[vm] Implement gradual refinement of types

runtime/vm/redundancy_elimination.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/redundancy_elimination.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph.h"
 #include "vm/hash_map.h"
 #include "vm/il_printer.h"
@@ skipping 1305 matching lines @@
 
   if (check == NULL) {
     return;
   }
 
   // Host CheckSmi instruction and make this phi smi one.
   Hoist(NULL, pre_header, check);
 
   // Replace value we are checking with phi's input.
   check->value()->BindTo(phi->InputAt(non_smi_input)->definition());
+  check->value()->SetReachingType(phi->InputAt(non_smi_input)->Type());
 
   phi->UpdateType(CompileType::FromCid(kSmiCid));
 }
 
 void LICM::OptimisticallySpecializeSmiPhis() {
   if (!flow_graph()->function().allows_hoisting_check_class() ||
       FLAG_precompiled_mode) {
     // Do not hoist any: Either deoptimized on a hoisted check,
     // or compiling precompiled code where we can't do optimistic
     // hoisting of checks.
@@ skipping 1957 matching lines @@
       if (to_index == 0) {
         join->phis_ = NULL;
       } else {
         join->phis_->TruncateTo(to_index);
       }
     }
   }
 }
 
 }  // namespace dart