Fixing issue 1898 (using HChange outside the insert-representation-changes phase).

src/hydrogen-instructions.cc

-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
@@ skipping 787 matching lines @@
   }
   if (right()->IsConstant() &&
       HConstant::cast(right())->HasInteger32Value() &&
       HConstant::cast(right())->Integer32Value() == nop_constant) {
     return left();
   }
   return this;
 }
 
 
+HValue* HChange::Canonicalize() {
+  return (from().Equals(to())) ? value() : this;
+}
+
+
 void HTypeof::PrintDataTo(StringStream* stream) {
   value()->PrintNameTo(stream);
 }
 
 
 void HChange::PrintDataTo(StringStream* stream) {
   HUnaryOperation::PrintDataTo(stream);
   stream->Add(" %s to %s", from().Mnemonic(), to().Mnemonic());
 
   if (CanTruncateToInt32()) stream->Add(" truncating-int32");
@@ skipping 1305 matching lines @@
 
 
 void HCheckPrototypeMaps::Verify() {
   HInstruction::Verify();
   ASSERT(HasNoUses());
 }
 
 #endif
 
 } }  // namespace v8::internal