Avoid checking for uses in try-blocks, when optimizing a function without try-catch.

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 699 matching lines @@
 
 void FlowGraphOptimizer::InsertConversionsFor(Definition* def) {
   const Representation from_rep = def->representation();
 
   for (Value::Iterator it(def->input_use_list());
        !it.Done();
        it.Advance()) {
     ConvertUse(it.Current(), from_rep);
   }
 
-  for (Value::Iterator it(def->env_use_list());
-       !it.Done();
-       it.Advance()) {
-    Value* use = it.Current();
-    if (use->instruction()->MayThrow() &&
-        use->instruction()->GetBlock()->InsideTryBlock()) {
-      // Environment uses at calls inside try-blocks must be converted to
-      // tagged representation.
-      ConvertEnvironmentUse(it.Current(), from_rep);
+  if (flow_graph()->graph_entry()->SuccessorCount() > 1) {
+    for (Value::Iterator it(def->env_use_list());
+         !it.Done();
+         it.Advance()) {
+      Value* use = it.Current();
+      if (use->instruction()->MayThrow() &&
+          use->instruction()->GetBlock()->InsideTryBlock()) {
+        // Environment uses at calls inside try-blocks must be converted to
+        // tagged representation.
+        ConvertEnvironmentUse(it.Current(), from_rep);
+      }
     }
   }
 }
 
 
 static void UnboxPhi(PhiInstr* phi) {
   Representation unboxed = phi->representation();
 
   switch (phi->Type()->ToCid()) {
     case kDoubleCid:
@@ skipping 9320 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