Ensure that BoxInt32 input is correctly preserved on the slow-path.

runtime/vm/locations.h

 // Copyright (c) 2013, 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_LOCATIONS_H_
 #define VM_LOCATIONS_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/bitfield.h"
@@ skipping 613 matching lines @@
 
   static LocationSummary* Make(Isolate* isolate,
                                intptr_t input_count,
                                Location out,
                                ContainsCall contains_call);
 
   RegisterSet* live_registers() {
     return &live_registers_;
   }
 
+#if defined(DEBUG)
+  // Debug only verification that ensures that writable registers are correctly
+  // preserved on the slow path.
+  void DiscoverWritableInputs();
+  void CheckWritableInputs();
+#endif
+
  private:
   const intptr_t num_inputs_;
   Location* input_locations_;
   const intptr_t num_temps_;
   Location* temp_locations_;
   Location output_location_;
 
   BitmapBuilder* stack_bitmap_;
 
   const ContainsCall contains_call_;
   RegisterSet live_registers_;
+
+#if defined(DEBUG)
+  intptr_t writable_inputs_;
+#endif
 };
 
 
 }  // namespace dart
 
 #endif  // VM_LOCATIONS_H_