Mark phi as producing a smi value if it is dominated by SmiChecks over its operands.

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 724 matching lines @@
   // The compile type may be requested when building the flow graph, i.e. before
   // type propagation has occurred. To avoid repeatedly computing the compile
   // type of the definition, we store it as initial propagated type.
   AbstractType& type = AbstractType::Handle(definition()->CompileType());
   definition()->SetPropagatedType(type);
   return type.raw();
 }
 
 
 intptr_t Value::ResultCid() const {
-  return definition()->GetPropagatedCid();
+  if (reaching_cid() == kIllegalCid) {
+    return definition()->GetPropagatedCid();
+  }
+  return reaching_cid();
 }
 
 
 
 RawAbstractType* ConstantInstr::CompileType() const {
   if (value().IsNull()) {
     return Type::NullType();
   }
   if (value().IsInstance()) {
     return Instance::Cast(value()).GetType();
@@ skipping 907 matching lines @@
     value->set_use_index(use_index++);
     value->AddToEnvUseList();
   }
   instr->set_env(copy);
 }
 
 
 #undef __
 
 }  // namespace dart