Ensure that LowerBound and UpperBound return overflow marker when overflow occurs.

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 1702 matching lines @@
 
   const RangeBoundary& min() const { return min_; }
   const RangeBoundary& max() const { return max_; }
 
   bool Equals(Range* other) {
     return min_.Equals(other->min_) && max_.Equals(other->max_);
   }
 
   static RangeBoundary ConstantMin(Range* range) {
     if (range == NULL) return RangeBoundary::MinSmi();
-    return range->min().LowerBound();
+    return range->min().LowerBound().Clamp();
   }
 
   static RangeBoundary ConstantMax(Range* range) {
     if (range == NULL) return RangeBoundary::MaxSmi();
-    return range->max().UpperBound();
+    return range->max().UpperBound().Clamp();
   }
 
   // Inclusive.
   bool IsWithin(intptr_t min_int, intptr_t max_int) const;
 
  private:
   RangeBoundary min_;
   RangeBoundary max_;
 };
 
@@ skipping 2584 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_