AOT: Enable branch merging for checked smi comparisons

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/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 1996 matching lines @@
   disallow_licm();
   for (BlockIterator block_it = reverse_postorder_iterator();
        !block_it.Done();
        block_it.Advance()) {
     BlockEntryInstr* block = block_it.Current();
     if (!block->IsCatchBlockEntry()) {
       block->RemoveEnvironment();
     }
     for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
       Instruction* current = it.Current();
-      if (!current->CanDeoptimize()) {
+      if (!current->CanDeoptimize() &&
+          (!current->MayThrow() || !current->GetBlock()->InsideTryBlock())) {
+        // Instructions that can throw need an environment for optimized
+        // try-catch.
         // TODO(srdjan): --source-lines needs deopt environments to get at
         // the code for this instruction, however, leaving the environment
         // changes code.
         current->RemoveEnvironment();
       }
     }
   }
 }
 
 
@@ skipping 282 matching lines @@
   ExtractNthOutputInstr* extract =
       new(Z) ExtractNthOutputInstr(new(Z) Value(instr), index, rep, cid);
   instr->ReplaceUsesWith(extract);
   InsertAfter(instr, extract, NULL, FlowGraph::kValue);
 }
 
 
 
 
 }  // namespace dart