AOT: Enable branch merging for checked smi comparisons

runtime/vm/constant_propagator.cc

Index: runtime/vm/constant_propagator.cc
diff --git a/runtime/vm/constant_propagator.cc b/runtime/vm/constant_propagator.cc
index 0ab4a71ee0df884dda776cebfa6d01c6f5dcd529..b63f8496f42b4bc7f2489f9e19d1844a51196711 100644
--- a/runtime/vm/constant_propagator.cc
+++ b/runtime/vm/constant_propagator.cc
@@ -941,6 +941,12 @@ void ConstantPropagator::VisitCheckedSmiOp(CheckedSmiOpInstr* instr) {
 }
 
 
+void ConstantPropagator::VisitCheckedSmiComparison(
+    CheckedSmiComparisonInstr* instr) {
+  SetValue(instr, non_constant_);
+}
+
+
 void ConstantPropagator::VisitBinarySmiOp(BinarySmiOpInstr* instr) {
   VisitBinaryIntegerOp(instr);
 }