AOT: Enable branch merging for checked smi comparisons

runtime/vm/branch_optimizer.cc

 // Copyright (c) 2016, 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/branch_optimizer.h"
 
 #include "vm/flow_graph.h"
 #include "vm/intermediate_language.h"
 
 namespace dart {
@@ skipping 29 matching lines @@
   // These are the branches produced by inlining in a test context.  Also,
   // the phi has no other uses so they can simply be eliminated.  The block
   // has no other phis and no instructions intervening between the phi and
   // branch so the block can simply be eliminated.
   BranchInstr* branch = block->last_instruction()->AsBranch();
   ASSERT(branch != NULL);
   ComparisonInstr* comparison = branch->comparison();
   if (comparison->InputCount() != 2) {
     return false;
   }
+  if (comparison->CanDeoptimize() || comparison->MayThrow()) {
+    return false;
+  }
   Value* left = comparison->left();
   PhiInstr* phi = left->definition()->AsPhi();
   Value* right = comparison->right();
   ConstantInstr* constant =
       (right == NULL) ? NULL : right->definition()->AsConstant();
   return (phi != NULL) &&
       (constant != NULL) &&
       (phi->GetBlock() == block) &&
       PhiHasSingleUse(phi, left) &&
       (block->next() == branch) &&
@@ skipping 289 matching lines @@
   if (changed) {
     // We may have changed the block order and the dominator tree.
     flow_graph->DiscoverBlocks();
     GrowableArray<BitVector*> dominance_frontier;
     flow_graph->ComputeDominators(&dominance_frontier);
   }
 }
 
 
 }  // namespace dart