines @@
 }
 
 
 bool BlockEffects::IsSideEffectFreePath(BlockEntryInstr* from,
                                         BlockEntryInstr* to) const {
   return available_at_[to->postorder_number()]->Contains(
       from->postorder_number());
 }
 
 }  // namespace dart