Avoid using a temp register when unboxing a known smi.

runtime/vm/intermediate_language.h

 // 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.
 
 #ifndef VM_INTERMEDIATE_LANGUAGE_H_
 #define VM_INTERMEDIATE_LANGUAGE_H_
 
 #include "vm/allocation.h"
 #include "vm/ast.h"
 #include "vm/growable_array.h"
@@ skipping 2977 matching lines @@
  public:
   UnboxDoubleInstr(Value* value, intptr_t deopt_id) {
     ASSERT(value != NULL);
     inputs_[0] = value;
     deopt_id_ = deopt_id;
   }
 
   Value* value() const { return inputs_[0]; }
 
   virtual bool CanDeoptimize() const {
-    return value()->ResultCid() != kDoubleCid;
+    return (value()->ResultCid() != kDoubleCid)
+        && (value()->ResultCid() != kSmiCid);
   }
 
   virtual bool HasSideEffect() const { return false; }
 
   // The output is not an instance but when it is boxed it becomes double.
   virtual intptr_t ResultCid() const { return kDoubleCid; }
 
   virtual Representation representation() const {
     return kUnboxedDouble;
   }
@@ skipping 632 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_