AOT: Enable branch merging for checked smi comparisons

runtime/vm/flow_graph.cc

Index: runtime/vm/flow_graph.cc
diff --git a/runtime/vm/flow_graph.cc b/runtime/vm/flow_graph.cc
index f513b304c012f92220fa118ad8641bb91b59e133..e2f8e825d21a3edd51fe5fbd8a849a5d8fdee077 100644
--- a/runtime/vm/flow_graph.cc
+++ b/runtime/vm/flow_graph.cc
@@ -2014,7 +2014,10 @@ void FlowGraph::EliminateEnvironments() {
     }
     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.