Make register allocator to disregard constant computation with no uses.

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"
 #include "vm/handles_impl.h"
 #include "vm/locations.h"
 #include "vm/object.h"
 
 namespace dart {
 
 class BindInstr;
 class BitVector;
 class BlockEntryInstr;
 class BufferFormatter;
 class ComparisonComp;
+class ConstantComp;
 class Computation;
 class ControlInstruction;
 class Definition;
 class Environment;
 class FlowGraphCompiler;
 class FlowGraphVisitor;
 class Instruction;
 class LocalVariable;
 
 
@@ skipping 824 matching lines @@
   // Precondition: use lists must be properly calculated.
   // Postcondition: use lists and use values are still valid.
   void ReplaceUsesWith(Definition* other);
 
   // Insert this definition before 'next'.
   void InsertBefore(Instruction* next);
 
   // Insert this definition after 'prev'.
   void InsertAfter(Instruction* prev);
 
+  // If this definition is a bind of a constant return it.
+  // Otherwise return NULL.
+  ConstantComp* AsConstant();
+
  private:
   intptr_t temp_index_;
   intptr_t ssa_temp_index_;
   // TODO(regis): GrowableArray<const AbstractType*> propagated_types_;
   // For now:
   AbstractType& propagated_type_;
   intptr_t propagated_cid_;
   Value* input_use_list_;
   Value* env_use_list_;
   UseKind use_kind_;
@@ skipping 2545 matching lines @@
   ForwardInstructionIterator* current_iterator_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FlowGraphVisitor);
 };
 
 
 }  // namespace dart
 
 #endif  // VM_INTERMEDIATE_LANGUAGE_H_