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

runtime/vm/compiler.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/compiler.h"
 
 #include "vm/assembler.h"
 #include "vm/ast_printer.h"
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 185 matching lines @@
           DEBUG_ASSERT(flow_graph->ValidateUseLists());
         }
 
         // Propagate types and eliminate more type tests.
         FlowGraphTypePropagator propagator(*flow_graph);
         propagator.PropagateTypes();
 
         // Verify that the use lists are still valid.
         DEBUG_ASSERT(flow_graph->ValidateUseLists());
 
+        // Propagate sminess from CheckSmi to phis.
+        optimizer.PropagateSminess();
+
         // Do optimizations that depend on the propagated type information.
         optimizer.OptimizeComputations();
 
         // Unbox doubles.
         flow_graph->ComputeUseLists();
         optimizer.SelectRepresentations();
 
         if (FLAG_cse) {
           flow_graph->ComputeUseLists();
           DominatorBasedCSE::Optimize(flow_graph->graph_entry());
@@ skipping 360 matching lines @@
     result = isolate->object_store()->sticky_error();
     isolate->object_store()->clear_sticky_error();
     isolate->set_long_jump_base(base);
     return result.raw();
   }
   UNREACHABLE();
   return Object::null();
 }
 
 }  // namespace dart